Understanding Congestion Control in Multi-hop Wireless Mesh Networks Sumit Rangwala, Apoorva Jindal, Ki-Young Jang, Konstantinos Psounis, and Ramesh Govindan University of Southern California Problem Description: Congestion Control in 802.11x Wireless Networks What is wrong with TCP? Congestion is a Neighborhood Phenomenon 1 2 3 4 5 6 7 8 9 All incoming and outgoing links from the sender, receiver, all the neighbors of sender, and all the neighbors of receiver 1 3 2 4 5 6 7 8 9 10 Link Neighborhood Link ≡ sender-receiver pair Stack Topology TCP starves the middle flow Proposed Solution: Neighborhood-Centric Transport WCP: AIMD Based Transport Protocol WCPCap: Explicit Rate Control Protocol Neighborhood congestion detection Any link in the link neighborhood is congested Neighborhood RTT Maximum RTT of all flows traversing a link neighborhood End-to-end behavior Reduce a flow’s rate if at least one of the traversed neighborhoods is congested Use the maximum RTT among all traversed neighborhood RTTs to “clock” the rate changes Neighborhood per flow rate Calculates sustainable fair rate for each flow in a link neighborhood Requires spare capacity calculation End-to-end behavior Flows send at a rate that is minimum of the rate assigned at each traversed neighborhood Evaluation: WCP fairer than TCP, WCPCap achieves max-min fairness 1 2 3 4 5 6 7 8 9 Diamond Topology Experimentation Setup Simulation Qualnet 3.9.5 802.11b with default parameters 11Mbps , no rate adaptation, 512 byte data packet Zero channel losses Buffer size: 64 packets Real World Experiments Click modular router on Linux Same code as in simulation Simulations: Diamond Topology 9 8 4 1 2 3 11 10 5 6 7 Simulations: Stack Topology Chain-cross Topology Simulations: Chain-cross Topology 10 26 14 12 13 15 22 24 23 16 11 20 19 17 18 Arbitrary Topology Real-world Experiments: Stack Topology Real-world Experiments: Arbitrary Topology