Several days we received a patch for SCTP support in OpenSER, courtesy of Connecticut College. Since then I investigated a bit more about SCTP but I was not able to find many SIP devices supporting it. Indeed, it is rather new transport protocol (although has been published as RFC in 2000, there is still some work in progress), but seems to be suitable for signaling protocols, as SIP is.
It is a reliable transmission protocol, like TCP, but brings many of UDP goodies (mainly one to many communication model). The overhead of maintaining SCTP connections for server is low, it can take care of fragmentation inside the protocol, unlike UDP which faces IP fragmentation. Besides that, encription can be achieved via TLS-SCTP, which was not possible with UDP.
I am looking at SCTP as a viable solution for carrying SIP messages, as they get bigger and bigger in IM&Presence. TCP reduces a lot the capacity of a SIP server, the resources needed to mange a TCP connection with each online subscriber is huge comparing with UDP and SCTP.
SCTP seems to be used mainly in trunking, with SIP-T and SIP-I, but shouldn’t be taken more and more in consideration for SIP phone devices?
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