Multimedia Transmission and Distribution in Heterogeneous Multicast Scenarios

The world of multimedia communication is characterized by heterogeneity: many different devices exist there, which differ by computing complexity and presentation/display capabilities. Also they use different access to fi xed or wireless networks, with different transmission rates and quality of services. It is not possible to supply many data streams of one source for each device type and current status of all networks used for access! Recent hierarchical audio and video compression methods are used as the basis for solving this problem. Our research activities in this area concentrate on the problem of using the possibilities of these compression methods of mobile heterogeneous devices. Mobile devices are dynamically assigned to multicast groups, depending on their presentation capabilities and current status of quality of transmission, as well as on the requested and subscribed level of quality. Corresponding to these parameters, a data stream is fi ltered out of the source data stream and assigned to the multicast group. A reduction of data traffi c in the networks is another result, because not more data is transmitted than can be processed by the devices.

Furthermore, we work on cryptographic models corresponding to hierarchical concepts. If (multicast) user groups receive the content of certain compression level depending on their presentations capabilities, network status or subscribed service class, it should be possible to receive the multimedia stream protected by conditional access by only one single decryption process. The key management has to be optimized for multicast scenarios and hierarchical compression.
Additional activities in the area of security for multimedia applications concern the extension of the SIP protocol to a security management protocol, the integration of security services into H.323 and SIP applications, as well as the realization of (Secure ) RTP . The security mechanisms provided by SRTP are expanded by real-time authentication of origin services based on digital signatures.