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One-way speech on Cisco ATA using H.323 and Cisco CallManager


Core Issue

The Cisco Analog Telephone Adaptors (ATAs) are being used as H.323 gateways in Cisco CallManager 3.1.2c.

This occurs in two scenarios:

  1. Calling between two Cisco ATAs. Speech is normal in both directions until one of the ATA users presses a Dual Tone Multifrequency (DTMF) digit. At this time, audio is lost in both directions for the call duration.
  2. Calling between a Cisco ATA and another phone controlled through Cisco CallManager (IP phone or Public Switched Telephone Network (PSTN) user). Speech is normal in both directions until the Cisco ATA user presses a DTMF digit. At this time, one-way audio is experienced (by the non-ATA user) for the entire call duration.

Note: This problem does not occur when Cisco CallManager is not involved in the configuration.


The problem occurs when the Cisco ATAs are set to 0x00150015 = Sets both lines to always send DTMF out-of-band. This setting causes one-way voice because there is no way to configure DTMF out of band on Cisco CallManager for H.323 phones.

Changing the AudioMode to 0x00050005 = Sets both lines to always send DTMF inband fixes the problem.