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

October 5, 2004MASCOTS 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

October 5, 2004MASCOTS Ad hoc Network

October 5, 2004MASCOTS 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)

October 5, 2004MASCOTS AODV Operation Source Destination RREQ RREP Data RERR Data

October 5, 2004MASCOTS 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.

October 5, 2004MASCOTS 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.

October 5, 2004MASCOTS AODV Modules

October 5, 2004MASCOTS 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.

October 5, 2004MASCOTS Variation of Signal Strength

October 5, 2004MASCOTS 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.

October 5, 2004MASCOTS Locally Generated Packet NF_IP_LOCAL_OUT Packet

October 5, 2004MASCOTS Experimental Environment  Redhat Linux 8.0 (kernel )  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

October 5, 2004MASCOTS Testbed Topology Node1 Running netserver Node2 Node3 Node4 Node5 Running netperf Airopeek Sniffer

October 5, 2004MASCOTS Routing Discovery Time (ms) HopsMinMedianMaxMeanStdDev , ,

October 5, 2004MASCOTS Round Trip Time

October 5, 2004MASCOTS TCP Throughput (Mbps) HopsStationarySlowMediumFast Slow Speed – 0.33 m/s Fast Speed – 1.0m/s

October 5, 2004MASCOTS Routing Overhead HopsData PacketsControl PacketsOverhead Ratio 224, , , , , , , , , , , , , , ,

October 5, 2004MASCOTS 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 , October 2000

October 5, 2004MASCOTS TCP rate-based-pacing Packet

October 5, 2004MASCOTS Simulations Results (TCP-RBP)

October 5, 2004MASCOTS Experimental Results Num HopsTCP RenoRBP TCP MeanSDevMeanSDev TCP Throughput (Mbps)

October 5, 2004MASCOTS 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!

October 5, 2004MASCOTS 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