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Fax machines via FXS ports not working

Posted on 2011-03-21
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Last Modified: 2013-11-12
We have had many issues with faxes. Our network consist of a cisco voice gateway, call manager and a Nortel pbx. The way it is set up right now is that all calls come into the voice gateway, from there the voice gateway either sends the call the call manager, the pbx or an fxs port. In this case, we have several fax machines that where having problems. So what we did was connect these fax machines directly to an fxs port. We have a cor list that directs fax calls to certain incoming dial peers that send the fax c all to fax machines via the fxs ports. When a fax is being sent out, the cor list sends the fax calls out of one of pri lines.
The problem is that faxes don’t seem to work properly. On some machines we get a no fax detected error, in others all we get is buys. But if we connect a phone to it and call the line is not busy.
We have over 20 fax machines in our environment and not all of them are having problems, just these. At first we thought it was a networking issue as we had slips on some of the lines, but we took care of that and issues still persist. We have also disabled ecm on all the machines with no luck.
Any help would be greatly appreciated.
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Question by:moibeats
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by:lrmoore
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How are you getting the 20+ fax machines to FXS ports? Through a VG200 gateway, or what?
What fax protocol do you have enabled on the gateway?
You have 4 choices. Try T38 or cisco

voice service voip
 fax protocol ?
  cisco         Use Cisco proprietary protocol
  none          Disable fax transport
  pass-through  Use an audio codec for fax transport
  t38           Use T.38 protocol
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Author Comment

by:moibeats
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Although we have over 20 fax machines we only have 4 connected to fxs ports. They are connected to our voice gateway via a 24 port fxs card.  Here is the relevent config:

voice service pots
 fax rate disable
!        
voice service voip
 allow-connections h323 to h323
 fax protocol pass-through g711ulaw
 h323

Hope this helps. To  be honest I think its the actual fax machines as they are about 15 years old, the thing is that they worked when they where connected to our pbx system and the pbx system connected directly to our PRI, but now all of our PRI connect to the voicegateway.
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by:lrmoore
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I would try changing the fax protocol setting to t38 or cisco and see if that makes a difference.
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Author Comment

by:moibeats
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we have t38 enabled on our voice gateway via mgcp:

mgcp fax t38 inhibit
no mgcp explicit hookstate
mgcp fax t38 gateway force

we are going to try new fax machines, i will update once we do.
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Author Comment

by:moibeats
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We have hooked up two fax machines to this port. It seems that the fax machines need to have ecm off and the baud rate needs to be lowered to 9600 for them to work, but even then I get about 1 or 2 failures out of every 20 faxes. That isn't to bad though.
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moibeats earned 0 total points
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a new fax machine did it.
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Author Closing Comment

by:moibeats
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This issue had to do with the actual hardware and not the config on the vg.
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