The transport protocol for SIP can be chosen among UDP, TCP and SCTP based on the requirements of services and network conditions. How does the choice of TCP or SCTP affect the scalability and performance compared to UDP?

Measurement of the impact of TCP on SIP server scalability and performance

We experimentally analyzed the impact of using TCP as a transport protocol for a SIP server. We measured scalability of a TCP echo server and found that maintaining 400,000 active TCP connections on a Linux machine does not affect the response time. Then, we measured SIP server performance for three cases of TCP connection lifetime: transaction, dialog, and persistent. We compared these results to the UDP case and found no significant difference in the transaction response time at 500 calls/second load. However, sustainable sending request rate is lower for TCP than for UDP, since using TCP requires more message processing that makes queuing delays larger at the server implementing thread-pool model. Finally, we suggest how to implement a scalable SIP server using TCP.