[asterisk-bugs] [Asterisk 0013405]: [patch] T38 gateway

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=13405 
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Reported By:                dafe_von_cetin
Assigned To:                dwaynemh
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Project:                    Asterisk
Issue ID:                   13405
Category:                   Applications/app_fax
Reproducibility:            N/A
Severity:                   feature
Priority:                   normal
Status:                     confirmed
Asterisk Version:           SVN 
SVN Branch (only for SVN checkouts, not tarball releases):  trunk 
SVN Revision (number only!): 140548 
Disclaimer on File?:        N/A 
Request Review:              
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Date Submitted:             2008-08-30 16:44 CDT
Last Modified:              2008-12-18 03:29 CST
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Summary:                    [patch] T38 gateway
Description: 
Hi all,

I'm sending you patch containing new application app_faxgateway.c
("FaxGateway") which is able to mediate T30 to T38 and vice versa.
Feature is using spands library (I used spandsp-0.0.4pre18 and
spandsp-0.0.5pre4).

Best regards
Daniel.

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 (0096607) dafe_von_cetin (reporter) - 2008-12-18 03:29
 http://bugs.digium.com/view.php?id=13405#c96607 
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Hi All,

some of you spotted problem with fax gateway when gatewaying from NAT-ed
network  out to the public.

FAX <-> AST (with fax gateway) <- (inside) ROUTER (outside) -> AST or FAX

The problem is caused by UDPTL NAT handling.
UDPTL applies NATted address (public one of the router) just when recieve
first packet.
But fax gateway (inside nat) was waiting for that packet from the peer
(outside nat) that is its usual flow.
The peer outside the nat was sending such packewts but with negotiated SIP
address (like 192.168.x.x) that is way the first packet never reach the fax
gateway inside NAT and whole T38 communication set up is failing.

I solved this by sending NULL packet from fax gateway. 
+    // a hack -> engage udptl nat on other side of T38 line
+    char nullChar [] = "\0";
+    t38_tx_packet_handler(&t38_state.t38, (void *) channels[0], (const
uint8_t *) nullChar, 1, 1);


This is a useless packet for T38 so it has (I hope) no efect on T38 stack
but it sets the IP address for  UDPTL nat so the communication can proceed.

Not nice but it works.

Enjoy.

Daniel. 

Issue History 
Date Modified    Username       Field                    Change               
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2008-12-18 03:29 dafe_von_cetin Note Added: 0096607                          
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