March 2006
Intermediate to advanced
464 pages
12h 16m
English
book
The IMS: IP Multimedia Concepts And Services, Second Edition
by Miikka Poikselka, Georg Mayer, Hisham Khartabil, Aki Niemi
Content preview from The IMS: IP Multimedia Concepts And Services, Second Edition
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4.5. SIP for presence
The Session Initiation Protocol (SIP) has been extended for presence by the creation of an event package called "presence". Event packages are described in Section 12.13.1. When subscribing to such an event, a subscriber places the "presence" token in the Event header.
Some definitions have been created to describe the subscriber and the notifier for the purpose of presence:
Presentity – the presence entity, a resource that provides presence information to a presence service.
Watcher – the entity that requests information (presence), about resources (presentities).
Two SIP entities are defined for presence in [RFC3856]:
Presence Agent (PA) – capable of storing subscriptions and generating notifications.
Presence User Agent (PUA) – manipulates presence information for a presentity and publishes such presence information.
As mentioned earlier, the NOTIFY request body carries the state information. In this case, the state information is the presence state of a presentity. The Multipurpose Internet Mail Extension (MIME) type of such content is "application/pidf + xml" as defined in [RFC3863]. This presence Extensible Markup Language (XML) document can be extended to carry more information than defined in [RFC3863].
The presentity uploads presence information using the PUBLISH method, which is described in Section 12.13.2.
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