Cisco Cisco Customer Voice Portal 8.0(1) Design Guide

When using this feature in conjunction with calls originated by Unified CM, the 
sourceCallSignalAddress populated by Unified CVP will be the IP address of Unified CM. If the call is 
transferred back to Unified CM, it will inspect this field and try to find a configured gateway with that 
IP address, but the call will fail because normally Unified CM will never be configured as a gateway. As 
a workaround to this problem, configure each Unified CM in the cluster as an H.323 gateway, but be sure 
to never configure the Unified CM dial plan to send calls using those gateways.

When more than one centralized Unified CM cluster are used for the remote sites, additional 
consideration must be given to routing calls based on agent selection. In a multi-cluster environment, 
each cluster manages a group of remote sites and tracks the voice calls to those sites within the 
locations-based call admission control mechanism. Using the changes discussed above, Unified CM 
considers H.323 calls within its locations-based call admission control mechanism. Because H.323 is a 
peer-to-peer protocol, an H.323 gateway can signal a call to any other call agent that will accept it. 
Considering the locations-based call admission control mechanism described above, it is necessary for 
the remote gateway to be told to signal a call to the Unified CM cluster that owns the location of that 
remote gateway. However, in a Unified CCE environment, Unified ICM tracks the availability of agents 
without considering on which cluster they are located. This ability provides great scalability for 
Unified CCE but must be accounted for in this type of implementation.

If a call coming in through a Unified CVP ingress gateway is destined for an IP Phone at a different site 
registered to a different cluster, the call must first be routed through the cluster that is handling call 
admission control for the ingress gateway, and then routed to the destination cluster. If the call is routed 
directly from the ingress gateway to the destination cluster, the cluster that is handling call admission 
control for the ingress gateway is not aware of the call traversing the WAN and does not deduct 
bandwidth appropriately.

This call routing can be handled by using the SigDigits feature in Unified CVP and its associated 
dial-plan configuration. The SigDigits feature in Unified CVP allows you to use the dial plan on the SIP 
Proxy or gatekeeper to route calls to a specific Unified CM cluster. When the call arrives at an ingress 
gateway, the gateway will prepend digits before sending the call to Unified CVP. Those prepended digits 
are unique to that site from a dial-plan perspective. When the call arrives at Unified CVP, Unified CVP 
will strip the prepended digits and store them in memory, resulting in the original DID on which the call 
arrived. When Unified ICM returns a label to Unified CVP in order to transfer the call to an agent phone, 
Unified CVP will prepend the digits that it stored in memory before initiating the transfer. The dial-plan 
configuration in the SIP Proxy or gatekeeper is configured with the prepended digits so that calls with a 
certain prepended digit string are sent to a specific Unified CM cluster. The digits are prepended as a 
tech-prefix when using H.323.

For more information on how the SigDigits feature works, see 

.