Enhancing SCTP loss recovery: An experimental evaluation of early retransmit

To reduce cost and provide more flexible services, telecommunication operators are currently replacing traditional circuit-switched telephony networks with packet-switched IP networks. To support the stringent requirements of telephony signaling (SS7), the SIGTRAN working group of the IETF specified the transport protocol SCTP. SCTP was developed to overcome a number of problems that follow from using TCP for signaling transport. However, the design of SCTP was to a great extent still based on TCP, and some problems related to signaling transport were inherited. For example, the loss recovery mechanisms in SCTP are almost identical to those of TCP. This is a problem as signaling traffic has stringent requirements on timely message delivery. TCP was not designed to meet stringent requirements on timely message delivery, and therefore the loss recovery was not optimized for it. To optimize SCTP’s loss recovery for signaling traffic, we consider the loss recovery enhancement early retransmit. To make early retransmit even better suited for signaling traffic we propose a packet-based version, which was also recently included in the early retransmit specification. By experimentally evaluating this algorithm, we show that the packet-based early retransmit algorithm, in some cases, can reduce SCTP’s loss recovery time by 62%.