TR-IIS-03-008    PDF format

Abstract

Proxy technologies are commonly used at boundaries of ISPs (Internet Service Providers) to reduce the bandwidth required in the backbone WAN. By caching portions of a video content in a video proxy closed to clients, the video playback quality can be dramatically improved and insufficient WAN bandwidth defeated. In the loss-less network environment, the OC (Optimal Cache) algorithm is proposed to use minimal cache storage in the video proxy, and to save maximal bandwidth required in the backbone WAN for QoS-guaranteed video playback. However, data packets may be lost while delivering video contents through the Internet that affects video playback quality. Consider an MPEG video in which an I-frame is referenced by all other frames (B- or P-frames) in the same GOP (Group of Picture). Losing packets from an I-frame makes it difficult to decode all of the following frames from the same GOP.

The major goal of this paper is to select the maximal high-priority frames (I-frames) cached into the video proxy in order to defeat decoding error caused by packet loss and improve error recovery while serving QoS-guaranteed video playback. We propose a PSC algorithm for solving this selected cache problem with linear time complexity. The PSC algorithm uses minimal cache storage in the video proxy as well as saves maximal bandwidth required in the backbone WAN (as does the OC algorithm). Additionally, experiments with several benchmark videos show that the PSC algorithm improves the ratio of I-frame data cached in video proxy by over 15% more than conventional OC algorithm.

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