Decoupling of TCP Congestion Control and Loss Recovery for Wireless Network

Y.S. Liaw, Q. Yin, J. Liew, and W. Seah (Singapore)

Keywords

TCP performance, wireless network, SACK, RED, ECN, loss recovery.

Abstract

TCP’s performance over wireless network is severely degraded by the frequent losses over the lossy wireless channel. TCP is unable to differentiate between congestive and non-congestive (i.e. BER) losses, and hence it indiscriminately invokes congestion control to reduce its sending rate whenever loss occurs. Explicit Congestion Notification (ECN) enables network router to signal congestion explicitly to the TCP sender, and hence allows TCP to decouple its congestion control from loss recovery. In this paper, we proposed that TCP’s congestion control be decoupled from its loss recovery based on ECN feedback, and an enhanced Selective Acknowledgement (SACK) be used to recover losses. We call this ECN-based TCP. We show it greatly enhances TCP performance over wireless under various network conditions, and with proper setting and some modifications to Random Early Detection (RED)’s marking probability function, it is no more aggressive than traditional TCP that also relies on losses as congestion feedback. Additionally, we suggest an additional field to determine whether all the routers along the path are ECN-enabled. This allows the deployment of ECN-based TCP in partial ECN network possible.

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