Traffic shaping for variable-bit-rate MPEG-2 video
Il-Sung. Lee · Library and Archives Canada (Government of Canada) · 1997
As digital video services become more prominent, the strain that they place upon networks will become more pronounced. The network of choice for carrying these transmissions will be the Broadband Integrated Services Digital Network using the Asynchronous Transfer Mode (ATM) transmission protocol. In particular, ATM is well suited for handling variable-bit-rate (VBR) transmissions because it is capable of statistical multiplexing. VBR coding is also advantageous because it is conducive for producing consistent image quality. This thesis outlines the conversion of a software MPEG-2 video coder to operate as a VBR coder and then as a traffic shaping one. The rate controller for the traffic shaping coder is based on the Leaky Bucket policing algorithm to ensure conformity to the network traffic descriptors. First, comparisons are made between constant-bit-rate encoded sequences and their VBR counterparts. As expected, the VBR sequences possess superior average peak signal to noise ratios (PSNRs) while maintaining a more consistent PSNR between frames. Secondly, traffic shaped sequences are introduced for comparison. Compared to the VBR case, these sequences exhibit a less erratic bit rate profile but also a lower average PSNR. However unlike the open-loop encoded data, the traffic shaped bit streams are not likely to encounter any network intervention when transmitted in any realistic network scenario. The effects of varying each network traffic descriptor (peak bit rate, sustained bit rate, and maximum burst size) are examined and the projected network-induced bit losses in the absence of traffic shaping are provided.