Jan Janak, one of project’s core developers, conducted a very interesting research project regarding energy efficiency of VoIP systems during 2010, a collaboration between iptel.org and Columbia University.

The team used the source code from sip-router.org GIT repository from January 2010, which corresponds to Kamailio (former OpenSER) and SER v3.0. The latest stable series v3.1 shares the same internal architecture with v3.0.

As part of the research work, Jan could also gather some figures about capacity and performances of v3.0 with a quite complex configuration file (involving authentication and NAT traversal as well).

You can read the paper about energy efficiency at:

The draft notes about capacity and performances of v3.0 are available at:

Some interesting results:

  • one instance of SIP server with 500 000 online users (mixed users – behind and not NAT routers) – consumed energy 210W
  • one instance of SIP server with 1 000 000 online users (no NAT involved) – consumed energy 190W
  • on a 32-bit machine with 4GB of memory and with 2.5GB reserved for SIP server, the server could support 43 000 simultaneous TLS connections – consumed energy 209W
  • one SIP server instance with 80 000 permanent TCP connections, the SIP server could still handle at least 1000 requests per second and a connection arrival rate of 1000 new connections per second, done for 20 000 new connections. CPU load generated by the SIP server was from 6% to 8%.

I added a new section to the draft notes to list the enhancements done for the latest stable release (v3.1.x) that contribute to performance improvements, like asynchronous TLS, fine tuning of memory for TLS connections and raw UDP sockets.