Report Number: CSL-TR-96-702
Institution: Stanford University, Computer Systems Laboratory
Title: Performance Evaluation of Ethernets and ATM Networks Carrying Video Traffic
Author: Dalgic, Ismail
Author: Tobagi, Fouad A.
Date: August 1996
Abstract: In this report the performance of Ethernets (10Base-T and 100Base-T) and ATM networks carrying multimedia traffic is presented. End-to-end delay requirements suitable for a wide range of multimedia applications are considered (ranging from 20 ms to 500 ms). Given the specific nature of the network considered and the maximum latency requirement, some data is lost. Data loss at the receiver causes quality degradations in the displayed video in the form of discontinuities, referred to as glitches. We define various quantities characterizing the glitches, namely, the total amount of information lost in glitches, their duration, and the rate at which glitches occur. We study these quantities for various network and traffic scenarios, using a computer simulation model driven by real video traffic generated by encoding video sequences. We also determine the maximum number of video streams that can be supported for given maximum delay requirement and glitch rate. We consider and compare the results for various types of video contents (video conferencing, motion pictures, commercials), two encoding schemes (H.261 and MPEG-1), and two encoder control schemes [Constant Bit Rate (CBR) and Constant-Quality Variable Bit Rate (CQ-VBR)], considering also scenarios where the traffic consists of various mixtures of the above. We show that when the video content is highly variable, both 100Base-T Ethernet and ATM can support many more CQ-VBR streams than CBR streams. When the video content is not much variable, as in a videoconferencing sequence, then the number of CBR and CQ-VBR streams that can be supported are comparable. For low values of end-to-end delay requirement, we show that ATM networks can support up to twice as many video streams of a given type as Ethernets for a channel capacity of 100Mb/s. For relaxed end-to-end delay requirements, both networks can support about the same number of video streams of a given type. We also determine the number of streams supportable for traffic scenarios consisting of mixtures of heterogeneous video traffic sources in terms of the video content, video encoding scheme and encoder control scheme, as well as the end-to-end delay requirement. We then consider multihop ATM network scenarios, and provide admission control guidelines for video when the network topology is an arbitrary mesh. Finally, we consider scenarios with mixtures of video and data traffic (with various degrees of burstiness), and determine the effect of one traffic type over the other.