Chapter 18 - Service Configuration in the IMS

Chapter 17 provided a description of the protocols at the user’s disposal for configuring services on the Internet. We saw that the service configuration architecture assumes an XML document stored on a server. The client retrieves a copy of the XML document, makes changes to it, and sends the delta back to the server. In IMS, the architecture for service configuration architecture is developed around the XML Document Management (XDM) architecture created by the Open Mobile Alliance (OMA) in the XDM [244] set of specifications. ...
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Chapter 18 - Service Configuration in the IMS Chapter 18Service Configuration in the IMSChapter 17 provided a description of the protocols at the user’s disposal for configuringservices on the Internet. We saw that the service configuration architecture assumes an XMLdocument stored on a server. The client retrieves a copy of the XML document, makeschanges to it, and sends the delta back to the server. In IMS, the architecture for service configuration architecture is developed around theXML Document Management (XDM) architecture created by the Open Mobile Alliance(OMA) in the XDM [244] set of specifications. XDM allows a user to modify XMLdocuments stored in remote network servers. It also allows the local copy of those XMLdocuments in the IMS terminal to be synchronized with the copy stored in network servers,so that if the user makes changes to one XML document from a given IMS terminal, otherterminals are updated with the latest changes. Last, the XDM architecture also provideslimited support for searches of information stored in these XML documents.18.1 XDM architectureLet us describe the XDM architecture with the help of Figure 18.1. The XDM architectureassumes a terminal that implements the role of an XCAP client, and one or more servers,called XDM servers, that implement the role of XCAP servers. XML documents are storedin any of the servers and kept synchronized with the copy in the client. When a user wants tochange a configuration setting in a service, such as adding a friend to a presence list, the userchanges the local copy of the XML document in the client and sends the change to the server,which applies it, and stores an updated version of the XML configuration document. The XDM architecture introduces the following concepts.XDM client (XDMC). This is an XCAP client running in the IMS terminal. The XDMC implements the core XDM features and some application-specific features.Aggregation proxy. This is an HTTP proxy that is configured as an HTTP reverse proxy. The Aggregation Proxy authenticates the XDMC towards an XDMS. It may also route XCAP requests towards an XDMS or towards an Aggregation Proxy located in remote network. It also routes search requests towards the Search proxy. When receiving responses, it can compress the body of the response.The 3G IP Multimedia Subsystem (IMS): Merging the Internet and the Cellular Worlds Third EditionGonzalo Camarillo and Miguel A . Garc ıa-Mart´n ´ ı© 2008 John Wiley & Sons, Ltd. ISBN: 978-0-470-51662-1 CHAPTER 18. SERVICE CONFIGURATION IN THE IMS390 Figure 18.1: XDM architectureSearch proxy. This is an HTTP proxy that processes search requests received from XDMCs towards XDMSs or remote Aggregation Proxies. On received responses, the Search proxy combines the results of the responses received from XDMSs and remote Aggregation Proxies before forwarding them to the XDMC.Shared XDM servers. XDM servers (XMDSs) that are used by several applications. Shared XDMSs are effectively XCAP servers. There are specialized shared XDMSs: shared list XDMS, shared group XDMS, shared profile XDMS, and shared policy XDMS.XDMSs. This is an application-specific server for service configuration purposes. Effec- tively, XDMSs are XCAP servers that serve a single application. Most of the interfaces of the XDM architecture are implemented with XCAP. This is thecase of the interfaces XDM-3, XDM-4, XDM-8. However, interfaces XDM-1 and XDM-2 areused for subscription to changes in XML documents, based on the XCAP event package forSIP. Consequently, XDM-1 and XDM-2 are SIP interfaces. Interfaces XDM-5, XDM-6, XDM-7, and XDM-9 implement the Limited XQuery over HTTP protocol. Unnamed interfaces inFigure 18.1 are defined by their respective applications, but they typically consist of XCAP,SIP for subscriptions to XCAP event packages, and Limited XQuery over HTTP. The XDM architecture considers different applications that can be customers of the XDMservice (or enabler, as it is called by the OMA). For example, the presence service is acustomer of XDM, because the list of watchers, the authorization policies, etc., are all storedin XML documents managed by XDM. Other services that use XDM include Push-to-talk18.2. DOWNLOADING AN XML DOCUMENT, ATTRIBUTE, OR ELEMENT 391over Cellular and PSTN/ISDN simulation services. Owing to this diversity of customers ofXDM, the XDM architecture considers the existence of different XDM servers, each oneperhaps specialized in serving a given application. An XDMS is a logical representation ofthe service configuration aspects of a service or application. In real products, it is expectedthat XDM servers are integrated into the specific server (e.g., presence server, PoC ...