[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:              2008-10-01 14:46 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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 (0093038) Hubguru (reporter) - 2008-10-01 14:46
 http://bugs.digium.com/view.php?id=12437#c93038 
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I am currently testing the Audiocodes Mediant 1000 Gateway with PRI and
firmware version 5.20A.027.004.

I'm getting the same results as I did with the dialogic.  The ac1000 sends
initial SDP with:
m=audio 6300 RTP/AVP 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=ptime:20
a=sendrecv
a=rtcp:6301 IN IP4 208.81.54.72
m=image 6302 udptl t38
a=T38FaxVersion:0
a=T38MaxBitRate:14400
a=T38FaxMaxBuffer:1024
a=T38FaxMaxDatagram:122
a=T38FaxRateManagement:transferredTCF
a=T38FaxUdpEC:t38UDPRedundancy

and Asterisk 1.4.21.1 responds back with only t38, no audio:
m=image 24420 udptl t38
a=T38FaxVersion:0
a=T38MaxBitRate:14400
a=T38FaxFillBitRemoval:0
a=T38FaxTranscodingMMR:0
a=T38FaxTranscodingJBIG:0
a=T38FaxRateManagement:transferredTCF
a=T38FaxMaxBuffer:122
a=T38FaxMaxDatagram:122
a=T38FaxUdpEC:t38UDPRedundancy

So I get this error at the CLI and the call drops:
ERROR[11074]: chan_sip.c:12399 handle_response_invite: Got error on T.38
initial invite. Bailing out. 

Issue History 
Date Modified    Username       Field                    Change               
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2008-10-01 14:46 Hubguru        Note Added: 0093038                          
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