A method for supporting time-constrained and nontime-constrained integrated services on a shared dual bus network is presented. The method is an extension of the basic distributed queue protocol defined in the IEEE 802.6 distributed-queue dual-bus (DQDB) MAN standard. The extended distributed queueing protocol differs from the basic protocol in allowing more than one outstanding request in the distributed queue at any one time. Used at the high priority and in conjunction with segment stream shaping and subscribed service limiting, the extended protocol provides bearer services with guaranteed bandwidth and bounded delays. Bearer services with fair but nonguaranteed bandwidth shares, suitable for nontime-constrained applications, are provided by the same protocol and bandwidth balancing operating at the lowest priority. A number of the desirable attributes of the proposed scheme are identified including the optimality of the delay variance introduced by the access protocol. An approximate analysis of the access delay experience by time-constrained streams is presented.>

A generic flow control (GFC) protocol is proposed to regulate multiple terminals within the broadband-ISDN customer premises network. The GFC protocol is based on multipriority distributed queuing preceded by a traffic shaping function, and meets the requirements for flexible allocation of service parameters, control of jitter and guarantee of bandwidth. This GFC protocol provides the necessary flexibility to match the constant bit rate (CBR) jitter performance and variable bit rate (VBR) service requirements to the particular service type. It integrates well with usage parameter control without imposing excessive burstiness on each virtual connection cell stream delivered to the network. By allowing connectionless users to access at the lowest priority, only when no higher priority users are queued, there is no reduction in guaranteed capacity available for other VBR and CBR users.>

Distortion measures are developed for the purpose of predicting the subjective quality of moving monochrome television pictures. The need for such measures is particularly recognized in the area of digital picture coding. Subjectively relevant distortion measures that mirror viewers' assessments of picture quality would make the task of designing and optimizing coding schemes considerably easier. The distortion measures are based on a spatiotemporal model of threshold vision that incorporates the filtering and masking processes. The visual filtering is carried out by parallel excitation and inhibition paths, each of which is separately linear but which combine in a nonlinear way to take account of the adaptation with background luminance. The masking is in the form of a point-by-point weighting of the filtered error based on the amount of spatial and temporal activity in the immediate surround. The processed error averaged over the picture is then used as a prediction of picture quality. Three Classes of distortion measure are considered: 1) the raw error measures that have been used in the past; 2) the filtered error measures where the filtering properties of vision are taken into account; and 3) the masked error measures where the masking processes are also included. It is shown that the filtered error measures are better predictors of picture quality than the raw error measures. The masked error measures lead to further improvements but only if local rather than global averaging procedures are used. It is postulated that this is because viewers tend to base their quality ratings on critical areas rather than on the whole picture.

Coding methods for television signals have been proposed which would rely on the frame-to-frame correlation. But it was to be expected that the instrumentation and efficiency of such methods would be severely impeded by the large influx of new samples caused by scene changes. If, however, the spatial resolution of the new scene could be temporarily reduced, the scene change problem could be largely overcome. In this paper, psychophysical experiments and their results are described which were designed to test the hypothesis that the human observer would not perceive a temporary reduction of spatial detail after scene changes. For the tests, the bandwidth of standard television signals was temporarily reduced after each scene change by means of a transient controlled low-pass filter, the minimum bandwidth and recovery time of the filter being the main experimental variables. An average recovery time of780msec was found permissible by the most critical observers, when the minimum bandwidth of the new scene was250kc, i.e., one twentieth of the system bandwidth, reached at the end of the recovery transient.