SCTP Congestion Control: Initial Simulation Studies

This paper uses simulation studies to explore the behaviour of SCTP congestion control. Several possible variants of SCTP congestion control are identified and each is compared with the behaviour of Reno TCP, a well-known TCP variant. We identify three flaws in the current SCTP congestion control mechanisms. 1. Efficient recovery after a packet loss is only possible if SCTP generates the optional Gap Ack Blocks in SACK messages. 2. The SCTP fast retransmit procedure is vulnerable to being mistakenly triggered multiple times leading to under-utilization of the network during recovery and duplicate retransmissions of the lost packet. 3. The SCTP fast retransmit procedure must wait for half a window of data to be acknowledged before retransmitting a lost packet yielding a slow response to packet loss. We also provide suggested remedies for these flaws. Finally we demonstrate how SCTP congestion control mechanisms can cause a burst of packets after recovery from a packet loss.