Cisco Cisco Unified IP Interactive Voice Response (IVR) 8.0(1) Administrator's Guide

CRS needs two types of channels to process calls:

A call control channel, which is provisioned through the JTAPI subsystem 
and corresponds to CTI port resources in Unified CM.

A media channel, which is provisioned through either the CMT subsystem or 
the MRCP subsystem and corresponds to the kernel resources for handling 
the media voice path with the caller. 

MRCP channels also correspond to additional resources on the MRCP 
server for performing speech recognition.

CRS needs access to a channel of each type in order to successfully process a call. 
However, the capabilities of the two channel types are not identical.

For example, consider a CRS system provisioned with a single JTAPI call control 
channel (that is, a CTI port) and a single CMT channel. The system can handle 
one call at a time; when that call terminates, the system must reinitialize the 
channel resources before it can accept another call. 

However, the time each channel takes to reinitialize is not equal—CMT channels 
take more time to reinitialize then CTI ports. For example:

The JTAPI call control channel may take approximately 1 millisecond to 
reinitialize

The CMT channel may take approximately 200 milliseconds to reinitialize. 

This example implies that the system will not be able to accept a new incoming 
call for 200 milliseconds after the first call terminates; although the JTAPI 
channel is available after one millisecond, the CMT channel is not and CRS needs 
both channels to process a call. 

Such a delay can become an issue when a CRS system is experiencing a high load 
condition or needs to handle a burst of incoming calls. Consequently, CMT 
channels require a higher channel count provisioning. 

To provision CRS systems to handle burst calls equally among all required 
resources, you must configure approximately 10% more CMT channels than CTI 
ports, and approximately 10% more MRCP channels than ASR licenses.