Cisco Cisco Customer Voice Portal 8.0(1) Design Guide

when using this model in a situation where more than one Unified CM cluster are being used to control 
the remote sites. For further discussion and information on this topic, see 

.

If Unified CM is sending or receiving calls from Unified CVP and there are Unified CVP gateways and 
IP phone agents co-located at remote sites, it is important to understand the call flows in order to design 
and configure call admission control correctly.

The gatekeeper and Unified  CM do not share bandwidth usage information. Networks shared by both the 
gatekeeper and IP phones will have two separate call admission control mechanisms determining if there 
is enough bandwidth to place a call. Instead of using the gatekeeper for call admission control, it is 
possible to use Unified CM Locations as the call admission control mechanism for Unified CVP calls. 
How Unified CM determines an endpoint’s location is key to designing call admission control properly.

Consider the basic call flow of a Unified CVP call versus a non-CVP call. When a user picks up an IP 
phone and makes a call from the remote site to the central site, Unified CM considers the location 
definitions of the endpoints and the codec requirements defined in the Unified CM Region 
configurations and decides whether or not to allow the call. Note that the call admission control and the 
codec requirements are controlled between these endpoints by Unified CM as the controlling call agent.

By default, Unified CM looks at the source IP address of an incoming H.323 call to determine which 
H.323 device is originating the call. Unified CM then uses the configuration of this device to determine 
its location and to perform call admission control for the call. When Unified CVP is delivering calls from 
a remote branch gateway to a Unified  CM IP Phone, Unified CVP is in the middle of the H.323 signaling, 
so the source IP address from Unified CM's perspective is the Unified CVP Server. Because the Unified 
CVP Server is centralized along with Unified CM, it is not possible to perform call admission control 
based on the Unified CVP Server's IP address. Unified CM must be aware that calls arriving from 
Unified CVP are actually coming from a gateway at a specific branch so that it can calculate call 
admission control correctly. In order to solve this problem, Unified CVP must be configured to insert 
information in the payload of the H.323 SETUP message that identifies the IP address of the originating 
gateway, and Unified CM must be configured to look at this information when determining on which 
gateway an H.323 call is arriving.

This requires enabling one Unified CM service parameter and ensuring that another parameter is set to 
its default value:

Change the cluster-wide service parameter Accept unknown TCP connection to True. (The default 
is False.)

Ensure that the service parameter Device Name of gatekeeper trunk that will use port 1720 
remains at its default setting of blank.

When set to True, the service parameter Accept Unknown TCP Connection changes the behavior for 
inbound H.323 calls. Unified CM accepts an unknown H.225 TCP connection and waits for the H.323 
SETUP message. Unified CM then extracts the User-to-User Information Element (UUIE) and examines 
the sourceCallSignalAddress field, which contains the IP address of the originating gateway. 
Unified CM compares this address against its configured gateways. If a match is found, the call is treated 
as if it originated from the voice gateway and not the Unified CVP Server. The Unified CVP Server IP 
address must not be configured as an H.323 gateway, otherwise Unified CM will match first on the 
source IP address and will not look at the information in the sourceCallSignalAddress field. In order to