UBC Theses and Dissertations
An MPEG2 to ATM converter to optimize performance of VBR video broadcast over ATM networks Wong, Paul
Whereas variable bit-rate (VBR) MPEG2 (Moving Pictures Expert Group) video is desirable for broadcasting applications due to its conservation of bandwidth, the resulting traffic characteristics are content-dependent and unpredictable. Before broadcasting video over an ATM (Asynchronous Transfer Mode) network, a service contract is established specifying the source traffic descriptors and the required quality of service (QoS). Usage parameter control (UPC) is performed to ensure conformity of the source traffic to its descriptors. This protects the network from misuse of resources by misbehaving sources, which can affect the QoS of other connections. For real-time variable bit-rate (rt-VBR) traffic, the key traffic descriptors for UPC are PCR (peak cell rate), MBS (maximum burst size) and SCR (sustainable cell rate). ATM cells conforming to the UPC parameters are guaranteed delivery with the specified QoS, while nonconforming cells are subject to loss when congestion occurs. As cell loss results in the degradation of the received video quality, source rate control is usually required to minimize their effects on video quality relative to human visual perception. This thesis presents a novel MPEG2-to-ATM converter for VBR video broadcast over ATM networks. It functions as an external post-coding source rate controller between any MPEG2 source (video archives, life programs, etc.) and an ATM network. Dynamic break points are employed to shape and partition the video data into high priority (HP) ATM cells which conform to the prevailing usage parameter control contract with the network, and nonconforming low priority (LP) cells which minimize the effects of cell loss due to network congestion on the subjective quality of the received video. Both high and low priority cells are transmitted over a common ATM virtual connection. Performance evaluations of actual VBR MPEG2 streams transmitted over a simulated converter and ATM network are presented to demonstrate the effectiveness of the proposed method.
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