Recently I was curious to find out what settings I could change with Ubuntu TCP, so I looked through the documentation. One option enables the 'Westwood+' algorithm. That looked interesting, so I wanted to find out why one should use Westwood+ instead of the default algorithm.
The man page says that Westwood+ has 2 advantages: 1) significantly increased fairness with Reno in wired networks, and 2) increased throughput over wireless links. With Westwood+, the sender dynamically sets SSTHRESH and CWND based on an end-to-end bandwidth estimation.
Fairness will be better because when a sender realizes that its sending rate is decreasing, it will react by more severely decreasing CWND, thus allowing for a faster rate convergence.
In wireless networks, loss is often due to interference, and Reno acts as if any loss is due to congestion. When a Westwood+ connection gets a duplicate ACK, it will take the steady bandwidth into consideration when it decrements CWND, and as a result the throughput will not fall as Reno's would.
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