Chapter 20 - The Presence Service in the IMS pdf

Chapter 20

The Presence Service in the IMS

Chapter 19 gave an overview of the presence service on the Internet, as defined by the IETF.

This chapter focuses on the use of the presence service in the IMS. We explore the IMS

architecture that supports the presence service and the applicability of presence to the IMS.

3GPP has defined, in 3GPP TS 24.141 [51], a presence service that runs over IMS, but

mostly, 3GPP is just maintaining the specification, not actively progressing it. The presence

service in IMS has since moved to OMA. OMA considers the presence service as an enabler,

i.e., the set of specifications that enables a service. The main specification of the OMA

Presence SIMPLE enabler is the OMA Presence SIMPLE specification [246]. This chapter

describes this OMA Presence SIMPLE enabler.

20.1 The Foundation of Services

When we described the presence service on the Internet we unveiled a few of the powerful

and rich possibilities that the presence service can offer to both end-users and other services.

On the one hand, end-users benefit from the presence service since they decide what

information related to presence they want to provide to a list of authorized watchers.

Presentities can decide the information they want to publish, such as communication address,

capabilities of the terminals, or availability to establish a communication. Watchers receive

that information in real time and decide how and when to interact with the presentity. All of

these features enrich the end-user communication experience.

On the other hand, presence information is not only available to end-users but also to

other services. These other services can benefit from the presence information supplied.

For instance, an answering machine server is interested in knowing when users are online

to send them an instant message announcing that they have pending voicemails stored in the

server. A video server can benefit by adapting the bandwidth of the streaming video to the

characteristics of the network where the presentity’s device is connected. For all of these

reasons we refer to the presence service as the foundation for service provision, as depicted

in Figure 20.1.

20.2 Presence Architecture in the IMS

Figure 20.2 depicts the presence IMS architecture in conjunction with the Service configu￾ration offered by the XDM architecture. The IMS terminal plays the role of both a watcher

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The 3G IP Multimedia Subsystem (IMS): Merging the Internet and the Cellular Worlds Third Edition

Gonzalo Camarillo and Miguel A. Garc

© 2008 John Wiley & Sons, Ltd. ISBN: 978- 0- 470- 51662- 1