CNR ExploRA

Rapporto tecnico, 2004, ENG

Comparison of FEC types to optimise the efficiency of TCP connections over AWGN satellite channels

Celandroni N.

ISTI-CNR, Pisa, Italy

The optimization of the end-to-end throughput of a TCP connection over geostationary satellite links is a challenging research topic. This is because the high delay-bandwidth product, together with a non-negligible random loss of packets, are conditions which differ considerably from the original environment for which TCP was originally designed. As a result TCP performance is significantly impaired by the channel bit error rate. The literature is full of suggestions for improving TCP goodput, most based on modifications of the protocol itself. We only investigated the application of different FEC (forward error correction) types for TCP goodput optimization, leaving the end-to-end protocol unaltered. Using a method midway between analysis and simulation to evaluate the throughput of a TCP long-lived connection, we first disprove the widely-held opinion that the packet loss rate, introduced by errors on the channel, should be negligible with respect to that caused by congestion. We then compare physical-level FEC techniques, such as convolutional encoding/Viterbi decoding, Reed Solomon, link-level erasure codes and their combinations, over a wide field of signal to noise conditions of the satellite channel. Furthermore, the case of multiple TCP connections sharing the same link is presented as well.