A Scheme for Real-Time Channel Establishment in Wide-Area Networks

Ferrari and Verma, UCB/Tenet

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Content Summary

A scheme for guaranteeing delays in packet-switched WANıs is proposed, based on the assumption that reasonable worst-case performance bounds for intermediate swtiches can be obtained. The scheme is based on deadline scheduling and distinguishes deterministic from statistical real-time channels; the latter are "probabilistically real-time" while the former offer hard guarantees even in continued bursty conditions. Mathematically rigorous tests are used to determine whether the criteria for each channel type can be met at an intermediate switch already serving a finite number of channels. An additional delay-bounds test, also mathematically rigorous, is used to avoid scheduler saturation, in which the approaching deadlines for a set of packets overlap so much that scheduler CPU cycles become the bottleneck to satisfying the scheduling constraints.

Simulation is used to derive preliminary results. As expected, the scheme gives the best load balancing and network utilization with bursty traffic (especially for statistical channels).

Relevance to Multimedia

The only paper Iıve seen so far that attempts a mathematically sound solution to real-time reservation. Unfortunately, itıs not clear that "reasonable" worst-case behavior can be parameterized in a way that does not result in poor utilization in the resulting network, and simulation is less compelling than a trial implementation not only in validating results but also flushing out potential bugs due to real-life scenarios not anticipated by the simulation.


3 out of 5: a bit dense to read but worthwhile for the mathematical approach, though I wish a real implementation had been presented.
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Armando Fox (fox@cs.berkeley.edu)