Presence service

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Presence service is a network service which accepts, stores and distributes presence information.

In computer networking, a network service is an application running at the network application layer and above, that provides data storage, manipulation, presentation, communication or other capability which is often implemented using a client-server or peer-to-peer architecture based on application layer network protocols.

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. A user's client provides presence information via a network connection to a presence service, which is stored in what constitutes his personal availability record and can be made available for distribution to other users to convey his availability for communication. Presence information has wide application in many communication services and is one of the innovations driving the popularity of instant messaging or recent implementations of voice over IP clients.

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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 logical connectivity to a single presence service. Also presence service may be implemented as direct communication among presentity and watchers, i.e. server is not required.

Presentity

The term presentity is a combination of two words - "presence" and "entity". It basically refers to an entity that has presence information associated with it; information such as status, reachability, and willingness to communicate.

Presence information watcher is an entity that requests presence information about a presentity from a presence service. 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.

Functional entities to support presence service

Presence server

The Presence Server, that reside in the presentity's home network, is able to receive and manage presence information. It is a SIP Application Server and is located using SIP URLs.

The Session Initiation Protocol (SIP) is a signaling protocol used for initiating, maintaining, and terminating real-time sessions that include voice, video and messaging applications. SIP is used for signaling and controlling multimedia communication sessions in applications of Internet telephony for voice and video calls, in private IP telephone systems, in instant messaging over Internet Protocol (IP) networks as well as mobile phone calling over LTE (VoLTE).

See also

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