VBR Traffic Shaping for Streaming of Multimedia Transmission

Abstract

In multimedia applications, media data such as audio and video are transmitted from server to clients via network according to some transmission schedules. Different from the conventional data streams, end-to-end quality-of-service (QoS) is necessary for media transmission to provide jitter-free playback. Therefore, each data packet has been assigned with related timing constraints for transmission. As network resources are allocated exclusively in fixed-size chunks to serve different data streams, it is simple to support constant-bit-rate (CBR) transmission. Grossglauser and Keshav (1996) have investigated the performance of CBR traffic in a large-scale network with many connections and switches. They concluded that the network queuing delay for CBR transmission is less than one cell time per switch even under heavy loading. Besides, resource allocation and admission control are simple as there are no variations in resource requirements. However, media streams are notably variable-bit-rate (VBR) in nature due to the coding and compression technologies applied (Garrett and Willinger, 1994). The average data rate of an MPEG-1 movie is usually less than 25% of its peak data rate. It is inherently at odds with the goals of designing efficient real-time network transmission and admission control mechanisms capable of achieving high resource utilization (Sen et al., 1997). The conventional CBR service model that allocates the peak data rate to transmit the VBR stream would be a waste of bandwidth. Furthermore, it requires a large size of client buffer. To ameliorate this problem, we need a good traffic shaping algorithm to transmit VBR video in a less bursty (i.e., smoother) manner by exploiting different performance measurements. In a multimedia system, we usually measure the performance of a transmission schedule by the following four indices: peak bandwidth, network utilization, initial delay and client buffer.