[asterisk-bugs] [Asterisk 0016756]: app_fax doesn't receive fax with T.38

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=16756 
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Reported By:                viniciusfontes
Assigned To:                
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Project:                    Asterisk
Issue ID:                   16756
Category:                   Applications/app_fax
Reproducibility:            always
Severity:                   major
Priority:                   normal
Status:                     feedback
Asterisk Version:           SVN 
JIRA:                       SWP-845 
Regression:                 No 
Reviewboard Link:            
SVN Branch (only for SVN checkouts, not tarball releases): N/A 
SVN Revision (number only!):  
Request Review:              
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Date Submitted:             2010-02-02 13:56 CST
Last Modified:              2010-02-05 04:38 CST
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Summary:                    app_fax doesn't receive fax with T.38
Description: 
When I try to receive a fax from a provider that supports T.38 using
ReceiveFAX() provided by app_fax.so, the fax transmission ends prematurely
with an error.

What happens (according to Kevin Fleming) is this:

"In this call, Asterisk sent a re-INVITE to T.38 mode
from audio mode, the provider accepted it, and then Asterisk
acknowledged it. Immediately afterwards, Asterisk sent a re-INVITE
*back* to audio mode, which the provider accepted (and included T.38
capabilities in their response). Because of this, the FAX reception
process failed since the T.38 session was destroyed."

For reference, here is a link to the original mailing list thread: 
http://lists.digium.com/pipermail/asterisk-users/2010-February/244136.html
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 (0117773) raivisr (reporter) - 2010-02-05 04:38
 https://issues.asterisk.org/view.php?id=16756#c117773 
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according to itu-t t.38 recommendation remote end announces maximum
datagram it is able to accept with T38FaxMaxDatagram attribute, that means,
that your end announces to far end that it is able to receive datagrams as
big as 1400 bytes and your provider announces that it is able to receive
datagrams as big as 610 bytes. when using maxdatagram=180 you tell your end
to forcibly use smaller datagram than far end announced when sending to it,
which is ok. if you turned on full logs, you would see how chan_sip tells
that it used overridden value. 

Issue History 
Date Modified    Username       Field                    Change               
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2010-02-05 04:38 raivisr        Note Added: 0117773                          
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