1. 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 x 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