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RR-TCP: A Reordering-Robust TCP with DSACK

Zhang, M; Karp, B; Floyd, S; Peterson, L; (2003) RR-TCP: A Reordering-Robust TCP with DSACK. In: Proceedings of the 11th IEEE International Conference on Network Protocols: ICNP 2003. (pp. 95 - 106). IEEE Computer Society: Los Alamitos, US.

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Abstract

TCP performs poorly on paths that reorder packets significantly, where it misinterprets out-of-order delivery as packet loss. The sender responds with a fast retransmit though no actual loss has occurred. These repeated false fast retransmits keep the sender's window small, and severely degrade the throughput it attains. Requiring nearly in-order delivery needlessly restricts and complicates Internet routing systems and routers. Such beneficial systems as multi-path routing and parallel packet switches are difficult to deploy in a way that preserves ordering. Toward a more reordering-tolerant Internet architecture, we present enhancements to TCP that improve the protocol's robustness to reordered and delayed packets. We extend the sender to detect and recover from false fast retransmits using DSACK information, and to avoid false fast retransmits proactively, by adaptively varying dupthresh. Our algorithm is the first that adaptively balances increasing dupthresh, to avoid false fast retransmits, and limiting the growth of dupthresh, to avoid unnecessary timeouts. Finally, we demonstrate that TCP's RTO estimator tolerates delayed packets poorly, and present enhancements to it that ensure it is sufficiently conservative, without using timestamps or additional TCP header bits. Our simulations show that these enhancements significantly improve TCP's performance over paths that reorder or delay packets.

Type:Proceedings paper
Title:RR-TCP: A Reordering-Robust TCP with DSACK
ISBN:0769520243
DOI:10.1109/ICNP.2003.1249760
Publisher version:http://dx.doi.org/10.1109/ICNP.2003.1249760
Keywords:reordering, TCP, adaptive, dupacks, dupthresh, congestion, control
UCL classification:UCL > School of BEAMS > Faculty of Engineering Science > Computer Science

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