Cisco Catalyst 6000 Series Switches

Field Notice: Cisco Catalyst 6500 Series Communication Media Module-VAD Enabled with G.729 Causes One Way Delay

Revised November 14, 2002

September 30, 2002

Products Affected




Catalyst 6500 Communication Media Module

Cisco IOS® Software Release 12.2(2)YK

This problem is resolved in Cisco IOS Software Release 12.2(YK1)

Problem Description

The delay problem is with voice activity detection (VAD) or Silence Suppression enabled on G.729 calls only, and will occur with T1 calls using either CAS or PRI interfaces. Its is heard only in the direction from the PSTN to the IP phone. It occurs with varying amounts of delay and can be reproduced in one out of 10 calls. Lastly, the delay will only occur if the call is originated from the PSTN, and not the IP phone.


The delay problem is with VAD or Silence Suppression enabled on G.729 calls only. This problem does not occur with VAD enabled on G.711.

Problem Symptoms

This bug affects a small percentage of calls when it does happen. The delay is intermittent, and is heard in the direction from the PSTN to the IP phone for calls that are originated from the PSTN to an IP phone.


The problem has been resolved in CMM Software release 12.2(2)YK1. Please upgrade to this version for a permanent solution for this problem. For More Information please refer to Release Notes for Catalyst 6500 Series and Cisco 7600 Series Communication Media Module Software Release 12.2(2)YK1.

Cisco highly recommends that you upgrade to the latest version of software. Should you choose not to, the workaround for this problem is to turn VAD off when using G.729. VAD is turned OFF by default.

Note: The CM sets VAD on/off in the service parameters settings under the Call Manager service.


To follow the bug ID link below and see detailed bug information, you must be a registered user and you must be logged in.



CSCdy54786 (registered customers only)

G.729 Vad on 1 Way Delay CAS&PRI every 1-10 calls PBX->Communication Media Module->7960.

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:

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