Evaluation of retransmission strategies in a local area network environment

Abstract

We present an evaluation of retransmission strategies over local area networks. Expressions are derived for the expectation and the variance of the transmission time of the go-back-n and the selective repeat protocols in the presence of errors. These are compared to the expressions for blast with full retransmission on error (BFRE) derived by Zwaenepoel [Zwa 85]. We conclude that go-back-n performs almost as well as selective repeat and is very much simpler to implement while BFRE is stable only for a limited range of messages sizes and error rates. We also present a variant of BFRE which optimally checkpoints the transmission of a large message. This is shown to overcome the instability of ordinary BFRE. It has a simple state machine and seems to take full advantage of the low error rates of local area networks. We further investigate go-back-n by generalizing the analysis to an upper layer transport protocol, which is likely to encounter among other things, variable delays due to protocol overhead, multiple connections, process switches and operating system scheduling priorities.