4.6. Presence service architecture in IMS
A user's presence information can be obtained from a multiplicity of entities in the Internet Protocol Multimedia Subsystem (IMS) network:it could be a PUA located in a foreign network, a PUA at the terminal or a PUA located as an entity in the network. The presence server is an example of an IMS application server. Watchers may be in the same home domain as the presentity or in a foreign domain.
Figure 4.2 represents a reference architecture to support a presence service in the IMS.
Figure 4.2. Reference architecture to support a presence service in IMS.
The entities are defined as follows:
Presence server – manages presence information uploaded by PUAs and handles presence subscription requests.
Watcher presence proxy – identifies the target network for a presentity and resolves its address.
Presentity presence proxy – identifies the presence server assigned to a certain presentity.
PUAs – assemble and provide presence information to the server.
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