Multicasting is a very important extension to the standard Internet protocols especially for multimedia streams. So far most applications neglected important features like secure communication, real-time requirements, and reliability. We suggest two protocol stacks which provide these features based on Internet standards/drafts (OPGP, RTP) and own developments (SMP). OPGP is a open standard (RFC2440) based on the widely used Pretty Good Privacy (PGP). We use the extended support for symmetric key management to provide a fast and secure packet management and we have integrated the two fast, free, and secure AES candidates RIJNDAEL and Twofish into our applications. The Real Time Transport Protocol (RTP) is an application layer transport protocol that has been especially designed for the transmission of data streams with real time characteristics such as audio or video. The Scalable Multicast Protocol (SMP) is a new reliable multicast transport service that was developed at the University of Mannheim. The main features are high reliability, good salability and different service classes. We have integrated and tested this protocol stack in the digital lecture board (http://www.informatik.uni-mannheim.de/~geyer/dlb/).

Ruediger Weis received his MS in Mathematics from the University of Mannheim, Germany. His PhD project covers cryptographic algorithms and protocols for distributed multimedia applications. Further research interests are smart cards, computer security, and mobil communication. Ruediger is also a member of the Chaos Computer Club and a cryptography consultant for convergence, Berlin. Dr. Werner Geyer is research scientist at the University of Mannheim. He received his MS and PhD degrees in Computer Science from the University of Mannheim, Germany. His research areas include CSCW, telecooperation, multimedia communication, interactive applications and Internet protocols. Christoph Kuhmuench received his MS in Computer Science from the University of Mannheim, Germany. Christoph's research concentrates on media scaling and coding, multimedia communication, interactive applications, and Internet protocols.