Cisco ICS 7700 Series Integrated Communication Systems

Voice mail messages on Unity from external callers using G.729 codec are blank. Field Notice

March 7, 2003

Products Affected



Unity Software

This is not a Unity problem. Voice gateways running Cisco IOS® Software releases earlier than 12.2(11)T3, 12.2(11)T5, or 12.2(11)T6 cause this problem on Unity when using H323 and G729a Codecs.

Problem Description

A gateway that negotiates a G.729 codec with 20 bytes in the call setup may send 40 bytes instead. When Unity receives 40 byte packets, it drops them.

Notable behavior includes external callers (calling from the PSTN) that leave voicemail messages that are perceived as empty or blank. There is no indication from Unity that the message was not recorded properly. When the recipient checks the message left from the external caller, they are presented with silence.


Any voice gateway running Cisco IOS Software releases earlier than 12.2(11)T3, 12.2(11)T5 or 12.2(11)T6 and using H323 protocol with G.729a codec will experience this problem. When Unity receives 40 byte packets, it drops them because of a bug in Cisco IOS Software releases earlier than 12.2(11)T5 and 12.2(11)T6.

Problem Symptoms

When an outside caller rings the IP phone and the phone forwards the call (Forward No Answer/Forward Busy) to Unity, the caller can hear the greetings and try to leave a voice mail. But if you press # and then 3 to review the voice mail, it is blank. You can confirm this problem on the gateway by running the debug voice ccapi inout and debug vtsp allcommands on the voice gateway and search for codec_bytes. You will see it going from 20 to 40.


The resolution to this problem is to upgrade your voice gateway to Cisco IOS Software Releases 12.2(11)T5 or 12.2(11)T6. The fix will also be in Release 12.2(13)T3 when it becomes available. Cisco IOS Software Release 12.2(13)T1 does not have the fix.


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



CSCea01498 (registered customers only)

AS5300 H323 GW having issues with CODEC byte size.

CSCea38592 (registered customers only)

Unity should be able to handle 40ms packets

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: