Performance Benefits of Avoiding Head-of-Line Blocking in SCTP

Mitigating the effects of head-of-line blocking (HoLB) was one of the major reasons the IETF SIGTRAN working group developed SCTP, a new transport protocol for PSTN signaling traffic, in the first place. However, studies of the impact of HoLB blocking on TCP and SCTP have given ambiguous results as to whether HoLB has, in fact, any significantly deteriorating effect on transmission delay. To this end, we have carried out a detailed experimental study on the quantitative effects of HoLB. Our study suggests that although HoLB could indeed incur a substantial delay penalty on a small fraction of the messages in an SCTP session, it has only a marginal impact on the average end-to-end transmission delay. We only observed improvements in the range of O% to 18% in average message transmission delay of using unordered delivery as compared to ordered delivery. Furthermore, there was a large variability in between different test runs, which often made the impact of HoLB statistically insignificant