Verena Kahmann

Collaborative Media Streaming

Supervisor(s) and Committee member(s): Prof. Dr.-Ing. Lars Wolf, TU Braunschweig (Supervisor), Prof. Dr.-Ing. Jörg Ott, Helsinki University (Second Reviewer)


At the time being, multimedia services using IP technology are a hot topic for network and service providers. Examples are IPTV, which stands for television broadcast over a (mostly closed) network infrastructure by means of the IP suite, or video on-demand, which allows for watching selected movies via Internet on TV devices or computers in the home.

Technically, these services can be classified under the notion of streaming. A server sends media data in a continuous fashion to one or several clients, which consume data portions as soon as they arrive, mostly displaying them also. By using a feedback channel customers may influence the play-back, since they may watch programs time-shifted or pause the program.

An enhancement of such streaming services is to watch those movies together with a group of people on several devices in parallel, independent from the location of the other group members. Similar approaches have been developed using IP multicast, for example for distributing lectures or conference talks to a group of listeners. However, users cannot control the presentation: pausing or skipping of more unimportant parts is impossible. Moreover, the streaming presentation is announced by means outside the application instead of adding others to the session directly within the application.

The costream architecture developed in this work offers a collaborative streaming service without these limitations: People may retrieve movies, join others watching a movie or invite others to such a collaborative streaming session. Participants of a collaborative streaming session can control the movie presentation like they do on a DVD player. Dependent on the desired course of the session the control operation is executed for all users, or the group is split into subgroups to let watchers follow their own time-lines. For this, a group management controls access to session control operations by means of user roles. Separate from the group management, the so-called association service provides for streaming session control and synchronization among participants.

This separation of duties is advantageous in the sense that standard components can be used: For group management, SIP conferencing servers are suitable, whereas session control can best be handled using RTSP proxies as already used for caching of media data.

Eventually, the evaluation of this architecture shows that such a service offers both low latency for clients and an acceptable synchronization of media streams to different client devices. Moreover, the communication overhead compared to usual conferencing or streaming systems is very low.

Communication and Multimedia Systems


The research in the Communication and Multimedia Systems (CM) group of Prof. Dr.-Ing. Lars Wolf is on architectures of communication and networking systems considering application requirements especially for, but not limited to, the Internet in a broad sense. Our research areas include

  • Multimedia networking and infrastructures, also for mobile and wireless systems
  • Wireless, especially ad-hoc and sensor networks, including also vehicular and delay-tolerant networks
  • Future network architectures and autonomic communication

These areas aren't separated but overlapping, leading to interesting influences on each other. Further, there are sometimes infrastructure and support oriented projects, e.g. for e-learning purposes. Please feel free to visit our project pages for any further information on ongoing and finished research.

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