[asterisk-bugs] [Asterisk 0015773]: SendFax without reliable transmission.

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=15773 
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Reported By:                ChrisDE
Assigned To:                kpfleming
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Project:                    Asterisk
Issue ID:                   15773
Category:                   Applications/app_fax
Reproducibility:            random
Severity:                   minor
Priority:                   normal
Status:                     feedback
Asterisk Version:           SVN 
Regression:                 No 
SVN Branch (only for SVN checkouts, not tarball releases): 1.6.0 
SVN Revision (number only!): 213837 
Request Review:              
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Date Submitted:             2009-08-24 14:14 CDT
Last Modified:              2009-08-24 16:22 CDT
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Summary:                    SendFax without reliable transmission.
Description: 
Using sendfax application there are random transmission errors.

Transmission has been tested extensively with different carriers,
different documents and also different asterisk versions but same results.


In some cases (approximately 50% of the cases) fax transmission is
SUCCESSFUL
In other cases (approx. 10%) fax transmission ends with

WARNING[14167]: app_fax.c:178 phase_e_handler: Error transmitting fax.
result=21: No response after sending a page.

in approx. 40% I get

WARNING[16247]: app_fax.c:178 phase_e_handler: Error transmitting fax.
result=20: Received no response to DCS or TCF.

Because only 50% of the faxes pass with OK the functionality is not
reliable and the severity of this problem is major.
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 (0109546) kpfleming (administrator) - 2009-08-24 16:22
 https://issues.asterisk.org/view.php?id=15773#c109546 
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It was possible that it was a SIP issue, if the T.38 negotiations in your
failure cases did not happen correctly. Just because there are UDPTL
packets present does not mean they are formatted in the way that the
receiver expects :-)

Yes, you are correct, the error codes are from the spandsp library itself.
SendFAX/ReceiveFAX just provide an easy to use interface to the library.
They do work in the vast majority of cases, we have many, many users who
use app_fax/spandsp for thousands of FAXes every month/week/day. In this
case, the fact that the problem appears to be in spandsp makes it nearly
impossible for us to resolve, the same as would be true if the spandsp
maintainers analyzed the UDPTL packet stream and determined that the
failure was in the remote T.38 endpoint... there is just a limit to what we
can do when we don't maintain the entire chain of communication.

I encourage you to contact the spandsp author; he is very willing to deal
with issues like this and improve his code. As an alternative, you can try
Digium's Fax For Asterisk product, which uses a completely different FAX
stack and may not suffer from this issue. 

Issue History 
Date Modified    Username       Field                    Change               
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2009-08-24 16:22 kpfleming      Note Added: 0109546                          
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