On the combined effects of Bit Error Rate and delay-distribution tail on TCP performance

The original design of the TCP retransmission timeout was implemented ignoring the recent measurement studies on the dynamics and features of network traffic and delay. Such studies have reported the highly variable characteristics of network delay, considered to be heavy-tailed distributed. Accordingly, depending on the heavy characteristics of the tail of the delay distribution, the actual implementation of TCP's retransmission timeout might be too conservative, or rather insufficient. This work aims to assess the optimal design of the retransmission timeout when heavy-tailed delay profiles are present. In our experiments, we have considered the case of low-bit error rate scenarios typical from wired networks as well as the high bit-error rates, typical from wireless networks. We show that the current implementation of the retransmission timeout is in broad terms very conservative, except in cases with extremely heavy tails.