[asterisk-dev] UAC leg cancel on early media / MoH.

[Alex Balashov]

Hi folks,

I ran into a problem where SIP calls were being dumped straight into a queue 
without being Answer()'d.  Music on hold from the queue was being
generated via 183 Session in Progress + SDP, i.e. early media / in-band
ringback.

After about 3 minutes of this, all SIP UACs I tested with would CANCEL
the leg, resulting in the caller being dropped out of the queue.  This
happened with a Cisco 7960 (SIP image), Polycom 501, and tne X-lite
softphone.

Anyway, I fixed the problem by simply furnishing an Answer() in the
dial plan, of course, but I was curious as to why SIP UACs react this
way.  I could not find any explanation for this in reviewing the
various SIP T-timers in the RFC, or the various RFCs and drafts dealing with 
early media.

In other words, I see no reason why the calling SIP agent should terminate the 
call after 3 minutes since the 183 + SDP have elapsed.  What gives?

Thanks,

--
Alex Balashov
Evariste Systems
Web    : http://www.evaristesys.com/
Tel    : +1-678-954-0670
Direct : +1-678-954-0671