Most common use case of Asterisk is that of a Sip Server. User Agents register to it and can call each other. But have anyone though of using it as a sip user agent emulator? This is exactly what we are doing ! Our main product is written in java which needs to register to a Sip Service Provider, receive calls, play automated answers/forward calls and all kind of play around with the Call. We looked into various open source sip stack written in C / java. We kind of overlooked Asterisk as its known as a sip server! We were just exploring asterisk sip stack to see if we can somehow reuse it, but we were surprised to find out we can use Asterisk as it is without any modifications! Asterisk is written as a B2B UA (Back to Back User Agent) model (not so good for sip servers from performance point of view) but more than fine for us! You can register to your sip service provider as a user agent , answer calls, play messages, collect dtmf, make outgoing call and many other cool stuff! Asterisk real-time even takes this in another level where you can do the all these things dynamically! The best point is, you can write your logic in any language (in our case java) with AGI and AMI which is just TCP message based programming ! Wait, if you are using java, life is even better for you! Asterisk-java is a wonderful abstraction written on AGI/AMI so you don’t even need to bother about TCP programming. Hats off to open source community, It would take us a Year to accomplish what we have accomplished in 3 months with asterisk.
The free book “Asterisk: The Future of Telephony” is a great resource but I am surprised to see how little information is there on net about using Asterisk as a Sip User Agent emulator! Are we the only one who is using asterisk this way !!!???