[asterisk-bugs] [Asterisk 0013976]: Invalid SDP attributes for boolean T.38 parameters (T38FaxFillBitRemoval, etc.)

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=13976 
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Reported By:                linulin
Assigned To:                
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Project:                    Asterisk
Issue ID:                   13976
Category:                   Channels/chan_sip/T.38
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     new
Asterisk Version:           SVN 
SVN Branch (only for SVN checkouts, not tarball releases):  trunk 
SVN Revision (number only!): 158959 
Disclaimer on File?:        N/A 
Request Review:              
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Date Submitted:             2008-11-26 10:39 CST
Last Modified:              2008-12-23 21:34 CST
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Summary:                    Invalid SDP attributes for boolean T.38 parameters
(T38FaxFillBitRemoval, etc.)
Description: 
SDP part with enabled T38FaxFillBitRemoval, T38FaxTranscodingMMR, and
T38FaxTranscodingJBIG parameters must look like:

  a=T38FaxFillBitRemoval
  a=T38FaxTranscodingMMR
  a=T38FaxTranscodingJBIG

instead of:

  a=T38FaxFillBitRemoval:1
  a=T38FaxTranscodingMMR:1
  a=T38FaxTranscodingJBIG:1

SDP part with disabled T38FaxFillBitRemoval, T38FaxTranscodingMMR, and
T38FaxTranscodingJBIG parameters must be empty instead of:

  a=T38FaxFillBitRemoval:0
  a=T38FaxTranscodingMMR:0
  a=T38FaxTranscodingJBIG:0

Otherwise interoperability issues with other T.38 implementations are
likely to arise.

Quoting ITU-T Recommendation T.38:

Section “D.2.3.1 UDPTL and TCP negotiation”:

“Note that options without values are boolean – their presence
indicates that they are valid for the session.”

Section “D.2.3.2 RTP negotiation”:

Those parameters are supplied in a semi-colon separated list of
“parameter” or “parameter=value” pairs using the “a=fmtp”
parameter defined in SDP; the “parameter” form is used for boolean
values, where presence equals “true” and absence “false”.

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 (0096923) arcivanov (reporter) - 2008-12-23 21:34
 http://bugs.digium.com/view.php?id=13976#c96923 
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putnopvut: Thanks for your comments.

I tried using my relaxed patch with IPcomms.net provider and the
non-standard attributes caused IPcomms to refuse re-invite with 488. Not
including the Gafachi-specific non-standard attributes fixed the problem.
While including the Gafachi-specific attributes could be controlled with
something like "t38pt_gafachi" parameter in the config file, I think I
agree with you that even doing that wouldn't be kosher. I will, therefore,
update the _relaxed patches to understand the non-compliant peers, but only
respond in a compliant manner. 

Issue History 
Date Modified    Username       Field                    Change               
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2008-12-23 21:34 arcivanov      Note Added: 0096923                          
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