Cabletron Systems 9A000 manual Chapter, Introduction, Overview of the ATM Standard

CHAPTER 1

Introduction

The Cabletron 9A000 and SFCS series ATM Switch brings ATM connectivity to LAN workgroup, LAN backbone, and LAN/WAN internetworking applica- tions. Together with the Cabletron series of ATM Computer Interfaces, the 9A000 and SFCS series meet the networking demands of today’s distributed, time-critical applications.

The Cabletron 9A000 and SFCS series ATM high-performance ATM switches deliver switching capacity and speed for ATM applications. A non-blocking switching capacity of 2.5 Gbps is continually available for connectivity to 16 users or networking devices, each running at speeds up to 622 Mbps or 24 users or network devices running at 100 Mbps.

This chapter provides an overview of the ATM Standard and Cabletron Sys- tems 9A000 and SFCS series Switches. It details the hardware and software requirements necessary to use the 9A000 and SFCS series and also provides information on the contents of the 9A000 and SFCS series Switch packages.

1.1Overview of the ATM Standard

Asynchronous Transfer Mode, or ATM, is a communication architecture based on the switching of small fixed length packets of data called cells. In ATM, all data is transferred in 53-byte cells. Each cell has a 5-byte header that identifies the cell’s route through the network and 48-bytes containing user data. This user data in turn carries any headers or trailers required by higher level protocols.

The operation of an ATM switch is conceptually quite simple. The header of each cell contains a virtual connection (VC) identifier, consisting of a virtual path identifier (VPI) and a virtual channel identifier (VCI). On each incoming link, an arriving cell’s VC identifier uniquely determines a new VC identifier to be placed in the cell header, and the outgoing link over which to transmit the cell. In the case of a multicast connection, the VC identifier maps to a set of new VC identifiers and outgoing links.

Perhaps the single most important advantage offered by ATM, in addition to the speed at which data is transferred, is its open-ended growth path. ATM is not locked into a single physical medium or speed. The fixed-size ATM cell allows traffic from multiple sources (simultaneous video, audio, and data

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