Making SCTP More Robust to Changeover

We present a problem in the current SCTP (RFC2960) specification that results in unnecessary retransmissions and “TCP-unfriendly” growth of the sender’s congestion window during certain changeover conditions. We first illustrate the problem using an example scenario. To gain insight into the ambient conditions under which cwnd overgrowth can be observed, we present an analytical model of this problem. As solutions, we then propose two changeover aware congestion control (CACC) algorithms which incorporate changeover awareness in SCTP’s congestion control mechanism: Conservative CACC (CCACC), and Split Fast Retransmit CACC (SFR-CACC). Using ns-2 simulations, we validate the model and evaluate the recommended solution. Based on the analysis, we make recommendations for modifications to SCTP.