Measurement study of RealMedia streaming traffic
Tianbo Kuang, Carey L. Williamson · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2002
With the growing popularity of real-time audio/video streaming applications on the Internet, it is important to study the traffic characteristics of such applications and to understand their implications on network performance. In this paper, we present a measurement study of RealMedia streaming traffic, where the focus is both on the application-layer view (i.e., the output of the audio/video encoder) and on the network-layer view (i.e., the departure process for network packets emanating from the RealMedia server). Our main observation is that, although RealVideo can be compressed as Variable-Bit-Rate (VBR) at the application layer, it is often streamed as Constant-Bit-Rate (CBR) at the network layer. The audio and video streams have a hierarchical traffic structure: at large time scales (minutes), the overall bit rate is constant; at medium time scales (seconds), the packets have an on and off pattern due to the interleaving of audio and video; at fine-grain time scales (sub-second), back-to-back packet trains of two or more packets are often seen. We also note that most CBR-coded RealVideo streams are not long-range dependent (LRD). We attribute this difference to the CBR nature of the coder, which dynamically changes the video frame rate to keep the Internet traffic demands near-CBR over moderate time scales.