Data devices, such as facsimile machines and modems, may not function optimally with an ATA. For the best fax and modem performance, continue to use a dedicated PSTN line.

By default, you send faxes with T.38 mode disabled. The fax data is encrypted from the ATA to the Cisco Webex Call service.

You may encounter problems with fax transmission through your ATA. Your administrator can enable T.38 mode to resolve these problems. Remember that when T.38 is enabled, your faxes aren't encrypted.

Before you begin

To reduce failures from incoming fax calls, set your fax machine to Fax mode or Auto Answer Fax mode. Otherwise, your fax machine may treat an incoming fax call as a voice call and cause a fax failure.


Ask your administrator to change your fax machine to use T.38 mode.


Send a test fax after you change to T.38 mode.

What to do next

If you still encounter problems with fax messages:

  • Restart your fax machine and analog telephone adapter (ATA).

  • Check all physical connections on your fax machine and ATA.

  • Check the status of your ATA in Cisco Webex Settings .

  • Lower the baud rate on your fax machine to 9600 or 2400 bps. Some fax machines provide Overseas mode, which sets a low baud rate.

  • Change the Error Correction Mode (ECM) value on your fax machine.

  • Reduce the number of pages that you transmit in a single fax call.