MS Exchange 2007 and Nortel CS1k UM Auto Attendants

Here is the scenario…….

Nortel CS1K
MS Exchange 2007
UM Auto Attendants Required

Main switchboard number was set to forward on busy to a UM Auto Attendant which would present a menu of available options for the caller to select as per the usual business call centre type.

The user would be forwarded to the UM Auto Attendant and if the UM Auto Attendant option selected was a phone number the phone would ring and if answered the call would continue as expected……
However…….
if the call was forwarded to an Exchange Voicemail number specifically or if the extension selected was busy or did not answer the caller would be asked to leave a message.
The caller would put on their best telephone voice and start to leave their message when after 10 seconds they would hear “Are you still there?”

Exchange could not hear the caller!

We ran traces….
We checked switch configuration…..
We Patched and Service Packed Exchange…..
We Patched and Service Packed CS1K…..
We stood on one leg with a knotted handkerchief on our heads at midnight….

Nothing worked….

We raised a call with Nortel….

This was the reply…..

“On initial investigation this appears to be a codec negotiation issue between the CS1K and EXUM ( although the contact information also appears strange to me) . Would it be possible to confirm that the EXUM is patched current , also can you send me the wiredcodeclist registry key info (HKEY_LOCAL_MACHINESOFTWAREMicrosoftMicrosoft Speech Server2.0WireCodecList) for review. Lastly from EXUM are there any event logs generated when this occurs ?”

The content of
HKEY_LOCAL_MACHINESOFTWAREMicrosoftMicrosoft Speech Server2.0WireCodecList
was

RTAudio16KHz
RTAudio8KHz
G.723.1(6.3)
G.711u
G.711A

Sent this to Nortel and the reply was….

“Also would it be possible to try reordering the wirecodeclist to insert A law before MU law ? Once updated you will need to restart the MS Exch Speech Engine Service. I have seen this also resolve some UEXM codec issues.”

Changed the Codec order to….

RTAudio16KHz
RTAudio8KHz
G.723.1(6.3)
G.711A
G.711u

Restarted MS Exchange Speech Engine Service
And all worked fine!

An obscure entry in a seemingly non relevant registry key!
Thank you Microsoft for making life so simple!