The influence of broad-band communication networks on the evolution of office communication terminals is considered. Three trends are predicted:\bulletthe evolution of presently existing dedicated terminals towards higher speed and more sophisticated functionality;\bulletthe push of multifunctional workstations allowing simultaneous operation in several modes of communication, such as voice, data, text, facsimile, and graphics;\bulletthe occurrence of new communication services relating to video and CAD/CAM applications. A more detailed description of these trends is given, and some first experimental steps already done are described. The emphasis in this paper is on application aspects rather than on interfaces, protocols, coding methods, etc.

We show that the error signal incurred by block quantizing stationary data is nonstationary under some conditions. Examples are presented that indicate that the mean square error is largest at the block edges. When block quantizers are used to encode pictures at low bit rates, this effect tends to make the block edges visible in the reconstructed picture.

An upper bound on the rate-distortion function for discrete ergodic sources with memory is developed by partitioning the source sample space into a finite number of disjoint subsets and bounding the rates for each subset. The bound depends only on the mean vectors and covariance matrices for the subsets and is easy to compute. It is tighter than the Gaussian bound for sources that exhibit clustering of either the values or covariances of successive source outputs. The bound is evaluated for a certain class of pictorial data using both one-dimensional and two-dimensional blocks of picture elements. Two-dimensional blocks yield a tighter bound than one-dimensional blocks; both result in a significantly tighter bound than the Gaussian bound.