| 摘要 |
<p>The present invention provides distributed communication services based on a presence technology platform. Presence messaging and communication techniques allow a variety of communication agents to cooperate with one another to provide distributed services. Essentially, the messaging between the agents is used to facilitate media sessions and update participating devices of state changes bearing on providing the services. In one embodiment, each of the participating devices is associated with a logic entity, referred to as a presentity, which subscribes to notification services for the other participating devices. When a state change occurs on any one of the participating devices, the corresponding presentity notifies the other devices of the state change. As such, each participating device knows the status of the other participating devices via the presentities and can systematically determine when and how to provide services based on its current state and the current state of the other participating devices.
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