Does Packet Replication Along Multipath Really Help ? Swades DE Chunming QIAO EE Department CSE Department State University of New York at Buffalo Buffalo, NY

Presentation Outline  Introduction  Motivation for improved routing in wireless networks  Cost issues with packet replication and selective forwarding  Performance studies  Results  Summary and conclusion

Introduction Possible features of ad hoc wireless networks  No centralized control  Nodes act as communicating entities as well as routers  Multihop source-destination routes  Wide usage: required highly affordable cost required  Nodes may have limited memory and processing power  Nodes may have limited mobility (e.g., in mobile ad hoc networks)  Nodes could be unattended: highly failure-prone nodes (e.g., in fiend sensor networks)  Robust routing technique necessary  Battery operated: limited battery resource  Energy-efficient routing required

Motivations for Improved Routing Existing multihop wireless routing techniques  Packet replication (PR) along multiple routes (noted in [Kulik’99, Ganesan’01])  simple but could be energy-intensive  Traffic splitting along multiple disjoint routes (D-MPR) [Lee’01,Tsirigos’01]  End node controlled – no routing flexibility at an intermediate stage  The preferred (primary) route is used, secondary routes are kept standby [Nasipuri’99, Ganesan’01]  Additional energy for route maintenance  Little traffic load balancing – may lead to quicker network partition  End-to-end ACK/NACK [Chen’99], or adjacent node NACK[Ganesan’01,Wan’02], or promiscuous listening [Johnson’96] based retransmission  Involved flow-control mechanism, additional buffer space, transmit/receive changeover delay, and receive power

Summary of Multipath Routing Approaches Multipath routing approaches  Disjoint multipath (D-MPR)  Meshed multipath (M-MPR) [ WCNC’03] Packet forwarding approaches  Packet replication (PR) (or limited flooding)  Selective forwarding [our proposed approach]  Preferential routing (primary/secondary routes)

Throughput Performance Evaluation Assumptions made in the analysis  Equal length routes  Regular mesh  Additive white gaussian channel noise  Equal failure probability of nodes (routers)  For PR along meshed route, only one of possible multiple correct reception is forwarded An example disjoint multipath route Meshed multipath routes considered for analysis even odd, even odd, odd

Throughput Performance Evaluation (..contd.) 500 nodes randomly uniformly distributed in 500 m sq. area Coverage range of each node 40 m Gaussian channel with SNR at the receiver 14 dB  Node failure probability: varied  Packet size 50 Bytes  1000 data blocks (packets) per message  Simulation results are within 95% confidence interval Simulation parameters

PR vs. SF: Analytic Results Throughput plot: 6-hop route

PR vs. SF: Simulation Results Throughput plot: average route length (hops) 9.06

Let PR vs. SF: Equivalent Resource Usage be the the packet throughput (obtained for D-MPR and M- MPR, with PR and SF, respectively be the message size in packets (blocks) be the # of error correcting blocks required (using FEC coding) for successful message reception Then, minimum # error correcting blocks required is: [by Ayanoglu’93] Equivalent energy usage Number of transmit-receive operations, i.e., Likewise, equivalent channel resource usage Number of transmit operations, i.e.,

PR vs. SF: Equivalent Resource Usage (..contd.) Simulated 6-hop multipath routes

PR vs. SF: Equivalent Resource Usage (..contd.)

PR vs. SF: Equivalent Resource Gain

Summary and Conclusion  There have been numerous proposals that suggest packet replication (limited flooding) along multipath as a potential routing approach in multihop wireless networks Our original analytic studies supported by simulations show that:  Packet replication approach has has higher per-packet throughput compared to the selective forwarding approach along disjoint multipath as well as meshed multipath  However, overall performance of selective forwarding approach, when resource usage is taken into account, is superior in either multipath routing approaches.  This observation throws potential insight in routing protocol design for energy-constrained applications, such as sensor networks.  Our meshed multipath routing approach (WCNC’03) along with the observations in this paper will appear in Elsevier Computer Networks, special issue on Sensor Networks.

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