Abstract

Over the past few years, there has been a strong and growing interest in faster network technologies such as FDDI and ATM. However, the perceived throughput at the application level has not always increased accordingly. Various performance bottlenecks have been encountered each of which has to be analysed and corrected.

This paper presents a performance evaluation of continuous video data streams over ATM networks and compares them with similar experiments over Ethernet networks. The ATM LAN testbed for these experiments consists of three SG R4000 Indigos workstations connected by ATM Fore first generation interface cards and a Synoptics ATM switch. It is expected that video applications would run faster on ATM networks than Ethernet networks. A preliminary examination suggested to us that data movements through the protocol stack and the processing overheads were considerably high and that with some parameter settings, experiments with Ethernet would perform four to five times better than those with ATM.

To address and explore this issue, a packetisation process has been added within the video application that would split each video frame into a number of packets. We show that by implementing a packetisation process at the application level, the end host is able to deliver cells at a faster rate. The sensitivity of these parameters, and also the overheads involved are discussed. The results are consistent over a range of video frame sizes: CIF(25K), QCIF(101K), and SCIF(405K).

Keywords: ATM networks, continuous video streams, packetisation process.

1 Introduction

The development of faster computer networks means that there is an inadequate performance between conventional network interface architectures and communication protocol implementations. For example, workstation users replacing 10 Mbps Ethernet with 100 Mbps FDDI (Fiber Distributed Data Interface) networks are not observing a tenfold increase in application to application throughput [CJRS89].

Asynchronous Transfer Mode (ATM) is an emerging communication architecture based on switching and multiplexing small fixed-length packets called cells [New92]. Although ATM was originally developed as an international standard for Synchronous Optical Networks (SONET)-based wide-area networks, its attractiveness for local area networks (LANs) has resulted in ATM LANs appearing well in advance of WAN ATM-based services [LMT93]. In the local area network, ATM can be used for the following purposes: