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

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

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)

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

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

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

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

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

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

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

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

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

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, 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

Structured Group Mobility Parameters Group Mobility –Number of groups nodes per group –Kept every parameter constant and varied one

iNSpect - Visualization tool

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

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

Performance Results

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

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

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

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

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

Questions?