You have installed a hardware transcoder in the Cisco Catalyst 6000 8 Port Voice T1/E1 and Services Module, and it does not work as expected (you cannot make calls between two users with no common codec).
Possible Cause
You may not have any available transcoder resources that are registered with Cisco Unified Communications Manager (must be hardware).
Recommended Action
Use the Cisco Unified Communications Manager Cisco Unified Real-Time Monitoring Tool to check the number of available resources by viewing the ResourceAvailable counter in the Cisco MTP Device object.
One E1 port (WS-X6608-E1 card contains 8x E1 ports) provides transcoder/MTP resources for 16 calls, as shown in the following trace.
11:51:09.939 CCM CallManager|MediaTerminationPointControl - Capabilities Received - Device= MTP00107B000FB1 - Registered - Supports 16 calls
The following hardware trace on the Cisco Catalyst 6000 8 Port Voice T1/E1 and Services Module indicates that the E1 port 4/2 in the card registered as an MTP/transcoder with Cisco Unified Communications Manager.
greece-sup (enable) sh port 4/2Port Name Status Vlan Duplex Speed Type
----- ------------------ ---------- ---------- ------ ----- ----------
4/2 enabled 1 full - MTP
Port DHCP MAC-Address IP-Address Subnet-Mask
-------- ------- ----------------- --------------- ---------------
4/2 disable 00-10-7b-00-0f-b1 10.200.72.32 255.255.255.0
Port Call-Manager(s) DHCP-Server TFTP-Server Gateway
-------- ----------------- --------------- --------------- -----------
4/2 10.200.72.25 - 10.200.72.25 -
Port DNS-Server(s) Domain
-------- ----------------- -------------------------------------------
4/2 - 0.0.0.0
Port CallManagerState DSP-Type
-------- ---------------- --------
4/2 registered C549
Port NoiseRegen NonLinearProcessing
----- ---------- -------------------
4/2 disabled disabled
 Note |
You cannot configure the same E1 port for both Conference Bridge and Transcoder/MTP
|
To make a call between two devices that are using a low bit rate code (such as G.729 and G.723) that do not support the same codec, you need a transcoder resource.
Assume Cisco Unified Communications Manager has been configured such that the codec between Region1 and Region2 is G.729. The following scenarios apply:
- If caller on Phone A initiates a call, Cisco Unified Communications Manager realizes it is a Cisco Unified IP Phone model 7960, which supports G.729. After the digits are collected, the Cisco Unified Communications Manager determines that the call is destined for User D who is in Region2. Because the destination device also supports G.729, the call gets set up, and the audio flows directly between Phone A and Phone D.
- If a caller on Phone B, who has a Cisco Unified IP Phone model 12SP+, initiates a call to Phone D, this time the Cisco Unified Communications Manager would realize that the originating phone only supports G.723 or G.711. Cisco Unified Communications Manager would need to allocate a transcoding resource so audio would flow as G.711 between Phone B and the transcoder but as G.729 between the transcoder and Phone D. If no transcoder were available, Phone D would ring, but as soon as the call was answered, the call would disconnect.
- If a user on Phone B calls Phone F, which is a Cisco Unified IP Phone model 12SP+, the two phones would actually use G.723, even though G.729 is configured as the codec to use between the regions. G.723 gets used because both endpoints support it, and it uses less bandwidth than G.729.