The Sensitivity of TCP to Sudden Delay Variations in Mobile Networks

This paper studies the impact of variable transmission delays on the Transmission Control Protocol (TCP). Sudden delay variations, which are not uncommon in mobile networks, may degrade the performance since they may cause spurious TCP timeouts. The most important parameter in this context is the TCP retransmission timer. In this paper, we analyze TCP’s round-trip time estimation for bulk data traffic over wireless links. The main contribution is a new analytical model that accurately predicts the timeout duration from given network parameters. As a first result, the model shows that the round-trip time sampling rate has a significant impact on the timer characteristics. Therefore, the standardized estimation algorithm does not harmonize well with timestamp-based measurement. Second, we quantify the risk of spurious TCP timeouts triggered by changing round-trip times, in particular long off periods. We conclude that delay variations are only critical when they are on the order of seconds.