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Configuring Presence Service
Restrictions for Presence Service
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Cisco Unified Communications Manager Express System Administrator Guide
OL-10663-02
Restrictions for Presence Service
• Presence features such as Busy Lamp Field (BLF) notification are supported for SIP trunks only;
these features are not supported on H.323 trunks.
• Presence requires that SIP phones are configured with a directory number (using dn keyword in
number command); direct line numbers are not supported.
Information About Presence Service
To configure presence service in a Cisco Unified CME system, you should understand the following
concept:
• Presence Service, page 886
Presence Service
A presence service, as defined in RFC 2778 and RFC 2779, is a system for finding, retrieving, and
distributing presence information from a source, called a presence entity (presentity), to an interested
party called a watcher. When you configure presence in a Cisco Unified CME system with a SIP WAN
connection, a phone user, or watcher, can monitor the real-time status of another user at a directory
number, the presentity. Presence enables the calling party to know before dialing whether the called party
is available. For example, a directory application may show that a user is busy, saving the caller the time
and inconvenience of not being able to reach someone.
Presence uses SIP SUBSCRIBE and NOTIFY methods to allow users and applications to subscribe to
changes in the line status of phones in a Cisco Unified CME system. Phones act as watchers and a
presentity is identified by a directory number on a phone. Watchers initiate presence requests
(SUBSCRIBE messages) to obtain the line status of a presentity. Cisco Unified CME responds with the
presentity’s status. Each time a status changes for a presentity, all watchers of this presentity are sent a
notification message. SIP phones and trunks use SIP messages; SCCP phones use presence primitives in
SCCP messages.
Presence supports Busy Lamp Field (BLF) notification features for speed-dial buttons and directory call
lists for missed calls, placed calls, and received calls. SIP and SCCP phones that support the BLF
speed-dial and BLF call-list features can subscribe to status change notification for internal and external
directory numbers.
Figure 53 shows a Cisco Unified CME system supporting BLF notification for internal and external
directory numbers. If the watcher and the presentity are not both internal to the Cisco Unified CME
router, the subscribe message is handled by a presence proxy server.