Analysis of TCP over wireless links implementing link-level hybrid FEC/ARQ-SR for error recovery
Since the TCP protocol uses the loss of packets as an indication of network
congestion, its performance degrades over wireless links, which are
characterized by a high bit error rate. Different solutions have been
proposed to improve the performance of TCP over wireless links, the most
promising one being the use of a hybrid model at the link level combining
FEC (Forward Error Correction), ARQ-SR (Automatic Repeat Request with
Selective Repeat), and an in-order delivery of packets to IP. The drawback
of FEC is that it consumes some extra bandwidth to transmit the redundant information. ARQ-SR consumes extra bandwidth only when packets are lost, its drawback is that it increases the round-trip time (RTT), which may deteriorate the performance of TCP. Another
drawback of ARQ-SR is that a complete packet can be retransmitted to correct
a small piece of errored
data. We study in this work the performance of TCP over a wireless link
implementing hybrid FEC/ARQ-SQ. The study is done by simulating and modeling
TCP transfers over wireless links 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 maximize the performance of TCP.
We provide results for different physical characteristics of the wireless
link (delay, error rate) and for different traffic loads.