Cache Management of Dynamic Source Routing for Fault Tolerance in Mobile Ad Hoc Networks

Outline Review DSR Protocol Simulation Results Conclusions References

Review DSR Route Cache A packet carries the list of routers in the path Two main operation Route Discovery Route Maintenance No periodic messages

Review DSR Source Node A If no route in A ’ s Cache Source Node B Source Node C Node B or C receives the RREQ packet from A, it check the route from it ’ s cache If the cache have the route Node reply the route information to sender node Else (the cache have no route about the RREQ packet) Add node ’ s address, and broadcast the RREQ to it ’ s neighbors again

Simulation of DSR protocol The performance is better without using cache. In “ Analysis of TCP Performance over Mobile Ad Hoc Networks ” Because DSR has no mechanism to immediately respond to dynamic network topology change. Reply from cache introduces more routing error.

Improve DSR Cache We have a idea from AODV Sending link layer beacons periodically for get signal strengths. But the idea disobeys the protocol ’ s design idea Improve Cache management

Protocol Description Protocol Overview Signal strength “ Confirm ” message “ Route ok ” message “ Link broken ” message “ Host needs recovery ” message “ Neighbor ” message

Protocol Overview Identify whether a route in the cache is correct or not. A route marked stale is a route which is likely broken. Neighbor links ’ stability By monitoring the signal strength of received packets from the neighbor node.

Signal Strength Signal strength of the received packets Threshold

“ Confirm ” and “ Route OK ” A BC BCX(S)CXX A senses B ’ s signal strength beyond the threshold and wants to recovery the “ stale ” route BCX as normal Node A sends a “ confirm ” message to node B to ask whether the route BCX can work or not. B receives A ’ s “ confirm ” message If B has route CX in its cache, then B sends “ route ok ” message to A with route BCX If B does not have any match with A ’ s “ confirm ” message or the route CX is marked as stale, then B does not do anything.

“ Link Broken ” ABC BCX CXX(s) D If C discards a “ stale ” route X, then is broadcasts a “ link broken ” message include node X Link broken message (X) B and D receives the “ link broken ” message, it discard the route and tries to find a route to that destination If found, then it stop and does nothing further. If no found, then it broadcasts “ link broken ” message again Link broken message (X) WX

“ Host needs recovery ” and “ Neighbor ” When a node restarts after its failure, it broadcasts “ Host needs recovery ” message to its neighbors. When a node receives a “ Host needs recovery ”, it uses “ neighbor ” message to show that it is his neighbor now.

Advantages and Disadvantages Advantage Do not send any periodic information or signals so that we can keep the advantages of DSR. Disadvantage We passively wait for packets and measure their signal strength. A link may be stable but we discard it since no packets are received form it.

Simulation Environment Network model consists of 30 nodes in a 1500*300 meter flat rectangular area. Each node picks a random destination and speed in the area and then travels to he destination in a straight line. Bandwidth:2Mbps Transmission radius:250m TCP packet size:1460 bytes

Simulation Results of Link Failure

Simulation Results of Host Failure

Conclusions The simulations showed that we have improved the performance of reply from the cache in DSR significantly, which is almost equivalent to that of no cache reply mechanism. For future work we suggest that when designing a routing protocol for ad hoc networks, it is important to consider the host failures as well as the link failures.

References G. Holland and N. Vaidya, “ Analysis of TCP Performance over Mobile Ad Hoc Networks ” in Proceedings of IEEE Mobicom ’ 99, Seattle, WA, Auguest1999, pp.219~230