Gugrajah_Yuvaan_ Ramesh_2003.pdf

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Routing Protocols for Ad Hoc Networks Chapter 2 speed in the network was increased DSR uses shortest hop routes, while ABR uses routes that are more likely to last longer. DBF performs poorly because more event triggered updates are generated when mobility increases. The delay results showed that ABR performed better in this regard as well. This can be attributed to the fact that beaconing provides a method of faster convergence when finding suitable routes. It is admitted [Gerla99] that power consumption is a problem with ABR, especially since nodes use portable power supplies. Another possible problem is the interception of beacons by unintended receivers, such as the enemy in a battlefield scenario, which would reveal a nodes location. 2.2.3.2. SSR Signal Stability Based Adaptive Routing [Dube97] is another on-demand routing protocol that selects routes based on network stability metrics. In SSR a route is selected based on the signal strength between nodes and a node's location stability. Periodic beacons are broadcast which allow neighbouring nodes to determine signal quality, which ·is recorded as either "weak" or "strong" in a Signal Stability Table (SST). A route search process is initiated if a valid route is not contained in the Routing Table (RT). Route requests are broadcast throughout the network but are only forwarded to the next hop if they are received over strong channels and have not been processed before. Once the destination receives a route request it ignores later copies that have taken different routes because it is assumed that the first route request arriving has arrived over the shortest path with the least congestion. The destination then replies using the same route along which the first route request arrived because it is assumed to be the route with the best signal quality. Route requests are dropped if the channel was recorded as weak. If the source does not receive a route reply within a specified timeout period, the source specifies in the header of the next route request that weaker links may be used since they may be the only links available. Erase messages are sent by the source node once it is informed of failed links by an intermediate node along a route. The erase message is sent to notify all nodes of the broken link. The source then reinitiates a route-search process. 2-16
Routing Protocols for Ad Hoc Networks Chapter 2 As in ABR, the routes selected by the SSR algorithm are more stable and longer lived resulting in fewer route reconstructions, while not necessarily being' the shortest. However no attempt is made to make partial route recovery as in ABR with the result that the source has to reinitiate the route search. Conversely, the "backtracking" method of localized route reconstruction in ABR may not reduce delay as much as is expected, compared to the source immediately initiating a route request when a broken link is found. Longer delays may also result in the route search process because unlike AODV and DSR, intermediate nodes are not allowed to respond with a route reply. 2.2.4. Location Based Routing Protocols Mobile nodes can be designed to obtain physical location information using Global Positioning System (apS) receivers. While these receivers may be relatively expensive, they will become cheaper with advancements in technology. The gains in using them for location information with routing in ad hoc networks could be significant due their being able to potentially reduce routing related overheads [K097]. The selective paging scheme in Personal Communication Service (PCS) networks has a purpose similar to utilizing location information with ad hoc networks. When a host needs to be located using selective paging, the network pages only a selected subset of the cells close to the last reported location. Tracking cost is thereby decreased. This subsection describes two routing protocols that use location information in the routing process. Location Aided Routing (LAR) [K098] is an on-demand routing protocol. In LAR a source node estimates the range of a destination node's location based on the destination node's last reported velocity, and broadcasts a route request only to nodes within a geographically defined request zone. In Distance Routing Effect Algorithm for Mobility (DREAM) [Basagni98] a node periodically transmits its location coordinates to other nodes in the network. DREAM is therefore considered a proactive protocol. The period of location transmission depends on the node's velocity and the geographic distance to nodes for which the location information is intended. 2-17
Page 1 and 2: Routing Performance In Ad Hoc Netwo
Page 3 and 4: ABSTRACT An ad hoc network is a mul
Page 5 and 6: ACKNOWLEDGEMENTS I would like to th
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Page 9: Chapter 2 LIST OF FIGURES AND TABLE
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Evaluation ofNetwork Blocking Proba
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Adaptation ofthe Fixed Point Approx
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Adaptation ofthe Fixed Point Approx
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Adaptation o/the Fixed Point Approx
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Conclusion Chapter 6 While the reac
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Conclusion 6.2. Future Work 6.2.1.
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REFERENCES References [Basagni98] B
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Angeles, Aug. 2000. References [Gil
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References [Kelly94] Kelly, F. P, L
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References Challenges and Direction
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