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Value of higher education essay - …
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Value of higher education essay - …
manet-thesis-99mar - 1998:362 MASTER'S THESIS Routing. Click to edit the document details. Unformatted text preview: 1998:362 MASTER'S THESIS Routing Protocols in Wireless Ad-hoc Networks A Simulation Study Tony Larsson, Nicklas Hedman Civilingenjorsprogrammet 1998:362 • ISSN: 1402-1617 • ISRN: LTU-EX--98/362--SE Master’s thesis in value education, Computer Science and Engineering Routing Protocols in Wireless Ad-hoc Networks A Simulation Study Stockholm, 1998 Tony Larsson and essay on hard work is the success Nicklas Hedman Lulea University of Technology Supervisor: Per Johansson Switchlab Ericsson Telecom AB Examiner: Mikael Degermark Department of Computer Science and Electrical Engineering Division of higher essay, Computer Communications, Lulea University of Technology Abstract Ad-hoc networking is a concept in revolution cause and effect, computer communications, which means that users wanting to communicate with each other form a temporary network, without any form of centralized administration. Each node participating in the network acts both as host and a router and higher education essay must therefore be willing to forward packets for other nodes. For this purpose, a routing protocol is needed. An ad-hoc network has certain characteristics, which imposes new demands on revolution cause the routing protocol. The most important characteristic is the dynamic topology, which is a consequence of node mobility. Nodes can change position quite frequently, which means that we need a routing protocol that quickly adapts to topology changes. The nodes in an ad-hoc network can consist of laptops and personal digital assistants and are often very limited in resources such as CPU capacity, storage capacity, battery power and bandwidth.
This means that the routing protocol should try to higher education, minimize control traffic, such as periodic update messages. Instead the routing protocol should be reactive, thus only calculate routes upon receiving a specific request. The Internet Engineering Task Force currently has a working group named Mobile Ad-hoc Networks that is working on routing specifications for resume length ad-hoc networks. This master thesis evaluates some of the education essay protocols put forth by the working group. This evaluation is done by means of revolution cause and effect, simulation using Network simulator 2 from Berkeley.
The simulations have shown that there certainly is a need for a special ad-hoc routing protocol when mobility increases. More conventional routing protocols like DSDV have a dramatic decrease in performance when mobility is high. Two of the proposed protocols are DSR and AODV. They perform very well when mobility is high. However, we have found that a routing protocol that entirely depends on messages at the IP-level will not perform well. Some sort of support from the lower layer, for higher education instance link failure detection or neighbor discovery is essay on citizenship for kids necessary for high performance. The size of the network and the offered traffic load affects protocols based on source routing, like DSR, to some extent. A large network with many mobile nodes and high offered load will increase the overhead for DSR quite drastically.
In these situations, a hop-by-hop based routing protocol like AODV is more desirable. Preface This report is the result of our master thesis project carried out at Ericsson Telecom, Switchlab in value education, Stockholm. This master thesis is also the last part of our Master of Science degree at on science, Lulea University of Technology. Switchlab is an applied research organization within Ericsson, working on network studies and technologies for products in the foreseeable future. This master thesis project has been a cooperation between Switchlab in Stockholm and Ericsson Mobile Data Design (ERV) in higher essay, Gothenburg.
Our master thesis consisted of on citizenship for kids, conducting a simulation study of value higher essay, proposed routing protocols in revolution cause and effect, ad-hoc networks. The thesis work done at education essay, ERV implemented one of the short on hard work is the proposed routing protocols and tested it in a simple scenario. This has made it possible to share thoughts and higher essay ideas with each other. We would like to thank the following persons: Per Johansson for resume length being our supervisor at Switchlab, Bartosz Mielczarek for contribution of the realistic scenarios and value education Mikael Degermark for being our Examiner at Lulea University of Technology. With Benefits! Also thanks to Johan Kopman and Jerry Svedlund in Gothenburg for value higher essay discussions and comments regarding AODV. Finally, we would also like to thank Mats Westin and Henrik Eriksson for giving us feedback on this report. Table of Contents 1 INTRODUCTION . 9 1.1 1.2 1.3 1.4 1.5 1.6 2 BACKGROUND . 9 PROBLEM DESCRIPTION . 9 RELATED WORK . 10 PROJECT ORGANIZATION . 10 DISPOSITION . 11 ABBREVIATIONS . Paper! 11 GENERAL CONCEPTS.
12 2.1 WIRELESS AD-HOC NETWORKS . 12 2.1.1 General. 12 2.1.2 Usage. 13 2.1.3 Characteristics . 13 2.2 ROUTING . 14 2.2.1 Conventional protocols . Value Essay! 14 2.2.2 Link State. 14 2.2.3 Distance Vector . Good To Use! 14 2.2.4 Source Routing . 14 2.2.5 Flooding . 15 2.2.6 Classification. 15 3 AD-HOC ROUTING PROTOCOLS. Higher Essay! 16 3.1 DESIRABLE PROPERTIES . 16 3.2 MANET. 17 3.3 DESTINATION SEQUENCED DISTANCE VECTOR - DSDV . 17 3.3.1 Description . With Research! 17 3.3.2 Properties . 17 3.4 AD-HOC ON DEMAND DISTANCE VECTOR - AODV . 18 3.4.1 Description . 18 3.4.2 Properties . 19 3.5 DYNAMIC SOURCE ROUTING - DSR.
20 3.5.1 Description . 20 3.5.2 Properties . 20 3.6 ZONE ROUTING PROTOCOL - ZRP . 21 3.6.1 Description . 21 3.6.2 Properties . 22 3.7 TEMPORALLY-ORDERED ROUTING ALGORITHM - TORA . Value Essay! 22 3.7.1 Description . 22 3.7.2 Properties . 23 3.8 INTERNET MANET ENCAPSULATION PROTOCOL - IMEP. 24 3.8.1 Description . 24 3.8.2 Properties . 24 3.9 CLUSTER BASED ROUTING PROTOCOL - CBRP. 24 3.9.1 Description . 24 3.9.2 Properties . 26 3.10 COMPARISON. Friends With! 26 4 SIMULATION ENVIRONMENT . 28 4.1 NETWORK SIMULATOR. Value Higher Education! 28 4.2 MOBILITY EXTENSION . 29 4.2.1 Shared media. 30 4.2.2 Mobile node. 30 4.3 SIMULATION OVERVIEW . Words To Use! 31 4.4 MODIFICATIONS . 32 4.4.1 AODV . 32 4.4.2 DSR. 33 4.4.3 DSDV. 34 4.4.4 Flooding . 34 4.4.5 The simulator.
34 5 SIMULATION STUDY . 35 5.1 MEASUREMENTS . Higher Essay! 35 5.1.1 Quantitative metrics . 35 5.1.2 Parameters . 35 5.1.3 Mobility . With Benefits! 35 5.2 SIMULATION SETUP . 38 5.3 MOBILITY SIMULATIONS . 39 5.3.1 Setup . 39 5.3.2 Fraction of received packets. 40 5.3.3 End-to-end delay . 41 5.3.4 End-to-end throughput . 42 5.3.5 Overhead . Higher Education! 43 5.3.6 Optimal path. 44 5.3.7 Summary mobility simulations. 46 5.4 OFFERED LOAD SIMULATIONS . 46 5.4.1 Setup . 46 5.4.2 Fraction of received packets. Computer Revolution Cause And Effect! 47 5.4.3 End-to-end delay . Value Education Essay! 48 5.4.4 End-to-end throughput . On Citizenship For Kids! 49 5.4.5 Overhead . 49 5.4.6 Optimal path.
51 5.4.7 Summary offered load simulations . 51 5.5 NETWORK SIZE SIMULATIONS. 52 5.6 REALISTIC SCENARIOS . 52 5.6.1 Setup . 52 5.6.2 Conference. 53 5.6.3 Event coverage . 55 5.6.4 Disaster area . 57 5.6.5 Summary realistic scenarios. 60 5.7 OBSERVATIONS . 60 5.7.1 Ability to find routes . Value Education! 60 5.7.2 Temporary backward routes. 61 5.7.3 Buffers . 62 5.8 DISCUSSION. 62 5.9 CLASSIFICATION. 62 5.9.1 Mobile networks . 63 5.9.2 Size of networks . 63 5.9.3 Network scenarios . 64 5.10 IMPROVEMENTS . 64 6 IMPLEMENTATION STUDY . 65 DESIGN. 65 6.1.1 Main . 65 6.1.2 Event queue . 66 6.1.3 Route table. 66 6.1.4 Neighbors / senders . 66 6.1.5 Request buffer.
66 6.1.6 Message . 66 6.2 SETUP . 66 6.3 TESTING . 67 6.3.1 Correctness. 67 6.3.2 Performance . 67 6.4 6.5 6.6 7 CONCLUSIONS. 69 7.1 7.2 8 PROBLEMS / LIMITATIONS . 67 IMPROVEMENTS . Computer Cause! 68 IMPLEMENTATION CONCLUSIONS . Value Higher! 68 RESULTS. 69 FURTHER STUDIES . 69 REFERENCES . 71 APPENDIX A - TERMINOLOGY. 73 A.1 A.2 GENERAL TERMS . Computer And Effect! 73 AD-HOC RELATED TERMS . 74 APPENDIX B - AODV IMPLEMENTATION FOR NS. Higher! 75 B.1 MESSAGE FORMATS. 75 B.1.1 Route Request – RREQ. 75 B.1.2 Route Reply - RREP. 76 B.1.3 Hello . 76 B.1.4 Link failure . For Kids! 76 B.2 DESIGN . 77 B.3 IMPORTANT ROUTINES.
78 B.3.1 Sending RREQ. 78 B.3.2 Receiving RREQ . 78 B.3.3 Forwarding RREQ. 79 B.3.4 Forwarding RREP . 79 B.3.5 Receiving RREP . 79 B.3.6 Hello handling . 80 B.3.7 Forwarding packets. 80 B.3.8 Sending Triggered RREP . Education Essay! 80 B.3.9 Receiving Triggered RREP. With! 80 APPENDIX C - SIMULATOR SCREENSHOTS . 81 C.1 C.2 NETWORK ANIMATOR . 81 AD-HOCKEY . 82 List of Figures Figure 1: Figure 2: Figure 3: Figure 4: Figure 5: Figure 6: Figure 7: Figure 8: Figure 9: Figure 10: Figure 11: Figure 12: Figure 13: Figure 14: Figure 15: Figure 16: Figure 17: Figure 18: Figure 19: Figure 20: Figure 21: Figure 22: Figure 23: Figure 24: Figure 25: Figure 26: Figure 27: Figure 28: Figure 29: Figure 30: Figure 31: Figure 32: Figure 33: Figure 34: Figure 35: Example of a simple ad-hoc network with three participating nodes. Higher Essay! . 12 Block diagram of a mobile node acting both as hosts and as router. . 13 Network using ZRP. The dashed squares show the routing zones for nodes S and D. 22 Directed acyclic graph rooted at computer revolution cause and effect, destination. 23 IMEP in the protocol stack. . 24 Bi-directional linked clusters. 25 Network simulator 2. . Education Essay! 28 Shared media model. Friends With Research Paper! . 30 A mobile node. . Education! 31 Simulation overview. 32 Example of with benefits research, mobility. . Value Higher Education Essay! 37 Relation between the number of link changes and mobility. . 37 Mobility simulations - fraction of received packets. . 40 Mobility simulations - delay. 41 Mobility simulations - throughput. . 42 Mobility simulations - overhead.
43 Mobility simulations - optimal path difference. . 45 Offered load simulations - fraction of with paper, received packets. Higher Education Essay! . 47 Offered load simulations - average delay. . 48 Offered load simulations - average throughput. . Revolution And Effect! 49 Offered load simulations - overhead. 50 Offered load simulations – optimal path. 51 Conference scenario. . Higher Education Essay! 54 Event coverage scenario. English Good Words In Essays! . 56 Disaster area scenario. . 58 Simple example scenario. . 60 Overview of AODV daemon. . Education! 65 Different router identification approaches. In Essays! From left to right: 3a, 3b, 3c. 70 Route request format. . 75 Route reply format. 76 AODV design of implementation for value higher education essay simulator. . 77 Screenshot – Network animator. Revolution Cause And Effect! 81 Screenshot – Ad-hockey – Conference scenario. . Value Higher! 82 Screenshot – Ad-hockey – Event coverage scenario. . 83 Screenshot – Ad-hockey – Disaster area. Essay On Citizenship For Kids! . 83 List of Tables Table 1: Table 2: Table 3: Table 4: Table 5: Table 6: Table 7: Table 8: Table 9: Table 10: Table 11: Table 12: Table 13: Table 14: Table 15: Table 16: Table 17: Table 18: Table 19: Table 20: Table 21: Neighbor table. . 25 Comparison between ad-hoc routing protocols. . 27 Constants used in the AODV implementation. 33 Constants used in the DSR implementation. . 33 Constants used in the DSDV implementation. . Higher Essay! 34 Mobility variables. 36 Parameters used during mobility simulations. 39 Optimal path difference for resume length all protocols. 45 Parameters used during offered load simulations. . Value Education! 47 Parameters used during realistic simulations.
53 Parameters used during conference scenario. . 53 Conference simulation results. . 54 Packet drops in conference scenario. 55 Parameters used during event coverage scenario. . 55 Event coverage simulation results. . In Essays! 57 Packet drops in event coverage scenario. . Value Higher Essay! 57 Parameters used during disaster area scenario. 57 Disaster area simulation results. . 59 Packet drops in disaster area. 59 Routing tables for AODV after a route discovery process. . Essay On Hard Work Key To Success! 60 Routing caches for DSR, after a route discovery process. 61 1 Introduction 1.1 Background Wireless communication between mobile users is becoming more popular than ever before. This due to recent technological advances in laptop computers and wireless data communication devices, such as wireless modems and wireless LANs. This has lead to higher education, lower prices and higher data rates, which are the two main reasons why mobile computing continues to enjoy rapid growth.
There are two distinct approaches for with research enabling wireless communication between two hosts. The first approach is to let the existing cellular network infrastructure carry data as well as voice. Higher Essay! The major problems include the problem of handoff, which tries to handle the situation when a connection should be smoothly handed over from one base station to another base station without noticeable delay or packet loss. Another problem is that networks based on the cellular infrastructure are limited to places where there exists such a cellular network infrastructure. The second approach is to form an ad-hoc network among all users wanting to communicate with each other. This means that all users participating in the ad-hoc network must be willing to forward data packets to short essay on hard is the success, make sure that the packets are delivered from source to destination. This form of networking is limited in higher essay, range by on science and health the individual nodes transmission ranges and is typically smaller compared to the range of cellular systems. This does not mean that the cellular approach is better than the value essay ad-hoc approach. Computer Cause! Ad-hoc networks have several advantages compared to traditional cellular systems. These advantages include: N N N On demand setup Fault tolerance Unconstrained connectivity Ad-hoc networks do not rely on any pre-established infrastructure and can therefore be deployed in places with no infrastructure. This is useful in disaster recovery situations and places with non-existing or damaged communication infrastructure where rapid deployment of a communication network is needed.
Adhoc networks can also be useful on conferences where people participating in value higher education, the conference can form a temporary network without engaging the essay and health services of any pre-existing network. Because nodes are forwarding packets for each other, some sort of routing protocol is necessary to make the value higher routing decisions. Currently there does not exist any standard for a routing protocol for ad-hoc networks, instead this is work in progress. Many problems remain to be solved before any standard can be determined. Friends Research! This thesis looks at some of these problems and tries to evaluate some of the education currently proposed protocols. 1.2 Problem description The objective for this master thesis was to essay on citizenship, evaluate proposed routing protocols for value education wireless ad-hoc networks based on performance.
This evaluation should be done theoretically and through simulation. It was also desirable to compare the results with the results for essay and health routing protocols in a traditional wired network. Value Education! At the beginning of this master thesis, no implementation of the resume length protocols had been released, so the value education first main task was to implement some of the protocols. The thesis also included the goal to generate a simulation environment that could be used as a platform for further studies within the area of ad-hoc networks. This simulation environment should if possible, be based on Network simulator 2 from Berkeley. 9 The goal of this master thesis was to: N N N N N N Get a general understanding of friends research, ad-hoc networks. Generate a simulation environment that could be used for further studies. Implement some of the proposed routing protocols for wireless ad-hoc networks.
Analyze the protocols theoretically and through simulation. Produce a classification of the higher essay protocols with respect to applicability in combinations of words to use, small/large networks, and value essay mobile/semi-mobile nodes. Recommend protocols for specific network scenarios. 1.3 Related work Many routing protocols have been proposed , but few comparisons between the different protocols have been made. Of the work that has been done in this field, only the work done by essay on science and health the Monarch1 project at Carnegie Mellon University (CMU) has compared some of the value education different proposed routing protocols and evaluated them based on the same quantitative metrics. Computer Cause! The result was presented in the article “A performance comparison of multi-hop ad hoc wireless network routing protocols”  that was released in the beginning of October 1998. There exist some other simulation results  that have been done on individual protocols. These simulations have however not used the same metrics and are therefore not comparable with each other. Value Essay! In parallel with our master thesis, a master thesis project in work key to success, Gothenburg  implemented the AODV  protocol and tested it in value higher education essay, a environment that consisted of 5 computers with wireless interfaces. The cooperation between our projects and computer cause their project made it possible to share thoughts and ideas with each other. 1.4 Project organization The following persons have been involved in this master thesis project: Simulation study and master thesis authors M.Sc.
Tony Larsson M.Sc. Nicklas Hedman Supervisor at higher, Ericsson Telecom AB, Switchlab Tekn.Lic. Per Johansson Examiner at short success, Lulea University of Technology Ph. D. Mikael Degermark Implementation study at Ericsson Mobile data design (ERV) in Gothenburg M.Sc. Johan Kopman M.Sc.
Jerry Svedlund Supervisor at ERV M.Sc. Christoffer Kanljung Contribution of realistic scenarios Ph.D. student at Chalmers University of Technology: Bartosz Mielczarek 1 MObile Networking ARCHitectures 10 1.5 Disposition This report consists of 8 chapters and two appendices. Chapters 1 and higher 2 explain the friends with benefits research paper concept of ad-hoc networks and value education essay routing in general. On Citizenship For Kids! Chapter 3 describes the education different routing protocols, analyzes and compares them. Chapters 4 and 5 describe the simulator and the simulations that were made. Friends With! Chapter 6 describes the implementation study of AODV that was made in Gothenburg.
Chapter 7 concludes the whole report and higher chapter 8 is the friends with benefits research references that we have used. The appendices contain some terminology, details about the higher education implementation of AODV that we did for the simulator and some screenshots of the simulator. 1.6 Abbreviations AODV CBR CBRP DSDV DSR IEEE IETF LAN IP MAC MANET OLSR PDA QoS TCP TORA UDP WINET ZRP Ad-hoc On-demand Distance Vector Constant Bit Rate Cluster Based Routing Protocol Destination Sequenced Distance Vector Dynamic Source Routing Institute of Electrical and Electronics Engineers Internet Engineering Task Force Local Area Network Internet Protocol Media Access Protocol Mobile Ad-hoc NETworks Optimized Link State Routing Protocol Personal Digital Assistant Quality of Service Transmission Control Protocol Temporally Ordered Routing Algorithm User Datagram Protocol Wireless InterNET Zone Routing Protocol 11 2 General Concepts 2.1 Wireless ad-hoc networks 2.1.1 General A wireless ad-hoc network is a collection of mobile/semi-mobile nodes with no pre-established infrastructure, forming a temporary network. Each of the nodes has a wireless interface and communicate with each other over either radio or infrared. Good Words To Use! Laptop computers and personal digital assistants that communicate directly with each other are some examples of nodes in value higher essay, an ad-hoc network.
Nodes in the adhoc network are often mobile, but can also consist of stationary nodes, such as access points to the Internet. Semi mobile nodes can be used to deploy relay points in areas where relay points might be needed temporarily. Figure 1 shows a simple ad-hoc network with three nodes. The outermost nodes are not within transmitter range of each other. However the middle node can be used to forward packets between the outermost nodes.
The middle node is resume length acting as a router and the three nodes have formed an ad-hoc network. Figure 1: Example of a simple ad-hoc network with three participating nodes. Value Higher Education Essay! An ad-hoc network uses no centralized administration. Essay On Citizenship! This is to be sure that the network wont collapse just because one of the mobile nodes moves out of transmitter range of the others. Nodes should be able to enter/leave the network as they wish. Because of the limited transmitter range of the nodes, multiple hops may be needed to reach other nodes.
Every node wishing to participate in an ad-hoc network must be willing to forward packets for other nodes. Thus every node acts both as a host and as a router. A node can be viewed as an abstract entity consisting of a router and a set of affiliated mobile hosts (Figure 2). A router is an entity, which, among other things runs a routing protocol. A mobile host is simply an IP-addressable host/entity in value higher essay, the traditional sense. Ad-hoc networks are also capable of handling topology changes and malfunctions in nodes. It is fixed through network reconfiguration. For instance, if a node leaves the on science hazards network and causes link breakages, affected nodes can easily request new routes and the problem will be solved. This will slightly increase the delay, but the network will still be operational.
12 Wireless ad-hoc networks take advantage of the nature of the wireless communication medium. Higher Education! In other words, in a wired network the physical cabling is done a priori restricting the on science and health hazards connection topology of the nodes. This restriction is not present in the wireless domain and, provided that two nodes are within transmitter range of each other, an instantaneous link between them may form. Host Host Router Host Figure 2: Block diagram of a mobile node acting both as hosts and higher essay as router. 2.1.2 Usage There is no clear picture of what these kinds of networks will be used for.
The suggestions vary from resume length, document sharing at conferences to infrastructure enhancements and military applications. Value Education! In areas where no infrastructure such as the Internet is available an ad-hoc network could be used by english good words to use a group of essay, wireless mobile hosts. This can be the case in areas where a network infrastructure may be undesirable due to friends with benefits research paper, reasons such as cost or convenience. Examples of such situations include disaster recovery personnel or military troops in cases where the normal infrastructure is either unavailable or destroyed. Other examples include business associates wishing to share files in an airport terminal, or a class of students needing to interact during a lecture. If each mobile host wishing to higher education essay, communicate is equipped with a wireless local area network interface, the group of mobile hosts may form an ad-hoc network.
Access to the Internet and on science hazards access to resources in networks such as printers are features that probably also will be supported. 2.1.3 Characteristics Ad-hoc networks are often characterized by a dynamic topology due to value higher education, the fact that nodes change their physical location by moving around. This favors routing protocols that dynamically discover routes over conventional routing algorithms like distant vector and link state . Another characteristic is that a host/node have very limited CPU capacity, storage capacity, battery power and bandwidth, also referred to as a “thin client”. This means that the power usage must be limited thus leading to a limited transmitter range. The access media, the radio environment, also has special characteristics that must be considered when designing protocols for ad-hoc networks. Essay! One example of this may be unidirectional links. These links arise when for example two nodes have different strength on their transmitters, allowing only value higher essay one of the host to hear the other, but can also arise from disturbances from the surroundings.
Multihop in on science hazards, a radio environment may result in an overall transmit capacity gain and education essay power gain, due to the squared relation between coverage and required output power. By using multihop, nodes can transmit the packets with a much lower output power. Resume Length! 13 2.2 Routing Because of the fact that it may be necessary to hop several hops (multi-hop) before a packet reaches the destination, a routing protocol is needed. The routing protocol has two main functions, selection of routes for various source-destination pairs and the delivery of messages to their correct destination. The second function is conceptually straightforward using a variety of protocols and data structures (routing tables). Higher Education! This report is focused on selecting and finding routes. 2.2.1 Conventional protocols If a routing protocol is needed, why not use a conventional routing protocol like link state or distance vector? They are well tested and with research most computer communications people are familiar with them. Higher Education! The main problem with link-state and friends benefits research paper distance vector is that they are designed for a static topology, which means that they would have problems to converge to a steady state in an ad-hoc network with a very frequently changing topology. Value Education! Link state and distance vector would probably work very well in an ad-hoc network with low mobility, i.e. a network where the topology is not changing very often. The problem that still remains is that link-state and distance-vector are highly dependent on periodic control messages.
As the number of network nodes can be large, the potential number of words to use, destinations is also large. Value Higher Education Essay! This requires large and frequent exchange of data among the network nodes. This is in contradiction with the fact that all updates in a wireless interconnected ad hoc network are transmitted over the air and thus are costly in resources such as bandwidth, battery power and CPU. Because both link-state and distance vector tries to maintain routes to all reachable destinations, it is essay work key to success necessary to maintain these routes and value education essay this also wastes resources for short on hard work key to the same reason as above. Another characteristic for conventional protocols are that they assume bi-directional links, e.g. Value Education! that the transmission between two hosts works equally well in both directions. In the wireless radio environment this is not always the case. Because many of the proposed ad-hoc routing protocols have a traditional routing protocol as underlying algorithm, it is necessary to on citizenship for kids, understand the basic operation for conventional protocols like distance vector, link state and source routing. Value Higher Essay! 2.2.2 Link State In link-state routing , each node maintains a view of the complete topology with a cost for each link. To keep these costs consistent; each node periodically broadcasts the link costs of its outgoing links to all other nodes using flooding. As each node receives this information, it updates its view of the network and applies a shortest path algorithm to choose the next-hop for each destination. Some link costs in a node view can be incorrect because of long propagation delays, partitioned networks, etc.
Such inconsistent network topology views can lead to resume length, formation of routing-loops. These loops are however short-lived, because they disappear in the time it takes a message to traverse the diameter of the network. 2.2.3 Distance Vector In distance vector  each node only monitors the cost of its outgoing links, but instead of broadcasting this information to all nodes, it periodically broadcasts to each of value higher education, its neighbors an estimate of the essay for kids shortest distance to every other node in the network. The receiving nodes then use this information to recalculate the routing tables, by value higher essay using a shortest path algorithm. Compared to link-state, distance vector is more computation efficient, easier to implement and requires much less storage space. However, it is essay on citizenship well known that distance vector can cause the education essay formation of both short-lived and long-lived routing loops. Good In Essays! The primary cause for this is that the value higher education essay nodes choose their next-hops in a completely distributed manner based on on citizenship for kids information that can be stale. 2.2.4 Source Routing Source routing  means that each packet must carry the complete path that the packet should take through the network. The routing decision is higher education therefore made at short on hard work success, the source. The advantage with this approach is that it is very easy to avoid routing loops.
The disadvantage is that each packet requires a slight overhead. 14 2.2.5 Flooding Many routing protocols uses broadcast to distribute control information, that is, send the control information from an origin node to all other nodes. A widely used form of broadcasting is flooding  and operates as follows. The origin node sends its information to value higher education, its neighbors (in the wireless case, this means all nodes that are within transmitter range). The neighbors relay it to their neighbors and so on, until the packet has reached all nodes in the network.
A node will only relay a packet once and to ensure this some sort of sequence number can be used. This sequence number is increased for each new packet a node sends. 2.2.6 Classification Routing protocols can be classified  into different categories depending on their properties. Revolution! N N N Centralized vs. Distributed Static vs.
Adaptive Reactive vs. Proactive One way to higher education essay, categorize the routing protocols is to divide them into centralized and distributed algorithms. In centralized algorithms, all route choices are made at a central node, while in distributed algorithms, the computation of short on hard is the key to success, routes is shared among the network nodes. Another classification of routing protocols relates to whether they change routes in response to the traffic input patterns. In static algorithms, the value higher education route used by source-destination pairs is and health fixed regardless of traffic conditions. It can only change in response to a node or link failure. This type of algorithm cannot achieve high throughput under a broad variety of traffic input patterns. Most major packet networks uses some form of adaptive routing where the routes used to route between source-destination pairs may change in value essay, response to congestion A third classification that is resume length more related to ad-hoc networks is to higher education, classify the routing algorithms as either proactive or reactive. Essay! Proactive protocols attempt to continuously evaluate the routes within the network, so that when a packet needs to higher essay, be forwarded, the computer route is already known and education essay can be immediately used. Computer Revolution And Effect! The family of Distance-Vector protocols is an education, example of a proactive scheme.
Reactive protocols, on the other hand, invoke a route determination procedure on short essay work key to demand only. Value Essay! Thus, when a route is needed, some sort of global search procedure is employed. The family of classical flooding algorithms belongs to the reactive group. On Science And Health! Proactive schemes have the advantage that when a route is needed, the delay before actual packets can be sent is value higher education essay very small. On the other side proactive schemes needs time to converge to a steady state. This can cause problems if the topology is changing frequently. 15 3 Ad-hoc routing protocols This chapter describes the different ad-hoc routing protocols that we have chosen to simulate and essay on citizenship analyze.
3.1 Desirable properties If the conventional routing protocols do not meet our demands, we need a new routing protocol. The question is education what properties such protocols should have? These are some of the english properties  that are desirable: Distributed operation The protocol should of course be distributed. Education! It should not be dependent on a centralized controlling node. Short Essay Work Is The! This is the case even for stationary networks. The difference is that nodes in education, an ad-hoc network can enter/leave the network very easily and because of mobility the on hard work key to network can be partitioned. Loop free To improve the overall performance, we want the routing protocol to guarantee that the routes supplied are loop-free. This avoids any waste of bandwidth or CPU consumption. Value Higher! Demand based operation To minimize the control overhead in the network and thus not wasting network resources more than necessary, the protocol should be reactive. This means that the protocol should only friends with benefits react when needed and that the protocol should not periodically broadcast control information. Unidirectional link support The radio environment can cause the value higher formation of unidirectional links.
Utilization of these links and essay and health not only the bi-directional links improves the routing protocol performance. Security The radio environment is especially vulnerable to impersonation attacks, so to ensure the wanted behavior from the higher education essay routing protocol, we need some sort of preventive security measures. Authentication and encryption is probably the way to go and the problem here lies within distributing keys among the with benefits nodes in the ad-hoc network. There are also discussions about using IP-sec  that uses tunneling to transport all packets. Power conservation The nodes in an ad-hoc network can be laptops and thin clients, such as PDAs that are very limited in battery power and therefore uses some sort of stand-by mode to save power.
It is therefore important that the routing protocol has support for these sleep-modes. Multiple routes To reduce the number of reactions to value education essay, topological changes and congestion multiple routes could be used. If one route has become invalid, it is possible that another stored route could still be valid and thus saving the routing protocol from initiating another route discovery procedure. Quality of service support Some sort of Quality of Service support is revolution and effect probably necessary to incorporate into the routing protocol. Higher Essay! This has a lot to do with what these networks will be used for. It could for essay on hard work instance be real-time traffic support. None of the proposed protocols from higher education, MANET have all these properties, but it is necessary to remember that the protocols are still under development and are probably extended with more functionality. The primary function is still to find a route to the destination, not to find the best/optimal/shortest-path route. The remainder of this chapter will describe the different routing protocols and analyze them theoretically.
16 3.2 MANET IETF has a working group named MANET (Mobile Ad-hoc Networks)  that is working in short essay on hard work is the success, the field of value higher, adhoc networks. English To Use In Essays! They are currently developing routing specifications for ad-hoc IP networks that support scaling to a couple of higher essay, hundred nodes. Their goal is to be finished in the end of year 1999 and on citizenship for kids then introduce these specifications to the Internet standard tracks. Even if MANET currently is working on routing protocols, it also serves as a meeting place and forum, so people can discuss issues concerning ad-hoc networks. Currently they have seven routing protocol drafts: N N N N N N N N AODV - Ad-hoc On Demand Distance Vector  ZRP - Zone Routing Protocol  TORA / IMEP - Temporally Ordered Routing Algorithm / Internet MANET Encapsulation Protocol  DSR - Dynamic Source Routing  CBRP - Cluster Based Routing Protocol  CEDAR - Core Extraction Distributed Ad hoc Routing  AMRoute – Ad-hoc Multicast Routing Protocol  OLSR - Optimized Link State Routing Protocol  Of these proposed protocols we have chosen to higher, analyze AODV, DSR, ZRP, CBRP and TORA theoretically. We have also analyzed DSDV, which is a proactive approach, as opposed to the other reactive protocols. We have not analyzed AMRoute because it is a multicast routing protocol, neither CEDAR because it is essay work is the primary a QoS routing protocol, nor OLSR, because it was submitted as an Internet draft so late. In those cases where a protocol supports both unicast and multicast routing we have only looked at the unicast routing part.
Of the theoretically analyzed protocols we have done simulations on AODV and DSR. 3.3 Destination Sequenced Distance Vector - DSDV 3.3.1 Description DSDV  is a hop-by-hop distance vector routing protocol that in each node has a routing table that for value essay all reachable destinations stores the next-hop and number of english good, hops for that destination. Like distance-vector, DSDV requires that each node periodically broadcast routing updates. The advantage with DSDV over value education, traditional distance vector protocols is that DSDV guarantees loop-freedom. Good To Use! To guarantee loop-freedom DSDV uses a sequence numbers to value higher, tag each route. Essay On Citizenship! The sequence number shows the freshness of a route and value essay routes with higher sequence numbers are favorable. A route R is considered more favorable than R' if R has a greater sequence number or, if the routes have the same sequence number but R has lower hop-count. The sequence number is increased when a node A detects that a route to a destination D has broken. English Good To Use! So the next time node A advertises its routes, it will advertise the route to D with an infinite hop-count and a sequence number that is larger than before. DSDV basically is value distance vector with small adjustments to make it better suited for ad-hoc networks.
These adjustments consist of triggered updates that will take care of topology changes in the time between broadcasts. To reduce the amount of friends with benefits research, information in value higher education, these packets there are two types of update messages defined: full and computer incremental dump. The full dump carries all available routing information and the incremental dump that only carries the information that has changed since the last dump. 3.3.2 Properties Because DSDV is dependent on value education periodic broadcasts it needs some time to converge before a route can be used. This converge time can probably be considered negligible in a static wired network, where the topology is not changing so frequently. In an ad-hoc network on the other hand, where the topology is expected to be very dynamic, this converge time will probably mean a lot of dropped packets before a valid route is detected. Friends Research Paper! The periodic broadcasts also add a large amount of overhead into the network. 17 3.4 Ad-hoc On Demand Distance vector - AODV 3.4.1 Description The Ad Hoc On-Demand Distance Vector (AODV)  routing protocol enables multi-hop routing between participating mobile nodes wishing to establish and maintain an education, ad-hoc network. AODV is based upon the distance vector algorithm. The difference is that AODV is reactive, as opposed to resume length, proactive protocols like DV, i.e. AODV only requests a route when needed and higher education essay does not require nodes to maintain routes to destinations that are not actively used in communications.
As long as the endpoints of a communication connection have valid routes to each other, AODV does not play any role. Resume Length! Features of value education, this protocol include loop freedom and that link breakages cause immediate notifications to be sent to the affected set of nodes, but only that set. Additionally, AODV has support for multicast routing and avoids the Bellman Ford counting to infinity problem . The use of destination sequence numbers guarantees that a route is fresh. The algorithm uses different messages to discover and maintain links. Whenever a node wants to try and computer cause find a route to another node, it broadcasts a Route Request (RREQ) to all its neighbors. The RREQ propagates through the network until it reaches the value destination or a node with a fresh enough route to the destination. Then the route is made available by unicasting a RREP back to the source. The algorithm uses hello messages (a special RREP) that are broadcasted periodically to short essay key to, the immediate neighbors. These hello messages are local advertisements for value essay the continued presence of the node and neighbors using routes through the broadcasting node will continue to friends benefits paper, mark the value routes as valid. With Benefits Research Paper! If hello messages stop coming from a particular node, the neighbor can assume that the node has moved away and higher education essay mark that link to the node as broken and notify the affected set of essay on science and health, nodes by sending a link failure notification (a special RREP) to that set of nodes.
AODV also has a multicast route invalidation message, but because we do not cover multicast in this report we will not discuss this any further. Route table management AODV needs to keep track of the following information for essay each route table entry: N N N N N N N Destination IP Address: IP address for the destination node. Destination Sequence Number: Sequence number for this destination. Hop Count: Number of hops to the destination. Resume Length! Next Hop: The neighbor, which has been designated to value higher education, forward packets to the destination for this route entry. Lifetime: The time for which the route is considered valid. Active neighbor list: Neighbor nodes that are actively using this route entry. Essay And Health! Request buffer: Makes sure that a request is only processed once. Route discovery A node broadcasts a RREQ when it needs a route to a destination and does not have one available. This can happen if the route to the destination is unknown, or if a previously valid route expires. After broadcasting a RREQ, the node waits for a RREP.
If the reply is not received within a certain time, the node may rebroadcast the education essay RREQ or assume that there is no route to the destination. Forwarding of RREQs is done when the node receiving a RREQ does not have a route to the destination. It then rebroadcast the RREQ. The node also creates a temporary reverse route to computer revolution cause and effect, the Source IP Address in its routing table with next hop equal to the IP address field of the neighboring node that sent the broadcast RREQ. This is done to keep track of a route back to the original node making the request, and value higher education essay might be used for an eventual RREP to find its way back to the requesting node. Words In Essays! The route is temporary in the sense that it is valid for a much shorter time, than an value education, actual route entry. Essay On Hard Key To Success! When the RREQ reaches a node that either is the destination node or a node with a valid route to the destination, a RREP is generated and higher essay unicasted back to the requesting node.
While this RREP is forwarded, a route is created to the destination and computer cause and effect when the RREP reaches the source node, there exists a route from the source to the destination. Value Higher Essay! 18 Route maintenance When a node detects that a route to short essay work key to success, a neighbor no longer is valid, it will remove the routing entry and send a link failure message, a triggered route reply message to the neighbors that are actively using the route, informing them that this route no longer is valid. Value Essay! For this purpose AODV uses a active neighbor list to keep track of the neighbors that are using a particular route. The nodes that receive this message will repeat this procedure. The message will eventually be received by resume length the affected sources that can chose to either stop sending data or requesting a new route by value education essay sending out a new RREQ. 3.4.2 Properties The advantage with AODV compared to classical routing protocols like distance vector and resume length link-state is that AODV has greatly reduced the number of routing messages in value education, the network. AODV achieves this by revolution cause and effect using a reactive approach. This is probably necessary in an ad-hoc network to get reasonably performance when the topology is changing often. AODV is also routing in the more traditional sense compared to for instance source routing based proposals like DSR (see 3.5). The advantage with a more traditional routing protocol in an ad-hoc network is higher education essay that connections from the ad-hoc network to a wired network like the Internet is most likely easier.
The sequence numbers that AODV uses represents the freshness of a route and is increased when something happens in the surrounding area. The sequence prevents loops from on hard work is the, being formed, but can however also be the cause for new problems. Higher Education! What happens for essay work success instance when the higher sequence numbers no longer are synchronized in the network? This can happen when the network becomes partitioned, or the sequence numbers wrap around. AODV only support one route for each destination. It should however be fairly easy to modify AODV, so that it supports several routes per short is the success, destination. Instead of requesting a new route when an value essay, old route becomes invalid, the next stored route to that destination could be tried.
The probability for that route to still be valid should be rather high. Although the Triggered Route Replies are reduced in number by only sending the Triggered Route Replies to essay on citizenship for kids, affected senders, they need to traverse the whole way from the failure to the senders. This distance can be quite high in higher essay, numbers of on science hazards, hops. AODV sends one Triggered RREP for education every active neighbor in the active neighbor list for all entries that have been affected of a link failure. This can mean that each active neighbor can receive several triggered RREPs informing about the same link failure, but for different destinations, if a large fraction of the network traffic is routed through the same node and this node goes down. Good To Use! An aggregated solution would be more appropriate here.
AODV uses hello messages at the IP-level. This means that AODV does not need support from the link layer to work properly. It is however questionable if this kind of protocol can operate with good performance without support from the link layer. Value Higher Essay! The hello messages adds a significant overhead to the protocol. AODV does not support unidirectional links.
When a node receives a RREQ, it will setup a reverse route to the source by using the node that forwarded the RREQ as nexthop. This means that the route reply, in most cases is unicasted back the on citizenship for kids same way as the route request used. Unidirectional link support would make it possible to utilize all links and not only the bi-directional links. It is however questionable if unidirectional links are desirable in a real environment. The acknowledgements in the MAC protocol IEEE 802.11 would for education instance not work with unidirectional links. 19 3.5 Dynamic Source Routing - DSR 3.5.1 Description Dynamic Source Routing (DSR)  also belongs to on citizenship, the class of reactive protocols and allows nodes to dynamically discover a route across multiple network hops to value, any destination. Friends Benefits Research Paper! Source routing means that each packet in its header carries the complete ordered list of nodes through which the packet must pass. DSR uses no periodic routing messages (e.g. no router advertisements), thereby reducing network bandwidth overhead, conserving battery power and value essay avoiding large routing updates throughout the ad-hoc network. Instead DSR relies on support from the essay for kids MAC layer (the MAC layer should inform the routing protocol about link failures). The two basic modes of operation in higher education, DSR are route discovery and route maintenance. Route discovery Route discovery is the mechanism whereby a node X wishing to send a packet to friends benefits research paper, Y, obtains the source route to Y. Node X requests a route by broadcasting a Route Request (RREQ) packet.
Every node receiving this RREQ searches through its route cache for value higher education a route to benefits paper, the requested destination. DSR stores all known routes in its route cache. If no route is found, it forwards the higher essay RREQ further and cause adds its own address to the recorded hop sequence. This request propagates through the network until either the destination or a node with a route to the destination is reached. When this happen a Route Reply (RREP) is unicasted back to the originator. This RREP packet contains the sequence of network hops through which it may reach the target. In Route Discovery, a node first sends a RREQ with the maximum propagation limit (hop limit) set to zero, prohibiting its neighbors from rebroadcasting it.
At the cost of a single broadcast packet, this mechanism allows a node to query the route caches of all its neighbors. Nodes can also operate their network interface in promiscuous mode, disabling the interface address filtering and causing the network protocol to receive all packets that the interface overhears. These packets are scanned for useful source routes or route error messages and then discarded. The route back to higher education, the originator can be retrieved in several ways. The simplest way is to reverse the hop record in the packet. Essay On Citizenship For Kids! However this assumes symmetrical links. Value Education Essay! To deal with this, DSR checks the route cache of the replying node. If a route is short is the key to found, it is used instead.
Another way is to piggyback the reply on a RREQ targeted at the originator. This means that DSR can compute correct routes in the presence of asymmetric (unidirectional) links. Once a route is found, it is higher education stored in the cache with a time stamp and friends paper the route maintenance phase begins. Route maintenance Route maintenance is the mechanism by which a packet sender S detects if the network topology has changed so that it can no longer use its route to the destination D. This might happen because a host listed in value essay, a source route, move out of wireless transmission range or is turned off making the resume length route unusable. A failed link is detected by either actively monitoring acknowledgements or passively by running in value, promiscuous mode, overhearing that a packet is forwarded by a neighboring node. When route maintenance detects a problem with a route in use, a route error packet is sent back to the source node. When this error packet is received, the hop in essay on science and health, error is removed from this hosts route cache, and all routes that contain this hop are truncated at this point.
3.5.2 Properties DSR uses the key advantage of source routing. Intermediate nodes do not need to maintain up-to-date routing information in order to route the packets they forward. There is also no need for periodic routing advertisement messages, which will lead to reduce network bandwidth overhead, particularly during periods when little or no significant host movement is taking place. Battery power is also conserved on the mobile hosts, both by not sending the advertisements and by not needing to higher education essay, receive them, a host could go down to sleep instead. This protocol has the advantage of learning routes by english good words in essays scanning for information in packets that are received. A route from value higher education essay, A to C through B means that A learns the resume length route to C, but also that it will learn the route to B. Value Higher Education Essay! The source route will also mean that B learns the route to A and C and that C learns the good words in essays route to A and B. This form of education essay, active learning is very good and reduces overhead in the network. 20 However, each packet carries a slight overhead containing the source route of the packet. Essay! This overhead grows when the packet has to go through more hops to reach the destination. So the packets sent will be slightly bigger, because of the overhead.
Running the interfaces in promiscuous mode is a serious security issue. Since the address filtering of the interface is value higher turned off and all packets are scanned for information. A potential intruder could listen to all packets and scan them for essay work key to useful information such as passwords and credit card numbers. Applications have to provide the value higher education essay security by encrypting their data packets before transmission. The routing protocols are prime targets for impersonation attacks and english words to use in essays must therefore also be encrypted. One way to achieve this is to use IPsec . DSR also has support for unidirectional links by the use of piggybacking the source route a new request. Education! This can increase the performance in essay on science, scenarios where we have a lot of unidirectional links.
We must however have a MAC protocol that also supports this. 3.6 Zone Routing Protocol - ZRP 3.6.1 Description Zone Routing Protocol (ZRP)  is higher essay a hybrid of a reactive and a proactive protocol. It divides the network into several routing zones and specifies two totally detached protocols that operate inside and between the routing zones. The Intrazone Routing Protocol (IARP) operates inside the routing zone and learns the minimum distance and routes to all the english good words to use in essays nodes within the value essay zone. Friends Benefits Research Paper! The protocol is not defined and can include any number of proactive protocols, such as Distance Vector or link-state routing. Different zones may operate with different intrazone protocols as long as the protocols are restricted to those zones. A change in topology means that update information only propagates within the affected routing zones as opposed to affecting the entire network. The second protocol, the Interzone Routing Protocol (IERP) is value education essay reactive and is used for finding routes between different routing zones.
This is resume length useful if the destination node does not lie within the value higher essay routing zone. English To Use! The protocol then broadcasts (i.e. Value Essay! bordercasts) a Route REQuest (RREQ) to all border nodes within the routing zone, which in turn forwards the short essay on hard work is the key to success request if the destination node is not found within their routing zone. This procedure is value education repeated until the resume length requested node is essay found and a route reply is sent back to the source indicating the route. IERP uses a Bordercast Resolution Protocol (BRP)  that is included in ZRP. Resume Length! BRP provides bordercasting services, which do not exist in IP. Bordercasting is the process of sending IP datagrams from one node to all its peripheral nodes.
BRP keeps track of the peripheral nodes and resolves a border cast address to the individual IP-addresses of the value higher peripheral nodes. The message that was bordercasted is on hard work is the success then encapsulated into a BRP packet and sent to each peripheral node. Value Essay! Routing Zone A routing zone is defined as a set of nodes, within a specific minimum distance in number of hops from the node in question. The distance is referred to as the zone radius. In the example network (Figure 3), node S, A, F, B, C, G and H, all lie within a radius of two from node F. Even though node B also has a distance of key to success, 3 hops from value education, node F, it is resume length included in the zone since the essay shortest distance is only 2 hops. Border nodes or peripheral nodes are nodes whose minimum distance to essay for kids, the node in question is equal exactly to the zone radius. In Figure 3, nodes B and F are border nodes to S. Value Education! Consider the network in Figure 3. Node S wants to send a packet to node D. Since node D is computer revolution cause and effect not in the routing zone of S, a route request is higher education sent to on science, the border nodes B and F. Higher Education Essay! Each border node checks to see if D is in their routing zone. Neither B nor F finds the requested node in their routing zone; thus the request is for kids forwarded to value higher education essay, the respectively border nodes. F sends the friends benefits request to S, B, C and H while B sends the request to S, F, E and G. Now the higher education essay requested node D is found within the routing zone of both C and friends benefits research E thus a reply is generated and sent back towards the source node S. 21 B E A Zone for D C S D F Zone for S G H Zone for F Figure 3: Network using ZRP. The dashed squares show the routing zones for education essay nodes S and D. To prevent the requests from essay on science hazards, going back to previously queried routing zone, a Processed Request List is used. This list stores previously processed requests and if a node receives a request that it already has processed, it is value essay simply dropped.
3.6.2 Properties ZRP is a very interesting protocol and for kids can be adjusted of its operation to the current network operational conditions (e.g. change the routing zone diameter). However this is not done dynamically, but instead it is suggested that this zone radius should be set by the administration of the network or with a default value by the manufacturer. The performance of this protocol depends quite a lot on this decision. Since this is a hybrid between proactive and reactive schemes, this protocol use advantages from value education essay, both. Routes can be found very fast within the routing zone, while routes outside the zone can be found by efficiently querying selected nodes in the network. One problem is however that the proactive intrazone routing protocol is not specified. And Health Hazards! The use of different intrazone routing protocols would mean that the nodes would have to support several different routing protocols. This is not a good idea when dealing with thin clients. It is better to use the same intrazone routing protocol in the entire network. ZRP also limits propagation of education essay, information about topological changes to the neighborhood of the change only (as opposed to resume length, a fully proactive scheme, which would basically flood the entire network when a change in topology occurred).
However, a change in topology can affect several routing zones. 3.7 Temporally-Ordered Routing Algorithm - TORA 3.7.1 Description Temporally Ordered Routing Algorithm (TORA)  is a distributed routing protocol. The basic underlying algorithm is value one in a family referred to words in essays, as link reversal algorithms. TORA is designed to minimize reaction to topological changes. A key concept in value higher education essay, its design is that control messages are typically localized to a very small set of nodes. It guarantees that all routes are loop-free (temporary loops may form), and revolution and effect typically provides multiple routes for any source/destination pair.
It provides only the higher essay routing mechanism and depends on short on hard work is the key to success Internet MANET Encapsulation Protocol (IMEP ) for other underlying functions. TORA can be separated into three basic functions: creating routes, maintaining routes, and value erasing routes. The creation of routes basically assigns directions to links in computer, an undirected network or portion of the network, building a directed acyclic graph (DAG) rooted at the destination (See Figure 4). Value Education! 22 D Figure 4: Directed acyclic graph rooted at destination. Short Work Is The Success! TORA associates a height with each node in the network. All messages in the network flow downstream, from a node with higher height to a node with lower height. Value Education! Routes are discovered using Query (QRY) and Update (UPD) packets. When a node with no downstream links needs a route to a destination, it will broadcast a QRY packet. This QRY packet will propagate through the network until it reaches a node that has a route or the destination itself. Friends Benefits! Such a node will then broadcast a UPD packet that contains the node height. Every node receiving this UPD packet will set its own height to a larger height than specified in the UPD message.
The node will then broadcast its own UPD packet. This will result in a number of directed links from the originator of the QRY packet to the destination. This process can result in multiple routes. Maintaining routes refers to essay, reacting to topological changes in the network in a manner such that routes to the destination are re-established within a finite time, meaning that its directed portions return to a destination-oriented graph within a finite time. Upon detection of a network partition, all links in the portion of the network that has become partitioned from the destination are marked as undirected to erase invalid routes. The erasing of routes is resume length done using clear (CLR) messages.
3.7.2 Properties The protocols underlying link reversal algorithm will react to link changes through a simple localized single pass of the education distributed algorithm. This prevents CLR packets to propagate too far in the network. A comparison made by on hard the CMU Monarch project has however shown that the overhead in TORA is quite large because of the value higher essay use of IMEP. The graph is english rooted at value higher, the destination, which has the lowest height. However, the source originating the QRY does not necessarily have the highest height. This can lead to the situation, where multiple routes are possible from the essay on hard success source to the destination, but only one route will be discovered. The reason for this is that the height is initially based on the distance in number of hops from the destination.
23 3.8 Internet MANET Encapsulation Protocol - IMEP 3.8.1 Description IMEP  is a protocol designed to support the operation of many routing protocols in Ad-hoc networks. The idea is to have a common general protocol that all routing protocols can make use of (see Figure 5). It incorporates many common mechanisms that the value education upper-layer protocol may need. These include: N N N N N Link status sensing Control message aggregation and encapsulation Broadcast reliability Network-layer address resolution Hooks for interrouter security authentication procedures IMEP also provides an essay on hard work is the, architecture for MANET router identification, interface identification and addressing. IMEPs purpose is to improve overall performance by reducing the value essay number of control messages and to put common functionality into one unified, generic protocol useful to all upper-level routing protocols. Resume Length! Routing IMEP IP Figure 5: IMEP in the protocol stack. Of the currently purposed protocols, only TORA and OLSR use IMEP. It must however be noted that TORA and IMEP where designed by the same author. 3.8.2 Properties The idea to higher, have a general protocol for common basic features is good, but from essay, a performance point of view this is not such a good idea. Education Essay! It adds another layer to english in essays, the protocol stack. Higher Education! As the work by the CMU Monarch projects has shown , IMEP generates a lot of overhead, mainly because of IMEPs neighbor discovery mechanism that generates at least one hello message per second, but also because of the friends research paper reliable in-order delivery of the packets that IMEP provides.
3.9 Cluster Based Routing Protocol - CBRP 3.9.1 Description The idea behind CBRP  is to divide the nodes of an ad-hoc network into a number of overlapping or disjoint clusters. One node is elected as cluster head for each cluster. This cluster head maintains the higher membership information for the cluster. Words To Use! Inter-cluster routes (routes within a cluster) are discovered dynamically using the membership information. 24 CBRP is based on source routing, similar to value higher, DSR. This means that intracluster routes (routes between clusters) are found by essay flooding the network with Route Requests (RREQ). The difference is higher that the cluster structure generally means that the number of nodes disturbed are much less. Flat routing protocols, i.e. only one level of hierarchy, might suffer from excessive overhead when scaled up. CBRP is like the english good to use other protocols fully distributed. This is necessary because of the very dynamic topology of the ad-hoc network. Furthermore, the protocol takes into consideration the existence of unidirectional links.
Link sensing Each node in CBRP knows its bi-directional links to its neighbors as well as unidirectional links from its neighbors to itself. To handle this, each node must maintain a Neighbor Table (see Table 1). Table 1: Neighbor ID Neighbor 1 Neighbor 2 … Neighbor n Neighbor table. Link status Bi/unidirectional link to me Bi/unidirectional link to me … Bi/unidirectional link to me Role Is 1 a cluster head or member Is 2 a cluster head or member … Is n a cluster head or member Each node periodically broadcasts its neighbor table in a hello message. The hello message contains the node ID, the nodes role (cluster head, cluster member or undecided) and the neighbor table. Value Education! The hello messages are used to update the neighbor tables at each node. If no hello message is received from a certain node, that entry will be removed from the table. Clusters The cluster formation algorithm is very simple, the node with lowest node ID is resume length elected as the cluster head. Value Higher Education Essay! The nodes use the information in the hello messages to decide whether or not they are the resume length cluster heads. The cluster head regards all nodes it has bi-directinal links to as its member nodes.
A node regards itself as a member node to a particular cluster if it has a bi-directinal link to the cluster head. It is possible for a node to belong to several clusters. Value Higher! Cluster 1 Cluster 2 3 4 Cluster head Cluster head 1 2 6 Figure 6: 5 Bi-directional linked clusters. 25 Clusters are identified by their respective cluster heads, which means that the cluster head must change as infrequently as possible. Computer Revolution And Effect! The algorithm is therefore not a strict lowest ID clustering algorithm. A noncluster head never challenges the status of an existing cluster head. Only when two cluster-heads move next to each other, will one of them lose the role as cluster head. In Figure 6 node 1 is cluster head for cluster 1 and node 2 is cluster head for value higher cluster 2. Routing Routing in CBRP is based on source routing and the route discovery is done, by flooding the network with Route Requests (RREQ). Resume Length! The clustering approach however means that fewer nodes are disturbed. Value Education! This, because only the on citizenship for kids cluster heads are flooded.
If node X needs a route to node Y, node X will send out a RREQ, with a recorded source route listing only itself initially. Any node forwarding this packet will add its own ID in this RREQ. Each node forwards a RREQ only once and it never forwards it to node that already appears in value higher, the recorded route. In CBRP, a RREQ will always follow a route with the following pattern: Source-Cluster head-Gateway-Cluster head-Gateway- . -Destination A gateway node for a cluster is with benefits paper a node that knows that it has a bi-directional or a unidirectional link to a node in another cluster. In Figure 6, node 6 is gateway node for cluster 1 and node 4 is gateway node for cluster 2. The source unicasts the RREQ to its cluster head. Each cluster-head unicasts the value higher education essay RREQ to each of its bidirectionally linked neighbor clusters, which has not already appeared in the recorded route through the corresponding gateway. There does not necessarily have to be an actual bi-directional link to a bi-directional linked neighbor cluster. For instance, in Figure 6 cluster 1 has a unidirectional link to essay is the key to, cluster 2 through node 3 and cluster 2 has a unidirectional link to cluster 1 through node 5, and the clusters are therefore bidirectional linked neighbor clusters. This procedure continues until the target is found or another node can supply the education essay route. When the RREQ reaches the target, the resume length target may chose to memorize the value higher essay reversed route to resume length, the source. It then copies the recorded route to a Route Reply packet and sends it back to essay, the source.
3.9.2 Properties This protocol has a lot of common features with the earlier discussed protocols. On Hard Work Key To Success! It has a route discovery and route removal operation that has a lot in common with DSR and AODV. The clustering approach is probably a very good approach when dealing with large ad-hoc networks. The solution is more scalable than the education essay other protocols, because it uses the on citizenship for kids clustering approach that limits the number of messages that need to be sent. CBRP also has the essay advantage that it utilizes unidirectional links.
One remaining question is however how large each cluster should be. This parameter is critical to how the protocol will behave. 3.10 Comparison So far, the protocols have been analyzed theoretically. Resume Length! Table 2 summarizes and compares the result from these theoretical/qualitative analyses and value essay shows what properties the protocols have and do not have. As it can be seen from Table 2, none of the protocols support power conservation or Quality of Service. This is however work in progress and will probably be added to the protocols. All protocols are distributed, thus none of the protocols is dependent on a centralized node and can therefore easily reconfigure in with benefits research paper, the event of topology changes.
26 Table 2: Comparison between ad-hoc routing protocols. DSDV AODV DSR ZRP Loop-free Yes Yes Yes Yes Multiple routes Distributed Reactive Unidirectional link support QoS Support Multicast Security Power conservation Periodic broadcasts No Yes No No No No No No Yes No Yes Yes No No Yes No No Yes Yes Yes Yes Yes No No No No No No Yes Partially No No No No No Yes Requires reliable or sequenced data No No No No TORA/ IMEP No, short lived loops Yes Yes Yes No No No No No Yes (IMEP) Yes CBRP Yes Yes Yes Yes Yes No No No No Yes No DSDV is the only proactive protocol in essay, this comparison. Short On Hard Work Success! It is also the protocol that have most in value essay, common with traditional routing protocol in wired networks. The sequence numbers were added to ensure loop-free routes. DSDV will probably be good enough in networks, which allows the protocol to converge in essay, reasonable time. This however means that the mobility cannot be too high. Value Education! The authors of DSDV came to the same conclusions and is the designed AODV, which is a reactive version of DSDV. Value Higher Education Essay! They also added multicast capabilities, which will enhance the performance significantly when one node communicates with several nodes.
The reactive approach in AODV has many similarities with the essay for kids reactive approach of education, DSR. They both have a route discovery mode that uses request messages to find new routes. The difference is that DSR is based on revolution source routing and will learn more routes than AODV. DSR also has the essay advantage that it supports unidirectional links. DSR has however one major drawback and it is the source route that must be carried in computer, each packet. This can be quite costly, especially when QoS is going to be used. ZRP and CBRP are two very interesting proposals that divide the value network into several zones/clusters. This approach is probably a very good solution for on citizenship for kids large networks. Within the zones/clusters they have a more proactive scheme and between the zones/clusters they have a reactive scheme that have many similarities with the operation of AODV and value education essay DSR. They have for work key to success instance a route discovery phase that sends request through the network. The difference between ZRP and CBRP is how the network is value essay divided.
In ZRP all zones are overlapping and in CBRP clusters can be both overlapping and essay and health hazards disjoint. None of the presented protocols are adaptive, meaning that the protocols do not take any smart routing decisions when the value higher education essay traffic load in the network is taken into consideration. As a route selection criteria the proposed protocols use metrics such as shortest number of hops and quickest response time to essay on citizenship for kids, a request. This can lead to value education essay, the situation where all packets are routed through the friends with benefits research same node even if there exist better routes where the traffic load is not as large. Higher Essay! 27 4 Simulation Environment The simulator we have used to simulate the ad-hoc routing protocols in is the Network Simulator 2 (ns)  from Berkeley. On Citizenship For Kids! To simulate the mobile wireless radio environment we have used a mobility extension to ns that is developed by the CMU Monarch project at Carnegie Mellon University. 4.1 Network Simulator Network simulator 2 is the result of an higher education, on-going effort of research and work is the key to development that is higher education administrated by researchers at Berkeley. It is a discrete event simulator targeted at networking research. It provides substantial support for simulation of TCP, routing, and multicast protocols. The simulator is written in C++ and resume length a script language called OTcl2.
Ns uses an Otcl interpreter towards the user. This means that the user writes an OTcl script that defines the network (number of value higher education essay, nodes, links), the essay on citizenship traffic in the network (sources, destinations, type of traffic) and which protocols it will use. This script is then used by value education essay ns during the simulations. The result of the simulations is an output trace file that can be used to do data processing (calculate delay, throughput etc) and to visualize the simulation with a program called Network Animator (NAM). See Appendix C for a screenshot of NAM. NAM is resume length a very good visualization tool that visualizes the packets as they propagate through the value higher education essay network. An overview of how a simulation is done in ns is shown in Figure 7. Resume Length! Otcl script Network Simulator 2 Output Data processing Network Animator Figure 7: Network simulator 2. The current version3 of the Network simulator does not support mobile wireless environments. The Network simulator alone is only intended for stationary networks with wired links. This caused us some problems in the beginning of this master thesis.
We needed mobility and therefore started to design and implement a mobility model that would extend the simulator. Value Higher Essay! We also started to implement the AODV protocol. This implementation of AODV is compatible with NAM and therefore gives a good picture of how AODV behaves. It is very easy to follow for instance the route discovery procedure. Essay On Science And Health Hazards! About two months later, in value higher, August 1998, two separate mobility extensions were released. Resume Length! These extensions had everything that we wanted from an extension, so we decided to higher essay, use one of them. This however meant that the implementation of AODV that we made earlier no longer was compatible and had to be ported. 2 3 Object Tool Command Language Network simulator 2.1b3 28 4.2 Mobility extension There currently exist two mobility extensions to essay and health hazards, ns.
These are: N N Wireless mobility extension developed by the CMU Monarch projects . Mobility support, mobile IP and higher education essay wireless channel support developed by C. Perkins at Sun Microsystems . Essay! The ns group at value, Berkeley has as intention to paper, integrate both these extensions to higher essay, ns. On Citizenship! This work is higher however not complete yet. We have chosen to use the essay and health hazards CMU Monarch extension, because this extension is targeted at ad-hoc networks. The version of the extension that we have worked with4 adds the following features5 to the Network simulator.
Node mobility Each mobile node is an independent entity that is responsible for computing its own position and velocity as a function of time. Nodes move around according to a movement pattern specified at the beginning of the simulation. Realistic physical layers Propagation models are used to decide how far packets can travel in air. These models also consider propagation delays, capture effects and higher education essay carrier sense . MAC 802.11 An implementation of the IEEE 802.11 Media Access Protocol (MAC)  protocol was included in the extension. The MAC layer handles collision detection, fragmentation and essay on citizenship acknowledgements. This protocol may also be used to value essay, detect transmission errors. 802.11 is a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol. Work! It avoids collisions by checking the channel before using it. If the channel is free, it can start sending, if not, it must wait a random amount of time before checking again. For each retry an exponential backoff algorithm will be used.
In a wireless environment it cannot be assumed that all stations hear each other. If a station senses the medium, as free, it does not necessarily mean that the medium is free around the receiver area. This problem is known as the value higher hidden terminal problem and to overcome these problems the Collision Avoidance mechanism together with a positive acknowledgement scheme is used. The positive acknowledgement scheme means that the receiver sends an acknowledgement when it receives a packet. The sender will try to retransmit this packet until it receives the short essay on hard acknowledgement or the number of retransmits exceeds the essay maximum number of retransmits. Computer Cause! 802.11 also support power saving and security. Power saving allows packets to be buffered even if the system is asleep. Security is provided by an algorithm called Wired Equivalent Privacy (WEP). It supports authentication and essay encryption. Resume Length! WEP is a Pseudo Random Number Generator (PRNG) and is based on essay RSAs RC4. One of the most important features of 802.11 is the ad-hoc mode, which allows users to build up Wireless LANs without an infrastructure (without an access point).
Address Resolution Protocol The Address Resolution Protocol, ARP  is implemented. ARP translates IP-addresses to hardware MAC addresses. This takes place before the packets are sent down to the MAC layer. Essay On Science And Health! Ad-hockey Ad-hockey is an application that makes it possible to visualize the mobile nodes as they move around and value higher education send/receives packets. Ad-hockey can also be used as a scenario generator tool to create the input files necessary for the simulations. This is short on hard work key to success done, by higher positioning nodes in a specified area.
Each node is then given a movement pattern consisting of short essay is the, movement directions at different waypoints, speed, pause times and communication patterns. Value Essay! Screenshots of short essay is the key to success, ad-hockey can be seen in Appendix C. 4 Version 1.0.0-beta, released in the middle of higher essay, August. At the end of friends with benefits research paper, November 1998, the CMU Monarch projects released version 1.1.0 of the extension. This new version contains some bug fixes and implementations of the AODV and value higher education essay TORA protocols. 5 29 Radio network interfaces This is a model of the hardware that actually transmits the packet onto the channel with a certain power and modulation scheme .
Transmission power The radius of the transmitter with an omni-directional antenna is about 250 meters in this extension. Antenna gain and receiver sensitivity Different antennas are available for simulations. Ad-hoc routing protocols Both DSR and short on hard work is the DSDV have been implemented and added to this extension. Value Higher Essay! 4.2.1 Shared media The extension is words to use in essays based on a shared media model (Ethernet in the air). This means that all mobile nodes have one or more network interfaces that are connected to value essay, a channel (see Figure 8). A channel represents a particular radio frequency with a particular modulation and coding scheme. Channels are orthogonal, meaning that packets sent on one channel do not interfere with the words to use transmission and reception of packets on value another channel. The basic operation is as follows, every packet that is sent / put on the channel is work is the received / copied to all mobile nodes connected to the same channel.
When a mobile nodes receive a packet, it first determines if it possible for it to receive the packet. This is determined by the radio propagation model, based on the transmitter range, the distance that the higher education essay packet has traveled and the amount of bit errors. Mobile Node Mobile Node Mobile Node Channel Figure 8: Shared media model. Short On Hard Is The Key To! 4.2.2 Mobile node Each mobile node (Figure 9) makes use of a routing agent for the purpose of calculating routes to other nodes in the ad-hoc network. Packets are sent from the application and are received by the routing agent. The agent decides a path that the packet must travel in order to reach its destination and stamps it with this information. It then sends the packet down to the link layer. Higher Essay! The link layer level uses an Address Resolution Protocol (ARP) to computer cause, decide the hardware addresses of neighboring nodes and map IP addresses to their correct interfaces. When this information is known, the packet is sent down to the interface queue and awaits a signal from the Multiple Access Control (MAC) protocol.
When the MAC layer decides it is ok to send it onto the channel, it fetches the packet from the queue and hands it over to the network interface which in value higher education essay, turn sends the essay on science and health hazards packet onto the radio channel. This packet is copied and is delivered to all network interfaces at the time at which the value higher essay first bit of the packet would begin arriving at the interface in a physical system. Friends Research! Each network interface stamps the packet with the receiving interfaces properties and essay then invokes the propagation model. The propagation model uses the transmit and receive stamps to determine the power with which the interface will receive the packet. The receiving network interfaces then use their properties to determine if they actually successfully received the packet, and sends it to the MAC layer if appropriate. If the MAC layer receives the packet error- and friends with benefits collision- free, it passes the packet to value higher education essay, the mobiles entry point. From there it reaches a demultiplexer, which decides if the packet should be forwarded again, or if it has reached its destination node. If the destination node is friends benefits reached, the packet is sent to a port demultiplexer, which decides to value higher essay, what application the packet should be delivered. If the packet should be forwarded again the routing agent will be called and the procedure will be repeated. Essay On Citizenship For Kids! 30 Entry point M U X Application Routing Agent Link Layer ARP Queue MAC Propagation model Network Interface Channel Figure 9: A mobile node.
4.3 Simulation overview A typical simulation with ns and the mobility extension is shown in education essay, Figure 10. Basically it consists of generating the following input files to ns: N N A scenario file that describes the movement pattern of the nodes. Essay Work Success! A communication file that describes the value higher education traffic in the network. These files can be generated by drawing them by hand using the visualization tool Ad-hockey (see 4.2) or by generating completely randomized movement and communication patterns with a script. These files are then used for short essay work success the simulation and as a result from this, a trace file is generated as output. Prior to the simulation, the parameters that are going to be traced during the simulation must be selected. The trace file can then be scanned and analyzed for the various parameters that we want to measure.
This can be used as data for plots with for instance Gnuplot. The trace file can also be used to visualize the simulation run with either Ad-hockey or Network animator. Higher Essay! 31 Scenario generation Scenario file Communication file Mobility extension Network Simulator 2 Output files Data processing Ad-hockey GnuPlot Figure 10: Network animator Simulation overview. 4.4 Modifications To be able to use ns for the simulations, we had to do some modifications. First of all, we did not have the routing protocols we wanted to simulate, so one of the first steps was to implement the on science and health protocols. 4.4.1 AODV We have implemented the AODV protocol (for more details, see appendix B). The implementation is done according to the AODV draft  released in August 1998. It must however be noted that a new version of the draft  was released in the end of November 1998. Value! The new draft contains some changes that would enhance the and health hazards performance. These changes that affect the unicast routing part is higher education essay primarily: N N Reduced or complete elimination of hello messages. Updates to important parameters to reflect recent simulation experiences.
To be able to test how the hello messages and link layer support affects the behavior of the essay hazards protocol we have implemented three versions: N N N AODV with only value higher education essay IP-based hello messages AODV with only Link Layer notification of broken links AODV with both IP-based hello messages and Link layer notification of broken links The implementation of the on science and health different versions has some major differences that will affect the performance. Value Education! First of work key to, all AODV with only MAC-layer support will not get the value education routes to the neighbors installed in the routing table, neither will it update the routes to the neighbor who forwarded a message to you. Both AODV versions that have hello messages will have this neighbor detection process that keeps track of the neighbors. This means that the protocols with this feature will have more information in the 32 routing tables. Without this support, buffering of the essay for kids packets may be necessary while a request is sent out in search for a node that could be a neighbor. It must however be noted that the removal of hello messages somewhat changes the behavior of the AODV protocol. The hello messages add overhead to the protocol, but also gives us some prior knowledge of link breakages. Removing the hello messages makes the protocol completely on-demand, broken links can only be detected when actually sending something on the broken link. The DSR implementation that was included in the mobility extension used a sendbuffer that buffered all packets that the application sent while the value higher routing protocol searched for a route. To get a fair comparison of the protocols we implemented the same feature for AODV. This buffer can hold 64 packets and packets are allowed to stay in revolution cause, the buffer for 8 seconds.
The parameters that can be adjusted for AODV and the values we have used is shown in Table 3. Some of these parameters are very important and value essay affects the performance of the resume length protocol in drastic ways. The hello interval is maybe the most important parameter when dealing with AODV that uses hello messages. If the interval is too long, link breakages would not be detected fast enough, but if the interval is to short, a great amount of extra control overhead would be added. Most of the parameters in Table 3 are obvious. The maximum rate for sending replies prevents a node to do a triggered route reply storm.
This means that AODV in each node is only allowed to send one triggered RREP per value, second for each broken route. This could for instance happen if a forwarding node receives a lot of data packets that the research node no longer has a route for. In this case the node should only send a triggered RREP, as a response to the first data packet and if the node keeps receiving data packets after that, a triggered RREP is education only allowed to be sent once per second. Paper! Table 3: Constants used in the AODV implementation. Parameter Hello interval Active route timeout Route reply lifetime Allowed hello loss Request retries Time between retransmitted requests Time to hold packets awaiting routes Maximum rate for sending replies for a route Value 1,5 s 300 s 300 s 2 3 3s 8s 1/s 4.4.2 DSR The DSR implementation that came with the extension uses promiscuous mode (i.e. eavesdropping), which means that the value education essay protocol learns information from packets that it overhears. The question is how realistic this is in a real environment. In a real case scenario we will probably have some sort of encryption, probably IP-Sec that uses IP-Sec tunneling to computer and effect, transport messages. We have made some small change to DSR that makes it possible to turn the value higher essay eavesdropping feature on and off. The parameters that are configurable for DSR are shown in Table 4. These values are the values specified in the DSR draft and have not been changed. Resume Length! The nonpropagating timeout is the time a node waits for a reply for higher essay a nonpropagating search. A nonpropagating search is computer revolution and effect a request that first goes to the neighbors.
If the education essay neighbors do not answer in essay hazards, this specified amount of a time, a new request that will be forwarded by the neighbors will be sent. The sendbuffer in the DSR can hold 64 packets and the packets are allowed to stay in the buffer for 30 seconds Table 4: Constants used in the DSR implementation. Education! Parameter Time between retransmitted requests Size of source route header carrying n addresses Timeout for nonpropagating search Time to hold packets awaiting routes Maximum rate for sending replies for a route 33 Value 500 ms 4n + 4 bytes 30 ms 30 s 1/s 4.4.3 DSDV The extension also included an implementation of the DSDV protocol. This implementation is on citizenship actually two implementations that handle the triggered update a little different. In the first version only a new metric for a destination causes a triggered update to be sent. In the second version, a new sequence number for value education a destination causes a triggered update to with research, be sent. We have modified DSDV so it always uses the version that triggers on new sequence numbers. This is the version that, we feel behaves according to the specification of DSDV. The parameters for DSDV are shown in Table 5 and are as specified in the DSDV paper .
Table 5: Constants used in higher education essay, the DSDV implementation. Parameter Periodic route update interval Periodic updates missed before link declared broken Route advertisement aggregation time Maximum packets buffered per node per destination Value 15 s 3 1s 5 4.4.4 Flooding We have implemented a simple flooding protocol that simply floods all user data packets to all nodes in the network. To have some sort cleverness in this flooding and avoiding data to bounce back and forth we use a sequence number in each packet. This sequence number is to use in essays incremented for higher education essay each new packet. Each node keeps track of (source IP, sequence number) for all destinations and does not process a packet if the packet has a sequence number smaller than the stored sequence number. The idea was to english good to use, do the higher education simulations on the flooding protocol and compare the results with the results for the routing protocols. After some initial simulations on flooding this plan was abandoned. The simulations took too long to english words to use, complete.
The reason is that flooding generates too many packets (events in the simulator). 4.4.5 The simulator To the actual simulator (ns + extension) we have added some new features to allow us to make the value education wanted measurements. Obstacles The visualization/scenario generator tool, Ad-hockey, allows the essay on citizenship for kids user to place obstacles (lines and boxes) into the scenario. The problem is that ns do not use these obstacles for any kind of computation. Two nodes can communicate, even through a wall. We wanted to simulate the protocols in a few realistic scenarios, so we added these computations to ns. The calculations consisted of two parts. Essay! The first part was to store all obstacles in a database that we later could use when calculating the intersection points and the second part was to extend the propagation model with the actual computations. The computations merely consisted of revolution cause and effect, deciding if there existed an intersection point between the value higher education straight line from the sending node to the receiving node and any obstacle in the database.
If such an intersection point exists, the communication is good in essays simply cut of. No fading of the signal, reflections etc is higher education taken into essay on science and health, consideration. The model is therefore very simple. The problem with these computations is education essay that it adds a lot of resume length, overhead in the simulations. The simulations will take significantly longer time to complete. The extra computation must be done for all packets. In a large scenario with many nodes that are sending a lot of traffic this will increase the simulation time significantly. Version management To allow us to higher education, test different versions of one protocol simultaneous, we have added a version control to ns. Computer Cause And Effect! This means that it is value possible to essay on science and health, give a version number to value higher education essay, a protocol when the simulation starts. This version number is given to the specified protocol and it is essay and health then up to the programmer to value higher, use it.
We currently use this feature with both AODV and english words DSR. The different versions are: N N N N N AODV 1 = AODV with only hello messages. AODV 2 = AODV with only MAC-layer feedback. AODV 3 = AODV with both hello messages and education MAC-layer feedback. DSR 1 = DSR with eavesdropping. DSR 2 = DSR without eavesdropping. 34 5 Simulation study The protocols that we have simulated are DSDV, AODV and DSR. DSDV is only used to get a comparison of how much better/worse the MANET protocols are than an ordinary proactive protocol. The simulations were conducted on an Intel PC with a Pentium-2 processor at 400 MHz, 128 Mbytes of RAM running FreeBSD6. 5.1 Measurements Before we go into the actual simulations, we will discuss which parameters  that are interesting to computer revolution cause and effect, measure when studying routing protocols in an ad-hoc network.
There are two main performance measures that are substantially affected by value education essay the routing algorithm, the average end-to-end throughput (quantity of service) and essay on science hazards the average end-to-end delay (quality of service). 5.1.1 Quantitative metrics The measurements that we have conducted can be seen from two angels: externally and internally. The external view is what the application/user sees and the internal view is how the routing protocol behaves. The external measurements are basically the value education end-to-end throughput and delay. The internal behavior can further be divided into routing accuracy and routing efficiency. Paper! N N Routing Efficiency: How much of the sent data is actually delivered to higher education essay, the destination? How much routing overhead is required to find routes? Routing Accuracy: How accurate, measured in number of english good words to use, hops are the supplied routes compared to value essay, the optimal shortest path.
5.1.2 Parameters The metrics has to be measured against some parameter that describes the characteristic behavior of an resume length, adhoc network and can be varied in a controlled way. The parameters that we have chosen to simulate with are: N N N Mobility, which probably is value education one of the most important characteristics of an ad-hoc network. This will affect the dynamic topology, links will go up and down. Essay On Citizenship! Offered network load. The load that we actually offer the network. This can be characterized by three parameters: packet size, number of connections and the rate that we are sending the packets with. Network size (number of nodes, the size of the area that the essay nodes are moving within). The network size basically determines the connectivity. Fewer nodes in the same area mean fewer neighbors to friends benefits, send requests to, but also smaller probability for collisions.
5.1.3 Mobility Because mobility is an important metric when evaluating ad-hoc networks we need some definition of mobility. There exist many definitions of mobility. The CMU Monarch project  has for instance used the pause time in the waypoints as a definition of mobility. If a node has a low pause time, it will almost constantly be moving, which would mean a high mobility. If a node has a large pause time it will stand still most of the time and have a low mobility. We did not think that this mobility definition was good enough, because even if the pause time is low and all nodes are constantly moving, they could all be moving with a very slow speed in the same area. We have defined mobility a little differently. Our definition is value higher essay based on the relative movement of the hazards nodes. This definition gives a very good picture of higher education essay, how the nodes are moving relatively to essay on hard work key to, each other. The definition is higher as follows: 6 FreeBSD 2.2.6 35 If several nodes move for a certain time, then the hazards mobility is the average change in education, distance between all nodes over that period of time.
This time is the simulation time T. Mobility is benefits paper a function of value, both the speed and the movement pattern. Essay! It is calculated with a certain sampling rate. During the simulations, we have used 0.1 seconds as sampling rate. This is the default time when logging the movement in the simulations, so it was appropriate to use the same value when calculating the mobility. Value Higher Education! Table 6 shows all variables that are used in the equations for the mobility factor. Table 6: Variable name dist(nx, ny)t n i Ax(t) Mx T t Mob Mobility variables.
Description the distance between node x and node y at time t number of nodes Index Average distance for node x to all other nodes at time t Average mobility for node x relative to all other nodes during the entire simulation time Simulation time Granularity, simulation step Mobility for entire scenario First of good to use, all, the average distance from each node to all other nodes has to be calculated. This has to be done at times t = 0, t = 0+X, t = 0+2X, . t = simulation time. For the node x at time t the formula is: n ¦ dist (n , n ) x Ax(t) = i i1 (5.1) n 1 After that, with the use of higher, (5.1), the average mobility for that particular node has to be calculated. This is the resume length average change in distance during a whole simulation. The mobility for node x is: T t ¦ A (t ) A (t 't ) x Mx = x t0 (5.2) T 't Finally, the higher education essay mobility for the whole scenario is the sum of the revolution mobility for education all nodes (5.2) divided with the number of nodes: n ¦M Mob = i i1 (5.3) n The unit for the mobility factor (5.3) is m/s.
The mobility factor therefore gives a picture of the average speed of the distance change between the nodes. Figure 11 shows some basic examples of how this mobility factor will reflect the actual movement. If the nodes are standing still, this will of course lead to a mobility of 0, but this would also be the case when the resume length nodes relative movement is zero, for higher education example when the on hard success nodes are moving in value education essay, parallel with the same speed. It is only when the nodes have a movement relative to each other that the mobility factor will be greater than zero. 36 Our mobility definition reflects how the mobility affects the essay and health dynamic topology, without considering obstacles or surroundings. Standing still 0.0 Parallel movement 0.0 Figure 11: Relative movement 0.0 Example of mobility. The reason for choosing mobility as a parameter in the simulations is essay first of success, all that the mobility is one of the most important characteristics of an ad-hoc network. But also because mobility is a parameter that is easy to grasp for people in general. Everyone has a rather good picture of what it means if the mobility is increased.
We have tested the mobility factor to see how it affects the education essay dynamic topology. As it can be seen in Figure 12, the computer revolution and effect number of link changes is directly proportional to value, the mobility factor. A link change basically means that a link changes state from either up/down to down/up. The plot is the average values for all simulations that we have done using 50 nodes and with benefits research an environment size of 1000x1000 meters. 3500 3000 Avg nr of link changes 2500 2000 1500 1000 500 0 0 0.5 Figure 12: 1 1.5 2 Mobility 2.5 3 3.5 Relation between the number of link changes and mobility. 37 4 5.2 Simulation setup In this chapter we will describe how the higher education essay simulations were done. And Health! We have done 4 different types of simulations: N N N N Mobility simulations: We vary the higher essay mobility to resume length, see how it affects the different metrics that we are measuring. Offered load simulations: We vary the load that we offer the higher education network, to see how the essay on science protocols behave when for instance the load is high. Network size simulations: We vary the number of nodes in the network. Realistic simulations: A few realistic scenarios were designed.
These simulations do not give a general view of the protocol, but instead tests certain characteristics of the protocols. Because we had different versions of both AODV and value DSR we decided to first compare the different versions of the same protocol. After that we did a more general comparison where we used one version of each protocol and compared them against DSDV. For Kids! The comparisons made are therefore: N N N Comparison of AODV with only hello messages, AODV with only link layer support and ADOV with both hello messages and link layer support. Value Higher! Comparison of DSR with and without eavesdropping. Comparison of DSDV, AODV with both hello messages and link layer support and DSR without eavesdropping. The reason for choosing DSR without eavesdropping in the last comparison, is on science and health hazards as mentioned earlier that this is more realistic. Higher Education! Security features like encryption will prohibit eavesdropping in for kids, the future. Value Higher Education! The choice of AODV with both link layer support and hello messages was made because first of all, link layer support is probably a necessity to achieve a performance that is for kids good enough and value higher secondly because the removal of hello messages somewhat changes the overall functionality of AODV. Removal of computer revolution cause and effect, hello messages would of course save us from the overhead of the hello messages, but also makes the protocol completely on-demand. A broken link could only be detected when a packet needs to be sent on the link.
In all simulations, except the realistic scenario simulations, we have used a randomized scenario. The randomized scenarios have different parameters that affect the movement patterns. Value Education Essay! The parameters that can be changed are: N N N N N Maximum speed: Every time a speed is going to be randomized it is randomized in the interval [0,maximum speed]. Number of nodes: This was constant during the simulations. We used 50 nodes for all simulation except the size simulation where we varied the with benefits number of nodes.
Environment size: Determines the size of the environment. We have used a size of 1000 x 1000 meters for education essay all simulations except the realistic simulations where we have used 1500 x 900. Short Essay Is The! Simulation time: The time for which the education simulations will be run at. We have used a simulation time of 250 seconds for all simulations except the realistic simulations where we used 900 seconds. Good! Pause time: Pause time is the time for which a node stands still before randomizing a new destination and value higher education the speed that will be used to reach this destination.
We have used a pause time for 1 second in all simulations. The randomizing of scenarios works like this: first of friends with research, all every node stands still for pause time seconds. After that each node selects a random destination, a waypoint somewhere in the environment space. Each node also randomizes a speed that will be used when moving to higher, the waypoint. This speed is randomized uniformly in the interval 0 to maximum speed. Short Essay Work Success! Every time a node reaches a waypoint, this procedure will be repeated. A factor that we have not taken into consideration with the value education essay scenarios is the fact that a real person is not likely to stand on the same place if the connection goes down. A real person is more likely to find a place where the reception is good enough. The system would be to complex if this factor were included also. Resume Length! We have assumed bi-directional links during all our simulations, i.e. the links work equally well in higher, both directions.
It is questionable if unidirectional links are desirable when using the IEEE 802.11 MAC protocol, because bi-directional links are necessary if 802.11 acknowledgements are supposed to friends with benefits paper, be used. 38 5.3 Mobility simulations 5.3.1 Setup The simulations where we varied the mobility where done by value essay randomizing scenario files. This method is very hard to perform, because we cannot prior a scenario generation say that we want a mobility factor of exactly X. Computer Revolution Cause And Effect! Instead we used the maximum speed parameter to control the scenario. The simulation parameters that have been used for the mobility simulations are shown in Table 7. Value Higher Essay! Table 7: Parameters used during mobility simulations. Parameter Transmitter range Bandwidth Simulation time Number of nodes Pause time Environment size Traffic type Packet rate Packet size Number of hazards, flows Value 250 m 2 Mbit 250 s 50 1s 1000x1000 m Constant Bit Rate 5 packets/s 64 byte 15 The scenario is a very crucial part of the simulation. We have therefore collected 10 measurements for each wanted mobility factor. Value Higher! The mobility factors that we simulated on are: 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5.
Because of the hard part of getting scenarios that are precise we have used an interval of r0.1 for the above mentioned mobility factors. The scenarios that where created where then analyzed in terms of unreachable hosts. Computer Revolution! We did not want to higher essay, investigate network partition at this stage, so all scenarios with extremely high degree of unreachable hosts where discarded. Computer Revolution Cause And Effect! By increasing the value education essay maximum speed in revolution, the scenario generation, the value education mobility will also increase. Resume Length! A mobility factor of 3.5 approximately corresponds to value higher education, a maximum speed of 20 m/s. For the randomized simulations we have varied the maximum speed in the interval 0 to 20 m/s. A speed of 20 m/s corresponds the speed of revolution cause, a vehicle, which will lead to higher education essay, a high mobility. We used the same communication pattern for on citizenship all mobility simulations. The traffic pattern consisted of value higher, 15 CBR sources that started at different times. Work Is The! We did not use TCP for the simulations, because we did not want to investigate TCP, which uses flow control, retransmit features and so on. We wanted to education essay, get a general view of essay on science, how the routing protocol behaves.
The communication pattern was randomly created. The parameters that was specified when randomizing the communication pattern were the number of essay, wanted sources, the packet size, the rate at which they were sending and the simulation time. In these simulations, we wanted to investigate how the mobility affected the protocols, so the load that we offer is very low. We only use 15 CBR sources sending 64 bytes large packets with a rate of 5 packets/s. The bandwidth of the links are 2 Mbit. 39 5.3.2 Fraction of received packets 0.8 Fraction received packets 1 0.8 Fraction received packets 1 0.6 0.4 0.2 0.6 0.4 0.2 AODV-HELLO-MAC AODV-MAC AODV-HELLO DSR-eaves dropping DSR 0 0 0 0.5 1 1.5 2 2.5 3 3.5 Mobility (m/s) 0 0.5 1 1.5 2 2.5 3 3.5 Mobility (m/s) 1 Fraction received packets 0.8 0.6 0.4 0.2 AODV-HELLO-MAC DSR DSDV 0 0 0.5 1 1.5 2 Mobility (m/s) Figure 13: 2.5 3 3.5 Mobility simulations - fraction of short work success, received packets. How many of the education sent data packets are actually received and why have the dropped packets been dropped?
Of the different AODV versions, it can been seen in Figure 13 that both AODV versions that have MAClayer support are almost receiving all packets that are sent. AODV with both hello messages and MAC-layer support is slightly better than the version with only MAC-layer support. The reason for this is the same as mentioned earlier, the hello messages gets some prior knowledge of link breakages. AODV with only hello messages is however dropping a very large portion of the packets when the mobility increases. This large fraction of dropped packets is of course not acceptable and the reason for these drops has to resume length, do with the interval of the hello messages. The interval between the hello messages and the number of education, allowed hello message losses are crucial for detection of link breakages. If the interval is decreased, link breakages are detected earlier, but it would also mean that the control overhead in the network increases. The issue here is to computer, try to find optimal values for higher education these parameters. The choice of these parameters is english words to use also very dependent on the behavior that is essay desired; a higher fraction of essay, received packets, a high throughput, low delay or a low overhead. The fraction of received packets for the DSR versions is very large even for high mobility.
The DSR version without eavesdropping has a slightly smaller fraction of received packets. Value Higher Essay! This difference is good words to use however so small that it is negligible. DSR with eavesdropping gets better result for the simple reason that it has a little more information when calculating the routes. A reason for higher the higher fraction received packets for DSR compared to AODV is that DSR allows packets to essay on citizenship, stay in the send buffer for as long as 30 seconds, AODV only 8 seconds (our implementation). Higher Education Essay! It must however be noted that the resume length AODV draft  does not specify how long a packet is allowed to stay in the sendbuffer. Value Higher Education! When comparing these results with the results for DSDV it can clearly be seen that a proactive approach is not acceptable at all when the essay on hard work key to mobility increases. The fraction received packets drastically goes down to education essay, 56-57 %. This value is essay and health however for a very large mobility factor (vehicles).
But the fraction of received packets is not even 100 % when the mobility is 0, as for all other protocols. The reason for this is essay that packets are sent before the routing tables have had enough time to converge and the packets are dropped. 40 The main reasons for dropping packets are that the protocol is sending packets on a broken route that it thinks is valid and essay that packet in the buffers are dropped because of congestion and value education essay timeouts. At this low load we only essay work have a small fraction of the packets that have been dropped because of collision. It can also be seen that IP-based hello messages as only link breakage detection mechanism is not a good idea. The results are very poor, even DSDV have slightly better results. Link layer feedback of link breakages informs the upper layer routing protocol is much quicker and it can therefore react immediately. 5.3.3 End-to-end delay AODV-HELLO-MAC AODV-MAC AODV-HELLO 0.14 0.12 Avg packet delay (seconds) 0.12 Avg packet delay (seconds) DSR-eaves dropping DSR 0.14 0.1 0.08 0.06 0.1 0.08 0.06 0.04 0.04 0.02 0.02 0 0 0 0.5 1 1.5 2 2.5 3 3.5 2.5 3 0 0.5 1 1.5 2 Mobility (m/s) 2.5 3 3.5 3.5 Mobility (m/s) AODV-HELLO-MAC DSR DSDV 0.14 Avg packet delay (seconds) 0.12 0.1 0.08 0.06 0.04 0.02 0 0 0.5 1 1.5 2 Mobility (m/s) Figure 14: Mobility simulations - delay. Value Higher Education! As seen in Figure 14, of the different AODV versions AODV with only hello messages has lowest delay on essay on science hazards the data packets that are received. The reason for value education essay this is not that it finds routes faster or that the routes are shorter or more optimal, instead AODV with only hello messages is the AODV version that gets significantly fewest packets through the network. Computer Cause And Effect! The packets that it successfully gets through the network have approximately the same low delay as for the other AODV versions.
The difference is that the other AODV versions have a portion of packets that have a higher delay (has been in a buffer a long time and still gets the packets through the network). Value Higher Education Essay! This affects the average delay, which becomes larger. In AODV with only hello messages, packets in the buffers that have been there for a long time are dropped. The reason is that ADOV does not successfully find a new route for those packets and because broken links are not detected fast enough, resulting in that a source can keep sending packets on a broken link believing that it is still working properly. Essay On Citizenship! AODV with both hello messages and MAC layer support has a slightly lower delay than AODV with only MAC-layer support. The reason for this is that as mentioned earlier, AODV with only MAC-layer support makes the protocol completely on-demand, it only essay detects link breakages when actually trying to send packets. Packets that are sent after this breakage is essay detected will have a higher delay, because they are buffered during the time it takes to education essay, find a new route.
AODV with both hello messages and Mac-layer support on the other hand will get some prior knowledge of the link breakage and friends research has a chance to find a new route before any new packets are sent. 41 Both DSR versions show a tendency to get higher delay when mobility is increased. Higher Education! The turning point comes at a mobility factor of approximately 1.0. DSR without eavesdropping has a negligible higher delay compared to DSR with eavesdropping. DSDV is the protocol that seems to have lowest delay in these results. The results are however somewhat misleading because DSDV drops so many packets that it cannot said to be valid. The packets that are dropped in DSDV will successfully get through when using for instance DSR, but has a slightly higher delay, because of on citizenship for kids, longer times in buffers etc.
These higher delay packets will make the average delay higher for DSR. The same can be said for AODV with only hello messages. The other two AODV versions have a slightly higher delay than the DSR versions. This has probably to do with the source routing concept of DSR. DSR gains so much information by the source routes that it will learn routes to many more destinations than a distance vector protocol like AODV.
This will mean that while DSR already has a route for value education essay a certain destination, AODV would have to send a specific request for that destination. The packets would in the meanwhile stay in a buffer until a valid route is essay hazards found. This will take some time and will therefore increase the average delay. In a packet based radio network without Quality of Service, the delays of the education essay packets will vary much. The packets that do not have a route will be buffered until a route is found. A critical parameter here is how long a packet should be allowed to stay in the buffer before it is essay on hard work is the key to thrown away. If the packets are allowed to value higher, be in the buffer for a long time, the following situation could happen: A packet is sent, but there does not exist any route to that destination so the resume length packet is essay buffered and a route request is sent. The destination node is friends research paper however unreachable so no route reply is value essay returned to the sending node.
After a long time, the destination node suddenly becomes reachable and the packet is sent. This packet will have a very large delay. Resume Length! Should this situation be allowed to happen? Should the packet be dropped from the buffer at a much earlier stage or do we want all packets to get through the network, even though the delay can be very large. In the case where we are using TCP, the retransmit operation will probably retransmit the packet at an earlier stage anyway, because no acknowledgement was received.
The allowed time for packets to higher, stay in the sendbuffer in DSR is 30 seconds and only 8 seconds for AODV. Resume Length! If a packet is received 30 seconds after it was sent, this will increase the value higher education essay average delay to some degree. 5.3.4 End-to-end throughput 2.4 2.2 2.2 Throughput (Kbit/s) 2.6 2.4 Throughput (Kbit/s) 2.6 2 1.8 1.6 1.4 2 1.8 1.6 1.4 1.2 1.2 AODV-HELLO-MAC AODV-MAC AODV-HELLO DSR-eaves dropping DSR 1 1 0 0.5 1 1.5 2 2.5 3 3.5 Mobility (m/s) 0 0.5 1 1.5 Mobility (m/s) 2.6 2.4 Throughput (Kbit/s) 2.2 2 1.8 1.6 1.4 1.2 AODV-HELLO-MAC DSR DSDV 1 0 0.5 1 1.5 2 2.5 3 3.5 Mobility (m/s) Figure 15: Mobility simulations - throughput. Resume Length! 42 2 2.5 3 3.5 Figure 15 shows the throughput curves for higher essay the different protocols with a packet size of 64 bytes. It must however be mentioned that the curves in on science and health hazards, this case are only higher education essay interesting from a relative view, as a comparison between the protocols. We have not tried to short essay on hard is the key to success, maximize the throughput, we have only tried to value higher essay, determine the relative difference in throughput for the different protocols with respect to the mobility factor and computer the specific load that we have used. The throughput curves for all protocols are very similar to the fraction received packet curves. This is logical because large packet drops will of course mean lower throughput. Both DSR versions and the AODV versions with link layer support have almost identical throughput. This throughput is also approximately constant, it decreases somewhat when mobility is as high as 2.5-3.5. AODV with only hello messages and DSDV have a throughput that drastically decreases when mobility increases.
AODV with only value higher education hello show a very poor result. In Essays! The throughput curve drops almost immediately to half of what it is when mobility is 0. 5.3.5 Overhead 25000 1.8e+06 AODV-HELLO-MAC AODV-MAC AODV-HELLO 20000 1.4e+06 Control overhead (bytes) Control overhead (packets) AODV-HELLO-MAC AODV-MAC AODV-HELLO 1.6e+06 15000 10000 1.2e+06 1e+06 800000 600000 400000 5000 200000 0 0 0 0.5 1 1.5 2 Mobility (m/s) 2.5 3 3.5 0 25000 0.5 1 1.5 2 Mobility (m/s) 2.5 3 3.5 1.5 2.5 3 3.5 2.5 3 3.5 1.8e+06 DSR-eaves dropping DSR DSR-eaves dropping DSR 1.6e+06 1.4e+06 Control overhead (bytes) Control overhead (packets) 20000 15000 10000 1.2e+06 1e+06 800000 600000 400000 5000 200000 0 0 0 0.5 1 1.5 2 2.5 3 3.5 0 0.5 1 Mobility (m/s) 25000 1.8e+06 AODV-HELLO-MAC DSR DSDV AODV-HELLO-MAC DSR DSDV 1.6e+06 20000 1.4e+06 Control overhead (bytes) Control overhead (packets) 2 Mobility (m/s) 15000 10000 1.2e+06 1e+06 800000 600000 400000 5000 200000 0 0 0 0.5 1 1.5 2 Mobility (m/s) 2.5 Figure 16: 3 3.5 0 0.5 1 1.5 2 Mobility (m/s) Mobility simulations - overhead. Because the value higher education routing protocol need to send control information to achieve the task of finding routes, it is interesting to see how much control information that is hazards actually sent for each protocol. There exists some sort of tradeoff between the value essay byte overhead and the number of control information packets sent. A large byte 43 overhead would of course mean a larger part of wasted bandwidth. Many small control information packets would however mean that the radio medium on which packets are sent is acquired more frequently. This can be quite costly in terms of power and network utilization. With Benefits! The values that we have plotted do not include any physical layer framing or MAC layer overhead. We have only looked at the overhead at value education, the IP-level. A completely fair comparison would also include the above mentioned overheads. We have chosen not to include these for the simple reason that the essay for kids MAC layer can be different in a real life implementation.
We wanted to investigate the overhead generally, not the overhead that is dependent on particularly the IEEE 802.11 MAC protocol. Value Higher Education Essay! The results are shown in Figure 16. The first column is overhead calculated in number of english to use, packets and the second column is the byte overhead. The number of control packets and byte overhead is a total for all simulations done where we have varied mobility. Of the different AODV versions, it can be seen that the higher education essay curves for revolution the AODV versions that have link layer support are similar in appearance. The difference of about 8000-9000 packets and 270000-290000 bytes that can be seen corresponds to the hello packets. The AODV version with only hello messages has a much more stable form of the curve. The small rise that is visible is the triggered route replies that are sent when a link goes down and value higher education essay the new requests that are sent to friends with benefits research paper, find a new route during route failures.
A route failure therefore triggers both triggered replies and new requests. Essay! This rise is much larger for the AODV versions with link layer support for the simple reason that it detects link failure much faster, which will lead to much more messages. Resume Length! DSR does not include the data packets in the number of control packet calculations, only the higher extra byte overhead from computer cause and effect, these packets is education included. Worth noting when observing the on citizenship DSR versions is that the DSR version that does not use eavesdropping has approximately the value education essay double amount of control overhead counted in number of messages and about 400000 bytes more of byte overhead than the DSR version with eavesdropping at the highest mobility 3.5. The somewhat strange behavior of the byte overhead for DSR can be explained as a sum of both the resume length sent packets and value essay the sent control messages.
As mobility increases, fewer packets will get through the and health hazards network. Value Higher Education! Fewer packets mean less byte overhead in essay on citizenship, the source route of the packets. Increased mobility also means more topology changes, which will increase the number of higher education essay, update messages. English To Use! The byte overhead is higher education therefore decreasing and at approximately mobility 1.5 the increase of control messages will cause the byte overhead to increase. The number of control messages in DSDV is fairly constant, even when the mobility is extremely high. This is the nature of a proactive protocol that is dependent on periodic broadcasts. The byte overhead on the other hand, will increase as mobility increases. The reason for this is that the resume length amount of information sent in each update message will be larger as the amount of education essay, link changes increases. 5.3.6 Optimal path One internal aspect of the routing protocol is the routing accuracy, e.g. Essay And Health! how good the actual routes are compared to the optimal routes. Value Education! To illustrate this we have compared the essay on science hazards actual hop count with the optimal shortest route for all received packets. Higher Education Essay! We have then, for each protocol, calculated how large fraction the received packets that have been routed through the optimal route, a route with hopcount that is one larger than the key to success optimal, a route with hopcount that is two larger than the optimal and value so on.
The result is resume length shown in Table 8. Higher Essay! The results are the essay and health total results for all simulations done with varying mobility. To better illustrate the difference between some of the value education protocols, we have also plotted the english good to use results for one AODV version, one DSR version and higher compared it with the only proactive protocol DSDV. It can clearly be seen in Figure 17 that DSDV is the protocol that has the highest degree of revolution cause, optimality, almost 90 % of the higher education essay received packets have been routed with optimal hop count. The AODV and DSR versions are almost identical. AODV is slightly better. This difference is however so small that it can neglected. The difference between the different DSR versions is quite large and can be explained with the extra information that DSR with eavesdropping has when calculating routes. This extra information is apparently very informative when calculating shortest possible routes. AODV with only essay on citizenship for kids hello messages has best results of the different AODV versions. These due to the similarities with a proactive protocol like DSDV that is highly dependent on periodic broadcasts.
Because of the periodic updates DSDV needs some time before it converges to a steady state. Value Essay! This happens when we have high movement with a lot of topology changes. On Citizenship! Most of the packets that are sent during this time are dropped and the rest of them get a little higher hopcount. All packets that are sent after the routing tables have converged to higher education essay, a steady state do however most likely have the resume length optimal shortest path. AODV with only hello messages have a similar behavior. Link breakages are dependent on higher essay the hello messages. This will mean that high movement and frequent topology changes will lead to many packet 44 drops during this time.
The packet that successfully gets through the with research network have done this during times when the network is somewhat stabile 1 AODV-HELLO-MAC DSR DSDV Packets (%) 0.8 0.6 0.4 0.2 0 0 2 Figure 17: 4 6 Nr of hops from optimal 8 10 Mobility simulations - optimal path difference. Because both DSR versions and the AODV versions with link layer support gets significantly more packets through the network when the number of higher essay, topology changes is friends benefits large, they will have a little lower fraction of packets that have a optimal route. In times of education essay, frequent movement it is essay easy to get a route that at education essay, first is optimal and english good words in essays then the moment later is 1-2 hops longer than another route that become the optimal route. The protocols will keep sending packets on the route that at first was optimal. A good relative comparison is to higher education essay, look at the average hop count difference for all packets received. DSDV has the smallest average with a hopcount at only 0.13 hops from the optimal path. Table 8: Protocol AODV 1 AODV 2 AODV 3 DSR 1 DSR 2 DSDV 0 79.1% 55.9% 68.4% 81.1% 63.2% 88.7% Optimal path difference for all protocols.
Number of hops from optimal path (% packets) 1 2 3 4 5 6 14.8% 3.68% 1.08% 0.30% 0.55% 0.06% 29.9% 9.04% 2.62% 1.09% 0.56% 0.20% 23.0% 5.37% 1.48% 0.84% 0.47% 0.14% 15.3% 2.73% 0.54% 0.13% 0.08% 0.01% 26.6% 7.21% 2.21% 0.56% 0.13% 0.05% 10.6% 0.59% 0.06% 0.00% 0.00% 0.00% 45 7 0.06% 0.38% 0.04% 0.02% 0.03% 0.00% Average 0.292170 0.682837 0.459423 0.234429 0.512004 0.126577 5.3.7 Summary mobility simulations The protocols that have link layer support for short essay on hard work is the key to link breakage detection will be much more stable. The fraction of packets received for these protocols is almost constant at 95 % even when mobility increases. This result indicates that these kinds of protocols will get the job done even when mobility increases. Value Higher! These protocols include both DSR versions and the two AODV versions that have this link layer support. Protocols that are highly dependent on periodic broadcast show a rather poor result, only little more than 50 % of the packet are received when mobility is increased. Because DSR is a source routing protocol it is always interesting to see how much overhead this kind of friends with paper, protocol will have. The byte overhead is larger than for instance the AODV version that uses both hello messages and link layer support for link breakage detection. The interesting thing with this is that the number of control messages is much smaller for DSR than any other protocol. This is higher interesting because this means that an essay on science, approach that uses a source routing based approach to find routes combined with a destination vector approach for sending data packets could be desirable. 5.4 Offered load simulations We have used these protocols for these simulations: N N N AODV with both hello messages and MAC link layer support. DSR without eavesdropping DSDV We only higher used the more realistic version of both AODV and DSR, for the same reason as mentioned in the previous section.
5.4.1 Setup The offered load simulations where done by varying the load that we offer the essay network. We had mainly three parameters to adjust the offered load: N N N Packet size Number of CBR flows Rate at which the value higher flows are sending The mobility simulations that we have done used a packet size of 64 bytes, a rate of 5 packets/s and 15 CBR flows. This is a fairly moderate offered load, so for short on hard work key to the offered load simulations, we wanted to investigate how the value education essay protocols behave when the load was increased. We could increase the packet size or the number of CBR flows, but the parameter that best describes the load is the rate at essay, which we are sending. By only increasing the value higher rate for short on hard is the the CBR flows, the load for each flow will increase. This also gives some hints of how large the throughput can be. We have used four different offered load cases: N N N N 5 packets / second (same as the mobility simulations) 10 packets / second 15 packets / second 20 packets / second The packet size was held constant at 64 bytes and the number of value higher education, flows at 15.
We used the same randomized scenario files as in the mobility simulations. The same communication file was also used, with the exception that we changed the rate for the CBR sources. The parameters that we used during the offered load simulation are shown in Table 9. 46 Table 9: Parameters used during offered load simulations. Parameter Transmitter range Bandwidth Simulation time Number of nodes Pause time Environment size Traffic type Packet rate Packet size Number of flows Value 250 m 2 Mbit 250 s 50 1s 1000x1000 m Constant Bit Rate 5 packets/s 64 byte 15 5.4.2 Fraction of received packets 0.8 Fraction received packets 1 0.8 Fraction received packets 1 0.6 0.4 0.2 0.6 0.4 0.2 AODV 5 pkt/s AODV 10 pkt/s AODV 15 pkt/s AODV 20 pkt/s DSR 5 pkt/s DSR 10 pkt/s DSR 15 pkt/s DSR 20 pkt/s 0 0 0 0.5 1 1.5 2 Mobility (m/s) 2.5 3 3.5 1 1.5 2 Mobility (m/s) 2.5 3 3.5 0 0.5 1 1.5 2 Mobility (m/s) 2.5 3 3.5 1 Fraction received packets 0.8 0.6 0.4 0.2 DSDV 5 pkt/s DSDV 10 pkt/s DSDV 15 pkt/s DSDV 20 pkt/s 0 0 0.5 Figure 18: Offered load simulations - fraction of received packets. At only 5 packets/s both AODV and DSR are rather constant, the on science and health fraction of received packets is only decreasing slightly when mobility increases (Figure 18). At 10 packet/s we can see that the fraction received packets is decreasing much faster when the mobility factor is greater than 2. At 15 packets/s and 20 packets/s both AODV and DSR are dropping a large fraction of the packets. At the highest mobility and a rate of 20 packets/s, only 50-60 % of the sent packets are received. The reason is more collisions in the air and congestion in buffers.
The results for higher essay AODV and DSR are fairly similar at a packet rate of 5 packets/s and 10 packets/s. Friends With Benefits Paper! At data rates of 15 packets/s and 20 packets/s, AODV shows a better result than DSR. At these rates the protocols are however dropping a large fraction of the packets, even at value, a mobility factor of 0. DSR will have a much larger byte overhead than AODV at higher data rates (Figure 21). The reason for this is the source route in each data packet. This also increases the load on the network and causes more packets to friends benefits research paper, be dropped; thus AODV will get more packets through the network.
47 DSDV is value higher education dropping a large fraction of the packets already at the lowest data rate 5 packets/s. It must however be noted that the increase in dropped packets is not as large for DSDV as for AODV and DSR. At the highest data rate, DSDV is almost as good as DSR. Essay Hazards! 5.4.3 End-to-end delay 0.7 0.7 AODV 5 pkt/s AODV 10 pkt/s AODV 15 pkt/s AODV 20 pkt/s 0.6 0.5 Avg packet delay (seconds) Avg packet delay (seconds) 0.6 DSR 5 pkt/s DSR 10 pkt/s DSR 15 pkt/s DSR 20 pkt/s 0.4 0.3 0.5 0.4 0.3 0.2 0.2 0.1 0.1 0 0 0 0.5 1 1.5 2 2.5 3 3.5 0 0.5 1 1.5 2 2.5 3 3.5 Mobility (m/s) Mobility (m/s) 0.7 DSDV 5 pkt/s DSDV 10 pkt/s DSDV 15 pkt/s DSDV 20 pkt/s Avg packet delay (seconds) 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.5 1 1.5 2 2.5 3 3.5 Mobility (m/s) Figure 19: Offered load simulations - average delay. The delay is also affected by high rate of CBR packets (Figure 19). The buffers becomes full much quicker, so the packets have to stay in the buffers a much longer period of value higher essay, time before they are sent. This can clearly be seen at the highest rate 20 packets/s. The high degree of packet drops, even at mobility 0 makes the delay high already from the start.
DSR has a much lower delay compared to AODV. The difference between AODV and DSR is most apparent at rate 10 packets/s. DSDV has the lowest delay of resume length, them all. This is value higher essay however an effect from the large fraction of packet drops that DSDV has, compared to DSR and good in essays AODV. The increase in delay for DSDV also comes from the increased time that the higher education essay packets must stay in the buffers. The high delay at a mobility factor of 0-1 and a data rate of 20 packets/s that can be seen for all protocols is a result of the extremely high data rate and friends the low mobility. Higher Education Essay! The high data rate will fill up the buffers very quickly. The low mobility will mean that already found routes are valid for a much longer time period. This means that found routes can be used for on science and health hazards more packets.
Even the packets that have stayed in the buffer for value higher a long time have a chance to get through. When mobility increases, more routes will become invalid and new requests are necessary. While the requests are propagating the network in search for a new route, buffers will get full and packets are dropped. These packets are the packets that have stayed in paper, the buffers for the longest time and therefore the delay will decrease. The increase in mobility actually results in essay, a load balancing of the traffic between the nodes; hot spots are “removed” due to mobility. For DSDV, the average delay at highest data rate will actually be lower than at the rate of 15 packets/s. This is a little strange but has probably something to essay on science, do with the fact that DSDV only uses a buffer that only value education essay has room for 5 packets per flow.
At the rate of 15 packets/s and 20 packets/s, when mobility starts to get so high that the topology changes frequently, only 40-60 % of the packets gets through the network. These 48 topology changes means that the protocol needs more time to converge before the packets can be sent. The buffers will therefore be congested almost all the time so the packets that actually get through have approximately the same the delay. 5.4.4 End-to-end throughput 8 8 6 Throughput (Kbit/s) 7 6 Throughput (Kbit/s) 7 5 4 3 5 4 3 2 2 AODV 5 pkt/s AODV 10 pkt/s AODV 15 pkt/s AODV 20 pkt/s 1 0 0 0 0.5 DSR 5 pkt/s DSR 10 pkt/s DSR 15 pkt/s DSR 20 pkt/s 1 1 1.5 2 Mobility (m/s) 2.5 1.5 2.5 3 3.5 0 0.5 1 1.5 2 2.5 3 3.5 Mobility (m/s) 8 7 Throughput (Kbit/s) 6 5 4 3 2 DSDV 5 pkt/s DSDV 10 pkt/s DSDV 15 pkt/s DSDV 20 pkt/s 1 0 0 0.5 1 2 3 3.5 Mobility (m/s) Figure 20: Offered load simulations - average throughput. Essay On Citizenship For Kids! At low CBR rates the throughput of DSR and AODV is unaffected of the mobility (Figure 20), it stays constant at 2,5 Kbit/s. At higher CBR rates, the value essay throughput will decrease when the mobility increases. Essay On Science Hazards! This can already be seen at CBR rate 10 packet/s.
The decrease at value higher, CBR rate 10 packets/s is however very small. Essay On Science And Health Hazards! At rate 15 packets/s and higher 20 packets/s the essay for kids throughput decreases very much for all protocols. This is essay however an effect from the large fraction of dropped packets. The result for AODV is slightly better than for DSR. It must however be noted that the offered load definition that we use only includes the rate at which we are sending packets with; no control packets are included in this definition. The same applies for the throughput, only the data packets are included in the calculations of on science and health, throughput. DSR have a much larger byte overhead than AODV at higher data rates (Figure 21). Higher Education Essay! This also increases the load on the network and causes more packets to be dropped; thus AODV will have a better throughput at higher data rate.
DSDV drops a large fraction of the packets already at a rate of essay and health, 5 packets/s. Higher Essay! This can be seen in short is the key to, the small decrease in the throughput at rate 5 packets/s. The throughput decreases more and more as the rate increases. Value Higher Education Essay! 5.4.5 Overhead In Figure 21, the difference between distance vector and source routing can clearly be seen. On Science And Health! The byte overhead for DSR is much larger than AODV even at low data rates and the difference becomes larger when the CBR rate increases. Value! At CBR rate 20 packets/s, the byte overhead for DSR is to use more than the value higher education essay double than for AODV. The reason for the larger byte overhead for DSR is of course the source route in each packet. Resume Length! The 49 number of control messages is though smaller for DSR. This is the other characteristic for source routing, it learns all routes in the source route and therefore does not need to send as many route requests. Education Essay! The reason for short is the key to success the increase in number of control packets is the MAC-layer support. The increase in rate means that the MAC-layer will detects link failures much faster.
This means that the triggered RREPs are sent much earlier also causing the source node to send out a new request much earlier. All link failures are detected earlier with increased rate; thus there will be time for more RREQs, RREPs and triggered RREPs. Value Education! 4e+06 35000 AODV 5 pkt/s AODV 10 pkt/s AODV 15 pkt/s AODV 20 pkt/s 30000 AODV 5 pkt/s AODV 10 pkt/s AODV 15 pkt/s AODV 20 pkt/s 3.5e+06 3e+06 Control overhead (bytes) Control overhead (packets) 25000 20000 15000 10000 2.5e+06 2e+06 1.5e+06 1e+06 5000 500000 0 0 0 0.5 1 1.5 2 Mobility (m/s) 2.5 3 0 3.5 0.5 1 1.5 2 2.5 3 3.5 Mobility (m/s) 35000 DSR 5 pkt/s DSR 10 pkt/s DSR 15 pkt/s DSR 20 pkt/s 30000 4e+06 3e+06 Control overhead (bytes) 25000 Control overhead (packets) DSR 5 pkt/s DSR 10 pkt/s DSR 15 pkt/s DSR 20 pkt/s 3.5e+06 20000 15000 2.5e+06 2e+06 1.5e+06 10000 1e+06 5000 500000 0 0 0.5 1 1.5 2 2.5 3 0 3.5 0 0.5 1 Mobility (m/s) 1.5 2 2.5 3 3.5 Mobility (m/s) 4e+06 DSDV 5 pkt/s DSDV 10 pkt/s DSDV 15 pkt/s DSDV 20 pkt/s 35000 DSDV 5 pkt/s DSDV 10 pkt/s DSDV 15 pkt/s DSDV 20 pkt/s 30000 3.5e+06 3e+06 Control overhead (bytes) Control overhead (packets) 25000 20000 15000 10000 2.5e+06 2e+06 1.5e+06 1e+06 5000 500000 0 0 0 0.5 1 1.5 2 Mobility (m/s) 2.5 Figure 21: 3 0 3.5 0.5 1 1.5 2 2.5 3 3.5 Mobility (m/s) Offered load simulations - overhead. The amount of control information in DSDV is not affected to english words to use in essays, any great extent by the data rate for higher education essay the CBR packets. By looking at Figure 21 it looks like the number of control packets is exactly the same for all data rates, but there is benefits paper actually a small difference. The number of control packets is actually a little smaller when the rate is 20 packets/s. Value Essay! This difference is about 80 packets.
The reason for this difference is that the high data rate causes more collisions, which means that some of the update messages are dropped. Computer Revolution Cause! These lost update messages will not be received by any node, and cannot therefore trigger new update messages. This means that when the next update message actually is higher received a much larger update message has to be sent, thus we can see a slight increase of byte overhead when the rate increases. But when the mobility increases more and more packets will be dropped. At the friends highest data rate, many of the update messages are dropped, 50 even the packets with a little more information. Higher Education! This causes the byte overhead for DSDV at higher data rates not to resume length, increase to the same extent as for higher education DSDV with lower data rates. 5.4.6 Optimal path Figure 22 illustrates the difference in hopcount from the optimal hopcount at with benefits research, a CBR rate of value higher education, 20 packets/s. It is the result for all simulations done at this rate. If we compare this figure with Figure 17, which illustrates the hopcount difference for the CBR rate 5 packets/s, we can clearly see that they are almost identical.
The rate does not affect the essay hazards number of hops that the higher education essay packets actually need to travel from source to destination. 1 AODV 20 pkt/s DSR 20 pkt/s DSDV 20 pkt/s Packets (%) 0.8 0.6 0.4 0.2 0 0 2 Figure 22: 4 6 Nr of hops from essay on citizenship, optimal 8 10 Offered load simulations – optimal path. Value Education! 5.4.7 Summary offered load simulations The performance of the in essays protocols differs slightly during different network loads. Education! The most apparent difference is the words byte overhead. Higher Education! While DSDV has a rather unaffected overhead, it increases both for AODV and DSR during higher loads.
A higher sending rate causes the protocol to detect broken links faster, thus reacting faster. This leads to a slight increase in control packets, which also affects the byte overhead. The most apparent is the increase in on hard work, DSRs overhead as we increase the send rate. Higher Education Essay! Since each data packet contains a source route, the revolution byte overhead increases dramatically. The increased send rate also set demands on the send buffer of the routing protocol.
Congestion occurs and packets are dropped. The faster a routing protocol can find a route, the less time the packets have to spend in buffers, meaning a smaller probability of value education essay, packet drops. 51 5.5 Network size simulations We did simulations on some of the resume length protocols and varied the number of nodes that participated in the network. Higher Education! We decreased the number of nodes to 35 and 25 nodes. The decrease in number of nodes basically meant that the connectivity also decreased; each node had fewer neighbors.
The results from resume length, these simulations did not give any new information regarding the performance of the value protocols. Essay Hazards! The relative difference between the protocols was the higher same. Resume Length! Decreased connectivity meant of course that we did not get as many packets through the network as in the mobility simulations, but it must however be noted that the dependency between the scenarios and higher education results are much larger in the network size simulations. The worst results for each protocol happened when the resume length mobility was 0. This may sound strange, but the reason for the bad result when the nodes is higher essay standing still is the randomized scenarios. If a randomized scenario has poor connectivity, this connectivity will be same during the whole simulation if the nodes are standing still. The nodes are not moving and cannot therefore affect the connectivity. In a scenario with moving nodes however, the connectivity will vary during the whole simulation. So even if a node is unreachable from the beginning, there is still a chance that it will be reachable some time later. 5.6 Realistic scenarios 5.6.1 Setup The randomized simulations we have done, gives a very good general picture of how the protocols behaves in respect to certain parameters, such as mobility, size and network load. This kind of simulations also has some problems: N N N It is hard to identify situations in english good, which the education protocols fail or have problems It has no connection to a real life situation. It may favor complex protocols, while in real life scenarios simpler protocols can find the routes almost as effectively.
It is therefore also very interesting to see how the protocols behave in a more realistic scenario. We have therefore done simulations on some scenarios believed to be realistic. The realistic scenarios do not give a full picture of resume length, how the protocols behave generally. Instead they give some sense of weak points in the protocols. The three basic types of scenarios that we have done simulations on value higher education are: N N N Conference type, with low movement factor.
Event coverage type, with fairly large movement factor. Could for instance be reporters trying to interview politicians. Disaster area, with some relatively slow nodes and some very fast nodes (mounted on a car or a helicopter). Friends With Paper! The environment size is 1500 x 900 meters for all realistic scenarios. This size is value higher scaled according to the range of the transmitters. In a real life conference scenario, the environment size would be significantly smaller and so would also the resume length transmitter range.
The same thing would apply for the speed of the value higher education essay people moving around. The speed is also scaled to short key to, 10 m/s. Higher! All parameters used during the short success realistic simulations are shown in Table 10. 52 Table 10: Parameters used during realistic simulations. Parameter Transmitter range Bandwidth Simulation time Number of value education essay, nodes Environment size Traffic type Packet rate Packet size Speed of a human Speed of a mobile node mounted on essay on science hazards a vehicle Value 250 m 2 Mbit 900 s 50 1500x900 m Constant Bit Rate 4 packets/s 512 byte 1 m/s 20 m/s 5.6.2 Conference This scenario simulates 50 people that are attending a conference, seminar session or some similar activity. It involves communication between some of the essay people. Parameters specific for the conference scenario are shown in Table 11 Table 11: Parameters used during conference scenario.
Parameter Number of to use, CBR sources Number of receivers Number of value essay, flows Value 2 6 6 The scenario is friends with benefits research paper characterized by: N N N N N Low mobility factor, 10 % of the higher nodes are moving during any period of time. Links are long lasting and involves many hops. The traffic is resume length concentrated to a few nodes, typically only the value higher speaker. Few obstacles which are far apart. Typically only one large obstacle, a wall with doors and windows that can be used for communication. Friends With Paper! Relatively large interference from education, other nodes, due to the concentration of transmitting nodes. This can in some cases lead to local congestion. English Good Words In Essays! The scenario basically tests the value education essay protocols: N N N Ability to respond to local changes for long links. Ability to cope with large concentration of computer revolution cause and effect, traffic.
Message overhead with low mobility factor. Figure 23 shows how the scenario was designed and created with ad-hockey. The scenario is divided into three zones that have their certain characteristics. N N N Zone 1 - Speaker zone: The speaker moves back and forth. This changes the education closest neighbor in the audience.
Zone 2 - Audience zone: Static audience that is essay on citizenship sitting still most of the time. Higher Education Essay! Very seldom does a node go outside to return a certain amount of time later. This will probably result in a link breakage of a longlasting link. Zone 3 - Outsider zone: Outsiders behind a wall that are trying to words, establish a connection between the speaker and each other. 53 Transmitter range Zone 1 Zone 2 Zone 3 = Node = Obstacle = Movement Figure 23: Conference scenario. The results for this scenario are shown in Table 12 and essay Table 13.
It must however be noted that we do not distinguish the results for nodes that are in zone 2 or zone 3. The calculated mobility factor for this scenario is very low. With Research! All protocols except DSDV and the AODV version that only uses hello messages show quite good performance, delivering between 92-99% of the packets with an value higher essay, average throughput between 14.8 – 15.7 Kbit/s. DSDV delivers only 75.6% of the in essays packets with an higher education, average throughput of 12.1 Kbit/s and the AODV version with only hello messages delivers 89.3 % of the english packets, with a throughput of 14.3 Kbit/s. This shows that an ad-hoc routing protocol must quickly adapt to link changes even for long lasting routes as in higher education essay, this case where mobility is very low. Essay On Citizenship! Table 12: Mobility factor Received Throughput Sent Average delay Dropped Received packets Packet overhead Byte overhead Average hopcount DSDV 0.0439350 75.6% 12.1 Kbit/s 21510 0.052 s 5250 16260 44054 6406036 5.32 Conference simulation results. DSR - 1 0.0439350 97.1% 15.55 Kbit/s 21510 0.210 s 614 20896 3129 3689865 5.73 DSR - 2 0.0439350 98.0% 15.7 Kbit/s 21510 0.23 s 422 21088 4109 4093220 5.79 54 AODV - 1 0.0439350 89.3% 14.30 Kbit/s 21510 0.26 s 2298 19212 43881 1660020 6.62 AODV - 2 0.0439350 92.3% 14.79 Kbit/s 21510 0.29 s 1644 19866 14537 610884 6.53 AODV - 3 0.0439350 94.0% 15.00 Kbit/s 21510 0.39 s 1376 20134 54677 2112716 6.45 Both versions of DSR have the lowest packet overhead in this scenario, while all versions of essay, AODV show the lowest byte overhead. The large byte overhead for DSR has to do with the fairly large amount of traffic and benefits research that the routes have an average hopcount that is as large as 5-6 hops.
As can be seen in Table 13. DSDV fails to deliver 3599 packets because of higher, route failures. This is friends benefits paper due to value higher education, the slow response time when links go down and the time it takes to with research paper, find new routes. Essay! A lot of computer revolution cause and effect, packets will be sent using a route that the protocol thinks is valid, while in fact the education route is resume length broken and higher the packets are dropped. Also a lot of packets are dropped in the interface queue. On Citizenship For Kids! AODV using only hello messages show the same tendency, dropping 1364 packets because of the same reasons. It is however fewer packets than for essay DSDV. This has to do with the time between the HELLO messages. The less time between the messages, the faster can the protocol react to broken links and avoid dropping the packets. In general, most of the packets are dropped in the sendbuffer. On Hard Work Is The Key To Success! Retransmission of value higher, these dropped packets could of course be handled by upper layer protocols, such as TCP.
Table 13: Cause for drop Sendbuffer Route failures ARP Interface queue End of simulation DSDV 3599 74 1567 10 Packet drops in conference scenario. DSR – 1 519 30 34 18 13 DSR – 2 303 98 4 0 17 AODV –1 894 1348 22 4 30 AODV – 2 1364 201 21 10 48 AODV -3 1096 202 14 0 64 5.6.3 Event coverage This scenario simulates a group of 50 highly mobile people that are changing position quite frequently. It could for instance represent a group of reporters that are covering a political event, music concert or a sport contest. In real life it would be nearly impossible to essay on hard key to, establish a wired network between the reporters, but they must be in constant communication with each other, enabling a fast reaction. Higher Essay! Parameters that are specific for the event coverage scenario are shown in Table 14. Table 14: Parameters used during event coverage scenario. Revolution And Effect! Parameter Number of CBR sources Number of receivers Number of flows Value 9 45 45 The scenario is value education characterized by: N N N N N Rather high mobility factor. Typically 50 % of the nodes are constantly changing their position during any time of period.
Every now and then the nodes tend to cluster. Links involve a few hops and relatively short-lasting. Traffic is spread all over the place. Essay On Citizenship! Many obstacles. Nodes can usually only communicate with a few nodes. Value Higher Education Essay! This will lead to and health, a low interference from the higher education essay other nodes, except for the moments of essay on citizenship for kids, clustering. 55 The scenario tests the value higher education essay protocols: N N Ability to respond to fast link changes and fluctuating traffic. Message overhead with constant topology updates. Figure 24 shows how the scenario was designed. 50 % of the nodes are moving randomly with a constant speed of 1 m/s. Every now and then a temporary cluster contain approximately 10 nodes will form.
These clusters remain static for resume length a certain amount of time. Temporary clusters = Node = Obstacle Figure 24: = Movement Event coverage scenario. The results for the event coverage scenario are shown in Table 15 and Table 16. As Table 15 shows, the value two protocols that has the on science and health lowest fraction of packets received are DSDV and the AODV version that entirely relies on feedback from link-layer. Higher! These protocols only have a fraction of short essay on hard success, packets received that lies around 91-92 %. For all other protocols/versions this value is at least 94 %. The mobility factor for education essay the scenario is essay 0.72, which is quite low even though considering we have about value higher education 50 % of the nodes in movement. On Hard Key To! The nodes are however only moving with a speed of education, 1 m/s. DSDV has the highest overhead of all the protocols, counted in on science and health, both number of essay, control packets and bytes. With Benefits Research! DSR both with and without eavesdropping have a very low overhead. Higher Education! It must however be noted that the traffic load in this scenario is very low and most of the essay and health communication is taking place in value education, a very small area, thus leading to a very low average hopcount of approximately 1.5 for all protocols. In this scenario, AODV with only hello message shows better results than AODV with only link-layer support and the reason is that the computer revolution and effect hello messages makes it possible to keep track of value, neighbors. Most of the communication is taking place within clusters, so to know the neighbors will probably mean that we will not have to short is the key to success, make as many requests.
The topology of the essay network is changing quite frequently. This causes a protocol like DSDV to have a very large overhead. The communication however, take mostly place within the clusters. This makes the job for the on-demand-based protocols much easier. The hopcount from friends paper, source to destination is very small so the protocols will find a route very quickly. The protocols which are entirely on-demand will have a slightly 56 higher delay and the protocols that uses some sort of higher essay, periodic messages (DSDV and the ADOV version that use hello messages) will have lower delay.
Table 15: Mobility factor Received Throughput Sent Average delay Dropped Received packets Packet overhead Byte overhead Average hopcount DSDV 0.721611 91.4% 14.75 Kbit/s 4500 0.075 s 385 4115 42415 10578764 1.46 hops Event coverage simulation results. DSR – 1 0.721611 97.5% 15.68 Kbit/s 4500 0.138 s 111 4389 1056 141196 1.53 hops DSR – 2 0.721611 97.7% 15.71 Kbit/s 4500 0.140 s 102 4398 1354 158420 1.57 hops AODV – 1 0.721611 94.5% 15.33 Kbit/s 4500 0.024 s 245 4255 31342 1137752 1.55 hops AODV – 2 0.721611 92.2% 14.89 Kbit/s 4500 0.214 s 352 4148 2722 117904 1.75 hops AODV – 3 0.721611 95.1% 15.36 Kbit/s 4500 0.015 s 219 4281 31443 1142180 1,55 hops Table 16 shows that most of the cause packets are dropped due to route failures and in those cases where there exists a sendbuffer, congestion/time-out in essay, the sendbuffer. English To Use In Essays! AODV that only uses link-layer support (AODV 2) has most of the dropped packets due to failed ARP requests and higher DSDV drops most of its packets at resume length, the interface queue. Table 16: Cause for education drop Sendbuffer Route failures ARP Interface queue End of on citizenship for kids, simulation DSDV Packet drops in event coverage scenario. DSR - 2 81 19 1 AODV - 1 100 83 61 1 102 48 235 DSR – 1 81 21 9 9 AODV - 2 131 32 178 10 1 AODV - 3 100 15 104 5.6.4 Disaster area This scenario represents some sort of disaster area in a region that lacks any sort of telecommunication infrastructure. It could for instance represent a natural disaster or a large rescue operation. Essay! Every rescue team member could have a personal communicator with ad-hoc network capability. These personal communicators are capable of communicating with each other and essay with relay nodes that are mounted on a vehicle, like a helicopter, car or boat.
The parameters that are specific for value higher the disaster area scenario are shown in Table 17. Table 17: Parameters used during disaster area scenario. For Kids! Parameter Number of CBR sources Number of receivers Number of flows 57 Value 38 87 87 The scenario is characterized by: N N N N N N A node movement, where approximately 95 % of the nodes are moving slightly, while the remaining 5 % are changing their position very often. Network partitioning now and then. Long and value education essay short lasting links that only are a few hops.
Traffic that is spread all over the nodes. Many obstacles. Low interference from the other nodes. The scenario tests the protocol: N N Ability to work with both slow and fast changing network topologies. Ability to cope with network partitioning. Figure 25 shows how the scenario was designed. There are two highly mobile nodes moving at the speed 20 m/s back and forth. There are also three separate subnetworks that can connect to each other through the relays mounted on the highly mobile nodes. Within each subnetwork, the movement is randomized at speed 1 m/s.
Subnetwork 2 Subnetwork 1 Vehicle 1 = Node Subnetwork 3 = Obstacle Figure 25: Vehicle 2 = Movement Disaster area scenario. The results for the disaster area scenario are shown in Table 18 and Table 19. The calculated mobility factor for this scenario is quite high. Many of the nodes are moving slightly (people), and some nodes are moving very fast (vehicles). The protocols that show the english good words best results in this scenario are the purely reactive approaches, that is AODV using both hello messages and MAC support and DSR with eavesdropping. They have a delivery ratio between 54–58 % of the packets with an average throughput of 14.1 – 14.8 Kbit/s. DSDV has the worst performance, delivering only value higher essay 29,5% of the packets with an resume length, average throughput of education essay, 12.42 Kbit/s. A delivery ratio of only 58 % for english to use in essays the best protocol may sound like a terrible ratio, but because of network partitioning, it is hard for any protocol to successfully deliver more packets than that. 58 DSDV show the lowest delay, but this is due to value higher education, the low delivery ratio. All versions of AODV keep an average delay between 0.89 – 1.05 seconds, while the DSR versions lie between 1.19 – 1.25 seconds. Both DSR versions keep a low packet overhead compared to the other protocols.
The byte overhead is however twice as large for DSR compared to AODV. As expected, DSDV uses the english to use shortest paths with an average of value higher education essay, 3.42 hops. The other protocols has an friends, average hopcount of 5.0-5.2 hops. Table 18: Mobility factor Received Throughput Sent Average delay Dropped Received packets Packet overhead Byte overhead Average hopcount DSDV 1.154619 29.5% 12.42 Kbit/s 29616 0.196 s 20867 8749 41402 6497476 3.42 hops Disaster area simulation results. DSR – 1 1.154619 58.0% 14.79 Kbit/s 29616 1.252 s 12440 17176 27048 4880992 5.01 hops DSR – 2 1.154619 54.50% 14.43 Kbit/s 29616 1.187s 13464 16152 30692 5137148 5.16 hops AODV – 1 1.154619 48.0% 13.07 Kbit/s 29616 0.888 s 15382 14234 61557 2426164 5.23 hops AODV – 2 1.154619 52.2% 13.49 Kbit/s 29616 1.052 s 14161 15455 50686 2426164 5.24 hops AODV – 3 1.154619 54.0% 14.09 Kbit/s 29616 0.988 s 13635 15981 77311 3096228 5.26 hops DSDV drops a lot of packets because of route failures. In this scenario, DSDV also drops a large amount of value, packets in the interface queue.
One large cause for drops in the other protocols, lies in the sendbuffer. English Good To Use In Essays! If routes are not found within time, packets in the buffer are dropped because of timeouts or congestion. Another large cause for packet drops is route failures. This scenario is higher education essay very interesting and should be investigated further, especially for the AODV protocol. We discovered when running the simulations that AODV tend to is the, form short lived routing loops. Since the author claim that this protocol should be loop free at all times, one possible cause for this might be invalid use of the sequence numbers or the fact that sequence numbers are unsynchronized during network partitioning. Very few packets were dropped because of value higher education, this (less than 5). Another interesting thing with this scenario is resume length that all main nodes send traffic both ways to each other.
This causes AODV to respond to requests with temporary routes set up by other requests. Since it is unclear from the draft whether the temporary routes should be regarded as a normal route in higher education essay, the routing table or not, we decided to try both in this scenario. By only allowing RREPs to use the temporary routes, and by revolution not allowing a node to respond to a RREQ with a temporary route, the routing loops could be avoided. However, the performance of the protocol decreased. We therefore used simulations where we considered the value essay temporary routes as a normal route.
Table 19: Cause for drop Sendbuffer Route failures ARP Interface queue End of simulation DSDV 15853 479 4528 7 DSR – 1 10033 1990 35 3 1 Packet drops in disaster area. DSR - 2 10277 2960 64 159 9 59 AODV – 1 9836 5047 292 34 2 AODV - 2 10693 3046 241 20 1 AODV - 3 10941 2470 64 44 116 5.6.5 Summary realistic scenarios The realistic scenarios show how the protocols behave in revolution cause, certain situations. For this purpose, three scenarios were designed and simulated with different versions of the protocols DSDV, DSR and AODV. DSR show the best performance results overall. If source routing is undesirable, another good candidate is AODV with only MAC layer support.
It has a slightly higher packet overhead, but an value essay, overall good delivery ratio. 5.7 Observations The protocols that we have worked with most are AODV and DSR, thus we have observed some important differences for these protocols, that in essay for kids, some way affect the performance of the protocols. 5.7.1 Ability to find routes AODV To illustrate AODVs ability to find routes, we use a simple scenario (see Figure 26). The scenario consists of four nodes A, B, C and D connected to each other. A C D B Figure 26: Simple example scenario. Node A needs a route to node D. No data has been sent earlier, thus the only routes known to the AODV protocol are the value higher education essay different neighbors in the scenario. This is because AODV uses hello messages to keep track of the neighbors of a node. A RREQ is generated by node A and broadcasted to its neighbors. The RREQ propagates through the network until it reaches node C. Since node C has a route to node D it can comply with the RREQ and generate a RREP.
During the and health hazards propagation of the essay RREQ, a reverse path is set up to node A. The RREP is unicasted back to A. English! It uses the temporarily backward route set up by the RREQ. During the higher essay propagation of the reply, a forward route is set up to node D by all intermediate nodes, resulting in the routing table shown in Table 20, thus all temporary routes are updated to active routes. Table 20: Node A Destination Nexthop B B D B Routing tables for AODV after a route discovery process. Node B Destination A C D Nexthop A C C Node C Destination B D A Nexthop B D B Node D Destination C Nexthop C After the route discovery process, only B and C have routes to all other nodes in the scenario. Resume Length! Node A does not know that there is higher education a route to node C, nor does node D know of the route to A and B. Thus AODV has to go through the route discovery process several times to discover all the routes. This leads to more control traffic and higher delays.
On the other hand, it saves memory by revolution not having to keep information about value education routes that might not be used. 60 DSR The ability to find routes differs slightly between the resume length DSR and AODV protocol. Value Education Essay! DSR can make use of the source route carried in each packet header to discover routes to nodes by which the packet has traveled through. If new routes are found, DSR can take advantage of this without having to go through a new route discovery phase, thus reducing the resume length number of control packets and value higher decreasing the delay. The memory usage of a node is instead increased by having to store more routes.
We consider the same scenario as for the AODV protocol (Figure 26). Node A needs a route to node D. On Hard Is The! No data has been sent earlier, thus DSR has no knowledge of any routes. Since no routes are known, the RREQ propagates until it reaches node D. Value Higher Education Essay! During the propagation of the RREQ, every node in its path learn a route back to all the nodes by which the RREQ has passed through. The RREP is unicasted back to A, using the routes learned during the propagation of the RREQ. As the computer revolution RREP propagates, each node also learns the routes to all nodes for which the RREP has passed through, resulting in the routing tables shown in Table 21. After the route discovery phase, each node has a route to higher education, every other node in this example. Table 21: Node A Destinatio n B C D Path B B-C B-C-D Routing caches for DSR, after a route discovery process. Node B Destinatio n A C D Path A C C-D Node C Destinatio n A B D Path B-A B D Node D Destinatio n A B C Path C-B-A C-B C 5.7.2 Temporary backward routes When a RREQ propagates in search for english in essays a route in AODV, a temporary backward route is set up towards the requesting node.
A RREP might use this backward route. Education Essay! This route is normally set to expire after 3 seconds if it is not used. It is not clear from the draft if this route may be used by application data as well. Using this route for data affects the behavior of the essay on hard work is the success protocol in some way and education it is revolution not described how the protocol should handle this. One of the value higher essay problems with this temporary route is with the way it is set up. When the on science hazards RREQ propagates, we do not know who will be using the essay backward route, so no active neighbors can be put into the active neighbor list. If during this time, a link failure or an with research paper, expired route entry somewhere breaks the route, the value education essay rest of the resume length nodes in the route are not informed of this and therefore have redundant routes in value higher, their tables.
When the route is used again, the essay on science hazards application data will come to a node in the route that does not have a valid entry for the destination and essay will therefore be dropped while a triggered RREP tries to revolution, inform the nodes in the route that it is broken. This problem will become more apparent in a network with a higher load. Another problem is the short lifetime if temporary routes are installed into higher, the routing table. Lets say node A sets up a temporary route to D. Node A can then respond with the temporary route to another request searching for short essay work key to success a route to value higher essay, D. Since the temporary route has a short lifetime, it might expire before the actual data has a chance to use it. This results in and effect, unnecessary control overhead and packet drops. To deal with this, the higher education routing agent could chose to only allow RREP to use the friends temporary route. Also a check of the expire time before responding with a RREP could be used to assure that the route wont timeout shortly after the node has responded with the information.
A question about this was directed to the author of the protocol with the response that this check should not be done, instead the protocol should rely on the sequence numbers to higher education, provide the freshness of a route. We implemented a version of the AODV protocol that used the temporary route for essay hazards all packets since it showed a slightly better performance result then if not allowing data packets to use the temporary route. The implementation done in Gothenburg used the temporary route only for route replies. So we have a small difference in higher education, our implementations. 61 5.7.3 Buffers The use of english good to use, send buffers in value higher essay, the routing protocol also affects the performance of the routing protocol; especially the size of the buffers and the time a packet is allowed to stay there before it is dropped. Resume Length! The send buffer buffers data packets while the routing protocol requests a route to the destination. In our simulations, AODV used a buffer capable of holding 64 packets and allowing them to stay in higher education, the buffer for maximum 8 seconds. Allowing the packets to stay in short essay on hard work key to, the buffer for value higher longer period of essay on citizenship, times will of course increase the amount of successfully routed packets, but also increase the average delay. Also the higher education essay choice of queuing discipline will affect the measured performance.
If the on citizenship for kids buffer is full, there must be some smart algorithm to decide which packets should be dropped. The routing protocol could decide not to buffer any packets at value education, all and computer depend on higher layer protocols such as TCP to retransmit lost packets. This would however affect the measured performance in the simulations and give unfair results for the protocol. Value Essay! 5.8 Discussion If we compare the work that we have done against on citizenship the work that was done by the CMU Monarch project , many similarities can be seen. Their conclusion was that both DSR and AODV performs well at value, all mobility rates and movement speeds.
We have come to the same conclusion, but we feel however that their definition of mobility (pause time) does not represent the dynamic topology to the same extent as our mobility factor that is based on essay hazards the actual relative movement pattern. The only higher education essay node speeds that they have tested are 1 m/s and 20 m/s, which are not showing the complete range. Our mobility factor has a speed range from 0 m/s up to 20 m/s and shows how the protocols behave in the complete range. They have also only shown the result for one DSR version and one AODV version. The DSR version that they show the results for is using eavesdropping, which we regard as being unrealistic, because of the security issuses discussed earlier. The AODV version that they have used is is the success not using hello messages, which changes the higher education essay behavior of on citizenship, AODV. We have tested different versions and shown that DSR with eavesdropping has a slightly better performance than DSR without eavesdropping. We have also shown that AODV with MAC-layer support and hello messages has better performance than AODV with only MAC-layer support. Value Education! Our results also show that it is necessary to use some support from the MAC-layer to resume length, achieve a performance that is good even at high mobility factors. Value Education! The CMU Monarch project, have used the number of essay is the key to, sources as a definition of the load that is offered the network. Their simulations with the value higher essay different number of sources are almost identical to short work is the key to success, each other.
The only protocols that showed a significantly difference was TORA, that only delivered 40 % of the packets with the higher essay lowest pause time and highest number of sources. Our definition of load was based on the rate that the sources are sending packets with. Even DSR that had the best results in the CMU paper fails to resume length, deliver a large fraction of the packets when the rate is increased. Value Essay! The increase of the rate also very clearly shows how much the overhead for DSR increases compared to for instance AODV. 5.9 Classification Why is there any need for classification of routing protocols? If one routing protocol is friends research superior than the other routing protocols for instance in very high mobile environments, why not always use that routing protocol? If it handles high mobile environments, it should also be good at low mobile environments. In real life, many parameters affect the behavior of the routing protocol.
It is also important to recognize the value higher education essay need that is required in computer revolution and effect, a particular scenario. In one scenario, there is maybe more need for high throughput than there is for low delay. In another scenario there is maybe more need for low delay etc. This is becoming more and value essay more important now, in particular when active networks  is becoming an interesting issue in networking. Essay On Citizenship For Kids! Active networking means that you add user controllable capabilities to the network. The network is no longer viewed a passive mover of bits, but rather as a more general computation engine. Value Higher Education! This makes it possible for instance to english good words, adjust the routing protocol depending on value education essay the scenario. You could basically send the routing protocol and let it install itself into the nodes. 62 5.9.1 Mobile networks As the simulation results show, the mobility of the network greatly affects the essay on citizenship performance of the protocols. It is crucial that the protocol ability to detect broken routes is fast enough and education essay that they also react to these changes.
DSDV Since DSDV is dependent of its periodic updates, its ability to deal with a dynamic topology is very poor. It has a poor ability to fast detect broken links and friends with research takes time to converge. This protocol should really be avoided for use in ad-hoc networks where it is crucial to deal with frequent changing topology. This protocol could however be an option for networks that are static during long periods of value education, times. AODV The original AODV protocol using only HELLO messages as link breakage detection shows poor results as mobility increases. Short Essay Is The! This protocol needs better link breakage detection. Using lower layers such as MAC to detect transmission errors can achieve this. If this is used, the protocol actually shows a very good performance. Value Higher! This protocol is a definite choice for highly mobile networks. DSR This protocol is highly optimized and also shows good results in the simulations.
The protocol could definitely be used in highly mobile networks as well as static networks. 5.9.2 Size of networks When talking about the size of friends with benefits research paper, a network, it is not only the value number of nodes in the network that is of interest. The area that the nodes are spread out over is also interesting. This basically decides the connectivity of the network. Friends Benefits! A large area with many nodes may mean longer routes then for a smaller area with the value higher education essay same number of nodes.
At the same time, many nodes close to essay is the key to success, each other means a higher collision probability. DSDV This protocol does not scale well. Its use of periodic broadcasts limits the higher education essay protocol to small networks. If the protocol would be used in words to use, large networks, the converge time to a steady state would increase when routes go up and down. The reason is that updates must propagate from one end of the network to the other. Value Higher Education Essay! AODV This protocol scales well, and could be used in both small and medium sized networks. The combination of on-demand and distance vector makes this protocol suitable for large networks as well. The information that each node must store for each wanted destination is rather small compared to for instance DSR that has to store whole source routes. In large networks however, the propagation of requests to all nodes is a waste of resources. A better solution is probably to benefits paper, divide the network into clusters or zones, like for instance ZRP and higher CBRP have done. DSR This protocol has some limitations when it comes to essay for kids, the size of the network.
A larger network often means longer routes and longer routes means that the source overhead in each packet grows. The current implementation limits each packet to carry a source route of maximal 16 hops. This can of course be adjusted, but one should keep in higher education essay, mind the resume length large overhead this causes. One could imagine a network with 20 nodes connected in higher essay, a straight line. Then this implementation would not manage to route to all nodes. We therefore recommend this protocol for small and english good to use medium sized networks.
63 5.9.3 Network scenarios Conference For low mobility scenarios, like the conference scenario that we did simulations on, DSR is the education essay best protocol to computer and effect, use if the hopcount is small (fewer than 5 hops). The reasons are high delivery rate, low delay and low message overhead in terms of value, packets and byte overhead. If the number of hops increases and get as many as 10 hops, each packet must carry a very large byte overhead, which can be very costly, when the load increases. Another good candidate for this scenario when the number of computer cause, hopcount increases is one of the AODV versions that use MAC-layer support. AODV has also a very high delivery ratio, but the number of control packets is somewhat larger.
Event coverage In average mobile scenarios, like the value essay event coverage scenario, where nodes tends to for kids, cluster and almost all communication is within the higher education clusters, DSR is by all means the best protocol. It has a very large delivery ratio and the overhead is essay on science very small, even counted in bytes, because of the few hops required to reach the destination. The AODV versions show a very good result also, but the overhead is larger. So for these type sort of networks DSR it the best protocol. Disaster In networks that become partitioned, DSR with eavesdropping show the best results in this scenario. Value Higher Essay! It has a high delivery ratio, high throughput, a delay around 1.2 seconds and friends with research paper low packet overhead.
It also uses only 5 hops in average to reach a destination. This protocol is therefore recommended in this type of scenario. Eavesdropping might however be undesirable because of security issues. One other candidate for this scenario is AODV with MAC support. It has almost as high delivery ratio as DSR and also a lower delay. The packet overhead is twice as high but the value essay byte overhead is smaller. 5.10 Improvements The simulations have shown that DSR with and without eavesdropping and the AODV versions that use linklayer support has the overall best result in almost all simulations. DSR has as mentioned earlier the advantage that it learns more information for each request it sends out. If a request goes from S to D and the reply from D to S, S will learn the route to good words to use, all intermediate routes between S and D. This means that it is not necessary to send out as many requests as for example AODV.
The source routing approach is therefore very good in value, the route discovery and route maintenance cases. However, source routing is not desirable to use for data packets. First of all, it adds a lot of overhead. Secondly it is not as traditional as for instance distance vector or link-state that are widely used in words, wired networks. Our proposal is therefore to implement a protocol that is a combination of source routing and distance vector. Source routing should be used in route discovery and route maintenance phases. These phases would also include that the routing tables where set up accordingly during the propagation of the requests and replies. Education Essay! When the data packets are forwarded a distance vector algorithm should be used. The packets are simply forwarded to the nexthop according to the routing table. This in computer revolution, combination with that the protocol stores several routes for each destination would probably mean a protocol with a performance that is even better than the protocols that have been simulated in this master thesis.
64 6 Implementation study The implementation study that was conducted at Ericsson Mobile Data Design in higher education, Gothenburg  has implemented the AODV protocol. The goal was to essay is the key to success, deliver a working routing protocol as specified in the original AODV draft . Higher Education Essay! 6.1 Design Main Event Queue Route Table Send Hello Send Request Check Neighb Check sender Remove route Neighbors / Senders Lookup Add Delete Update Need route? Add Delete Update time Is member? Host unreachable Lookup failed Message Request buffer Send request Send reply Send hello Receive msg Add Delete Is member? Rreq Rrep Hello Route add Route del User space /dev/route Iotcl() Icmp.c UDP FIB Kernel Table Kernel route.c Other daemons Figure 27: Overview of AODV daemon. The implementation that has been done should only be considered as a prototype to confirm the usefulness of on citizenship for kids, AODV. It is implemented as a daemon in user space. The advantage with this is value higher education that debugging and testing is essay much easier to do.
A final implementation should be made in kernel space with more optimized design. Thus abandon the value higher modular design and optimize the friends with benefits research paper code to go really fast. Figure 27 shows the design of the user space daemon and education essay how it interacts with the kernel code. Friends Paper! The different modules will be explained in the following chapters. 6.1.1 Main Main ties together all other modules of the user space daemon. It is also in main that the AODV specific code lies. 65 6.1.2 Event queue Queue for events that are supposed to higher essay, be performed at certain times. These events include: N N N N Periodic hello messages Send / retransmit route requests Timeouts of route entries Hello timeout 6.1.3 Route table This module is an essay on citizenship for kids, interface against the submodules Daemon Table and Kernel Table. It takes care of these two, so when you want to value higher essay, lookup or change a route from Main, you only have to do one call to this module instead of computer revolution, two to the both submodules.
The entries in Daemon Table module have all the fields that is required for AODV, sequence number, list of value essay, active neighbors and so on. The operations supported are Lookup, Add and essay hazards Delete. The Kernel Table is not a table in the sense Daemon Table is, instead this submodule just communicates with the kernel, sending messages about adding and essay deleting entries and receives netlink need-route messages. 6.1.4 Neighbors / senders Keeps track of the neighbors of a node. A neighbor is a host that sends/receives hello messages that is directly received/sent by essay on science and health another node. This demands that the links are bi-directional. At first it was thought that the WaveLAN cards would take care of this, but it was not the case. The signal strength and value higher the range was different between the hosts. To be able to with benefits research, guarantee bi-directional link, the concept Sender was added. A host is classified as a sender if it can be heard by at least one other node. Value Essay! When sending hello messages a node sends the list of current Senders and if the receiver of the resume length Hello messages is in this list, it is a Neighbor and can start act as one 6.1.5 Request buffer This buffer prevents the network of being flooded by value essay multiple request for the same address.
This buffer stores already processed requests. 6.1.6 Message Handles the different types of messages that the resume length daemon can send and receive. Value Higher Education! These messages are: N N N Hello Route Request Route Reply. 6.2 Setup The computers used for benefits research paper this implementation study was: N N 2 stationary computers with Lucent WaveLAN ISA cards. Value Essay! 3 laptops with Lucent WaveLAN PCMCIA cards.
The implementation started first with the 2 stationary computers running FreeBSD7. The choice of FreeBSD was primarily made because FreeBSD offers the best documentation of its kernel source. It was later discovered when the essay and health hazards laptops arrived that FreeBSD was incompatible with the Lucent WaveLAN PCMIA cards in the laptops. Linux8 however has support for value higher education both variants of the to use LucentWaveLAN cards and Linux was therefore chosen as development operating system. It is not very hard to port the code to FreeBSD in the future if so desired. 7 8 FreeBSD 2.2.6 Linux Red Hat 5.1 66 6.3 Testing The purpose of testing the implementation is to verify that the implementation works correctly and to see if the performance is suitable for real life applications. Higher Essay! 6.3.1 Correctness To verify that the implementation of resume length, AODV behaved correctly, computers were placed in different scenarios to test the different parts of the protocol. The following tests where made: N N N N N N N Bi-directional links and neighbors: Tests that two nodes can send hello messages to each other and registry the education counterpart as a neighbor. Is The Success! Unidirectional links and neighbors: It tests the value higher education same as above, but with the difference that we only have an uni-directional link, so only one of the nodes can hear the other and registry him as a neighbor. Neighbor link down: Tests that neighbors moving away from english to use in essays, each other causes the link between them to go down. Zero hop route requests: Tests that a request to a neighbor that also is the essay requested destination generates a reply that is short essay work correctly received.
This is not the normal operation of the protocol, but could happen if two nodes are in range but have not accepted each other as neighbors. Single hop route request: Tests the situation where node S searches the route to D and we have one node B in between. S broadcasts a request that is caught by B, which knows the route to D and sends a reply back to S. Multihop route request: Almost the same situation as the value essay single hop route request. The difference is english good in essays that we have two nodes between the requesting source and the destination. The route request must therefore be forwarded one hop before a reply can be generated.
Triggered route reply: Tests that the value higher education essay triggered route reply is generated whenever a route goes down. 6.3.2 Performance No actual performance tests were done. The results for good words to use in essays so few nodes would be misleading. Instead tests with real applications like Netscape and Telnet were done. The problems that occurred with these tests were related to higher education essay, the on-demand nature of AODV. Telnet for instance returns host-unreachable when trying to telnet to resume length, a computer on the first attempt. Higher Education! The second attempt however is successful. The reason is that when Telnet makes its first attempt, no route to the destination exists.
This will result in an error message from the revolution cause kernel to higher, Telnet, at the same time as a new request is sent to the neighbors. Benefits Research Paper! This request will eventually find a route to the destination and it is installed in the routing table. When Telnet makes a second attempt connect to the same host, a route will already exist in value higher education, the routing table and telnet will successfully reach the destination host. The solution to this problem is simply to take care of the error messages that the kernel sends to the application. The error message should be buffered and english to use in essays if a route is education essay not found in a certain amount of on science and health hazards, time, the error message should be sent to value higher education essay, the application, but if a route is actually found the error message can be discarded. 6.4 Problems / Limitations Problems that occurred during the english words to use implementation include: N N N FreeBSD incompatibilities: As mentioned before, lack of functional drivers to FreeBSD forced the implementation study to value education, be done under Linux. Address: The current prototype requires that each node participating in computer revolution and effect, the network have a predefined unique IP-address. There is a great need for a dynamic assigned IP-address architecture, which assigns nodes IP-addresses as they enter the network. IPv6 holds such functionality. Higher Education! This prototype is however done for IPv4 so no consideration has been done to implement such functionality. Three-way handshake: To guarantee bi-directional links, a three way handshake was necessary for the hello messages before two nodes can be certain of the other nodes existence.
The handshake uses piggybacking. It concatenates a list of all nodes it receives hello messages from to the hello messages it sends. Success! When a node receives a hello message and finds its own address in the concatenated list it will add the value higher sending node to its own list of neighbors which it has bi-directional links to. Three hello 67 N messages instead of one wastes bandwidth, but could also in a worst case scenario mean that it could take as long as two full hello intervals before two nodes in range of each other accepts the bi-directional links. Temporary routes: When a request is broadcasted from a node, it will propagate through the network and at the same time install a temporary route back to the source.
The problem with this temporary route is first of all that the request is unaware of if the essay on citizenship route ever will be used and secondly who will use it. This means that it does not know the value higher active neighbors that are using this entry and can therefore not inform these neighbors if a link should go down on this route. The solution that was implemented differs somewhat of what was done in short on hard work key to, the simulation study. The solution is to store the education essay temporary routes separately and only install them in work success, the routing table when the route reply is propagating back through the education essay network. Friends With Benefits Research! 6.5 Improvements Possible features that could be added to this prototype: N N N N Link layer hellos: The addition of value essay, link layer feedback from 802.11 would significantly increase the performance as the simulation study has shown. Resume Length! Redundant routes: Store all routes to a destination, not only the one we are currently using. If a route goes down due to a link failure, the next stored route would be tried before a new request is to be sent. This saves a lot of overhead a and makes the delay somewhat smaller. Dynamic IP-addresses: As mention under limitations, dynamic address assignment is a requirement for these kind of networks.
Multicast: Multicast groups within a ad-hoc network could be added. The latest AODV draft has support for this. 6.6 Implementation conclusions The implementation of the AODV protocol has shown that it is possible to higher, get these protocols to work in real-life. It must however be noted that real-life in this case only consisted of for kids, five computers. Value Education! The AODV prototype has also given some insight into the problems that arise when trying to run real applications on short essay on hard work is the key to success an ad-hoc network. Applications like Netscape and Telnet get host unreachable in the first attempt. The second attempt finds the route successfully. This has to do with the on-demand feature of the value essay AODV protocol.
68 7 Conclusions 7.1 Results The simulations have shown that there certainly is a need for a special ad-hoc routing protocol when the mobility increases. It is however necessary to have some sort of feedback from the link-layer protocol like IEEE MAC 802.11 when links go up and down or for essay on citizenship for kids neighbor discovery. To only education essay be dependent on periodic messages at the IP-level will result in a very high degree of packet losses even when mobility increases a little. On Hard Work Key To! The simulations have also shown that more conventional types of education, protocols like DSDV have a drastic decrease in performance when mobility increases and are therefore not suitable for mobile ad-hoc networks. AODV and DSR have overall exhibited a good performance also when mobility is high.
DSR is however based on on hard source routing, which means that the byte overhead in each packet can affect the total byte overhead in the network quite drastically when the offered load to the network and the size of the network increases. In these situations, a hop-by-hop based routing protocol like AODV is more desirable. One advantage with the source routing approach is value education essay however that in its route discovery operation it learns more routes. Source routing is however not desirable in ordinary forwarding of data packets because of the large byte overhead. A combination of AODV and DSR could therefore be a solution with even better performance than AODV and DSR. Another key aspect when evaluating these protocols is to test them in realistic scenarios. We have tested them in three types of scenarios. English Good Words To Use In Essays! DSR had the best performance, but the large byte overhead caused by value education the source route in each packet makes AODV a good alternate candidate.
It has almost as good performance. The implementation study conducted at resume length, ERV in Gothenburg has shown that it is possible to get a real ad-hoc network up and running. The main problems that did occur were related to the testing of the education essay protocol with real applications. When a route was needed by essay and health the application and the route did not exist in value education essay, the routing table, the kernel informed the applications of a connection error before giving the routing protocol enough time to find a route. 7.2 Further studies Ad-hoc networking is a rather hot concept in computer communications.
This means that there is much research going on and many issues that remains to be solved. Due to good in essays, limited time, we have only focused on the routing protocols. However there are many issues that could be subject to further studies. Value Education Essay! First of all, the simulator environment could be improved. Essay For Kids! These are just some of the higher education improvements that could be made: N N More routing protocols, for instance TORA, ZRP and CBRP. Measurement of computing complexity.
Secondly, there are many issues related to ad-hoc networks that could be subject to further studies: N N N Simulations which take unidirectional links into consideration. Some sort of analysis of whether many small control messages are more costly to send in essay work key to, terms of resources than fewer large control messages. Security: A very important issue that has to be considered is the security in an ad-hoc network. Routing protocols are prime targets for impersonation attacks. Because ad-hoc networks are formed without centralized control, security must be handled in a distributed fashion.
This will probably mean that IP- 69 N N N N N N Sec  authentication headers will be deployed, as well as the necessary key management to distribute keys to the members of the ad-hoc network. Quality of Service (QoS): What needs are there for Quality of Service in an ad-hoc network? This is related to what the networks actually will be used for. Hand-over of real-time traffic between nodes. How should real-time traffic smoothly be handed over to value higher education, another node when a route goes down? Should flooding be used before a route is found? Multicast: We have only looked at unicast routing. Multicast routing is also an interesting issue that has to be considered.
Connecting ad-hoc networks to the Internet through access points: How do you connect an ad-hoc network to the Internet? It is not possible to just add the access point as default in the routing tables. This would mean that nodes without a route to a certain destination would be routed to the Internet. Mobile IP: Integration of mobile IP into ad-hoc networks. Addressing of hosts: How should the hosts in computer cause, an ad-hoc network be addressed? What happens if one adhoc network is partitioned in to two separate networks or two ad-hoc networks are merged into one new larger ad-hoc network? IP Index Router IP Router (IP) Index Index Figure 28: Router (RID) IP IP Different router identification approaches. Value Education! From left to right: 3a, 3b, 3c. There are basically three types of identifiers to consider (Figure 28): 1) Interface identifiers: Interfaces are present on both routers and hosts.
In the Internet addressing architecture, interfaces are identified by IP addresses. 2) Host identifiers: Can either be a permanent identifier or a temporary identifier. 3) Router identifiers: Is unspecified and generally depends on the routing policy. For Kids! There are three approaches to MANET router identification and addressing currently being considered: a) Single IP address (AODV): Identifies a MANET node (both the router and the host) with a single IP address. This approach leaves several issues open: N How to support sets or subnets of hosts attached to a MANET router?
N How to support the use of multiple wireless interfaces? b) Single IP address with interface indexes (DSR): Identifies a MANET router with a single IP address and each interface with a single-byte interface index. This makes it possible to enable simultaneous support for multiple wireless technologies, with the IP address acting as router identifier. Value Higher Essay! The problem with this scheme is that it is not IP in on science and health, the classical sense where interfaces are identified by education IP addresses. The use of a non-standard addressing architecture will likely complicate interoperability. Computer! c) Router identifier and IP interface addresses (IMEP): Identifies a MANET router with a router Identifier (RID) and identifies each interface with an IP address. This approach can support sets or subsets of value, attached hosts and simultaneous use of multiple wireless technologies.
Approach a) and b) seem tailored to support a mobile host that acts like a router. Approach c) is intended to on science and health hazards, support a mobile router platform to which one or more host-like devices may be permanently or temporally affiliated. These approaches say nothing about value higher essay how IP addresses are assigned to interfaces (on hosts or routers), or what the RID is and how it is and health assigned. This is a separate problem, although one which is related to routing. Value Higher Education Essay! 70 8 References  Dimitri Bertsekas and Robert Gallager, “Data Networks - 2nd ed”. Prentice Hall, New Jersey, ISBN 013-200916-1. Benefits!  Bommaiah, McAuley and Talpade. AMRoute, “Adhoc Multicast Routing Protocol”, Internet draft, drafttalpade-manet-amroute-00.txt, August 1998. Value Higher Education! Work in resume length, progress. Value Higher!  Josh Broch, David A. Maltz, David B. Friends With Benefits Paper! Johnson, Yih-Chun Hu and Jorjeta Jetcheva, “A performance Comparison of Multi-hop Wireless Ad Hoc Network Routing Protocols”. Mobicom'98, Dallas Texas, 25–30 October, 1998. Value Higher Education Essay!  Josh Broch, David B. Johnsson, David A. Maltz, “The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks”. Internet Draft, draft-ietf-manet-dsr-00.txt, March 1998. Work in progress.  Scott Corson and Joseph Macker, “ Mobile Ad Hoc Networking (MANET): Routing Protocol Performance Issues and Evaluation Considerations”.
Internet-Draft, draft-ietf-manet-issues-01.txt, March 1998. Work in progress. Computer And Effect!  M.Scott Corson, S. Papademetriou, Philip Papadopolous, Vincent D. Park and Amir Qayyum, “An Internet MANET Encapsulation Protocol (IMEP) Specification”. Internet draft, draft-ietf-manet-imepspec01.txt, August 1998. Value Essay! Work in progress.  Kevin Fall and Kannan Varadhan, “ns notes and documentation”. Computer Revolution And Effect! The VINT project, UC Berkeley, LBL, USC/ISI, and essay Xerox PARC, May 1998. Work in essay hazards, progress.  Zygmunt J. Haas and value higher Marc R. Pearlman, “The Zone Routing Protocol (ZRP) for Ad Hoc Networks”, Internet draft, draft-ietf-manet-zone-zrp-01.txt, August 1998.
Work in progress.  IEEE Computer Society LAN MAN Standards Committee, “Wireless LAN Medium Access Control (MAC) and essay on hard work is the key to success Physical Layer (PHY) Specifications”, IEEE Std 802.11-1997. The Institute of value, Electrical and Electronics Engineers, New York.  Philippe Jacquet, Paul Muhlethaler and Amir Qayyum, “Optimized Link State Routing Protocol”. Internet draft, draft-ietf-manet-olsr-00.txt, November 1998. Work in progress.  Mingliang Jiang, Jinyang Li and Yong Chiang Tay, “Cluster Based Routing Protocol (CBRP) Functional specification”. Internet draft, draft-ietf-manet-cbrp-spec-00.txt, August 1998. Work in progress.  David B. Johnson and David A.Maltz, “Dynamic source routing in ad hoc wireless networks”. Key To Success! In Mobile Computing, edited by Tomasz Imielinski and Hank Korth, chapter 5, pages 153-181. Kluwer Academic Publishers.  David B. Value Essay! Johnson and on science David A. Higher Essay! Maltz, “Protocols for adaptive wireless and mobile computing”. In IEEE Personal Communications, 3(1), February 1996. Resume Length!  Stephen Kent and Randall Atkinson, “Security Architecture for the Internet Protocol”, Internet draft, draft-ietf-ipsec-arch-sec-07.txt, July 1998.
Work in progress. Higher Essay!  Mobile Ad-hoc Networks (MANET). URL: http://www.ietf.org/html.charters/manet-charter.html. (1998-11-29). Work in english words in essays, progress. 71  Vincent D. Higher Education Essay! Park and M. Scott Corson, “Temporally-Ordered Routing Algorithm (TORA) Version 1: Functional specification”. Short On Hard! Internet draft, draft-ietf-manet-tora-spec-01.txt, August 1998. Value Essay! Work in progress.  Vincent D. Park and M. Scott Corson, “A performance comparison of the Temporally-Ordered Routing Algorithm and Ideal Link-state routing”. In Proceedings of IEEE Symposium on Computers and Communication ’98, June 1998.  Charles E. Perkins, “Mobility support, Mobile IP and cause and effect Wireless Channel Support for ns-2”, presentation slides. URL: http://www.svrloc.org/ charliep/mobins2/, (1998-11-29). Work in progress.  Charles E. Perkins, “Ad Hoc On Demand Distance Vector (AODV) Routing”. Internet draft, draft-ietfmanet-aodv-01.txt, August 1998.
Work in progress.  Charles E. Perkins, “Ad Hoc On Demand Distance Vector (AODV) Routing”. Internet draft, draft-ietfmanet-aodv-02.txt, November 1998. Work in progress.  Charles E. Value Education Essay! Perkins, “Mobile Ad Hoc Networking Terminology”. Internet draft, draft-ietf-manet-term00.txt, October 1997. Work in progress. Words In Essays!  Charles E. Perkins and Pravin Bhagwat, “Highly dynamic Destination-Sequenced Distance-Vector routing (DSDV) for mobile computers”. Value Education Essay! In Proceedings of the SIGCOM '94 Conference on Communications Architecture, protocols and Applications, pages234-244, August 1994. A revised version of the paper is available from http://www.cs.umd.edu/projects/mcml/papers/Sigcomm94.ps. (1998-11-29)  Larry L. Peterson and Bruce S. Davie, “Computer Networks - A Systems Approach”. San Francisco, Morgan Kaufmann Publishers Inc. ISBN 1-55860-368-9.  Plummer, D., An Ethernet Address Resolution Protocol - or - Converting Network Protocol Addresses to essay hazards, 48.bit Ethernet Address for Transmission on Ethernet Hardware, RFC-826, MIT, November 1982. Value Essay!  Theodore S. Rappaport, “Wireless Communications: Principles and short on hard success Practice”. New Jersey, Prentice Hall. Value Education! ISBN 0-13-375536-3. On Citizenship!  Raghupathy Sivakumar, Prasun Sinha and essay Vaduvur Bharghavan, “Core Extraction Distributed Ad hoc Routing (CEDAR) Specification”, Internet draft, draft-ietf-manet-cedar-spec-00.txt, October 1998.
Work in resume length, progress. Education!  Martha Steenstrup, “Routing in communication networks”. Essay Hazards! New Jersey, Prentice Hall. ISBN 0-13010752-2.  Jerry Svedlund and Johan Kopman, “Routing protocols in wireless ad-hoc networks - An implementation study”. Uppsala: Uppsala University. Higher! Master thesis. Essay On Science!  D. L. Tennenhouse and D. Wetherall, “Towards an active network architecture”. In Multimedia Computing and Networking 96, San Jose, CA, Jan 1996.  The CMU Monarch Project. Education! “The CMU Monarch Projects Wireless and Mobility Extensions to ns”. Key To! URL: http://www.monarch.cs.cmu.edu/. Higher! (1998-11-29).
Work in progress. 72 Appendix A -Terminology This appendix contains some terminology  that is related to ad-hoc networks. A.1 General terms Bandwidth: Total link capacity of a link to and health, carry information (typically bits). Value Higher Education Essay! Channel: The physical medium is resume length divided into logical channel, allowing possibly shared uses of the medium. Channels may be made available by subdividing the medium into distinct time slots, distinct spectral bands, or decorrelated coding sequences. Convergence: The process of higher essay, approaching a state of equilibrium in which all nodes in the network agree on a consistent state about the topology of the network.
Flooding: The process of delivering data or control messages to every node within the any data network. Host: Any node that is not a router. Interface: A nodes attachment to with research paper, a link. Link: A communication facility or medium over which nodes can communicate at the link layer. Loop free: A path taken by a packet never transits the same intermediate node twice before arrival at the destination. MAC-layer address: An address (sometimes called the link address) associated with the higher education link interface of a node on a physical link. Next hop: A neighbor, which has been designated to forward packets along the way to a particular destination. Computer! Neighbor: A node that is within transmitter range from another node on the same channel. Node: A device that implements IP.
Node ID: Unique identifier that identifies a particular node. Higher Essay! Router: A node that forwards IP packets not explicitly addressed to itself. In case of ad-hoc networks, all nodes are at short essay on hard is the key to, least unicast routers. Value Higher! Routing table: The table where the routing protocols keep routing information for various destinations. This information can include nexthop and the number of hops to the destination. Scalability: A protocol is scalable if it is resume length applicable to large as well as small populations. Source route: A route from the value education essay source to the destination made available by the source. Throughput: The amount of data from a source to a destination processed by the protocol for which throughput is to be measured for instance, IP, TCP, or the MAC protocol. 73 A.2 Ad-hoc related terms Ad-hoc: For this special or temporary purpose or a special case without generic support. AODV: Ad-Hoc On-Demand Distance Vector.
Routing protocol for wireless ad-hoc networks. Asymmetric: A link with transmission characteristics that are different of the transmitter and receiver. Friends With Benefits! For instance, the range of value education, one transmitter may be much higher than the range of another transmitter on good to use the same medium. The transmission between the two hosts will therefore not work equally well in both directions. See also symmetric. Beacon: Control message issued by a node informing other nodes in its neighborhood of its continuing presence. Value Higher Essay! Bi-directional: see symmetric. CBRP: Cluster Based Routing Protocol. Routing protocol for wireless ad-hoc networks.
Cluster: A group of nodes typically in range of english good words to use, each other, where one of the nodes is elected as the cluster head. The cluster head ID identifies the cluster. Each node in higher education essay, the network knows its corresponding cluster head(s) and to use therefore knows which cluster(s) it belongs to. DSDV: Dynamic Sequenced Distance Vector. Routing protocol for wireless Ad Hoc networks. DSR: Dynamic Source Routing. Routing protocol for wireless Ad Hoc networks. Proactive: Tries to maintain the value higher routing map for the whole network all the time.
See also reactive. Reactive: Calculates route only upon good words, receiving a specific request. See also proactive RREQ: Routing Request. A message used by value essay AODV for the purpose of discovering new routes to on science, a destination node. RREP: Route Reply. Value Essay! A message used by AODV to reply to route requests. Symmetric: Transmission between two hosts works equally well in both directions.
See also asymmetric. TORA: Temporally Ordered Routing Algorithm. Routing protocol for wireless ad-hoc networks. English! Unidirectional: see asymmetric. ZRP: Zone Routing Protocol. Value Higher Education Essay! Routing protocol for for kids wireless ad-hoc networks. 74 Appendix B - AODV implementation for ns This appendix contains a little more details about the value higher essay implementation of AODV that we did for cause and effect ns. The implementation of AODV is higher education done according to the draft  released in resume length, August 1998. B.1 Message formats AODV have four different messages that it uses for route discovery and route maintenance.
All messages are sent using UDP. B.1.1 Route Request – RREQ The format of the value higher education route request message is revolution cause shown in Figure 29. 0 1 2 31 01234567890123456789012345678901 Type Reserved Hop count Broadcast ID Destination IP address Destination Sequence Number Source IP address Source Sequence Number Figure 29: N N N N N N N N Route request format. Type: Type of message. Reserved: Reserved for future use. Education! Currently sent as 0 and ignored on reception. Hop count: Number of hops from the with paper source IP address to higher education essay, the node handling the request. Broadcast ID: A sequence number identifying the particular request uniquely when taken in revolution cause, conjunction with the source nodes IP address.
Destination IP address: IP address of the destination for which a route is higher education essay required. Destination sequence number: The last sequence number received in the past by the source for any route towards the destination. Resume Length! Source IP address: IP address of the node that originated the value higher education request. Source sequence number: Current sequence number for route information generated by the source of the route request. 75 B.1.2 Route Reply - RREP The format of the resume length route reply message is shown in education, Figure 30. Essay On Science And Health! 0 1 2 31 01234567890123456789012345678901 Type L Reserved Hop count Destination IP address Destination Sequence Number Lifetime Figure 30: N N N N N N N Route reply format. Type: Type of message. L: If the essay L-bit is set the message is a hello message and contains a list of the nodes neighbors. Reserved: Reserved for future use. Currently sent as 0 and ignored on reception. Hop count: Number of hops from the source IP address to the destination IP address.
Destination IP address: IP address of the destination for which a route is supplied. Destination sequence number: The destination sequence number associated to the route. Lifetime: Time for which nodes receiving the on science and health hazards Reply consider the route to be valid. B.1.3 Hello Hello messages are a special case of Route reply messages. The difference is that a hello message always supplies the route to itself. This means that the hop count field is set to 0, the destination address set to the nodes IP address and the destination sequence number set to higher education, the nodes latest sequence number.
B.1.4 Link failure Link failure messages are also special Route reply messages, but in on science, this case the destination reflects the value education essay route that has broken. The broken route is assigned an infinite hop count and a sequence number that is on science hazards increased with one. Value Essay! 76 B.2 Design Figure 31 shows how AODV was designed when implemented for short essay on hard success ns. Education Essay! AODV OTcl C++ AODV_Agent Hdr_AODV Request Buffer Figure 31: AODV_RTable AODVConstants AODV design of short essay on hard is the key to, implementation for simulator. AODV The tcl script that starts the AODV routing agent and creates all mobile nodes that are using AODV as routing protocol. AODV_Agent Implements all AODV specific parts.
Handles RREQ, RREP, Hello and Triggered RREP. It also has a send buffer that buffers packets while a route is searched for. The timers that handles timeouts on route entries and the send buffer are also implemented here. Hdr_AODV Defines the message format for all messages that AODV uses. Education Essay! Request Buffer Implements the computer request buffer that prevents a node to process the same RREQ multiple times. AODV_RTable The routing table that AODV uses. The routing table also implements the value higher active neighbor list for each route entry. AODVConstants All AODV constants are defined here, which makes it easy to paper, modify for instance the hello interval. 77 B.3 Important routines B.3.1 Sending RREQ RREQ will only be sent by the source nodes (no intermediate nodes sends RREQs), if there does not exist any route for the destination. 1. 2. 3. 4. Value! 5. 6. 7. 8. For Kids! 9. 10. Essay! 11.
12. B.3.2 if ( no route exists ) else Receiving RREQ When a node receives a RREQ, it must first of all decide if it already has processed the RREQ. The RREQ is discarded if it has been processed. Otherwise the source address and the broadcast ID from RREQ will be buffered to prevent it from being processed again. 1. 2. 3. 4. Essay On Science And Health Hazards! 5. if ( (source addr, broadcast ID) in request buffer ) else The next step is to create or update the route entry in the routing table. This route can be used by the RREP when a route is found.
1. 2. 3. 4. 5. 6. 7. 8. if ( no route to source addr ) elseif ( source seqno in RREQ source seqno in route entry ) elseif ((source seqno in RREQ = source seqno in higher, route entry) AND ( hop count in RREQ hop count in route entry )) Then, the node must check if it knows the resume length route to the wanted destination. If the node knows the route it will unicast a RREP to the source. Otherwise it will forward the education RREQ. 1. 2. English To Use! 3. Value! 4. Essay On Science Hazards! 5. 6. 7. 8. 9. 10. if ( you are destination of RREQ ) elseif (( have route to destination ) AND (destination seqno in route entry = destination seqno in RREQ)) else 78 B.3.3 Forwarding RREQ When a node receiving a RREQ that it has not processed yet does not have a route, it will forward the RREQ. 1. Value Higher Essay! 2. And Health Hazards! 3. 4. 5. create a RREQ packet: copy all fields from education, received RREQ into new packet increment hop count field locally broadcast new RREQ packet discard received RREQ B.3.4 Forwarding RREP When a node receives a RREP that is not addressed for the node, it will set up the forward route by updating the routing table and short work is the key to success forward the RREP back to the requesting source. This part is value higher education however not explicit specified in the AODV draft. 1. 2. 3. On Citizenship For Kids! 4. 5. 6. 7. 8. 9. 10. 11. 12.
13. if ( route to requested destination does not exist ) elseif(destination seqno in RREP destination seqno in route entry) elseif ((destination seqno in RREP = destination seqno in value education essay, route entry ) AND ( hop count in RREP hop count in entry )) if (route to requesting source exists) B.3.5 Receiving RREP When the originating source receives the RREP it will update the routing table. 1. 2. 3. 4. And Effect! 5. 5. 6. 7. 8. 9. 10. 11. if (route to destination does not exist) elseif (destination seqno in RREP destination seqno in route entry) elseif (( destination seqno in RREP = destination seqno in education essay, route entry ) AND (hop count in RREP hop count in entry )) else 79 B.3.6 Hello handling Each node periodically broadcasts a hello message to all neighbors. Essay Work Success! When a node receives a hello message it knows that the higher education sending node is on science and health a neighbor and will update the routing table. Higher Education Essay! 1. 2. 3. 4. 5. 6. 7. 8. 9. B.3.7 if (route entry for revolution cause and effect HELLO source exists) else Forwarding packets AODV uses a active neighbor list to keep track of which neighbors that are using a particular route. Value! These lists are used when sending triggered route replies. The neighbor lists are updated every time a packet is essay on citizenship for kids forwarded. 1. 2. 3. 4. 5. 6. B.3.8 if (route entry to higher education essay, destination exists) Sending Triggered RREP Link breakages are detected by either the link layer which notifies the routing agent or by using hello messages. If a node has not received hello messages from a node for a certain amount of time it will assume that the on citizenship for kids link is value higher down. Every time a link is detected as down, AODV will send a Triggered RREP to inform the affected sources. On Citizenship! 1. 2. 3. 4. B.3.9 for (each address in the active neighbor list for a route entry) Receiving Triggered RREP Every time a Triggered RREP is received informing about value education a broken link, the affected route entry must be deleted and neighbors using this entry must be informed.
1. 2. 3. Benefits Research! 4. if (have active neighbors for broken route) delete route entry for value education broken route 80 Appendix C -Simulator screenshots This appendix shows some screenshots of Network animator and Ad-hockey. Network animator is the visualization tool for ns and Ad-hockey is the visualization for the mobility extension developed by the CMU Monarch project. C.1 Network animator Figure 32 shows a screenshot of Network animator. The scenario contains 19 nodes in a wired network. Some of the nodes are sending packets, which also can be seen in the figure. English Good! With this tool it is very easy to trace packets as they propagate through the network. The circles represent the nodes and the lines between the education circles are the physical wired links that connect the english words to use in essays nodes with each other. Figure 32: Screenshot – Network animator. 81 C.2 Ad-hockey The screenshots of value essay, Ad-hockey that can be seen in Figure 33, Figure 34 and Figure 35 shows the essay hazards playback trace of the realistic scenarios that with did simulations on.
The big white rectangle in the middle is the movement area. Education Essay! The different colored circles are the nodes. The colors of the nodes represent what action the essay on citizenship for kids nodes are performing at the moment. It could for instance be that the higher essay node is sending, forwarding or receiving a packet. The lines between the nodes do not represent wired links. The lines are actually packets that propagate from node to node. The detached rectangles and lines that also can be seen within the movement area are obstacles. Figure 33: Screenshot – Ad-hockey – Conference scenario. Words In Essays! 82 Figure 34: Screenshot – Ad-hockey – Event coverage scenario. Figure 35: Screenshot – Ad-hockey – Disaster area. 83 . TERM Spring #039;00 PROFESSOR Hesham TAGS Computer network, . routing protocol, ad-hoc network.
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07 Adhoc Networks. Nodes J and K both broadcast RREQ to node D Since nodes J and K are hidden from Vietnamese-German University, Binh Duong Province EEIT 28 - Winter 2016 Lecture (11-14) -On-Demand-Driven Reactive Routing protocols Chandra Prakash Assistan. Copyright © 2017. Value Higher Education! Course Hero, Inc. Essay! Privacy Terms.
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Simple Software for Better Interview Skills. Learn how to value higher education essay, land the job with Big Interview’s powerful video tutorials and virtual interview practice software. 13 Resume Mistakes That Make You Look Dumb. Before you get invited in for an interview, employers and recruiters look at resume length, your resume to see if you’re a good enough candidate for higher essay the job to be worth their time. If your resume doesn’t look good, you don’t look good. Even if you’re qualified, a silly mistake on your resume can kill your chances. Think of your resume as your 60 second audition in friends with benefits research paper, front of a judge on one of those reality TV talent shows.
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There are better ways to demonstrate your creativity. Save the arts and crafts for Pinterest. Also, avoid using weird colors, weird formats or weird paper stock. Your resume should be simple and elegant. Computer Revolution Cause And Effect. Go minimalist and let the essay, words speak for themselves. If you’re presenting a hard copy of essay on citizenship, your resume in person, make sure it doesn’t look like it was just pulled out value higher education of the trash can (or it’s very likely to end up back in the circular file). After all, you wouldn’t go to an interview wearing a dingy shirt or a hideous tie so don’t hand out a wrinkled, smudged, or coffee-stained resume. When you bring your resume to an interview, carry it in a folder to keep it crisp and essay on science and health hazards fresh. In general, try to higher essay, keep your resume to 1-2 pages in length.
Recent graduates should aim to stick to one page while more experienced candidates can get away with using more space. If you’re still short on work experience and short essay key to are having difficulty filling a page, think about listing relevant school coursework and extracurricular activities. Include volunteer work and value education the contributions you’ve made in that arena. You’ll also have space to benefits, list pertinent skills — including your prowess with different software programs and other tactical skills that apply to the job (review the job description and use the employer’s language). As you develop in your career and add more jobs to your resume, you won’t have space for these “extras.” However, during the early days of your career, this information can help a potential employer see your potential. Remember to use common sense here: No need to mention your collection of Twilight memorabilia or that you were runner-up in value, the 2010 SpongeBob look-alike competition. Even if you’ve been working for many years, you should try to keep your resume to 2 pages if possible. There are exceptions — CVs for academic positions and some other roles tend to be longer and more detailed. (I know this first-hand since I just reviewed a 79-page resume from very accomplished academic client). However, keep in mind that employers are always going to be most interested in the jobs that you’ve held recently. Use your space wisely to share more details about your most current and computer cause relevant work experience and edit down the value essay, descriptions of your earlier jobs to the bare necessities.
As your resume gets longer, you may even be able to drop early positions that have little to resume length, do with your current career path. Formatting can also help you reduce your page count — just don’t get too creative (see Mistake 2 above). If you lie on your resume, you’re taking a big risk. First of all, you’re very likely to get busted during the background and value higher essay reference checks. Short On Hard Is The Key To Success. Even if you get lucky and make it through the hiring process, dishonesty on value higher education essay, your resume can get you fired down the road — even if you’ve been doing a great job. Just ask former Yahoo!
CEO Scott Thompson. If you haven’t yet graduated from college, for example, put down the revolution cause, name of the school you’re attending and state your expected graduation date. Education. Don’t say you’ve graduated if you haven’t. Another common fib is resume length, with languages. Value Education. Many people list under “skills” that they can speak a foreign language (or two…or four), when in fact they can only string a few sentences together. Don’t think you won’t eventually be found out – you will. Short Essay Success. And trust me, it’s tough to education, learn Japanese in a weekend. One of the work key to success, main things that employers focus on is how long you worked at your previous jobs. They are going to be scanning for dates and zeroing in on short tenures and long gaps between positions. Make sure to higher essay, put down, for each job, the date that you started working and with paper the date that you left (month and year is sufficient). You’re not fooling anybody by value higher education essay leaving these out if they don’t make you look good.
A lack of dates will read as an attempt to hide something. If you have gaps in your resume, you can read our article on dealing with resume gaps. Proof the dates carefully. Short Essay Is The Key To Success. It’s easy to overlook mistakes when it comes to numbers. Value Higher Education. You don’t want your resume to on citizenship, say “May 2020” instead of “May 2010.” This may sound silly, but it happens more often you might think: people forget to update their resumes to include their most recent contact information. If you’ve moved or changed phone numbers, make sure that your phone number, address and e-mail information is up to date. If you don’t, you could be waiting for a call or a message that you’ll never receive. Also, make sure you have a professional sounding email address. If your name is John Smith, using the address “email@example.com” (which you hilariously created in 2005) is not a good idea.
It’s always better to create a new email address that’s somewhat professional. Even if you can’t get [yourname] @gmail.com – at value higher essay, least get something neutral sounding (like jsmith92 or smithjohn11 ). Also, don’t get an address that’s too long and weird (like john34A5mith2@gmail.com) . It’s too easy for a typo to in essays, happen when someone is emailing you – and it’ll drive people crazy. If you want to include an higher education, objective in your resume, make sure that it’s as tailored as possible to english words to use, the job that you’re applying for. Avoid vague statements like: Looking to apply my skills and experience in a fast-paced, challenging environment. It will catch your reader’s eye much more if your objective clearly matches the job description. Value. For example, [Looking for a mid-level marketing position at a premiere/reputable/growing fashion/advertising firm.] You should also think about whether including an for kids, objective statement is really the best use of that prime real estate at the top of your resume.
In most cases, we recommend using a Professional Summary instead of an Objective. However, an objective statement can be useful for some candidates — new grads with resumes that don’t otherwise convey career goals in a clear way and career changers who are seeking a position that’s not an obvious next step. Your resume should be focused, concise and emphasize achievements and higher skills that fit the job you’re applying for. Friends With Benefits Research. If you are applying for a sales position, for example, you should emphasize targets that you’ve met in prior jobs. Higher Education Essay. Including percentages and numbers can be useful. For example, [“Increased _______ by 25% in Store XYZ” or “Reduced operations backlog by 50% for the fiscal year in essay on hard key to, 2009.”] Think about how best to present your experience and skills in value higher, a way that would impress your potential employer. This probably means customizing your resume for each position, especially if you are considering more than one type of opportunity. Carefully review the job description and then take the time to tailor your resume to emphasize the strengths and revolution cause experience that are most relevant for the position.
11. Including “red flag” information. Your goal is to land an interview by giving the employer a compelling overview of the higher, job skills and experience that make you a good candidate. Don’t sabotage your chances by including information that could raise concerns. Don’t list things like “left previous role because of internal political issues” or “I took this job because it was close to home.” There will be time to discuss your reasons for leaving and cause taking positions in the interview. By then, you will have used Big Interview to prepare and value higher essay practice so that you can discuss your reasons in a positive and professional way. You want your employer to friends benefits, know what you did in your previous jobs, but you don’t need to include the kitchen sink. Describe your job duties in enough detail to give the employer a good idea of your general responsibilities. Leave out value education essay unnecessary or minute details that won’t lift you up as a candidate.
More importantly: Highlight your job achievements. Use bullet-points to help the reader focus in on your accomplishments. Too many candidates make the mistake of including a detailed job description instead of emphasizing individual contributions. Rather than just listing your job duties, which can be passive and boring, use action verbs that imply you actively got things done. Revolution Cause. Here are some good examples: Led, Created, Delivered, Managed, Implemented, Increased, Achieved, Organized, etc. The thesaurus can be your friend if you find you are overusing certain words on your resume. Just don’t get too crazy trying to impress them with your awesome vocabulary — you want them to value essay, actually understand what you did (skip “confabulate” and “propagage” and other Word-of-the Day entries).
Your resume is your first face forward to the employer, so it’s very important that you take the time to to make sure it looks great and revolution cause and effect is an accurate and education essay powerful representation of your qualifications. Common mistakes (even the seemingly little ones) can kill your chances of getting an short essay on hard work is the, interview. When it comes to higher, your resume, you really can’t be too perfect. Humor: If you’re in the mood, here’s Resume Richard offering you his “solid” advice on computer revolution and effect, making your resume stick out. Pamela Skillings is co-founder of higher education essay, Big Interview. As an revolution and effect, interview coach, she has helped her clients land dream jobs at companies including Google, Microsoft, Goldman Sachs, and JP Morgan Chase. She also has more than 15 years of experience training and advising managers at organizations from essay, American Express to the City of New York. Resume Length. She is an value essay, adjunct professor at New York University and an instructor at the American Management Association.
55 Comment to 13 Resume Mistakes That Make You Look Dumb. Can I put smart art in my resume? Great advice, thank you! Thanks, this was helpful! What is essay on citizenship for kids, better one column format or two column format in resume?
Pamela Skillings is value higher education essay, co-founder of Big Interview. As one of the resume length, country's top interview coaches, she has helped her clients land dream jobs at value higher education essay, companies including Google, Microsoft, Goldman Sachs, and english words JP Morgan Chase. She also has more than 15 years of experience training and value higher essay advising managers at english good words to use, organizations from American Express to the City of value higher education, New York. She is an adjunct professor at New York University and an instructor at to use in essays, the American Management Association. Continue reading. Copyright © 2017 Big Interview – Job Interview Training - All Rights Reserved.
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Adiposity and cancer at major anatomical sites: umbrella review of the literature. Objective To evaluate the strength and validity of the evidence for the association between adiposity and risk of developing or dying from cancer. Design Umbrella review of systematic reviews and meta-analyses. Value Essay! Data sources PubMed, Embase, Cochrane Database of Systematic Reviews, and manual screening of resume length, retrieved references. Eligibility criteria Systematic reviews or meta-analyses of observational studies that evaluated the association between indices of adiposity and higher education, risk of developing or dying from cancer. Data synthesis Primary analysis focused on cohort studies exploring associations for on citizenship for kids continuous measures of education, adiposity.
The evidence was graded into research paper strong, highly suggestive, suggestive, or weak after applying criteria that included the statistical significance of the random effects summary estimate and of the largest study in education a meta-analysis, the number of cancer cases, heterogeneity between studies, 95% prediction intervals, small study effects, excess significance bias, and sensitivity analysis with credibility ceilings. Results 204 meta-analyses investigated associations between seven indices of adiposity and developing or dying from 36 primary cancers and their subtypes. Of the good to use, 95 meta-analyses that included cohort studies and used a continuous scale to measure adiposity, only 12 (13%) associations for nine cancers were supported by value education essay strong evidence. An increase in body mass index was associated with a higher risk of developing oesophageal adenocarcinoma; colon and rectal cancer in computer revolution cause and effect men; biliary tract system and pancreatic cancer; endometrial cancer in premenopausal women; kidney cancer; and multiple myeloma. Weight gain and waist to essay, hip circumference ratio were associated with higher risks of postmenopausal breast cancer in women who have never used hormone replacement therapy and short essay, endometrial cancer, respectively. Higher Essay! The increase in the risk of developing cancer for every 5 kg/m 2 increase in body mass index ranged from research, 9% (relative risk 1.09, 95% confidence interval 1.06 to 1.13) for rectal cancer among men to 56% (1.56, 1.34 to 1.81) for biliary tract system cancer.
The risk of postmenopausal breast cancer among women who have never used HRT increased by 11% for each 5 kg of weight gain in adulthood (1.11, 1.09 to 1.13), and higher education essay, the risk of endometrial cancer increased by 21% for each 0.1 increase in english waist to hip ratio (1.21, 1.13 to value education essay, 1.29). Essay On Citizenship For Kids! Five additional associations were supported by strong evidence when categorical measures of adiposity were included: weight gain with colorectal cancer; body mass index with gallbladder, gastric cardia, and ovarian cancer; and value higher education essay, multiple myeloma mortality. Conclusions Although the association of essay and health hazards, adiposity with cancer risk has been extensively studied, associations for only 11 cancers (oesophageal adenocarcinoma, multiple myeloma, and cancers of the gastric cardia, colon, rectum, biliary tract system, pancreas, breast, endometrium, ovary, and kidney) were supported by strong evidence. Other associations could be genuine, but substantial uncertainty remains. Obesity is becoming one of the biggest problems in public health; evidence on value higher essay, the strength of the associated risks may allow finer selection of with, those at higher risk of cancer, who could be targeted for personalised prevention strategies. Cancer is a leading cause of death worldwide, with an estimated 12.7 million new cases and education, 7.6 million deaths from cancer annually.1 Excess body weight is associated with an increased risk of developing and dying from many diseases, including cancer, type 2 diabetes, and cardiovascular disease.2 Obesity has become a major public health challenge3; its prevalence worldwide has more than doubled among women and essay and health, tripled among men in value higher education the past four decades.4 The number of overweight and obese people has risen from short essay on hard success, approximately 857 million in education essay 1980 to essay on citizenship for kids, 2.1 billion in 2013.5. Higher Essay! Several meta-analyses support the link between obesity and cancer, but substantial heterogeneity exists between studies.6 The reported associations may be causal, but they may also be flawed, as inherent study biases such as residual confounding and selective reporting of positive results may exaggerate the effect of obesity on cancer.78910 A recent umbrella review found that, despite strong claims of a statistically significant association between type 2 diabetes and several cancers, only a fraction (14%) of the 27 studied associations were supported by robust evidence, without any potential bias.11. To summarise and words to use, evaluate the education essay, existing evidence and appraise its quality, we performed an umbrella review of systematic reviews and meta-analyses that investigated the association between adiposity indices and risk of developing or dying from cancer. Umbrella reviews systematically appraise the evidence on an entire topic across many meta-analyses of multiple putative risk factors on research, multiple outcomes.1112131415161718.
We searched PubMed, Embase, and the Cochrane Database of Systematic Reviews from inception to May 2015 for systematic reviews or meta-analyses that investigated the association between adiposity indices and risk of developing or dying from any cancer using a predefined search algorithm (see the supplementary file for details of the value higher education, algorithm). Adiposity indices were body mass index, waist circumference, hip circumference, waist to hip ratio, weight, weight gain, and words, weight loss from value, bariatric surgery. We hand searched the references of the retrieved systematic reviews and meta-analyses and the proceedings of relevant conferences for resume length articles missed by the electronic search and unpublished data. We included systematic reviews and value higher education essay, meta-analyses of observational epidemiological studies in humans that assessed continuous or categorical measures of adiposity. We excluded studies in which physical activity, height, or prenatal factors (such as birth weight or maternal obesity during pregnancy) were the exposures of interest and those in which cancer incidence or mortality were not the good words, outcomes of interest. We excluded meta-analyses of prognostic studies that investigated cancer survival or other outcomes among patients with cancer and meta-analyses that did not include comprehensive data from individual studies—such as relative risks, 95% confidence intervals, number of cases and controls, or total population. When we found more than one meta-analysis on the same association between exposure and education, outcome, we included the one with the largest number of primary studies to resume length, avoid duplication. We subsequently examined whether the summary estimates showed concordance between the included and duplicate meta-analyses. We extracted the name of the first author, year of value higher essay, publication, outcome, and exposure from short work success, each eligible systematic review or meta-analysis. From each individual study in a meta-analysis, we extracted the higher essay, first author, year of publication, epidemiological design, number of cases and controls in case-control studies or total population in cohort studies, maximally adjusted relative risk (odds ratio in case-control studies and hazard ratio or standardised incidence or mortality ratio in cohort studies) and 95% confidence intervals. Two investigators (IK, MK) independently searched the revolution cause, literature, assessed the value education essay, eligibility of the retrieved papers, and extracted the data.
Disagreements were resolved by short is the key to success discussion with a third investigator (KT). Estimation of summary effect —For each exposure and education, outcome pair, we calculated the summary effect and the 95% confidence interval using fixed and random effects methods.19. Computer And Effect! Assessment of heterogeneity —The heterogeneity between studies was assessed with Cochran’s Q test20 and value education essay, the I 2 statistic.21 Substantial inconsistency could reflect either genuine heterogeneity between studies or bias. To assess the uncertainty around heterogeneity estimates, we calculated 95% confidence intervals.22. Estimation of prediction intervals —To further account for heterogeneity between studies we calculated 95% prediction intervals for the summary random effect estimates, which represent the range in short essay on hard work is the key to success which the effect estimates of future studies will lie.23. Assessment of small study effects —We examined whether smaller studies gave higher risk estimates than larger studies, which is an indication of publication bias, true heterogeneity, or chance.1124 Indication of small study effects was based on the Egger’s regression asymmetry test (P?0.10) and value higher, whether the random effects summary estimate was larger than the point estimate of the largest study in the meta-analysis. Evaluation of cause and effect, excess significance —We assessed excess significance bias by value higher education evaluating whether the observed number of studies with nominally statistically significant results (“positive” studies, P0.05) in the published literature was different from the expected number of studies with statistically significant results.25 The expected number of statistically significant studies in each meta-analysis was calculated from the short essay work success, sum of the statistical power estimates for each component study using an essay, algorithm from a non-central t distribution.2627 The power estimates of each component study depend on the plausible effect size for the tested association, which was assumed to be the effect of the largest study (that is, the smallest standard error) in each meta-analysis.28 Sensitivity analyses were conducted using the summary fixed and random effects estimates as alternative plausible effect sizes. Excess significance for individual meta-analyses was determined at P?0.10.25. Credibility ceilings —We used credibility ceilings, a sensitivity analysis tool, to account for potential methodological limitations of revolution and effect, observational studies that might lead to spurious precision of combined effect estimates.29 The main assumption of this method is that every observational study has a probability c (credibility ceiling) that the true effect size is in a different direction from the one suggested by the point estimate. The pooled effect size and the heterogeneity between studies were re-estimated using a wide range of credibility ceiling values.2930. The associations between measures of adiposity and cancer were categorised into strong, highly suggestive, suggestive, or weak depending on the strength and validity of the evidence.131518 A strong association was claimed when the P value of the random effects meta-analysis was smaller than 10 ?6 , a threshold that might substantially reduce false positive findings313233 if the value higher, meta-analysis has more than 1000 cancer cases, the largest study in the meta-analysis is nominally statistically significant (P0.05), the I 2 statistic of for kids, heterogeneity between studies is smaller than 50%, the essay, 95% prediction intervals excludes the null value, small study effects or excess significance bias are not indicated, and the association survives a credibility ceiling of at least 10%.
The association was considered highly suggestive if P10 ?6 , the meta-analysis had more than 1000 cases, and essay work is the success, the largest study in the meta-analysis was nominally statistically significant. The criteria for suggestive were: random effects P10 ?3 and the meta-analysis had more than 1000 cases. All other associations with a nominally statistically significant P value for the random effects meta-analysis were deemed to provide weak evidence. The primary analysis in this umbrella review focused on cohort studies using continuous measures of adiposity, which was considered a more valid and standardised way of higher education essay, presenting and computer and effect, synthesising individual study estimates than using categorical measures. Sensitivity analyses were conducted using case-control studies and categorical measures. All statistical analyses were performed using Stata version 13 (College Station, TX),34 and all P values were two tailed. No patients were involved in setting the research question or outcome measures, nor were they involved in developing plans for design or implementation of the study.
No patients were asked to advise on interpretation or writing up on results. The results will be disseminated to the general public through public presentations and the authors’ involvement in different charities. Education Essay! Characteristics of the meta-analyses. Overall, 49 eligible papers were identified that included a total of 204 meta-analyses. These meta-analyses summarised 2179 individual study estimates from 507 unique cohort or case-control studies (fig 1 ? ).35363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283 Of the 507 unique studies, 371 (73.2%) had a cohort design, 134 (26.4%) were case-control studies, and revolution, two (0.4%) were cross sectional studies. A median of 7 (range 2-72) study estimates were combined for each meta-analysis. The median number of value higher education essay, cases and on citizenship for kids, population or controls in each meta-analysis was 5645 and 1 766 389, respectively. A total of 177 meta-analyses had at least 1000 cancer cases. The 204 meta-analyses included associations between seven indices of adiposity (body mass index, waist circumference, hip circumference, waist to hip ratio, weight, weight gain, and weight loss through bariatric surgery) and the incidence (n=196) or mortality (n=8) from cancer at higher education, 36 anatomical sites and by subtypes. A total of good to use in essays, 194 meta-analyses included cohort studies (see supplementary tables 1 and 2).
Of these, 95 used a continuous scale to measure adiposity (for example, body mass index in value higher essay adults or at around age 20 per short on hard work is the success, 5 kg/m 2 , waist circumference per value higher education, 10 cm, hip circumference per 10 cm, waist to hip ratio per computer and effect, 0.1, weight per value higher, 5 kg, and short essay key to, weight gain per 1 kg or 5 kg). Value Higher! These 95 meta-analyses studied 28 different cancer sites or subtypes and included 818 individual study estimates, with body mass index in adults being investigated most frequently (n=57 meta-analyses). We identified more than one published meta-analysis with the same exposure and for kids, outcome pair for 11 cancers. All duplicate meta-analyses showed agreement on the direction, magnitude, and statistical significance of the summary associations (see supplementary table 3). When we used a threshold of P0.05, the summary fixed effects estimates were significant in 76 of the 95 meta-analyses (80%) and the summary random effects were significant in 72 (76%) (see supplementary table 1 and supplementary figures 1-28). At a stricter threshold of P0.001, 66 (69%) and 59 (62%) meta-analyses produced significant summary results using the value education, fixed and random effects models, respectively. At P10 ?6 , 54 (57%) and resume length, 35 (37%) meta-analyses were significant, respectively. Value! Of those 35 meta-analyses, 31 found an short on hard work key to success, increased risk of cancer with higher adiposity for oesophageal adenocarcinoma, multiple myeloma, and cancers of the colon, rectum, liver, biliary tract system (cancers of gallbladder, extrahepatic bile duct, and ampulla of Vater), pancreas, postmenopausal breast, endometrium, and kidney. Four of the essay, 35 meta-analyses indicated an inverse association for oesophageal squamous cell carcinoma and lung cancer. The magnitude of the observed summary random effect estimates ranged from 0.57 to 1.90; 61% of the hazards, estimates lay between 0.80 and 1.20 (fig 2 ? ). In meta-analyses with small variances a trend of summary effects towards 1.00 was observed. The largest study of each meta-analysis showed a nominally statistically significant association in 65 meta-analyses (68%), and the relative risks of the largest studies were more conservative (closer to value essay, null) than the summary random effects in 53 (56%) meta-analyses.
Fig 2 Association of meta-analysis summary effect sizes with inverse of the variance. The summary estimates were similar between men and women for eight of 11 cancers (oesophageal adenocarcinoma, oesophageal squamous cell carcinoma, multiple myeloma, leukaemia, and resume length, gastric, lung, kidney, and thyroid cancers). Value Higher! However, the on citizenship, incidence of colon and higher education, rectal cancer was higher per 5 kg/m 2 increase of body mass index in men (relative risk 1.30, 95% confidence interval 1.25 to essay on citizenship, 1.35) and 1.09 (1.06 to 1.13), respectively) than in women (1.12 (1.06 to 1.17) and 1.02 (0.99 to 1.05), respectively). This was also true for other adiposity indices. Moreover, body mass index was associated with an increased risk of value education, melanoma in men (relative risk per 5 kg/m 2 1.17, 1.05 to 1.30) but not in women (0.96, 0.93 to good to use, 1.00). ?he Q test was significant at P?0.10 in 42 of 95 meta-analyses (44%) (see supplementary table 2). Twenty meta-analyses (21%) showed considerable heterogeneity (I 2 =50-75%) and 15 meta-analyses (16%) showed substantial heterogeneity (I 2 75%) for some adiposity indices and value essay, several cancers (oesophageal squamous cell carcinoma; colon, liver, lung, endometrial, prostate, and benefits, thyroid cancers; melanoma; and leukaemia). We further assessed the uncertainty of the higher essay, summary effects by calculating 95% prediction intervals; the null value was excluded in only 27 associations. Thirteen meta-analyses had evidence indicating small study effects, but only on hard success seven included 10 or more studies and therefore had enough statistical power for the Egger’s test to value higher education, adequately identify presence of small study effects (colon, liver, lung, ovarian, and advanced prostate cancer; see supplementary table 2). Supplementary figures 1 to 28 show the funnel plots for each cancer site. Nineteen meta-analyses had evidence of excess significance bias for resume length some adiposity indices using the largest study estimate as the plausible effect size (colon, rectal, liver, pancreatic, endometrial, ovarian, prostate, advanced prostate, and kidney cancer; supplementary table 2).
Using summary fixed or random effects estimates as plausible effect sizes gave similar results. A credibility ceiling of 0% corresponds to the random effects model calculation. Of the higher education, 95 meta-analyses, 72 (76%) retained nominal statistical significance (P0.05) with a credibility ceiling of 5%. Fifty (53%), 33 (35%), and 19 (20%) meta-analyses remained statistically significant with ceilings of 10%, 15%, and 20%, respectively. Heterogeneity between studies gradually decreased with increasing ceilings. With a ceiling of 10%, no meta-analyses of cohort studies with continuous exposure gave an on citizenship for kids, I 2 estimate larger than 50% (supplementary table 4). We explored whether the reported associations between adiposity and value higher essay, developing or dying from essay for kids, cancer were supported by strong, highly suggestive, suggestive, or weak evidence (table 1 ? ). We found that 77% of the 95 meta-analyses presented at least weak evidence (P0.05 for the summary random effects).
Supplementary table 5 shows these associations in cohort studies using continuous measures of adiposity (also see supplementary table 6 for associations using categorical measures of value higher essay, adiposity in cohort studies and supplementary table 7 for all associations regardless of study type or exposure metric). Summary of evidence grading for meta-analyses associating continuous measures of essay on science hazards, obesity and risk of cancer—cohort studies only. Risk refers to cancer incidence unless otherwise stated. Education! Only 13% of for kids, meta-analyses (12 of 95) were supported by strong evidence. They summarised data on body mass index (n=10), waist to hip ratio (n=1), and weight gain (n=1). An increase in body mass index was associated with a higher risk of developing oesophageal adenocarcinoma; colon and higher education essay, rectal cancer in good men; biliary tract system and pancreatic cancer; endometrial cancer in premenopausal women; kidney cancer; and multiple myeloma. Weight gain and waist to hip circumference ratio were associated with higher risks of postmenopausal breast cancer in women who have never used hormone replacement therapy and endometrial cancer, respectively.
The increase in the risk of developing cancer for every 5 kg/m 2 increase in body mass index ranged from 9% (relative risk 1.09, 95% confidence interval 1.06 to 1.13) for colorectal cancer among men to 56% (1.56, 1.34 to 1.81) for biliary tract system cancer. The risk of postmenopausal breast cancer among women who have never used HRT increased by value higher 11% for each 5 kg of weight gain (1.11, 1.09 to short on hard work is the key to success, 1.13), and higher, the risk of endometrial cancer increased by 21% for each 0.1 increase in waist to hip ratio (1.21, 1.13 to 1.29). Seventeen meta-analyses (18%) were supported by highly suggestive evidence, and they found positive associations for colon (with body mass index and waist circumference), liver (with body mass index), postmenopausal breast (with body mass index), total endometrial (with body mass index in adults and at around age 20, waist circumference, weight, and weight gain), postmenopausal, type I and type II endometrial (with body mass index), and kidney cancer (with body mass index). Inverse associations were found for essay body mass index in adults with oesophageal squamous cell carcinoma (overall and in women) and lung cancer (overall and in men). Twenty four meta-analyses (25%) were supported by higher suggestive evidence for an association, and 19 meta-analyses (20%) were supported by weak evidence. The evidence was graded similarly in the 194 meta-analyses of english words, cohort studies that assessed continuous and categorical measures of adiposity (supplementary table 6). Five additional associations were supported by strong evidence: weight gain with incidence of colorectal cancer, body mass index with incidence of higher essay, gallbladder, gastric cardia, and ovarian cancers, and mortality from multiple myeloma. When both cohort and case-control studies were assessed for continuous and categorical measures of adiposity (supplementary table 7), two additional associations were supported by strong evidence: body mass index and risk of melanoma and research, meningioma, both of which were judged as weak associations when only cohort studies were evaluated.
The strong evidence for an association between body mass index and incidence of biliary tract system cancerwas downgraded to suggestive evidence when both case-control and education essay, cohort studies were evaluated. We reviewed 204 meta-analyses to evaluate the current evidence for computer revolution and effect associations between seven adiposity indices and higher education, the risk of benefits paper, developing or dying from value higher education essay, 36 primary cancers and their subtypes. Twelve associations, stemming from cohort studies using continuous measures of adiposity, were supported by strong evidence, inferred by strongly statistically significant results and no suggestion of bias. These associations were primarily between body mass index and malignancies of resume length, digestive organs (oesophageal adenocarcinoma and value essay, cancers of the colorectum (in men only), biliary tract system, and computer revolution, pancreas), hormone related cancers (such as postmenopausal breast in women who have never used HRT), premenopausal and overall endometrial cancer, kidney cancer, and multiple myeloma. Five additional associations were supported by strong evidence when categorical measures of adiposity were used: weight gain with risk of higher education, colorectal cancer risk and body mass index with risk of gallbladder, gastric cardia, and ovarian cancer, and mortality from multiple myeloma. The effect of obesity on the incidence and mortality of friends benefits paper, cancer is well recognised66284 and was evident in our umbrella review, with approximately 77% of the included meta-analyses reporting a nominally statistically significant summary random effects estimate.
Although the reported associations are plausibly accurate and potentially causal, the risk of reporting, selection, and other inherent biases may overestimate the suggested associations, as shown in other recently published umbrella reviews in cancer epidemiology.111327 The extent to which the literature is affected by such biases is difficult to prove definitively. We used statistical tests and sensitivity analyses to value higher, look for evidence of bias. When lower P value thresholds (P10 ?6 ) were used, the proportion of significant associations decreased to 37%. Large heterogeneity (I 2 ?50%) was observed in 37% of the essay on citizenship, meta-analyses. When we calculated the higher, 95% prediction intervals, which further account for heterogeneity, we found that the null value was excluded in only about one third of the associations. Moreover, some meta-analyses had evidence of small study effects or excess significance bias. Most meta-analyses (53%) preserved their statistical significance with a 10% credibility ceiling, but only one in to use in essays five preserved significance at a ceiling of 20%, indicating that many associations between adiposity and cancer remain uncertain. Our grading of the evidence largely agrees with systematic analyses of the literature performed by the World Cancer Research Fund (WCRF) and the International Agency for value essay Research on words to use, Cancer (IARC).68485 The WCRF currently lists seven cancers for which the essay, evidence supports a convincing causal relationship with obesity (oesophageal adenocarcinoma and cancers of the good to use in essays, pancreas, colorectum, postmenopausal breast, endometrium, kidney, and liver). We also found strong evidence that obesity increases the risk of value higher education, these cancers, except for essay on citizenship for kids liver cancer, for higher education which the evidence was considered highly suggestive because of small study effects, excess significance bias, and substantial heterogeneity between studies. The association between obesity and five more malignancies (gallbladder, stomach cardia, ovarian, advanced prostate, and resume length, premenopausal breast cancer) was graded as probably causal by WCRF and received lower evidence grades in our main analysis using only continuous measures of value education essay, adiposity.
IARC found sufficient evidence to support the association between excess body fat and 13 of 24 cancer sites (oesophagus (adenocarcinoma), gastric cardia, colorectum, liver, gallbladder, pancreas, postmenopausal breast, endometrium, ovary, kidney, meningioma, thyroid, and multiple myeloma).84 Our results are similar to those of the computer, IARC report for higher essay most cancers, except for essay on hard work is the key to success gastric cardia, liver, ovarian, meningioma and thyroid cancers. These cancers received lower than strong evidence grades in our main analysis, owing to small numbers of cancer cases, very large heterogeneity between studies, or evidence of small study effects and excess significance bias. However, the associations between adiposity and risk of gastric cardia and essay, ovarian cancer were judged to be supported with strong evidence when we evaluated categorical measures of adiposity. Similarly, evidence for essay for kids an association between adiposity and risk of value, meningioma was considered strong when case-control studies were included in the evaluation. Several methods exist for rating evidence, but they are inconsistent and allow some degree of arbitrariness.86 The WCRF and IARC used expert groups and criteria similar to Bradford Hill criteria to assess the on citizenship for kids, association between obesity and risk of 17 and 24 primary cancers, respectively, whereas we assessed the robustness of the value, evidence using sensitivity analyses and work is the key to success, statistical tests to evaluate 36 primary cancers and their subtypes, defined by anatomical location, histology, and receptor status.
We also explored associations by potential effect modifiers (eg, sex, menopausal status, smoking status, and use of value essay, HRT). Our criteria for grading evidence should not be considered causal criteria, especially when used individually, but we think that they are useful for identifying biases when used together.12. Most of the associations between adiposity indices and endometrial cancer were supported by strong or highly suggestive evidence. In particular, the association between waist to revolution, hip ratio and risk of total endometrial cancer was supported by strong evidence, indicating that central obesity, which is linked to hyperinsulinaemia and type 2 diabetes, has a major role in value the development of this disease. Strong evidence also supported the association between body mass index and premenopausal endometrial cancer. We found the resume length, associations between body mass index in value higher adults or at around age 20, waist circumference, weight, and friends with paper, weight gain and value education, total endometrial cancer, and computer and effect, between body mass index and higher education, postmenopausal type I and II endometrial cancer to be highly suggestive owing to with research paper, substantial heterogeneity between studies and potential for excess significance bias. These results were in agreement with the value higher, WCRF and IARC, which did not provide separate ratings for menopausal status or histological subtype of resume length, disease.8487 The difference in evidence ratings between premenopausal and value education, postmenopausal endometrial cancer is probably related to heterogeneity caused by use of HRT among postmenopausal women.88 We found that the associations between body mass index or weight gain and postmenopausal endometrial cancer were statistically significantly stronger in never users compared with ever users of HRT, but the relevant meta-analyses included only 2-6 studies and had fewer than 1000 cancer cases, so the evidence was deemed weak. The WCRF found that the associations between waist circumference or waist to hip ratio and total endometrial cancer were probably causal,87 which largely agreed with our findings. Essay! We found strong evidence to support the higher, association between weight gain in adulthood and friends with research paper, postmenopausal breast cancer among women who have never used HRT, yielding an 11% higher risk per 5 kg of weight gain.
We found highly suggestive evidence to support the positive association of body mass index with postmenopausal breast cancer, irrespective of HRT. Weight gain may be a better metric than body mass index for measuring the dynamic nature of adiposity during adulthood, when obesity becomes central and has more metabolic effects.49 Another reason for the lower grading of the evidence for body mass index was the large heterogeneity between studies,62 which could at least partially be explained by a potential interaction with HRT use. Some cohort studies have found a positive association between body mass index and postmenopausal breast cancer only higher education among women who have never used HRT,8990 but we did not capture this potential interaction because published meta-analyses have not performed this subgroup analysis.6278 The evidence for an association between adiposity indices and premenopausal breast cancer was weaker and only reached suggestive evidence for an inverse association with body mass index in a meta-analysis of 20 cohort studies. These results largely agree with the WCRF and IARC findings of a convincing causal positive association between adiposity and essay for kids, postmenopausal breast cancer8491 and a probable causal inverse association for premenopausal disease.91 Two recent Mendelian randomisation studies found that a higher body mass index in adults was associated with a lower risk of postmenopausal breast cancer, contradicting the higher education, epidemiological evidence.9293 This may be due to the genetic risk score for resume length body mass index in adults being a stronger determinant of early compared with later life body mass index; epidemiological studies have found inverse associations between body mass index in childhood and both premenopausal and postmenopausal breast cancer.9495 The positive association between body mass index in adults and postmenopausal breast cancer found in epidemiological studies may be driven by weight gain in adulthood. Value Essay! We found strong evidence to support the association between weight gain in adults and essay, postmenopausal breast cancer, but weight gain is probably linked to environmental factors that are not captured by education essay genetic risk factors.96 Moreover, some evidence exists that these associations may differ according to oestrogen and progesterone receptor status of the tumour (supplementary tables 6 and 7),6897 but large investigations in this area are lacking. The association between body mass index and colon cancer was supported by strong evidence in men and suggestive evidence in women. Twenty four cohorts investigated the association in men, totalling a 30% higher risk of colon cancer for each 5 kg/m 2 increase in body mass index. The risk was 12% higher for each 5 kg/m 2 increase in body mass index among women in a meta-analysis of friends research, 20 cohorts that showed substantial heterogeneity and evidence of small study effects and excess significance bias. The association between body mass index and rectal cancer in men was supported by strong evidence, but with a summary relative risk considerably smaller than for colon cancer (1.09 v 1.30). We found no association between body mass index and rectal cancer in women.
The evidence for most of the value education, other adiposity indices was suggestive, as few studies have investigated these associations. The insulin signalling pathway is resume length, a possible mechanism underlying the association between obesity and colorectal cancer in men.98 The increased concentrations of circulating insulin induced by education essay adiposity are higher among men than women,99 and short work is the key to success, men are more prone to value, abdominal fatness than women.100 Furthermore, endogenous and exogenous oestrogens have been associated with protective effects against colorectal cancer among women, which might explain why the association of adiposity with colorectal cancer is computer revolution cause, stronger in men than in women.101102 Two Mendelian randomisation studies found statistically significant positive associations between adult body mass index and value higher education, colorectal cancer but did not perform analyses by resume length sex.92103. We found that higher body mass index was associated with an increased risk of oesophageal adenocarcinoma, and this was supported by value education strong evidence. We found an inverse association for oesophageal squamous cell carcinoma, which was supported by highly suggestive evidence due to considerable heterogeneity between studies. Similar summary associations were found by the WCRF and on citizenship for kids, IARC, which concluded that adiposity convincingly increased the risk of value essay, oesophageal adenocarcinoma.84104 A Mendelian randomisation study supports this association.105 Oesophageal squamous cell carcinoma has stronger associations with smoking and alcohol consumption than oesophageal adenocarcinoma,106 but we were unable to capture the words to use, potential residual confounding or effect modification of higher essay, smoking and alcohol in the associations between adiposity and oesophageal squamous cell carcinoma because the published meta-analysis did not report these subgroup analyses.62. We found an inverse association between body mass index and lung cancer that was supported by highly suggestive evidence but had substantial heterogeneity between studies and evidence of small study effects. When we investigated this association by smoking status, we found an inverse association between body mass index and good, lung cancer among smokers, which was supported by education essay suggestive evidence.
We found a non-significant association among non-smokers. These results may be due to residual confounding, reverse causation, or effect modification by smoking, which led the WCRF and IARC to grade this evidence as inadequate.84107 Two recent Mendelian randomisation studies found that body mass index was statistically significantly associated with an increased risk of squamous and small cell lung cancer but had a borderline significant inverse association with lung adenocarcinoma.92108 One of the Mendelian randomisation studies found a statistically significant inverse association between body mass index and total lung cancer among never smokers and a null association in ever smokers,108 which contradicts the epidemiological evidence. However, these analyses were underpowered. Resume Length! Future large prospective studies should evaluate associations according to smoking status among different disease subtypes. Furthermore, we found that the associations between body mass index and multiple myeloma and cancers of the biliary tract system, pancreas, and kidney were supported by strong evidence. Value Education! The WCRF and IARC ratings were similar, except the short work, WCRF did not study multiple myeloma.8485 The associations for less common malignancies are supported by limited data and value higher education essay, show substantial heterogeneity between studies; we need prospective studies to better characterise these associations. Our review relied on previously published meta-analyses and the literature searches performed by the authors of short is the success, those meta-analyses. Some studies may have been missed, although this is unlikely to education, have influenced our findings because our assessment of duplicate meta-analyses on the same exposure-outcome associations gave similar summary results.
Some of the meta-analyses that used continuous measures of adiposity were published as long ago as 2008, which may mean that we didn’t include the most recent evidence. However, we found that the resume length, evidence grading for recently published meta-analyses investigating the association of categorical terms of body mass index with the same cancers was similar. We evaluated all study specific results that were reported in education the meta-analyses (for example, primary cancers, cancer subtypes, sex, menopausal status, smoking status, and HRT use), but we may have missed other subanalyses that were not reported with sufficient study specific data. Resume Length! Assessing the quality of the primary studies included in the meta-analyses was beyond the scope of this umbrella review. Finally, the statistical tests we used to assess bias do not prove its definitive presence or its exact source. Education! However, our estimates are likely to on science and health, be conservative, as a negative test does not exclude the higher essay, potential for bias. Moreover, our evidence grading was not sensitive to work key to, the use of 95% prediction intervals, excess significance tests, or credibility ceilings, because when we consecutively removed these criteria from the quality of evidence algorithm, the resulting inference remained the same. The association between obesity and risk of developing or dying from value higher education, cancer has been extensively studied.
We found strong evidence to support the positive association between obesity and 11 of the 36 cancer sites and subtypes that we examined, predominantly comprising cancers of the digestive organs and hormone related malignancies in women. Short On Hard Work Key To Success! Substantial uncertainty remains for the other cancers. To draw firmer conclusions we need prospective studies and higher education, large consortiums with better assessment of the with research, changing nature of body fatness and with comprehensive standardised reporting of analyses. As obesity becomes one of the greatest public health problems worldwide, evidence of the strength of the value, associations between obesity and cancer may allow finer selection of people at high risk, who could be selected for personalised primary and secondary prevention strategies. What is friends research paper, already known on value education, this topic.
Cancer is a leading cause of death worldwide, and the prevalence of and health, obesity has more than doubled over the past 40 years. Numerous meta-analyses support the link between excess body weight and value higher, increased risk of developing and friends benefits, dying from several types of cancer. The reported associations may be causal for higher some malignancies, but they may be flawed owing to inherent biases that exaggerate the effect of obesity on cancer incidence and mortality. Strong evidence supported the short essay work key to, association between obesity and only 11 of 36 cancer sites and value higher essay, subtypes, predominantly comprising cancers of cause, digestive organs and hormone related malignancies in women. Other associations could be genuine, but substantial uncertainty remains.
Contributors: MK, PMH, EP, and KKT conceived and designed the study. IK, MK, and KT acquired and collated the data. Value Essay! IK, MK, GM, and essay hazards, KKT analysed the data. All authors drafted and critically revised the manuscript for important intellectual content and education essay, gave final approval of the version to be published. Benefits Research! MK and IK contributed equally to the manuscript (joint first authors). MK is the guarantor. Funding: This work was supported by Genesis Research Trust (Garfield Weston Foundation, P63522 to higher, MK); Sigrid Juselius Fellowship (P52483 to resume length, IK and MK); World Cancer Research Fund International Regular Grant Programme (2014/1180 to KKT); Ovarian Cancer Action (PS5827 and PSA601to MG and MK); the Imperial Experimental Cancer Medicine Centre, the Cancer Research UK Imperial Centre, Imperial Healthcare NHS Trust NIHR BRC (P45272:MK). Essay! None of the essay on science and health hazards, funders had any influence on the study design; in value education the collection, analysis, and english to use in essays, interpretation of data; in value education the writing of the report; and in the decision to submit the article for publication. Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an short on hard is the, interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work. Ethical approval: Not required.
Data sharing: No additional data available. Transparency: The lead author (MK) affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned have been explained. This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to value higher education essay, distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: http://creativecommons.org/licenses/by/4.0/ Download this article to computer and effect, citation manager. BibTeX (win mac)Download EndNote (tagged)Download EndNote 8 (xml)Download RefWorks Tagged (win mac)Download RIS (win only)Download MedlarsDownload. If you are unable to import citations, please contact technical support for your product directly (links go to external sites):
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Value of higher education essay - …
conclusion ww2 essay WW2 swords may or may not have a tang stamp. Some of these tang stamps may represent traditionally made swords. This issue is however hotly debated, and some of the higher education, arguments below may be considered controversial by some. There are those that argue that all tang stamps indicate a non-traditional sword. However, this argument does not stand up to analysis. Not all tang stamps are equal. The star stamp, for resume length example, was used to indicate blades made by value, smiths of the Rikugun Jumei Tosho (Army approved swordsmiths). Resume Length? Similarly, the higher, Minatogawa Kikusui mon indicates the blade was made at the Minatogawa Shrine. The Minatogawa Shrine forged traditionally made blades, i.e. gendaito, for the Navy. Minatogawa swords are relatively rare as only a few hundred were made, and resume length they are avidly sought by collectors.
The same applies to the Yasukuni Shrine swords, which were made for the Japanese Army. Only 8,100 of these blades were made, and they are also considered rare. Any sword made at education the Yasukuni Shrine forge by a Shrine smith is, by definition, a gendaito. Essay On Citizenship For Kids? These blades are considered to be among the best quality traditionally made blades of the WW II era. Essay? A list of revolution cause Yasukuni Shrine swordsmiths is available at Chris Bowen's Tokyo Kindai Tosho Index. Swords of the essay, WW2 period which have received origami (authentification papers) from the Nihon Bijutsu Token Hozon Kai (NBTHK) or Nihon Token Hozon Kai (NTHK) are also considered gendaito.
However, not all of a smith's blades are gendaito simply because one blade amongst many has received origami. It was not uncommon for smiths to make both gendaito and showato during the war. Again, each blade must be judged on its own merits, and resume length not just on the signature of the value higher, swordsmith. Which brings us to the common tang stamps, such as Showa, Seki and with benefits paper Mukden stamps. There is a popular view that these swords are all (a) machine made (b) rubbish. Whilst there is some truth in this argument, it is far too much of an over-generalisation. I first came across this argument thirty years ago. I had a sword with a Showa stamp, and there was a Japanese togishi in value education essay London. I, being the very new to the field, took my sword to english good in essays see the togishi, to see if he would polish it.
He wouldn't. Education Essay? He took a cursory glance and handed it back. Rubbish! he said, machine made from a single piece of resume length steel. No hamon! So I asked him about value education essay sharpening it. His advice was that I could safely sharpen it the same way as a western knife or sword, since it was made the same way. So I got out my whetstone and oilstones and sharpened it up - and sharpened straight through the skin metal.
One screwed Japanese sword. You see, the problem was that it wasn't made of a single piece of steel. It had core and good to use skin steel. Etching subsequently demonstrated that it had a gunome hamon, although it had been obscured by the wartime polish; I never had a chance to find out if it was water tempered. Value Higher? For all I know, it may have been laminated. The togishi had relied upon the assumption - unfortunately incorrect - that showato were all machine-made rubbish. That after all was – and essay often still is – the essay, received wisdom. On Science Hazards? I for my part assumed that he was correct because he was the authority on swords. As a result, I have learned that I should never believe in value higher essay authorities, no matter how well established or revered.
With hindsight, the short, togishi’s reaction was unsurprising. Value Higher Education Essay? Most Japanese, togishi included, have never seen such swords because they are illegal in resume length Japan. They therefore know little about them, apart from value higher essay assumptions and received wisdom. In fact most of the research in these swords has been conducted in the UK. Nevertheless, the resume length, argument is still influential and education essay widely accepted. However, as my old academic mentor once remarked, if data disagrees with theory, then theory is wrong, no matter how attractive the theory is. In this case there is evidence to resume length contradict the theory as a general case, and none - apart from assumptions - to support it. If someone feels the need to justify the received wisdom, they are going to have back up their argument with statistical data from education essay a statistically significant sample. The practice of essay on science and health saying that it is so because a certain authority said it was so should have gone out with the medieval period.
Tang stamps are found on some of the education, poorest blades the on citizenship, Japanese ever made. However, the purpose of tang stamps was only indicate that the sword’s manufacture was non-traditional in essay some way. To be considered traditional, the starting material must be tamahagane, and the sword must be forged in the traditional manner, and differentially tempered using yakire and water as a quenching agent. If only one of good words to use in essays those things is non-traditional, then the sword as a whole is not considered traditional. If, for example, the starting point is not tamahagane, but foreign imported steel, then the sword is not traditional; it is not a nihonto. From 1933 onwards, swords that were not traditional were required to be stamped with a tang stamp. Education? Since the war swords with a tang stamp have been regarded as poor swords by essay on science hazards, virtue of being non-traditional. As we shall see, there are serious problems in applying this argument in all cases. For now it should be noted that the value higher education essay, use of non-traditional materials is neither new, nor is the result necessarily inferior to a traditionally made sword. To argue otherwise is simply evidence of prejudice. Tamahagane is not the most ideal starting material for a sword; the perfection of the Japanese sword is resume length down to the ability of generations of Japanese smiths to overcome the limitations of their starting material.
Japanese smiths were, like any perfectionists, always on value higher education the lookout for on citizenship anything to improve their swords. The Edo period smith, Yasutsugu, was the first to higher education essay use foreign steel rather than tamahagane, and proudly marked this fact on his tangs. It meant a better sword. By today's rules, Yasutsugu’s swords would not be considered traditional because of the inclusion or use of foreign iron. If they had been made during WW2, the law would have required them to bear a tang stamp. These days they would be classified as showato and regarded as inferior. They are however considered traditional because they are antique and essay are regarded as superior examples of value higher nihonto. Spot the english words to use in essays, illogic. To enquire further into the issue of tang stamps, we must first understand the methods of sword manufacture used in Japan prior to the end of WW2. Value Higher Education Essay? Richard Fuller describes nine manufacturing methods: 1. Tamahagane gendaito.
Fully hand forged and differentially hardened in the traditional manner using water as a quenching agent. Possesses an active hamon and hada. 2. Mill-steel gendaito. Fully hand forged from mill steel or (more often) 19th century railway tracks made from Swedish steel. Differentially hardened in the traditional manner using water as a quenching agent. Possesses an active hamon and hada. 3. Koa-isshin Mantetsu-to. Made from with Manchurian steel by a special process. Value Higher Education? Partly forged, partly engineered, and differentially hardened in for kids the traditional manner using water as a quenching agent. Higher Essay? Possesses an active hamon and hada.
4. Han-tanren abura yaki-ire-to. Partially forged from mill stock, some folding, differentially hardened using oil. Does have a hamon although it is nowhere near as active as a water-quenched sword, but lacks hada. 5. Sunobe abura yaki-ire-to. Drawn down, forged to shape, not folded. Revolution Cause And Effect? Differential hardened using oil, may have a fairly inactive hamon, but no hada. 6. Mantetsu-to. Rolled from Manchurian railway tracks. Differential hardening using oil, may have a fairly inactive hamon, but no hada. 7. Murata-to. Rolled or drawn, oil hardened but not differentially hardened.
Yakiba but no visible hamon and no hada. 8. Tai-sabi-ko. Stainless steel, oil-hardened, no grain, no hamon, possible yakiba. Made for the Imperial Japanese Navy to resist salt corrosion. 9. Machine made. Higher Education? Serial number in key to the blade. Value Higher Essay? No forging; stamped out and quenched in oil without differential hardening, assuming that they are hardened at all. No hada and no hamon. Some may in fact be plated, and in the worst cases the hamon may be acid etched onto the steel.
The classic example is the cause and effect, NCO swords. Higher Education? On a par with Chinese fakes, and the most commonly faked sword. Only the tamahagane gendaito is considered traditional, i.e. a nihonto. All the rest, including the ‘mill steel’ gendaito, would have to bear a tang stamp. Whilst ‘mill steel’ gendaito can be very, very good indeed, the non-traditional group includes some pretty awful examples of swordmaking. As a result, the work is the key to, whole group tends to essay be known by short on hard key to, the worst examples. This is probably unsurprising; the value essay, bulk of this group consist of oil-hardened blades (abura yaki-ire-to). Essay Is The Key To Success? That doesn’t mean that the value essay, entire group followed this pattern. The ‘mill steel’ gendaito radically differ from the abura yaki-ire-to; they are like chalk and cheese. The 'mill steel' gendaito could be regarded as following the precedent set by and health hazards, Yasutsugu and his use of namban-tetsu.
The best ‘mill steel’ gendaito are made from mid-19th century railway tracks that were manufactured from value Swedish steel and exported to Japan. Swedish steel has been highly prized for its excellence and english words in essays purity for centuries. In the essay, 19th century it was ‘puddled’ to produce sponge iron of exceptional quality. The sponge steel was then forged into bars and subsequently baked for weeks with an appropriate quantity of charcoal. This resulted in blister steel. The carbon content of blister steel was very unequal, so the bars of blister steel were broken up, forgewelded together, and the block then folded and repeatedly welded to produce a consistent carbon content of about 0.7%. The block was then rolled and heat treated to benefits produce pearlitic railway tracks. Value Higher Education? The metal also contained some manganese, which made the tracks tougher and and effect harder than straight carbon steel. As a result of the essay, manufacturing processes, the rails had an inherent grain. This was due to the forgewelding process, and the steel having slight variations in its carbon content.
As a result, a polished rail of the period has a grain resembling a coarse hada, for exactly the same reasons that a tamahagane sword has a hada. In short, the process of making the tracks was analogous to short essay on hard work success the earliest stages in making a sword from tamahagane. However, the average Japanese sword has a carbon content of 0.5%. Value Higher Education Essay? Some particularly vicious cutters have a carbon content of resume length 0.7%, but these are unusual, and value are probably Koto blades. The use of good Swedish steel therefore meant that the smith could make a blade that was potentially in the same category as the highest performing traditional blades.
Furthermore, the presence of manganese means that the english good words to use, metal is tougher than straight carbon steel. Add traditional hand forging and construction techniques, plus decarburisation of the value higher essay, steel forming the core, and you have a blade that would be likely to outperform all other WW2 blades except, possibly, a Koa Isshin blade. However, even a Koa Isshin blade would have a run for for kids its money. All it requires is the smith having the ability to realise the full potential of this material. I have a sword made this way. It is a work of higher education art.
It has a lovely skilful hamon and a hada. It is also beautifully balanced and in full polish. Oddly enough, the smith has used the sugata of resume length a Koto blade, rather than the standard WW2 design. Anyway, I had it out the other day, and value higher education essay set the bare blade down to short work is the study it. It slipped a couple of inches, and higher education essay sliced cleanly through a canvas bag it encountered on the way as if the bag were not there. In skilled hands it could easily take off a leg, and arm or a head without noticing. Similarly good results may be achieved by forgewelding together a lamination of friends benefits research differing grades of mill steel. This method has been perfected in the post-war period by American smiths, and has also resulted in blades of prodigious performance. Such swords have a hada and an active hamon, although they are usually more easily distinguished from nihonto.
I am, however, unaware of any WW2 Japanese smiths doing this, although it should be said that most smiths never documented their methods, and refused to talk about their wartime work in the post-war period. Some perceived, rightly or wrongly, that there might be some repercussions for being part of the Japanese war machine. Manchurian steel was highly esteemed by WW2 swordsmiths. In fact the higher education, Dairen Manchurian Railroad Factory (Mantetsu) thoroughly analysed the and effect, Japanese sword with a view to improving it, including reducing its susceptibility to higher essay cold fracture in extreme climactic conditions. And Health? The resulting protype subjected to higher education essay an appraised cutting test. The prototype was, as a result, appraised in error as a Koto sword forged by Tadayoshi of Hizen, on resume length the grounds that only value higher essay, a Tadayoshi sword could cut like that (more preconceptions!). Encouraged by this, in 1937 Mantetsu went on to manufacture the Koa Isshin sword, turning out and effect some 400 a month. Koa Isshin swords are not traditionally made swords, and are therefore not ‘art swords’. However they are, from an engineering point of value education view, superbly made. The cutting edge has a hardness of Rc 72 (far in excess of all western blades and many Japanese swords), whilst the construction is resume length far more consistent than many traditionally forged Japanese blades. The result is not an inferior sword at all, but a superb, high quality, cutting instrument that exceeds all but the higher, very best Koto ‘art swords’ for effectiveness.
Koa Isshin swords are therefore highly valued by martial artists. Or to put it another way for my re-enactment friends, practical tests indicate that a sword edge of mid-Rc 60s hardness will cut chainmail. A Koa Isshin sword at Rc72 would, in all probability, make mincemeat of chainmail and would probably seriously damage modern plate armour. I doubt that it would affect medieval tempered plate to a serious degree though. I might note in passing the similarities in steel manufacture between the Koa Isshin swords and the swords made from Swedish steel.
Both start with extremely pure sponge iron. Essay? The former, and possibly the latter, cut as well as the best Koto ‘art’ swords. The secret of higher essay making Koto swords has been lost for centuries, and Japanese smiths have spent generations trying to recover it. It would be ironic if the Japanese had rediscovered the secret without knowing it. You see, the Chinese had puddling furnaces (chaolu) by the 1st century AD at the latest, and tamahagane would be an ideal feedstock for essay on citizenship such a furnace. The Chinese had also discovered how to accurately control the carbon content of steel. Perhaps the secret of Koto blades lies in the method of steel manufacture, rather than in the subsequent forging of that steel. Both Koa Isshin swords and ‘mill steel’ gendaito are therefore superb cutting implements despite – or rather because of value higher education – their non-traditional elements. Are they however ‘quality’ swords? Well, it depends upon what we mean by ‘quality’.
The quality of a Japanese sword is judged, not on its cutting ability, but on the evidence of craftsmanship that it shows. Performance and quality are however usually related; as a general rule (and bearing in mind the exceptions), the lower the craftsmanship, the english to use in essays, poorer the sword, and the poorer it performs. This is value higher true regardless of whether the sword is made from tamahagane or not. It is a bit like judging breeds of dogs; points are awarded for the craftsmanship shown in creating the shape of the sword, the hamon, the hada and all the other bits that go to make up a traditional sword. By definition, oil tempered swords, which make up the essay on science hazards, bulk of the non-traditional swords, will lack essential elements. The more elements they lack, the poorer they are. A Koa Isshin sword is value higher a simple, workmanlike piece that was designed to function as an effective cutting tool. Ideas of artistry were very secondary. ‘Mill steel’ gendaito were however crafted by good in essays, skilled smiths who brought all their skill and artistry to bear in making them. Fuller’s list is organised in terms of descending quality. Koa Isshin swords and ‘mill steel’ gendaito probably perform equally well, although the latter has a marked edge when it comes to evidence of craftsmanship. Fuller also places ‘mill steel’ gendaito lower than tamahagane gendaito as far as quality is concerned, although the former can probably, as a general rule, outcut the latter.
In fact the difference in quality between tamahagane and value essay ‘mill steel’ gendaito probably isn’t that high. True, tamahagane gendaito generally show greater quality when taken as a whole . However, the tamahagane gendaito class includes the work of Japan’s top smiths, who had an uninterrupted supply of tamahagane, and therefore did not experiment with ‘mill steel’ gendaito. No doubt they could have done so, but tradition was against short essay is the, it. The smiths who made mill steel gendaito did not work in such a rarefied atmosphere. There was probably little difference in quality between the gendaito produced by an individual smith, regardless of the starting material. In swords, as in statistics, one should compare like with like. The proof of the pudding is, in this case, in the legislation. Tang stamps were introduced precisely because swordsmiths and collectors could not distinguish the value higher essay, best quality non-traditional swords (i.e. ‘mill steel’ gendaito) from traditionally made swords.
It was discovered that, as a result, some smiths were forging replicas of older swords, giving them false signatures (gimei), and passing them off as the real thing. Several smiths were subsequently arrested. Resume Length? Amidst mounting concern, the higher essay, government passed a law in 1933 requiring all swords that were non-traditional in any way to be marked with a tang stamp, although the actual stamp used was left to essay on citizenship for kids the manufacturer. Education? These stamps should not however be confused with the friends research paper, smith’s personal seal or ‘kokuin’. The system was not fully implemented until 1940. That means that there could be a fair number of swords of non-traditional manufacture not bearing tang stamps, of value higher education essay which some will be ‘mill steel’ gendaito. Resume Length? It would be fairly easy to differentiate between an oil-hardened sword and essay a traditionally made sword, even if the former lacked a tang stamp. Friends Benefits Research? However, there would probably be little or no chance of differentiating between a ‘mill steel’ gendaito and higher essay a tamahagane gendaito. Cause? It is value higher not impossible that some examples have since received origami.
Again, a togishi can remove a tang stamp so that it looks as if one was never there. Some smiths stamped their tangs very lightly, thus complying with the friends, law, but making it easier for value essay their customers to remove the stamp. The legislation produced a profusion of stamps, ranging from sword factory stamps, to computer the stamps of sword sellers. The commonest are illustrated at the beginning of this essay. The best known of essay these is the well known Showa stamp. Essay On Science Hazards? This is a general army stamp; contrary to received wisdom, it is not an arsenal mark. The earliest known example dates from higher May 1940. The Showa stamp seems to have been restricted to swords that were sold off-the-peg through the on hard, Army Officers Club (Kaikosha). Here we already have a potential element of confusion; does a Showa stamp necessarily indicate a non-traditional sword, or did it simply indicate a sword that was sold ‘off-the-peg’ via a certain organisation, the bulk of the swords sold being non-traditional in some way?
In short, were the swords stamped because they were ‘off-the-peg, regardless of method of higher essay manufacture, or were off-the-peg swords limited to non-traditional swords. Short On Hard Work Key To Success? If the former is true, then some swords with a Showa stamp may indeed by traditional swords. More research is needed. The Showa stamps were superseded in late 1941-early 1942 by the various arsenal marks. Higher Essay? Japan had moved to a war footing following Pearl Harbour, and now needed to on hard key to supply its army and navy with as many swords as possible as quickly as possible.
As a result, swords with arsenal marks are almost certainly always oil tempered, because it was the quickest method of manufacture. I qualify the preceding remark however, because you can almost always find an exception to the rule with Japanese swords. However, you are highly unlikely to find a good sword amongst them, and the quality drops as the war goes on. The machine-made swords, and the end of war swords are possibly the worst swords ever made in Japan, and are pretty much overlong butter knives. The former can be recognised by the serial number near the habaki. WW2 tang stamps are thus a far more complex subject than they might appear to higher education essay be at first sight. Each WW2 sword needs to be closely examined on its own merits, with assumptions put aside. There is however one important consideration to bear in mind. If a blade with tang stamp is shipped into Japan it will be seized, and it may be destroyed. This is because Japanese law classifies it as a weapon, rather than as a work of art.
A gendaito on the other hand is a cultural asset. As a result, one may occasionally find swords in which the Showa stamp has been obliterated in order to send it to Japan for with benefits polishing or assessment. Value Essay? The distinction between the traditionally made sword as art, and the non-traditional sword as weapon was originally enshrined in law by General MacArthur. Whilst there is a long history of the Japanese sword being considered art, in my opinion its primary function as a weapon often gets overlooked. As a bottom line, the samurai weren’t too fussed about a sword being pretty. They were far more concerned about its effectiveness; their lives depended upon work is the key to success it throughout much of value higher essay Japanese history.
Generally ‘prettiness’ indicated a high quality sword that was also extremely effective. As a result, and given the lack of english good to use in essays Rockwell testing equipment in medieval Japan, signs of craftsmanship became revered as an indication of blade quality. Mind you, the higher education, Japanese of that period were also pragmatic; test cutting was also a good indication - preferably on criminals condemned to be executed. The problem is friends benefits that, in the more peaceful Edo period, prettiness was sometimes elevated for value essay its own sake, without reference to the primary function. For example, some people admire large nie inclusions. However, nie is the essay work is the key to, visible evidence of a enlarged grain structure at value higher education the transitional zone of the hamon. It means that the steel was held for too long at critical heat, and the grains enlarged. The larger the resume length, grain is, the weaker the sword. That’s basic metallurgy, and is the reason stainless steel blades snap unexpectedly in essay use. However, the end result looks very pretty, particularly in the ji, and some people like it.
Nevertheless, swords exhibiting strong, large nie should probably not be used for tameshigiri. The view of the Japanese sword as art has become somewhat entrenched since WW2, particularly following MacArthur's intervention. From my point of view however the sword cannot be separated from its primary function as a weapon. Resume Length? Form follows function, not the education essay, other way about. The modern Japanese smith is essay work key to success also further constrained. Legislation has locked him into using materials and methods that have remained unchanged since the 16th century. Higher Education Essay? There is also a limit on the number of swords that can be made each month.
Any departure from the traditional is forbidden since the resume length, smith would then be making a weapon and not a cultural artefact. Value Education? As a result, Japanese smiths cannot follow Yasutsugu’s example and use ‘foreign’ steel. It should however be noted that some add ‘old steel’ to their mix, and this ‘old steel’ may well be of foreign manufacture. English Good Words In Essays? Technically speaking, that makes such swords non-traditional. As for the prevalence of this practice – well it has been observed that many Japanese swords are harder than they were a generation or two ago. American swordsmiths do not operate not under such constraints. Value Higher Essay? ‘Mill steel’ gendaito produced by American mastersmiths such as Walter Sorrels are amongst some of the english good words, most formidable blades ever produced, and education they are still improving. Short Work Is The? The quality of their work, as defined by Japanese standards, is also high and value education essay improving all the time – there have been occasions when a sword made by an American smith has been mistaken by english good in essays, a Japanese expert for value education essay a nihonto. Essay On Science? Swords made by value, the American smiths are, however, not cheap; they may set you back £2,000-£3,000. Words? They are not however Japanese swords, because those have to value higher education be made in Japan, by a Japanese smith, and by traditional methods.
If you want a sword for collecting, then it also comes down to whether or not you care about english good whether it is classed as a true nihonto or not. Collectors of nihonto find the question absolutely central and value higher will ignore swords bearing tang stamps. Friends With Benefits Research? On the other hand, the question is completely irrelevant as far as collectors of militaria and value essay students of gunto are concerned. And as far as martial artists are concerned, all swords exist to be used; the only question is, how good is the sword as a cutting tool, and what sort of balance does it have? Whilst I think it unlikely that any martial artist would turn down a gift of a nihonto, they would probably be equally happy to receive a ‘mill steel’ gendaito or a Koa Isshin blade. To recap, if there is short on hard work success a hada, an active hamon, and no evidence of value higher education a tang stamp being removed, then you almost certainly have a tamahagane gendaito. Almost - but not quite. Essay On Citizenship? You see, before the 1933 law was brought in, it was not necessary to stamp the tangs to indicate a non-traditional sword. A very high grade early 'mill steel' gendaito (the sort the government was worried about) may not be marked. Value Education? That's why I'm often very cautious in describing something as a nihonto unless I have definitive evidence and opinions that it is not an early ‘mill steel’ gendaito.
OK, so this is being picky, and other people would rightly point that if it hasn't got a tang stamp, and it has got a hada and active hamon, then its a gendaito by definition, and thus a nihonto. Ah, but there are those pesky very early non-traditional swords that lack tang stamps to take into friends with benefits account, some of which will be ‘mill steel’ gendaito. Higher? Unfortunately there's no way to distinguish these from the tamahagane versions that I know of. The only thing I would suggest is to examine each sword minutely and judge it on its merits. Even that may not suffice. Of course, you could do a metallurgical analysis for on science and health hazards manganese, but I suspect that some people might not go for this, since they might not like the results. It is higher education not impossible that a few papered WW2 gendaito from the 1930s were actually made from Swedish steel and not tamahagane. English Good In Essays? Yes, ‘mill steel’ gendaito can be considered that good if you remove the tang stamp, or if they were made before the law required them to have a tang stamp. To put it another way, imagine a cutting ability comparable to the Koa Isshin allied with the craftsmanship of the tamahagane gendaito. If you have an active hamon but can't see a hada (not uncommon given wartime polish and a very tight hada), and there's no tang stamp, chances are reasonably high that you may have a gendaito, although see the arguments above. Higher Essay? If you have very high class mounts as well, it is pretty certain.
However. you need a window polish to clear things up. It should however be recalled that some traditionally made swords are forged with such a tight hada that they are muji - there is good words no visible grain. That's not the higher essay, same as saying that there is english words to use no grain. If you have got a tang stamp, work on the assumption that the blade is non-traditional in some way. If you've got a tang stamp, a hada and a water tempered hada - ah well now you've got a mild puzzle. Which is where this little essay started. Finally, if a hada is not present, the hamon seems a little dead and there is higher a tang stamp, then you’ve got a bog standard, oil-hardened gunto. Computer? However, these swords are good for training, as long as you don’t attempt tameshigiri.
Japanese swords are one of those areas where it is unwise to be dogmatic. The best advice therefore is to study each individual sword in its own right, assess its quality, keep in mind your purpose for buying one, and take your time in making up your mind.