SIP Connected before answer

Unanswered Question
steven.lass Tue, 09/30/2008 - 12:50

An FXS/FXO does not have setup acknowledge, progress indication, and etc. like ISDN and other signaling protocols. The ringing and connect are in-band, so the gateway will send back that is it connected as soon as it grabs the line.


CHRIS CHARLEBOIS Wed, 10/01/2008 - 09:48

I would imagine that the same thing happens with a SCCP phone, except that, when using SIP, the call is 'connected' with the H.323 or MGCP-controlled gateway while it is ringing. With SCCP, the phone only receives call control commands from the Call Manager.

steven.lass Wed, 10/01/2008 - 11:11

That is interesting. I would have expected the callmanager to map the signaling from the MGCP/H323 gateway to the equivalent SCCP and SIP messages.

I was not able to find a solution when I noticed this with an IOS gateway using a SIP trunk to an FXO. Your setup is different.

If you have loop-start FX, "supervisory answer dualtone" in the voice port config may change what is signaled to the callmanager, and possibly ba mapped differently.

Unfortunately, I no longer have any FXO lines in my lab, so I cannot try this myself.



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