The Eifel retransmission timer

Abstract

We analyze two alternative retransmission timers for the Transmission Control Protocol (TCP). We first study the retransmission timer of TCP-Lite which is considered to be the current de facto standard for TCP implementations. After revealing four major problems of TCP-Lite's retransmission timer, we propose a new timer, named the Eifel retransmission timer , that eliminates these. The strength of our work lies in its hybrid analysis methodology. We develop models of both retransmission timers for the class of network-limited TCP bulk data transfers in steady state. Using those models, we predict the problems of TCP-Lite's retransmission timer and develop the Eifel retransmission timer. We then validate our model-based analysis through measurements in a real network that yield the same results.

A machine learning framework for TCP round-trip time estimation

“…Our experimental results show that RTT predictions using the proposed technique are considerably more accurate when compared to TCP's original RTT estimation algorithm and the well-known Eifel [4] timer. We then evaluate how this increased accuracy affects network performance.…”

“…Trace-driven simulations reported in [6] to evaluate different RTT estimation algorithms show that the performance of the estimators is dominated by their minimum values and is not influenced by the RTT sample rate [6]. This last conclusion was challenged by the Eifel estimation mechanism [4], one of the most cited alternatives to TCP's original RTT estimator; Eifel can be used to estimate the RTT and set the RTO. Eifel's proponents identify several problems with TCP's original RTT estimation algorithm, including the observation that a sudden decrease in RTT causes RTTVAR and consequently the RTO to increase unexpectedly c .…”

“…We implemented both the fixed share experts algorithm and the Eifel algorithm [4] in the Linux kernel version 2.6.28.3. We modified the function tcp_rtt_estimator() to return the output of the RTT as evaluated by either of the RTT prediction algorithms.…”

“…We modified the function tcp_rtt_estimator() to return the output of the RTT as evaluated by either of the RTT prediction algorithms. Our implementation of the Eifel algorithm, to the best of our knowledge, is faithful to the algorithm described in [4] for predicting the RTT and setting the RTO.…”

Effect of Delays on TCP Performance

“…This is because the TCP retransmission timeout is updated dynamically based on the smoothed mean and variance of RTT samples of the connection. The TCP retransmission timer can be considered overly conservative [17]. However, TCP does not react well to large delays (several times the usual RTT) that occur suddenly.…”