[asterisk-bugs] [Asterisk 0012437]: Asterisk negotiates only T.38 when answering even if the other end offers audio

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=12437 
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Reported By:                marsosa
Assigned To:                
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Project:                    Asterisk
Issue ID:                   12437
Category:                   Channels/chan_sip/T.38
Reproducibility:            always
Severity:                   major
Priority:                   normal
Status:                     confirmed
Asterisk Version:           1.4.18 
SVN Branch (only for SVN checkouts, not tarball releases): N/A 
SVN Revision (number only!):  
Disclaimer on File?:        N/A 
Request Review:              
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Date Submitted:             2008-04-14 08:31 CDT
Last Modified:              2008-10-20 08:12 CDT
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Summary:                    Asterisk negotiates only T.38 when answering even if
the other end offers audio
Description: 
One of our gateways (audiocodes mp-118) offers ulaw,g729 and t.38 when an
incoming call is sent to asterisk, and asterisk answer() with t.38 only,
instead of using ulaw. T.38 is enabled on the gateway because this is
needed for reinvites, if i disable it, the call works ok but fails later
when the ata wants to do reinvite for receiving faxes with t.38 '488 not
acceptable'.
The main problem here is that, after answering with t.38, asterisk sends
invites with t.38 only to the ip phones, and they rejected with not
acceptable.
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 (0093966) csabka (reporter) - 2008-10-20 08:12
 http://bugs.digium.com/view.php?id=12437#c93966 
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@gerd1000, I think they know it, just they need the T.38 funcionality as
well.

Of course it is not so nice, that in the initial SDP the T38 codec as well
coming, but I think this shouldn't broke asterisk's normal call. I think
asterisk should ignore the initial SDP T.38, and only in case of fax should
be accepted.

I have tested the newest firmware of Patton (5.x) and It works fine with
asterisk (it sends t.38 sdp only when fax transmission detected...).