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Unified Communications
SIP Specific: Speaking SIP
UC Mag
Jonathan Rosenberg
co-author of SIP and SIMPLE

A Commanding Presence

For as long as technologies have existed to enable communication, technologies have been needed to control communication. Back in the early days of telephones, human operators acted as gatekeepers, ringing the called parties and checking their availability before connecting them to callers. With the arrival of automatic switching, other techniques were needed. It was common practice for people to take their phones off the hook when they didn't want to be bothered, thereby blocking incoming calls and conveying a busy signal to callers.


These techniques were really the earliest forms of presence. The arrival of the Internet brought with it new communications tools - email and instant messaging. Along with those tools came much improved mechanisms for presence. Users could see, in advance, whether the target of a communication was online or not and even see a status message. Call this "basic presence".


Today, communications are more complicated. Users have many devices (mobile, desk and soft phones) on which they can use many services (voice, video, IM, text, push-totalk, email). In this more complicated environment, the information provided by basic presence is insufficient. Basic presence needs to evolve to the next step: rich presence.


Rich presence allows a user (called the presentity) to convey a wealth of information to other users (called watchers) who seek to communicate with the presentity. Rich presence tells the watcher information about presentities, their devices and their communications services on those devices. This wealth of information is necessary because the watcher needs to make a choice: Should I communicate now, and if so, how? Should I call? If so, should I call their mobile or their desk? Should I use IM? Try texting? Is he too busy to contact now, and should I try someone else? Rich presence needs to provide enough information so the watcher can make an intelligent choice from the various options.


Consider the following example: Bob is a project manager. He is commuting to work while dialed into a conference call from his mobile phone. His mobile phone supports corporate instant messaging as well. Bob also has a phone in his office. With basic IM, Bob's status would show him as available for IM since his phone, being 3G enabled, is logged in to the corporate IM system while he is on the call. Mary is working with Bob on an important project and needs to contact him. Since Bob appears available, Mary sends Bob an instant message. Bob tries to read it while driving and gets into an accident.


However, with rich presence, Mary can see a lot more. Rich presence would tell Mary that Bob is in a meeting, that he is on the phone, and that the call is a conference call. It would tell Mary that Bob is in transit and perhaps even give Mary an indication of where Bob is. Rich presence would tell Mary that Bob can be contacted by IM and by voice, and that Bob has mobile and desk phones. With that information, Mary can determine whether the topic is important enough to interrupt Bob, in which case she would call his mobile, or she can elect to wait until he gets to the office and then call his desk phone or send him an instant message. She decides to call him. They chat quickly and Bob arrives at the office safe and sound.


Technically, a rich presence system has two components. The first is a mechanism for representing and exchanging rich presence information. Fortunately, that part of the problem has been solved: IETF has defined a suite of specifications for exchanging rich presence information. The problem's second part involves integrating presence servers with other system components so that rich presence is automatically determined. Users don't keep their information up-to-date, so rich presence must be extracted from existing information sources, such as calendars, conferencing systems, call agents, IM systems and the network infrastructure with location awareness. Those sources, combined, are sufficient to automatically produce the rich presence in the example above. The need for rich presence is really linked with a simple concept: The richness of presence must match the richness of the communications it manages. With basic telephone service, taking the phone off the hook was good enough. With basic IM, an online/offline indicator was good enough. Rich communications - voice, IM and video across multiple devices - demand rich presence.


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