Chapter 19
The Presence Service on the Internet
Presence is one of those basic services that, day by day, is becoming omnipresent. On the one hand, the presence service is able to provide an extensive customized amount of information about a given user to a set of users. On the other hand, third-party services are able to read and understand presence information, so that the service provided to the user is modified (actually, we should say customized) according to the user’s needs and preferences expressed in the presence information.
19.1 Overview of the Presence Service
Presence is the service that allows a user to be informed about the reachability, availability, and willingness of communication with another user. The presence service is able to indicate whether other users are online or not, and if they are online, whether they are idle or busy (e.g., attending a meeting or engaged in a phone call). In addition, the presence service allows users to give details of their communication means and capabilities (e.g., whether they have audio, video, instant messaging, etc., capabilities and in which terminal those capabilities are present).
The presence framework defines various roles, as shown in Figure 19.1. The person who is providing presence information to the presence service is called a presence entity, or for short, a presentity. In Figure 19.1 Alice plays the role of a presentity. The presentity is supplying presence information (i.e., the set of attributes that characterize ...
