Contributions toward real-time services on packet switched networks

Packet switched communications services with real-time delay constraints, such as voice and video, combine the established fields of digital signal processing and data communications networking. Each field is outlined, and new open problems due to the combination are identified. A simulation study investigates layered coding using a packet voice Markov chain source model. Information is partitioned into two or more priority layers to protect important components from loss. A parameter, $\alpha$, identifies the proportion of traffic placed in each priority. Packet loss rates for each priority and $\alpha$ are used to compute the signal to noise ratio, which is a more appropriate performance measure for voice and video services than loss rates alone. Dynamic feedback control of the priority partition based on network load conditions is shown to be effective, even with substantial feedback delay. Feedback, in conjunction with priority, provides graceful service degradation with increasing load and loss rate. A queueing analysis of this system is also investigated using a two-dimensional Markov chain source model that represents both load and $\alpha$, which vary dynamically. The simulation and analytic models are compared. Two methods for reducing the numerical complexity are given. A two-hour long empirical sample of variable rate video is derived by applying a simple intraframe video compression code to an action movie. Statistical characteristics are measured, including an accurate model for the heavy-tailed marginal distribution of video frame bandwidth. A statistical property called long-range dependence is described, measured, and shown to be significant for this data. A new traffic source model results from combining the marginal distribution with long-range dependence. Extensive trace driven simulations characterize network queueing behavior and allocation of bandwidth/buffer resources. Statistical multiplexing gain of variable rate video is evaluated as well as the advantage due to multiplexing video with data services. We discuss the implications of this traffic analysis for for the design of congestion control mechanisms for integrated packet networks. We close with some comments on the ramifications of advancing electronic hardware speed and complexity for multi-media communications.