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Signal-Strength-Aware Routing in Ad hoc Networks

Signal-Strength-Aware Routing in Ad hoc Networks. Abhinav Gupta Ian Wormsbecker Carey Williamson Dept. of Computer Science University of Calgary. Ad hoc Networks.

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Signal-Strength-Aware Routing in Ad hoc Networks

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  1. Signal-Strength-Aware Routing in Ad hoc Networks Abhinav Gupta Ian Wormsbecker Carey Williamson Dept. of Computer Science University of Calgary

  2. Ad hoc Networks • An ad hoc network is dynamically formed when two or more mobile hosts with wireless capability come into transmission range of each other • Advantage of ad hoc networks: • Can be set up ‘on-the-fly’ • Requires no existing infrastructure MASCOTS 2004

  3. Ad hoc Network MASCOTS 2004

  4. Objectives • Implementation of Signal-strength-aware AODV • Study the effect of AODV routing, user mobility, and number of hops on TCP throughput. • Study the effectiveness of rate-based-pacing of TCP (TCP-RBP) MASCOTS 2004

  5. AODV Operation Data Data RREQ Source RERR RREP Destination MASCOTS 2004

  6. Ad hoc On-Demand Distance Vector Routing Protocol (AODV) • Reactive in operation • Route discovery and maintenance using control packets (RREQ, RREP, RERR and HELLO) • The route freshness determined using sequence numbers associated with the control packets. MASCOTS 2004

  7. AODV UU • Implementation carried out in user-space. • Consists of 3 kernel modules and some user space modules. • Uses Netfilter hooks for packet mangling from kernel space to user space. • Packets analyzed in user-space to trigger AODV events. • Packets are queued on to user-space using libipq which communicates with ip_queue, standard queue handler for IPv4. MASCOTS 2004

  8. AODV Modules MASCOTS 2004

  9. Signal-strength-aware AODV • Rationale: Don’t allow route freshness to be determined solely on the basis of sequence numbers • Checks signal strength of control packets coming from adjacent Mobile Host to before it creates, updates or deletes routes. • Signal strength of control packets determined by link_strength module and used by aodv_socket to choose whether or not to let the packet through. MASCOTS 2004

  10. Variation of Signal Strength MASCOTS 2004

  11. Operation • If the packet is a broadcast or is intended for the current host, then it is handled as usual by Linux. • If the packet is not intended for the current host and a route exists, it is forwarded to the next hop. • If no route exists, the packet is dropped. • If the packet is generated by the local host, it is buffered in user-space, and a route discovery initiated and routed to next hop when a route is found. MASCOTS 2004

  12. Locally Generated Packet Packet NF_IP_LOCAL_OUT MASCOTS 2004

  13. Experimental Environment • Redhat Linux 8.0 (kernel 2.4.18-14) • 5 laptops • 3 IBM Thinkpads (Processor P4) • 2 Compaq Evos (Processor P3) • Cisco Aironet 350 PCMCIA Wireless Cards • Netperf and Netserver used as source and sink for TCP traffic. • Kernel Probes added to TCP code to monitor the TCP statistics • Airopeek Sniffer used to count the control packets MASCOTS 2004

  14. Testbed Topology Node1 Running netserver Node2 Node3 Node5 Running netperf Node4 Airopeek Sniffer MASCOTS 2004

  15. Routing Discovery Time (ms) MASCOTS 2004

  16. Round Trip Time MASCOTS 2004

  17. TCP Throughput (Mbps) Slow Speed – 0.33 m/s Fast Speed – 1.0m/s MASCOTS 2004

  18. Routing Overhead MASCOTS 2004

  19. TCP rate-based-pacing (TCP RBP) • Rationale: “Spread-out” the TCP Packets in time to improve TCP performance • InterPacketDelay=RTT/(CurrentWindow+V) • Performed simulations and experiments with Reno TCP and RBP TCP Related Work: [1] Z.Fu et al, “The Impact of Multi-hop Wireless Channel on TCP Throughput and Loss”, Proceedings of IEEE INFOCOM’03, San Francisco, April 2003 [2] J.Ke and C.Williamson, “Towards a Rate-Based TCP Protocol for the Web”, Proceedings of MASCOTS 2000, San Francisco, pp. 36-45, October 2000 MASCOTS 2004

  20. TCP rate-based-pacing Packet Packet Packet MASCOTS 2004

  21. Simulations Results (TCP-RBP) MASCOTS 2004

  22. Experimental Results • TCP Throughput (Mbps) MASCOTS 2004

  23. Conclusions • Signal-strength-aware AODV is a good choice for ad hoc networks because of low overhead and good performance • Design choices made for signal-strength-aware AODV were effective • Performance of RBP TCP is highly sensitive to channel contention and AODV routing dynamics • Simulation results should be interpreted with caution, unless validated against experimental measurements MASCOTS 2004

  24. Thank You!

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