Chapter 17 - Service Configuration on the Internet pdf

Chapter 17

Service Configuration on the

Internet

Many services require a mechanism for allowing users to manage their service configuration.

For example, a presence server requires presentities (users) to authorize which watchers can

see their presence information. A Push-to-talk over Cellular (PoC) service requires users to

create and manage groups. Likewise a conference may require users to configure a dial-out

or dial-in list of participants, their privileges (who can speak or who can send or receive

which media type), and so on. All of these use cases share many commonalities: a user has

to perform non-real-time operations on a server to manipulate one or more documents that

configure or personalize their instance of the service.

Usually the user creates a configuration document locally in their terminal and then

uploads it to a server. Sometimes, the user just needs to make a small change to an existing

document, so it is not worth uploading the complete document. Instead, it is desireable to

have the capability to update part of the document. In some other cases the user changes their

usual terminal and uses a different one, so they may first need to download a fresh copy of

the current configuration document, make some changes, and upload it (either complete or a

part of it) to the server.

Typically, configuration documents are highly structured. Owing to this, the trend

nowadays is to use the Extensible Markup Language (XML) (specified by the World Wide

Web Consortium in the W3C recommendation XML 1.1 [93]), for formatting documents that

personalize the instance of the service.

So, we know that configuration documents are effectively XML documents, but how are

they sent to and received from the server that stores them? The XML Configuration Access

Protocol (XCAP) solves this vacuum.

17.1 The XML Configuration Access Protocol (XCAP)

The problem of document management can be depicted in its most simplified way as in

Figure 17.1. A user creates an XML document in his computer and wants to upload it to a

server. The server will use the document at a later time to produce a personalized instance of

the service.

The problem to be solved requires designing a protocol that allows such an upload

procedure. HTTP (specified in RFC 2616 [144]) provides a good baseline, since it provides

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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