Page 2 Lecture Notes in Computer Science 2865 Edited by G. Goos ...

On-demand Routing in MANETs 47In the ideal environment, hop count is a valid metric for selecting routes. But withshadowing model, the shortest path means that there is high possibility that two nodesare on the edge of their transmission ranges. If signal power fluctuates, the link willbe assumed broken, or more retransmissions are needed to send packets successfully.Based on the wok we did so far, we believe link status may be a better metric forselecting routes in shadowing model. The link status of a node is a historic recordwith its neighbors. A node may not add the link to the route if the link is weak. Thislink status will be monitored passively to reduce overhead. A node may keep multipleroutes to the same destination, and these routes can be ordered based on their status.Updating the route status is a future research topic, especially for inactive routes.However, salvaging is a mechanism that has to be used carefully. Sometimes thesender may salvage the packet only because of not receiving the ACK. The consequenceof aggressively using salvaging is that the same packet is transmitted on multipleroutes to the same destination, and multiple Route Error messages are sent to thesource, which cause longer packet delay, duplicated packets and wastes network resource.We are currently working on(1) Route maintenance: because of node mobility, selected solid routes may becomeunstable again. A node may monitor the signal strength for packets received/overheardfrom its neighbors, and inform the source once the link quality drops below acertain threshold. Alternatively, a node could monitor the number of retransmissionattempts necessary to forward a packet to the next node and deduce the link qualityand its rate of change in that way.(2) Finding an appropriate threshold for different node density and β values. We canalso use different thresholds for Route Requests and Route Replies so that a sourcecan discover at least one route to send packets. This may be done adaptively, where asource node may have to reduce the threshold if it cannot discover a route.(3) More formally defining equivalent simulation scenarios under different parametersof the physical layer model as well as exploring additional physical layer models.References1. C. E. Perkins and P. Bhagwat, Highly Dynamic Destination-Sequenced Distance-VectorRouting (DSDV) for Mobile Computers, Proceedings of the Conference on CommunicationsArchitectures, Protocols and Applications, pages 234-244, London, England August,1994.2. V. Park and M.S. Corson, A Highly Adaptive Distributed Routing Algorithm for MobileWireless Networks, Proceedings of the IEEE Conference on Computer Communications(INFOCOM ’97), Kobe, Japan, April 1997.3. D. B. Johnson and D. A. Maltz, Dynamic Source Routing in Ad Hoc Wireless Networks.In Mobile Computing, Chapter 5, pages 153-181, Kluwer Academic Publishers, 1996.4. R. Dube et al., Signal Stability-Based Adaptive Routing (SSA) for Ad Hoc Networks.IEEE Personal Communications, February 1997.5. C. E. Perkins and E. M. Royer, Ad-hoc On-Demand Distance Vector Routing. Proceedingsof the 2 nd IEEE Workshop on Mobile Computing Systems and Applications, pages 90-100,New Orleans, LA, February 1999.