Congestion control based dynamic encoding algorithms for voice and video streams in integrated services communications networks.

摘要

The dynamic encoding algorithms for real-time services, including voice and video, have been known to be effective for congestion-control in packet networks. Under such an algorithm, the voice and video information is first separated into multiple streams marked with different priorities according to the significance in the reconstructing process carried out at the decoder. At a multiplexer or a switch within a network, a bit/cell-discarding algorithm is used so that when high congestion conditions are observed, less significant information is discarded. In this study, the system performance under such a mechanism is extensively studied. In the first part of this study, we consider an application of the voice dynamic encoding algorithm in a satellite network. A load-adaptive/TDMA satellite communications link which serves to interconnect broadband multi-media stations is considered. Each station supports packetized voice and data message streams and employs a dynamic voice encoding algorithm. Two distinct backbone channel allocation algorithms are introduced. We develop analytical methods for the analysis and design of such integrated networks. The effects of the propagation delay across the backbone link are especially demonstrated. Also illustrated are the performance improvements attained due to the use of the load-adaptive/TDMA scheme. In the second part of this Dissertation, the voice/video quality control under dynamic encoding algorithms is studied. In previous studies done by others, the quality of the voice/video streams has been examined for a single stream, without incorporating the impact of the multiplexing operation. In addition, only long-term quality has been considered. We take into account the high burstiness embedded in the voice and video traffic, and show that, due to this high burstiness, if not carefully designed, a dynamic encoding algorithm can cause severe short-term quality degradations. To correct this situation, we introduce various bits/cell-discarding algorithms which take into account the features of the burstiness. New voice and video degradation indicators are introduced to measure the short-term voice/video quality degradation levels. Through numerical examples, we identify and compare the system performance under the introduced bit/cell-discarding algorithms. It is shown that, under a prescribed long-term voice/video quality level, the introduction of a probabilistic component in the bit/cell-discarding process significantly improves the system performance. Moreover, it is observed for video streams that the short-term video quality performance is further improved by dynamically calculating the value of the probabilistic component according to the frame-level burstiness information.