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The deployment of multimedia services in nextgeneration networks is a challenge due to the high configuration complexity of the streaming process in different stationary and mobile sub-networks and for various user devices. The Session Initiation Protocol (SIP) has proven to be a suitable mechanism to handle the control of multimedia services in such networks. However, the current standardization and implementation of SIP do not allow the simultaneous coordination of multiple concurrent applications on a single device, as the prescribed realization of the SIP state machines (transactions) does not consider mutual access of applications to a single SIP stack. This paper presents a SIPbased mechanism for synchronized management of services in a shared environment. We have developed a middleware that facilitates the uniform access of multiple applications towards one or multiple SIP stacks to enable prioritization of services and centralized resource coordination of concurrent SIP applications on a single terminal or server.

Absbact-In this paper we present a system for IP based networks which allows Policy based Handover between different access network technologies. The policy rules for selection of the access network are provided by the networklservice provider. An Interface Selection Subsystem on the mobile terminal triggers the handover according to these policy rules, and a Service Subsystem initiates adaptation of the media stream to match the network resource availability. We provide performance measnremen& to analyze the handover behaviour of our system during a running video session. These measurements show that with the proper intenvorking between interface selection in the mobile terminal and media adaptation in the video server, an almost seamless Policy based Handover between heterogeneous wireless networks is possible.

Stream adaptation is a key technology for enabling communication between heterogeneous multimedia devices and applications, possibly located in heterogeneous wired or wireless networks. Converting already compressed multimedia streams into a format suitable for a certain receiver terminal and network can be achieved by transcoding or by filtering of media streams. Transcoding allows more flexible adaptation operations but is in general a very CPU-intensive process. Therefore, scalable media formats have been developed, which allow more efficient adaptation of media streams through media filtering. Several filter techniques for specific media formats have been proposed and implemented during the last decade. Recently, the MPEG-21 Digital Item Adaptation standard has defined a set of new tools for multimedia adaptation. In this paper, we provide a comparative study of several adaptation techniques for scalable multimedia streams. We compare generic MPEG-21-based adaptation techniques with filter mechanisms for specific media formats with respect to the required processing resources and scalability. We also compare filter techniques with stream adaptation through transcoding. Moreover, we compare how adaptation of multiple media streams performs on systems with single-core and with multi-core processors.