Internet Communications Using SIP : Delivering VoIP and Multimedia Services With Session Initiation Protocol {2Nd Ed.}

We refer the reader to the original document on the presence data model [15]

for a detailed discussion of the meaning of the various presence data elements.

Indication of Message Composition for IM

Commercial IM systems have introduced a useful presence indication for IM

users, also sometimes called is-typing, that alerts the remote party to wait

for the message. This avoids the nuisance of crossed messages in an interactive

communication. In the SIP standard for this type of presence notification, the

status message is called isComposingand has been defined not only for text-

based IM but also for voice and video exchanges that require some time to pre-

pare [20]. A state machine has been defined that can understand the behavior

of the composer with the help of activity timers and generate the idleand

activestates that are then communicated as presence information in an XML

document with a well-defined namespace and XML schema.

Rich Presence Information

More comprehensive work on the use of presence is reflected in the Rich Pres-

ence Extensions to the Presence Information Data Format (RPID) [21]. The

presence information data in RFC 3863 that is intended for humans has been

extended to be generated by applications for consumption by automata, while

maintaining backward compatibility with RFC 3863. Applications such as the

calendar or UAs can generate such rich information presence, often without

any human intervention. Rich presence information documents avoid the use

of the <note>element that is intended for humans.

Rich presence data elements describe the person, the services, and the

devices. Here are some examples for rich presence data elements:

■■ Activities (many can be generated by the calendar)

■■ appointment

■■ away

■■ breakfast

■■ busy

■■ dinner

■■ holiday

■■ in transit(in a car)

■■ looking for work

■■ lunch

■■ meal

236 Chapter 13