Cisco BTS 10200 Softswitch User Manual page 21

Cisco BTS 10200 Softswitch T.38 Fax Relay
Enable T.38 Packet Redundancy.
Step 8
The T.38 fax relay packet redundancy feature can be turned on by configuring the following command
under the appropriate dial peers on both gateways:
gateway-name (config-dial-peer)#fax protocol t38 Ls-redundancy X Hs-redundancy Y
where X> 0 and Y= 0 (only make changes to Ls-redundancy).
This feature can alleviate T.38 fax relay failures due to packet loss. However, T.38 packet redundancy
significantly increases bandwidth usage and it is preferable to eliminate packet loss where possible.
Set the fax NSF command to all zeroes.
Step 9
The fax NSF command can be helpful in troubleshooting the brands of fax machines that alter the NSF
field during fax negotiation for proprietary encodings. This command allows the gateway doing T.38 fax
relay to override the settings made by fax machines that are trying to implement proprietary encodings.
Before the fax NSF command was available, fax relay would fail for these brands of fax machines.
Typically the fax NSF command is used to set the NSF field to all zeroes, which forces a standard fax
negotiation from both sides. Using this command has been successful with certain brands such as Harris
and Lanier, and it is recommended when T.38 fax relay is failing.
When all else fails ...
Step 10
If the preceding troubleshooting steps did not resolve the T.38 fax relay issue, the problem may require
more advanced troubleshooting. Listed below are additional steps to try before you open a case with the
Cisco Technical Assistance Center (TAC).
Learn the brands and models of the fax machines that are failing, and investigate those brands
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and models for known issues.
Sometimes there are defect reports that address known problems for certain brands of fax machines.
These defects are not in the Cisco IOS Software; they are known incompatibilities with the fax
machines' proprietary fax signaling protocol when these fax devices are used on each side of a
connection. The workaround is to disable the proprietary protocol on the fax machines or to disable
T.38 fax relay and use a higher bandwidth codec.
Use search tools to look for known fax problems in the Cisco IOS Software release where the
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problem is occurring.
In the previous step, searches were made for a specific fax brand in the hope of identifying a known
issue between a certain fax brand and the Cisco T.38 fax relay code. The next step is to perform a
generic search since there could be a fax relay defect in the Cisco IOS Software release installed.
For example, if T.38 fax relay is not working in a particular Cisco IOS Software release, you can
search for defects using the Bug Toolkit on CCO. If a defect in a particular release causes all T.38
fax relay to fail, then an upgrade is needed to a release in which this defect is no longer present.
Eliminate hardware faults.
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In some cases it is easier to isolate the problem by excluding potential problem sources one by one.
You can do this by replacing different hardware parts and using alternative IP connections between
the gateways.
When extra hardware is available, the following steps can help.
–
Use different ports on the gateways—
If your configuration involves two gateways connected to PBXs or the PSTN with T1 (or E1)
and if you have the FXS ports available, try to connect the fax machines directly to the FXS
ports on the voice gateways. This procedure will help further isolate the problem by excluding
the possibility of the T1 (or E1) cards failing, problems on the telephony side, or T1 (or E1)
clock synchronization or cable problems.
Cisco BTS 10200 Softswitch T.38 Fax Relay Support
Troubleshooting Fax Relay
21