Accurate modeling of H.261 VBR video sources for packet transmission studies

This paper examines the segmentation of variable bit rate video information produced by an H.261 codec, modified for variable bit-rate output, for transmission over packet-switched and Frame Relay networks. It is shown that packetizing at the Group of Blocks level is required to match the characteristics of such networks and that this requires a more sophisticated statistical model of the resulting data stream than the frame-level models that are frequently used. A Transform Expand Sample (TES) technique is used to obtain an accurate model of the autocorrelation and the marginal probability distribution of the bit-rate variations at this level. Furthermore, a new, simplified but accurate, method is introduced for dealing with the periodic components that are present in the autocorrelation when modeled at this level. The model is extended to permit simulations of systems in which the codec quantization rate can be controlled by network congestion notifications.