Summary form only given. The requirements for high bandwidth networking to support telescience and the science community are discussed. High-rate sensors (such as synthetic aperture radars and high-resolution infrared spectrometer) can generate data at 300 Mb/s. Interaction with remote laboratories requires transmission of video images. Low delay is required for remote control, implying high bandwidth in the networks. Graphic workstations interacting with supercomputers require high-bandwidth connections. Access to remote multimedia databases requires the ability to browse and retrieve such data at high rates and low delay. Tools supporting cooperative research (e.g. multimedia computer supported teleconferencing) require significant bandwidth and low delay.>

Provides an overview of the technical articles and features presented in this issue.

There are many design choices that must be made in the development of a packet radio network. There is usually no single correct choice, and the decisions are dependent on the environment that the network must work in, the requirements for performance and other functionalities, and the cost and other limitations, in addition, as new hardware and software technologies become available, the parameters governing the decisions change and often result in different selections. This paper outlines a number of design issues and choices available. The intent is to provide an overview of the design decisions that must be made so as to provide a context for the decisions made in a number of existing and developing packet radio networks. It is hoped that this will allow future designs to take advantage of both the wealth of experience available as well as new technologies. Three areas of design decisions are identified. The first area deals with the physical aspects of the network and concentrates on the radio connectivity and channel sharing. The second area deals with the automated management of the network and concentrates on issues such as link management and routing. The third area deals with the interface of the network to the users and some practical aspects of operating and maintaining a network.

A model is presented that allows the computation of the approximate level of communication performance for an arbitrary packet radio network using one of a variety of protocols. The communication performance is specified in terms of the end-to-end message delays incurred for a given level of end-to-end traffic rates. The network is specified in terms of its link capacities. While the model makes a variety of assumptions to allow simple computation of the performance level, agreement within a factor of two is obtained with results from simulation. As the number of nodes in the network and its connectivity is increased, the model is expected to give better accuracy. Thus, the model should prove to be a useful tool in the design and analysis of large packet radio networks where detailed analysis and simulation would prove too cumbersome.

The problem of distortion-rate functions for vector sources is considered. Two fidelity criteria are treated. The first considers the maximum of the weighted component distortions and then takes the per-letter average. The second takes the maximum of the weighted component per-letter averages. In either case, a well-defined distortion-rate function results, giving the minimum possible distortion achievable at a given rate of transmission. Upper and lower bounds to these distortion-rate functions are derived in terms of more easily calculated functions.

The definition of the rate-distortion function is extended to the case of a stationary-ergodic source with side information, and the appropriate coding theorem is proved. Inequalities between the joint, marginal, and conditional rate-distortion functions for ergodic processes are given, and their implications in terms of universal coding are discussed.

A class of lower bounds to rate-distortion functions of stationary sources with context-dependent fidelity criteria is derived by mapping the source and distortion measure into an equivalent restricted-transition stationary source with a single-letter fidelity criterion, and then applying the composite bound. This approach is seen to yield bounds which, although sometimes quite loose, apply to general stationary sources and context-dependent fidelity criteria. Two examples are presented.