At its basis "presence" gives you information whether a person you might want to call is actually "present" and ready to answer. This kind of presence is the familiar "online," "busy," and "away" we get with instant messaging.
However, for enterprise communication the notion of presence is broader. Presence can mean any useful notion of state that to be applied to people, to any aspect of a job, or to business processes in general. In this broader sense the presence of a person can include the job he is currently working on, the amount of time he has been doing it, or even his physical location (as is becoming available from mobile carriers). With this kind of information an enterprise can be more intelligent about how use personnel to handle current issues.
Going one step farther, with presence assigned to business processes, a communications system can provide a unified way to assure responses to important business events. In this way, for example, a customer account that transitions to the "request termination" state can cause immediate and appropriate contact with the customer.
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