Troubleshooting Fax Relay - Cisco BTS 10200 Softswitch User Manual

Cisco BTS 10200 Softswitch T.38 Fax Relay

Troubleshooting Fax Relay

The purpose of this section is to provide basic troubleshooting procedures for anyone trying to resolve
Cisco BTS 10200 Softswitch T.38 fax relay issues. The technical intricacies of faxing and fax relay are
not covered in detail, but you will get a basic understanding and be able to perform troubleshooting for
a majority of common fax relay issues.
It is important to know the following information:
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The following steps have been shown to resolve the majority of issues involving T.38 fax relay over
packet networks.
Identify and isolate the problem.
Step 1
The first step to take when you troubleshoot any fax relay issue is to reduce the problem to its simplest
form. Many issues arise in situations where multiple fax machines are not able to pass fax traffic. It is
easier to isolate two fax machines that are having problems and concentrate on a simple topology. First,
determine how these two machines are connected to one another and resolve the issue between this pair.
In addition, you should draw a complete picture of the network topology and determine how all the fax
machines are interconnected.
Troubleshooting one issue at a time minimizes confusion and allows for methodical troubleshooting.
It is also possible that the solution for this problem will resolve other fax relay problems in the network.
Most fax relay problems result from poor packet network configuration or network design. These lead
to basic connectivity problems and physical line or packet loss and jitter problems.
After you have identified and isolated the problem, the next steps relate to verifying the basic voice over
packet network configuration and monitoring the health of the network.
Check basic network connectivity.
Step 2
Basic fax connectivity issues can be the result of the following factors:
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Phase in which the fax transmission error occurred.
Whether the gateways or fax machines terminated the connection, and if it was a fax machine, which
one.
What fax protocol events took place prior to the connection being terminated.
Normal voice connectivity problems —Confirm that normal voice calls can be completed before
investigating fax connectivity. If there is no telephone attached to the fax machine, unplug it and
connect a regular telephone. If normal voice calls do not connect, the issue may be network-related
and you should troubleshoot the problem as a connectivity issue before fax troubleshooting.
Configuration problems related to dial peers , such as:
Wrong dial peer being matched—
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After ensuring that voice calls can be successfully completed in both directions through the
network, issue the show call active voice brief command and note the dial peers that are being
matched with each voice call.
When you have VoIP trunks, you should be able to see all the call legs with the show call active
voice brief command. Ensure that the configured dial peer is the peer that is being matched.
A common cause of fax relay problems is that the correctly configured dial peer is not the one
being matched. It is also common that there is no particular incoming VoIP dial-peer configured
on the terminating gateway and the Cisco IOS software selects the first appropriate (including
default) VoIP dial peer as the incoming dial peer. Hence the parameters for this incoming dial
peer may not match those of the outbound dial peer on the originating gateway.
Cisco BTS 10200 Softswitch T.38 Fax Relay Support
Troubleshooting Fax Relay
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