[asterisk-users] receive fax from PRI using spandsp 65% failure rate

Justin Killen jkillen at allamericanasphalt.com
Fri Nov 15 11:49:02 CST 2013

Turns out I had my timing sources setup incorrectly, so the te820 wasn't synchronizing with the Telco.  Turns out the spandsp FAQs are pretty good for diagnosing: http://www.soft-switch.org/spandsp_faq/ar01s08.html

From: asterisk-users-bounces at lists.digium.com [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Justin Killen
Sent: Thursday, November 14, 2013 3:28 PM
To: Asterisk Users Mailing List - Non-Commercial Discussion
Subject: [asterisk-users] recieve fax from PRI using spandsp 65% failure rate


On one of our servers, we're having problems with incoming faxes.   The connections come in through a PRI into a Digium TE820 card.  'fax show stats' yields the following:

FAX Statistics:

Current Sessions     : 0
Reserved Sessions    : 0
Transmit Attempts    : 0
Receive Attempts     : 740
Completed FAXes      : 740
Failed FAXes         : 486

Spandsp G.711
Success              : 254
Switched to T.38     : 0
Call Dropped         : 46
No FAX               : 0
Negotiation Failed   : 0
Train Failure        : 4
Retries Exceeded     : 20
Protocol Error       : 219
TX Protocol Error    : 44
RX Protocol Error    : 153
File Error           : 0
Memory Error         : 0
Unknown Error        : 0

I've read that doing rx/tx tuning on the PRI is supposed to help, but nothing there seems to make a difference (I tuned RX down to -6.5 per the article here: http://www.voip-info.org/wiki/view/Asterisk+zapata+gain+adjustment so that the RX is at around 50%.  I haven't found a good way to do TX tuning, as setting it via 'dahdi set swgain tx' doesn't seem to have any effect on the dahdi_monitor output).  I've enabled fax debugging (fax set debug on), but that doesn't seem to do anything either (perhaps I need to raise asterisk's debug level as well?).

What steps should I try next?

Thanks in advance,
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