This paper compares different techniques for improving TCP performance and evaluates them in the context of wireless links. The main 3 categories that they evaluated were end-to-end protocols, link layer protocols, and also split connection protocols. The results of the paper showed that link layer protocols were the most beneficial if they are TCP aware.
Thinking back on the various papers we read about TCP, when it was designed, the major issues that we read about were mostly about contention and congestion. Several switch design papers proposed mechanism to deal with congestion, and combined with TCP's resend mechanism it would prevent contention. However, now that we're using TCP over a very lossy link, if the guarantee mechanism was only on the end points, then if the link is lossy, we would possibly need to resend over and over again because the probability of packet loss is high in the middle of transit. Thus, intuitively, it's more beneficial to implement recovery services also at the link layer because of the lossy attributes at each link (back to the end to end argument). All in all, a comparison of different mechanisms for TCP over wireless links confirmed the intuition.
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