formats are described in Section 7.5. (2) description: For a control point to learn more about the device and its capabilities or to interact with a device, the device summarizes its services and capabilities and sends them in a description to the con- trol point. The device description includes a list of actions the service responds to and a list of variables that model the state of the services. (3) control: Given knowledge of a device and its services, the control point can ask these services to invoke actions. (4) eventing: The device can send an event to control points when values of state variables in a device change. A device may subscribe to receive event notification. (5) presentation: A device should provide an HTML-based administrative interface that allows a user to directly control the device and view the device status. 7.3 SIP In this section, we briefly describe functionalities of SIP. SIP is a signaling, presence, and instant message protocol to establish, modify, and finish multi- media session in one-to-one or among multiple participants in the application layer. SIP also provides the delivery of presence and instant messages. It is defined in RFC3261 [5]. In SIP, the following clients and servers are defined: User agent: A user agent is a SIP-enabled end device. The user agent provides communication services to a user. A user agent client (UAC) is a functional module issuing a request and a user agent server (UAS) is a functional module responding to a request. In VoIP, a UAC is a calling party and a UAS is a called target party. SIP server: A SIP server supports communication establishment between a UAC and a UAS. Three types of a SIP server exist. A proxy server transfers a SIP request, which a UAC issues to a UAS and other servers. Multiple-hop transfer is also available. Moreover, the server provides authentication, authorization, network access control, and routing. A © 2009 by Taylor & Francis Group, LLC Home Networking System with SIP redirect server receives a request and sends a curren