WTCP - Performance Enhancements

Performance Enhancements

Instead of replacing TCP completely, WTCP works with it to enhance TCP's performance over wireless. It accomplishes this by handling the negative effects of the wireless channel, including high bit error rates that are known to occur in bursts over the wireless medium.

It detects wireless-related problems (such as lost or corrupted segments due to multipath fading or high BER) with the use of timeouts and duplicate acknowledgments. WTCP then attempts to mitigate the problem by retransmitting a lost segment only once, until it receives an acknowledgment back from the mobile host that it was received. Any other lost segments will have to wait in the WTCP's buffer until the first one is confirmed to have been received.

There are times when packets will sit in WTCP's buffer for many milliseconds. In order to avoid having either TCP end host go into its congestion avoidance mode, (due to TCP looking at a segment's timestamp and determining that it took a long time to arrive, therefore wrongly assuming it's due to congestion) WTCP uniquely hides the time spent by the packets at the WTCP proxy, so that the RTT estimation is not affected.

In one study on WTCP's performance in Wireless WANs, WTCP showed an improvement of 20%-200% over comparable TCP algorithms such as New Reno, Vegas, and Snoop.