Cisco Unified Communications Manager

CUCM is not only the call control, dial plan, and call routing system for Unified Communications. CUCM also has basic presence functionality built in. All telephony presence requests and responses are handled by the CUCM. The protocols used by the telephony devices are SCCP and SIP. Inside the cluster, the CUCM sends responses to requests. When the request is for a nonlocally registered device, the CUCM forwards the request to an external presence control device.

• SCCP: SCCP messages are exchanged between CUCM and users when in the same CUCM cluster. SCCP messages leaving the CUCM cluster use a SIP trunk.

• SIP: SIP SUBSCRIBE messages are exchanges between the SIP line and the CUCM. SIP NOTIFY messages are exchanged between the SIP line and CUCM. When SIP or SCCP requests are leaving the CM cluster, a SIP trunk is used to communicate with the external presence entity. The CM forwards the request and returns presence status to the watcher.