This section describes the integration of external presence entities into the native presence solution.
All presence requests for users, whether inside or outside a cluster, are processed by CUCM, as shown in Figure 14-2.
Figure 14-2 CUCM Native Presence
A CUCM watcher that sends a presence request will receive a direct response, including the presence status, if the watcher and presence entity are both located within the cluster.
If the presence entity exists outside the cluster, CUCM will query the external presence entity through the Session Initiation Protocol (SIP) trunk. For A watcher that is not in a CUCM cluster, the CUCM can send a presence request off cluster entity by way of a SIP trunk. If the off-cluster entity supports presence, it will respond with the current presence status. If the off-cluster entity does not support presence, it will reject the presence request with a SIP error response.
Skinny Client Control Protocol (SCCP) endpoints can request the presence status of the indicated presence entity by sending SCCP messages to CUCM. If the presence entity resides within the CUCM cluster, CUCM responds to the SCCP line-side presence request by sending SCCP messages to the presence watcher that indicate the status of the presence entity.
CUCM uses the term SIP line to represent endpoints supporting SIP that are directly connected and registered to CUCM, and the term SIP trunk to represent trunks supporting SIP. SIP line-side endpoints acting as presence watchers can send a SIP SUBSCRIBE message to CUCM requesting the presence status of the indicated presence entity.
If the presence entity resides outside the CUCM cluster, CUCM routes a SUBSCRIBE request out on the appropriate SIP trunk, based on the SUBSCRIBE CSS and presence groups. When CUCM receives a SIP NOTIFY response on the trunk that indicates the presence entity status, it responds to the SCCP line-side presence request by sending SCCP messages to the presence watcher indicating the status of the presence entity.