vide the necessary integrated functionalities. The functions of each of the servers are briefly described below: The XML document management Server (XDMS) is responsible for han- dling the management of network user XML documents such as presence authorization rules, static presence information, contact and group lists (see "resource list server" next), policy data, and SO forth. The Resource List Server (RLS) handles subscriptions to Presence Lists. It creates and manages back-end subscriptions to all resources in the Presence List. The list content is retrieved from the XDMS. SIP Presence Server is responsible for accepting, storing, and distributing presence information on behalf of resources. It obtains the required resources data such as authorization rules from the XDM server, and manages subscrip- tions and generates notifications. 9.2.3 Indirection Service In its simplest form, the Indirection Service translates a channel name into the video server address from which the client could stream the video content. The Indirection Service can be invoked through SIP protocol, either directly by the client or as part of a chain of service invocations. In either case, the service should behave exactly the same way. The channel mapping table may contain information about the video contents, for example, video formats and bit rates, to aid media capability negotiation. The negotiation process, however, may be handled by a separate service making use of the information obtained from the Indirection Service. In our testbed, the Indirection Service is implemented as a SIP servlet, hosted on Mobicents Platform [14]. Mobicents SIP Servlets is an open-source implementation of the SIP servlet's open standard [15]. The implementation of the Indirection Service is general enough to run on any platform that supports the standard, for example, Sun's SailFin [16]. 9.2.4 Network Service The Network Service, implemented as SIP servlet in Mobicents, packages and exposes proprietary network functionalities such as bandwidth managem