Dynamic Data Path Reconfiguration
Key: GZ01-1
Author: Carsten Griwodz, Michael Zink
Date: October 2001
Kind: In proceedings
Book title: International Workshop on Multimedia Middleware 2001 at ACM Multimedia 2001
Abstract: In video distribution systems research, we have felt a strong demand for a prototype that allows the integration of experimental mechanisms. For its deployment in cooperative projects, it is necessary that it is also standard-compliant and interoperable, ie. to support RTP/RTCP and RTSP. For this reason, we have looked for existing code that would allow us to integrate our experimental features. Due to the interaction of RTP and RTCP, and the possibility of receiving data from several sources at a single port, this code would have to support a non-cyclic graph of modules on the data path. The possibility of packets from unexpected senders in RTP, which must be handled in an application-defined way ranging from dropping to the establishment of a new trunk in the graph, requires that the data path is dynamically reconfigurable at run-time in a non-blocking manner. The necessity exists also for high-level principles such as optional write-through caching: if a user's pause request is received for a stream that is forwarded to that user and also cached on disk, the trunk towards the user must be suspended without packet loss. If the user resumes viewing, the application must create a new graph, which retrieves the data from the cache. While feasible abstractions for streaming applications and have frequently been designed and published they are not found in free, open source systems. Available approaches implement either hard-coded sequences, or they consider frameworks that allow the specification of an end-to-end behavior for complex multimedia systems. The latter kind of systems aim at a much coarser granularity than feasible for us, and include networking. We found that a theoretical solution to the real-world need for dynamic data path reconfiguration is insufficient, and show an implementation. We explain our design decisions that are derived from our requirements.

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