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Published on October 30, 2007

Author: Nathaniel

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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:  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 Ad hoc Network:  Ad hoc Network Objectives:  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) AODV Operation:  AODV Operation Source Destination RREQ RREP Data RERR Data Ad hoc On-Demand Distance Vector Routing Protocol (AODV):  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. AODV UU:  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. AODV Modules:  AODV Modules Signal-strength-aware AODV:  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. Variation of Signal Strength:  Variation of Signal Strength Operation:  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. Locally Generated Packet:  Locally Generated Packet NF_IP_LOCAL_OUT Packet Experimental Environment:  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 Testbed Topology:  Testbed Topology Node1 Running netserver Node2 Node3 Node4 Node5 Running netperf Airopeek Sniffer Routing Discovery Time (ms):  Routing Discovery Time (ms) Round Trip Time:  Round Trip Time TCP Throughput (Mbps):  TCP Throughput (Mbps) Slow Speed – 0.33 m/s Fast Speed – 1.0m/s Routing Overhead:  Routing Overhead TCP rate-based-pacing (TCP RBP):  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 TCP rate-based-pacing:  TCP rate-based-pacing Packet Packet Packet Simulations Results (TCP-RBP):  Simulations Results (TCP-RBP) Experimental Results:  Experimental Results TCP Throughput (Mbps) Conclusions:  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 Thank You!:  Thank You! Contributions:  Contributions Provides a working implementation of signal-strength-aware AODV Demonstrates the functionality and performance of the protocol Presents empirical measurements of TCP throughput in multi-hop wireless ad hoc network Evaluates the effectiveness of TCP rate-based-pacing in an experimental setting

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