[asterisk-bugs] [Asterisk 0011873]: [patch] minimal API to control SIP T38 from application

[noreply at bugs.digium.com]

A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=11873 
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Reported By:                dimas
Assigned To:                
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Project:                    Asterisk
Issue ID:                   11873
Category:                   Channels/chan_sip/T.38
Reproducibility:            always
Severity:                   feature
Priority:                   normal
Status:                     new
Asterisk Version:           SVN 
SVN Branch (only for SVN checkouts, not tarball releases):  trunk 
SVN Revision (number only!): 100974 
Disclaimer on File?:        N/A 
Request Review:              
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Date Submitted:             01-29-2008 18:21 CST
Last Modified:              02-05-2008 14:03 CST
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Summary:                    [patch] minimal API to control SIP T38 from
application
Description: 
file,
this is minimalistic implementation of API I need for T38 app_fax. I took
your idea to control channel T38 switchover with AST_FRAME_CONTROL*
messages and added other facilities I have already emailed you about.
Please see Additional Infor for detailed information about changes.

I believe this patch is small enough and can be commited and be improved
later if needed. Adoption of this patch would allow me submitting final
version of app_fax patch with T38 support which would be good addition to
1.6.
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---------------------------------------------------------------------- 
 dimas - 02-05-08 14:03  
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Second attempt attached.
Hope that http://bugs.digium.com/view.php?id=1 and
http://bugs.digium.com/view.php?id=2 are handled now.

Regarding the 4 - it was briefly discussed on IRC but I explain here for
records:
For the fax application, non-blocking T38 negotiation is the best way to
go. This is because you never know if remote party will accept or reject
your offer. Or will it answer at all. Because of this algorithm of the fax
receiver is something like:

* Do the "regular" aka "audio" fax reception (inband)
* At the same time try negotiating T38 with remote side.
* If (and only if) remote side agrees on T38, stop audio transmittion and
switch to T38. Otherwise continue in the audio mode.

Also, I do not use setoption at the moment. Only queryoption is used - to
get _current_ state of T38 on the channel. This is because fax application
does not know in what environment it starts - probably T38 was already
negotiated before starting app_fax. After fetching initial status, app_fax
does NOT do queryoption repeatedly - insted it gets T38 statys updates from
CONTROL frames. 

Issue History 
Date Modified   Username       Field                    Change               
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02-05-08 14:03  dimas          Note Added: 0081719                          
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