Transparent consumption of Digital Items between terminals using MPEG-21 Session Mobility
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There is an augmented use of multimedia applications for communication, information access and entertainment. Furthermore, a wide set of devices has become capable of consuming multimedia. This has created a need for Users to easily and transparently switch between these devices. Session mobility is a concept that aims at enabling seamless switching between terminals during a session. It involves capturing and transferring of session information, and finally reconstruction of the session at the destination terminal. One approach to session mobility is MPEG-21, which is an open framework for multimedia delivery and consumption. The vision of MPEG-21 is to provide seamless and universal delivery of multimedia over a wide range of terminals and networks. Session mobility based on MPEG-21 would therefore solve problems regarding differences in terminal capabilities and network characteristics between the participating devices. The transaction unit in the MPEG-21 framework is a Digital Item; a digital object that associates metadata with multimedia resources. Three parts of MPEG-21 are of importance in the context of session mobility. Digital Item Declaration determines the availability of the multimedia resources. Digital Item Adaptation provides tools for session mobility and adaptations of Digital Items. Digital Item Processing enables control of the session handover and enhances interoperability by allowing the content creator to provide suggested processing instructions. An implementation of session mobility is performed. It demonstrates how MPEG-21 tools are able to realize session mobility in an interoperable way. Digital Item Adaptation tools are used to automatically adapt the Digital Item according to the usage environment. A media player API is developed to provide an interface from the Digital Item to the terminal's media platform. This is necessary in order to let the content creator collect and reconstruct the application specific session state. The solution requires the terminal to support this API in addition to MPEG-21 Digital Item Processing. Consequently, the current specification of MPEG-21 Digital Item Processing is not specific enough to realize session mobility without making any assumptions about the terminal.