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  set of specifications. XDM allows a user to modify XML documents stored in remote network servers. It also allows the local copy of those XML documents 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, other terminals are updated with the latest changes. Last, the XDM architecture also provides limited support for searches of information stored in these XML documents.
18.1 XDM architecture
Let us describe the XDM architecture with the help of Figure 18.1. The XDM architecture assumes 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 stored in any of the servers and kept synchronized with the copy in the client. When a user wants to change a configuration setting in a service, such as adding a friend to a presence list, ...