If you are new to the world of playing with SIP servers, you may not realize there are two different variations of the same basic platform. I have previously published an OpenSER tutorial however there is another SIP server called SER.

In September of 2001 Andrei Pelinescu at the Fraunhofer Fokus research institute in Berlin, Germany started work on SER. By the fall of 2002 the SIP Express Router (SER) project was released open source under the GPL license.

By 2003, SER has become a leading open-source SIP proxy server and is quickly adopted by many SIP-based services, FWD and sipphone to name a couple. Come 2004 SER is a full fledged SIP server that was adopted by numerous forward looking VoIP Providers.

Citing different views, polices about contributions and release cycles, in June 2005 two core SER developers and one main contributor to the SER project elected to start the OpenSER project by creating a fork of the SER project, which is allowed under the GPL.

After only one and half years, the OpenSER project had over 80 contributors and 20 regular developers. They had deployed a very aggressive release schedule in an effort to move the development forward as quickly as possible.

Ever since OpenSER has made significant changes to the original SER architecture and additional modules have been deployed, which extend OpenSER’s abilities into the other areas of SIP, including presence and additional scripting abilities.

It is my understanding that the SER project has chosen to limit the amount of community contributions and has focused more on creating commercial, binary only modules — meaning if you find a problem you don’t have the source to fix the problem yourself.

If you are just getting started with running your own openser sip server, I recommend you choose OpenSER v1.1.1. OpenSER v1.2 has made very significant changes, some of which seems to have caused some instability issues, at least for me.

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SER/OpenSER Configuration Wizard
OpenSER and Asterisk Training
OpenSER Code Hack: Calling Stored Procedures
Unexpected Behavior With OpenSER When Using TLS and TCP
VoIP Blog