NXG03-5: Head-of-line Blocking in TCP and SCTP: Analysis and Measurements

Many signaling protocols in IP networks need a protection against message loss, but they do not require a strict in-sequence data delivery. Since TCP provides reliable in-order transport, end-to-end delays may be unnecessarily increased due to head-of-line blocking. An alternative transport protocol is SCTP, which is optimized for signaling applications and provides mechanisms for reliable, partial-ordered or unordered message delivery. In this paper, we quantify the impact of head-of-line blocking on the response time of transaction-based signaling applications. In order to mitigate this problem, we compare different solutions based on TCP and SCTP. Both a new analytical model and measurements on state-of-the-art operating systems show to which extend SCTP can improve transport delays by leveraging transmission over multiple parallel streams or using unordered data delivery. Our analysis reveals that using one or multiple parallel TCP connections can result in much higher end-to-end delays, even for moderate packet loss probabilities. We also observe significant differences in the TCP performance of different operating systems.