Presence information

Presence information

In computer and telecommunications networks, presence information is a status indicator that conveys ability and willingness of a potential communication partner—for example a user--to communicate...

 watcher is an entity

Entity

An entity is something that has a distinct, separate existence, although it need not be a material existence. In particular, abstractions and legal fictions are usually regarded as entities. In general, there is also no presumption that an entity is animate.An entity could be viewed as a set...

 that requests presence information about a presentity

Presentity

Presentity is an term used to describe an entity that provides presence information to help other entities, such as individuals, know whether it is acceptable to initiate a communications session, such as a phone call, a videoconference or an instant message session...

 from a presence service

Presence service

Presence service is a network service which accepts, stores and distributes presence information.Presence service may be implemented as a single server or have an internal structure involving multiple servers and proxies. There may be complex patterns of redirection and proxying while retaining...

. Usually in order to get presence information a watcher have to subscribe for it to a presence server. When subscribed, the watcher receives event notifications as presence information changes. Alternatively watcher may fetch presence information without subscribing to it.