Analyzing T38 Fax Relay Packet Captures

Packet capture programs such as the freely available Wireshark program can decode T.38 fax relay and even graphically display the fax messaging that is being transported by T.38. For more information about Wireshark and how to acquire this software program, refer back to the section IP Troubleshooting in this chapter. TIP Sometimes the T.38 fax relay information in Wireshark is not displayed properly by default, and this usually occurs when NSEs are used for the switchover. If the T.38 packets...

T38 Fax Relay and Modem Passthrough Configuration for MGCP

A common scenario for handling regular faxes along with modems or SG3 fax devices at the same time is to use a fax relay protocol for the fax traffic and modem passthrough for the modem or SG3 fax traffic. Although this scenario can be configured for the H.323, SIP, MGCP, or SCCP voice signaling protocols using T.38 or Cisco fax relay, Example 10-5 shows how this scenario is configured specifically for an MGCP voice gateway running NSE-based T.38 fax relay and modem passthrough. Example 10-5...

Debugging T30 Fax Messaging

The most frequently used tool for troubleshooting fax relay problems is the IOS command debug fax relay t30 all-level-1. This command displays the T.30 messaging that is passing through the Cisco voice gateway from the perspective of the gateway's DSP. Output that is equivalent to this IOS command can be found on Cisco non-IOS gateways using the procedures discussed at the end of this section. Before using this command, you should have already determined that the Cisco voice gateways are...