Can ECN Be Used to Differentiate Congestion Losses from Wireless Losses?

TCP was designed and tuned to work well on networks where losses are mainly congestion losses. The performance of TCP decreases dramatically when a TCP connection traverses a wireless link on which packets may be lost due to wireless transmission errors. Explicit Congestion Notification (ECN) is known as an effective mechanism that can be used with Active Queue Management (e.g. RED) to control congestion on wired networks. ECN is used by routers to signal incipient congestion to end points. We evaluate the ability of ECN signals as a tool to distinguish between congestion losses and wireless losses. The occurrence of an ECN signal is a bad predictor of imminent congestion losses. We conclude that when TCP senders are responsive to ECN signals, congestion losses appear to be as random as wireless losses. Based on this observation, we propose a simple technique, TCP-Eaglet, to improve TCP over wireless for ECN responsive flows. Simulations results show an improvement in throughput of up to 60%.