Equation-based congestion control has been a promising alternative to TCP for real-time multimedia streaming over the Internet. However, the behavior of equation-based congestion control as exemplified by TFRC (TCP Friendly Rate Control, RFC3448) is very much unknown in MANET, where the degrees of network dynamics are far more diverse than those in wireline networks. For instance, wireless link’s bandwidth can vary greatly in very small time-scale, due to the randomness in channel contention and signal fading. Packet loss can occur due to congestion-related queuing loss, wireless-related random loss, and mobility-related routing loss. Under this environment, it is unclear whether TFRC will be able to compete fairly with TCP, and if not, what are the factors that contribute to such behavior.
In this project, we study the behavior of TFRC in MANET via ns-2 simulations. Our finding indicates that, while TFRC is able to maintain smooth rate change, its throughput is often “beaten” down by competing TCP flows to a certain degree, especially under heavy background traffic and dynamic topology conditions. To explain TFRC’s conservative behavior, we analyze several factors including loss rate discrepancy, inaccuracy of loss rate prediction, and lack of auto-correlation in MANET’s loss process. We also explore TFRC’s response to the tuning of its loss event interval estimator, and show that its conservative behavior cannot be completely corrected. Our study shows the limitations of applying TFRC to the MANET domain, and reveals some fundamental difficulties in doing so.
- Kai Chen, Klara Nahrstedt, Limitations of Equation-based Congestion Control in Mobile Ad hoc Networks, in Proc. of International Workshop on Wireless Ad Hoc Networking (WWAN 2004) in conjuction with ICDCS-2004, Tokyo, Japan, March, 2004.
- Kai Chen, Klara Nahrstedt, Limitations of Equation-based Congestion Control in Mobile Ad hoc Networks, accepted to International Journal of Wireless and Mobile Computing (IJWMC), special issue on Wireless Ad Hoc Networking, Inderscience Publishers . pdf