In a call-processing environment that uses Session Initiation Protocol (SIP), use SIP trunks in order to configure a signaling interface with Cisco CallManager for SIP calls. SIP trunks, or signaling interfaces, connect Cisco CallManager clusters with a SIP proxy server. A SIP signaling interface uses port-based routing, and Cisco CallManager accepts calls from any gateway as long as the SIP messages arrive on the port that is configured as a SIP signaling interface. The SIP signaling interface uses requests and responses in order to establish, maintain, and terminate calls between two or more endpoints.
In order to choose this method, go to Device > Trunk and choose SIP Trunk in the Cisco CallManager Administration.
Also, configure route groups and route patterns that use the SIP trunks to route the SIP calls.