[asterisk-bugs] [Asterisk 0011614]: [patch] T38 support for SendFax/ReceiveFax

[noreply at bugs.digium.com]

A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=11614 
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Reported By:                dimas
Assigned To:                file
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Project:                    Asterisk
Issue ID:                   11614
Category:                   Addons/New Feature
Reproducibility:            always
Severity:                   feature
Priority:                   normal
Status:                     assigned
Asterisk Version:            SVN 
SVN Branch (only for SVN checkouts, not tarball releases):  trunk 
SVN Revision (number only!): 497 
Disclaimer on File?:        N/A 
Request Review:              
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Date Submitted:             12-21-2007 06:57 CST
Last Modified:              01-12-2008 10:32 CST
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Summary:                    [patch] T38 support for SendFax/ReceiveFax
Description: 
Adding T38 support to SendFax/ReceiveFax applications. See Additional
Information for details.

There are two patches:
* appfax-v3.patch for asterisk-addons/trunk rev 497 - modifications to the
fax application
* asterisk-t38.patch - temporary (see below) patch for asterik/trunk
revision 94396

!IMPORTANT NOTE! This patch is considered work in progress because it
depends on not yet finished feature of Asterisk - ability to request T38
reinvite on a SIP channel.
Currently, the patch adds this ability itself (asterisk-t38.patch) but it
adds it in a very rude way. It is clearly a hack. When file finishes his
t38insanity branch and Aterisk will get official way of requesting
re-invite, I will update app_fax to use that way instead and
asterisk-t38.patch won't be needed anymore.

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---------------------------------------------------------------------- 
 irroot - 01-12-08 10:32  
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the way i understand it is the translator sits between the channels and
passes data back and forward to the channels through there read/write
bits.

The codec translators operate on frames that may or may not be RTP
Zap/mISDN certainaly is not RTP and translation takes place a better
example is perhaps woomera that uses sockets and can translate ...

this is what app_fax does but to/from a file to the T38 device it
reads/writes frames on the channel.

chan_sip will need to be updated to set the codecs on the reinvite ...

but if app_fax can read and write data from a T38 device there should be
no reason for dial to be able to brige a T30 <-> T38 call via zap and
friends.

the structure of a translator seems to lend itself to this there is a
private structure that will be able to store t38_gateway_state_t as it uses
a buffer the call back t38_tx_packet_handler is suited to this ...

if the t38_gateway_state is null (pvt) init the T38 gateway (will be nice
to use settings from chan_sip ie fill/ecm) frames will be read on both
sides using t38_core_rx_ifp_packet/t38_gateway_rx and sent via
t38_gateway_tx and the callback used to init the T38 gateway.

if app_fax is reading and writing T38 frames why cant they be transcoded
on any channel ... 

sure it can be hacked into app_dial this will not be accepted by digium
(similar approach to callweaver) or a new T38Dial app can be knocked out
(not ideal) if im on the right track then a addition of AST_FORMAT_T38FAX
in frame.h some small changes in chan_sip to set the format to
AST_FORMAT_T38FAX in the reinvite/SDP and asterisk should take care of the
rest. 

Issue History 
Date Modified   Username       Field                    Change               
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01-12-08 10:32  irroot         Note Added: 0076805                          
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