TCP Westwood Simulation Studies in Multiple-Path Cases

Best-effort traffic has been the dominant traffic type in the Internet, and TCP has been playing the major role for carrying such traffic. Today, Internet is again moving toward more reliable and robust network services including QoS. Provisioning multiple paths as backup routes is one of the feasible solutions to designing fault-tolerant network. When multiple paths are selected, traffic transmission can be either flow-based or packet-based allocation to the multiple paths. The packet-based connection allocation usually shows a better load balancing effect and ease of flow management in the presence of network failures. However, it causes TCP segments to be distributed over delay-different multiple paths and to be delivered out-of-sequence. These out-of-sequence packet deliveries make TCP receiver generate many duplicate acknowledgments (ACKs), and TCP sender, in turn, misinterprets network congestion from the duplicate ACKs. In this paper, we expose the side effects of the multiple path deployment on TCP Reno and SACK performance. Also, based on simulation experiments, we shows that TCP Westwood effectively handles the multiple path situation and outperforms the other TCP flavors.