Video quality control under cell-discarding algorithms in an ATM network supporting layer-encoded video streams

We consider a multiplexer station which supports ATM video traffic streams. The system model also applies to the multiplexing operation carried out at the output queue of each output-queueing ATM switch. We assume that video signals are encoded by a two-level layered encoding algorithm under which each ATM cell is properly marked as a high-priority (HP) or low-priority (LP) cell according to the significance of the information carried by the cell. The video multiplexer implements a congestion-control based cell-discarding algorithm under which, when high congestion conditions an observed, the LP cells an discarded. We take into account the high burstiness embedded in the video traffic as observed by the multiplexer at the cell-level and the frame-level time scales. We show that, if not carefully designed, a cell-discarding algorithm can cause both inter-frame and infra-frame short-term video quality degradations. To correct this situation, we introduce new cell-discarding algorithms which incorporate a probabilistic mechanism into their cell discarding scheme and which take into account the features of the bursty inter-frame and intra-frame processes. Two video degradation indicators are introduced to measure the short-term inter-frame and intra-frame video quality degradation features experienced by a video stream. Through numerical examples, we identify and compare the system performance behaviour under the introduced cell-discarding algorithms