AN ANALYSIS OF A VARIABLE BIT-RATE MULTIPLEXER USING LOSS PRIORITIES

The network of the future will carry a variety of video applications, which are characterized by high bandwidth and stringent requirements o n delay and loss. In this paper, we develop a new analytic model for a variable bit rare video source, which can model a variety of video ap plications by a suitable choice of model parameters. Using the model w e study the performance of a video multiplexer that multiplexes severa l full motion video sources. The video sources are assumed to use a la yered coding technique, We propose a service strategy that guarantees delivery of packets marked essential, whereas non-essential packers ma y be dropped in the event of congestion. The study shows that with lay ered coding that classifies packets as essential and non-essential, on e can get good tail probabilities for a given number of sources at the expense of some loss for non-essential packets, Alternatively, for an allowed loss rate of non-essential packets (i.e., for a given picture quality), one can multiplex a larger number of such video sources. We also investigate the performance of the video multiplexer when: (a) t he video sources are correlated, and (b) when independent video source s with different thresholds for essential packet rate are multiplexed together. We suggest that the coding scheme should distribute the bits generated by a scene change over several successive frames to prevent deterioration of picture quality when sources are correlated. Since t he perceived quality of the picture at the receiver depends on the thr oughput of non-essential packets, we suggest a loss or service priorit y structure within the non-essential class to guarantee a contracted p icture quality.