SDSR – “Superior” DSR

1. SDSR – “Superior” DSR Jay Chen Siddharth Gidwani Christopher Yap

2. Mobile Ad-Hoc Networks - MANETS • Mobile Ad-Hoc Networks • A collection of wireless mobile nodes forming a communication network without centralized administration or existing network infrastructure • Nodes perform both host and routing duties in order to transmit packets across the network • Applications • Wireless computing • Sensor networks • Security infrastructure • Military • Search and rescue operations

3. MANET Routing Protocol Overview • Destination Sequenced Distance Vector (DSDV) • Nodes maintain next-hop information • Periodic broadcast routing updates • Temporally Ordered Routing Algorithm (TORA) • Broadcast-determined routes; errors backflow packets • Periodically transmitted heartbeats to maintain neighbor list • Ad-Hoc On-Demand Distance Vector (AODV) • Uses on-demand DSR route discovery/maintenance • Hop by hop routing and periodic beacons like DSDV • Dynamic Source Routing (DSR) • Packets carry the entire hop by hop source route to the destination • No setup overhead, everything done on-demand (no periodic broadcasts for neighbor connectivity)

4. MANET Routing Protocols - Continued • MANET protocols present a spectrum of choices varying from on-demand routing to shortest-path routing (periodic updates) • Turns out DSR is the most popular of the lot, as it offers superior performance under common applications and various deployment scenarios • A major reason DSR is preferred in MANETS is due to the elimination of the overhead from periodically updating state

5. DSR Routing Mechanisms • Route discovery • DSR nodes perform a flooding route request, which is propagated through the network • Eventually it will be propagated to a node that knows a path to the destination (ultimately the destination node) • This node returns a route reply containing the source route to the requested destination • Route maintenance • Should a sent packet be unable to progress due to link failure, a route error is generated and propagated back to the sender • The sender will then resort to either other cached routes, or perform a route discovery as a last resort

6. DSR - Weakness • Even though route requests are on demand, each request is a propagated broadcast • Results in unnecessary congestion both from the route requests and the associated route replies

7. The Approach • Considerations • Trend of mobile computing is that of more powerful nodes • This is the not the case in sensor networks • Idea • Add some hierarchy • Reduce route flooding by limiting route request functionality to a subset of nodes • Interaction with the proxy should be unicast

8. Related Work - Spine Routing • Spine Routing • Adds a level of hierarchy to the routing • Select a set of nodes to perform the bulk of the routing operations • Non-spine nodes communicate through spine nodes in order to interact with the network • Exactly what we wanted, but… • Optimal spine networks require global knowledge of the topology – very difficult in MANETs where nodes are mobile

9. The Goal • Maintain the demand-based attractiveness of DSR and leverage the advantages of Spine Routing without the overhead of maintaining a highly consistent spine • Maintaining some extra state at each node to lift some network overhead caused by flooding route requests

10. SDSR – Protocol Description • Selective Dynamic Source Routing – (SDSR) • Maintain the on-demand advantages of DSR, we’ll maintain a “weakly consistent” spine that is also demand determined • Elect a few nodes in the network to serve as proxies • These proxies perform route request on behalf of their clients • Re-election of proxies as needed • All other operations fall back on standard DSR • Our lower bound for routing overhead if all nodes act as proxies is the same as DSR

11. Implementing & Testing the Protocol • NS-2 network simulator • Modified the DSR implementation available in ns-2 to add the concept of proxies • Traffic model • We generate simple all pairs random traffic scenarios • Mobility model • Research area in itself • Random waypoint • Random direction • Terrain mappings • Structured group mobility • Flocking/swarming groups • We spend some effort implementing “interesting” and more realistic mobility models

12. Mobility Models • Random waypoint • Most previous work done on this topic involved the random waypoint model and it is a point of basis for validating results • Structured group mobility • Probably of use to military/disaster recovery efforts • May be a good fit with SDSR versus DSR since each group operates in close proximity with each other and we can reduce the out of group traffic to a single node ideally

13. Simulation Parameters • Simulation Area • 500m x 500m • Number of Nodes • 10, 25, 50 nodes • Motion – uniform/non-uniform speed • 1-20, 20-25, 1-50, 20-50 m/s • Pause selection – constant/uniform • 1, 10 s • Number of connections • 1, 10, 100 connections/s • TCP connections instead of CBR (constant bit rate) since CBR seems to be geared more towards sensor networks

14. Structured Group Mobility Parameters • Group Mobility • Number of groups • 1-4 • 10 nodes per group • Kept every parameter constant and varied one

15. iNSpect - Visualization tool

16. Performance Metrics • Routing overhead • Route request packets sent/forwarded • Route replies sent/forwarded • Route availability • Performance ratio defined as the number of resend attempts on data packets vs the number actually sent • Note that a single packet may be attempted to be resent many times or zero times before it is actually sent out • This is essentially a measure of the standard concept of availability negatively weighted by the duration of each un-available route

17. Performance Metrics - Continued • Route lengths • We expect to be worse, since for non-proxy nodes the routes will contain an extra hop corresponding to the proxies

18. Performance Results

21. Preliminary Results • Cases where we do worse • Cases where we do better • Group mobility model • Parameter tweaking

22. SDSR Flexibility – Parameter tweaking • SDSR performance is tied to five very important parameters that are set • Proxy request timeout (client) • Maximum time to wait for a get proxy response before declaring itself as the proxy • Get request timeout (client) • Time to wait for a proxy route response before attempting to find a new proxy • Client list timeout (proxy) • Time to wait before purging a non-communicating client • Client threshold (proxy) • Number of clients proxy must maintain to continue being a proxy • Initial proxy timeout (proxy) • Grace period for new proxies before being subjected to the client threshold

23. SDSR Flexibility – Parameter tweaking • By tweaking these parameters we can greatly influence the performance of our protocol • Preliminary experimentation shows that we can improve the performance of certain test cases over DSR • A point of future work might be to investigate determining these parameters dynamically, in order to optimally fit the situation at hand

24. Conclusion • Random waypoint model • 50% fewer routing related messages in some cases • Structured group mobility model • Differences in performance are minimal • Parameter tweaking • Control knob for tradeoff between individual node load and network congestion

25. Future work • Microbenchmarks of actual CPU load and memory usage • Not possible in ns-2 • More runs for statistical significance of our test simulations • Investigation of other topologies and mobility models • Actual implementation and testing

26. Questions? • Questions?