Analysis of TCP latency over wireless links supporting FEC/ARQ-SR for error recovery

We study in this paper the performance of TCP over a wireless link implementing hybrid FEC/ARQ-SR at the link layer. The study is done by simulating a large number of TCP transfers over a wireless link showing Bernoulli errors. We are motivated by how to tune link-level error recovery, e.g. amount of FEC, persistency of ARQ, so as to minimize the latency of TCP. We provide results for different physical characteristics of the wireless link (delay, error rate), different traffic loads and different file sizes. Our main finding is that the latency of TCP always improves with the persistency of ARQ, except for some extreme cases where the delay is large, files are small, and the loss rate is low. When adding FEC, the latency of TCP improves then deteriorates, and the deterioration is more pronounced in the case of large files, high loss rate and small delay. Another finding of our study is that with the hybrid mechanism, the wireless link is able to carry more traffic than when FEC and ARQ-SR are separately used.