Cisco IGX 8400 Series Switches

Field Notice: Fax Failure on IGX-UVM in Software Release 9.106 and Earlier 9.1 Releases

February 18, 1999

Products Affected




This problem has not been observed in software releases 8.2.5x or 8.5.xx.

Problem Description

Fax and modem transmissions fail because Permanent Virtual Circuits (PVCs) terminated on universal voice modules (UVMs) do not increase bandwidth to 64kBps. Fax and modem transmissions require that the PVC bandwidth upgrade to full 64Kbps (or a Cisco-proprietary 32kBps bandwidth) in order to properly negotiate the protocols between the two end devices.

Problem Symptoms

Users may observe that some or all fax or modem calls may not initiate or complete properly.


The UVM can detect certain tones coming from the connected customer premise equipment that identify a fax or modem call is to be placed. The detection of these tones causes the specific channel to increase its allotted bandwidth up to 64kBps to allow proper operation of these higher speed signals. The channel circuitry that detects the appropriate tones, which is 2100 Hertz in most cases, disables echo cancellation, increases PVC bandwidth which turns off any compression algorithm.

This bug prevents the PVC from remaining in the "upgraded" state which causes the fax or modem protocol and feature negotiation to fail.

This defect has Cisco bug IDs CSCdk75382 and CSCdk40766. If you are a registered CCO user and you have logged in, you can view the bug details.

View CSCdk75382 (registered customers only)

View CSCdk40766 (registered customers only)



Try these steps to workaround the issue:

  1. Try connecting the fax or modem again.

  2. the failure rate is very high, try using the Fax Relay feature, as described below:

    • Enable fax-relay on the channel or channels with the cnfchfax command.

    • Disable V.25 modem detection on the channels with the cnfvchparm command.

  3. Add all connections as "P" type connections if available trunk bandwidth permits.


Upgrade software to release 9.1.07 or later.

Switch software may be downloaded from the CCO WAN Switches Software Center with your CCO user account at the URL below:

Select the "Cisco WAN Switching Upgrade Planner" link to find the latest software and firmware.

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods: