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SIP as VoIP service in qaul.net

Mathias Jud
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I met a VoIP specialist this week and we discussed the pros and cons of
SIP protocol for VoIP.

General:
SIP is a very traditional and stable protocol and would not be a bad choice.

The biggest downside of SIP:
As SIP was invented in the old telephony days, there are two separate
channels for communication: the signalling channel and the
voice-voice-stream channel. Those channels are independent and use
different protocols. This has the big downside that one never knows if
the other stream is making it through the network too. So the most
relevant critique on SIP is that you can make all the signalling and
handshakes to establish a call, but the sound stream never makes it
through the network as it is using a different channel with a different
protocol.

Other problems:
* Some things in the SIP specification are not 100% clear and are
therefore not always compatible from implementation to implementation.

Questions:
Do we want to be compatible with other SIP infrastructure?


Just in case we wanted to build our own solution, here a few tips:

* use the same channel for signalling and voice data.
* Start with only one codec (to ease codec negotiation)
* implement a SIP compatible/inspired signalling.