Presence
Presence is the ability of endpoints to provide information to other users about their current status - such as
whether they are offline, online, or in a call. Any entity which provides presence information, or about whom
presence information can be requested, is known as a presentity. Presentities publish information about their
own presence status, and also subscribe to the information being published by other presentities and FindMe
users.
Endpoints that support presence, such as Jabber Video, can publish their own status information. The VCS
can also provide basic presence information on behalf of endpoints that do not support presence, including
H.323 endpoints, as long as they have registered with an alias in the form of a URI.
If FindMe is enabled, the VCS can also provide presence information about FindMe users by aggregating the
information provided by each presentity configured for that FindMe user.
The Presence application on the VCS supports the SIP-based SIMPLE standard and is made up of two
separate services. These are the Presence Server and the Presence User Agent (PUA). These services can
be enabled and disabled separately.
The Presence status pages provide information about the presentities who are providing presence
information and the users who are requesting presence information on others. The status pages are
organized into:
n Publishers
n Presentities
n Subscribers
Note that any one presentity can only subscribe to a maximum of 100 other presentities, and can only have a
maximum of 100 other presentities subscribed to it.
Presence is supported by clustering. For specific information about how Presence information is managed
across peers in a cluster, see Clustering and Presence [p.167].
Presence Server
The Presence Server application on the VCS is responsible for managing the presence information for all
presentities in the SIP domains for which the VCS is authoritative. The Presence Server can manage the
presence information for locally registered endpoints and presentities whose information has been received
via a SIP proxy (such as another VCS).
The Presence Server is made up of the following services, all of which are enabled (or disabled)
simultaneously when the Presence Server is enabled (or disabled):
n Publication Manager: receives PUBLISH messages, which contain the status information about a
presentity, and writes this information to the Presence Database. PUBLISH messages are generated by
presence-enabled endpoints and by the Presence User Agent (PUA).
n Subscription Manager: handles SUBSCRIBE messages, which request information about the status of a
presentity. Upon receipt of a SUBSCRIBE message, the Subscription Manager sends a request to the
Presentity Manager for information about that presentity, and forwards the information that is returned to
the subscriber. The Subscription Manager also receives notifications from the Presentity Manager when a
presentity’s status has changed, and sends this information to all subscribers.
n Presentity Manager: an interface to the Presence Database. It is used to support VCS features such as
FindMe and the PUA, where the presence information provided by a number of different devices must be
Cisco VCS Administrator Guide (X8.1.1) Page 238 of 507
Applications
Presence
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