Cabletron Systems SFCS-200WG - Manual (Page 15)

1-1
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.
1.1 Overview 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