Compaq AA-RHGWB-TE manual Preparing ATM Adapters, ATM Overview

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Preparing ATM Adapters

The Compaq Tru64 UNIX operating system supports Asynchronous Transfer Mode (ATM). TruCluster Server supports the use of LAN emulation over ATM for client access.

This chapter provides an ATM overview, an example TruCluster Server cluster using ATM, an ATM adapter installation procedure, and information about verifying proper installation of fiber optic cables. See the Tru64 UNIX Asynchronous Transfer Mode manual for information on configuring the ATM software.

7.1 ATM Overview

In synchronous transfer methods, time-division multiplexing (TDM) techniques are used to divide the bandwidth into fixed-size channels dedicated to particular connections. If a system has nothing to transmit when its time slot comes up, that time slot is wasted. Also, if the system has lots of information to transmit, the system can only transmit when its turn comes up, even if other time slots are empty.

ATM eliminates the inefficiencies of TDM technology by sharing network bandwidth among multiple logical connections. Instead of dividing the bandwidth into fixed-size channels dedicated to particular connections, ATM uses the entire bandwidth to transmit a steady stream of fixed-size (53-byte) cells. Each cell includes a 5-byte header containing an address to identify the cell with a particular logical connection.

If a connection needs more bandwidth, it is allocated more cells. When a connection is idle, it uses no cells and consumes no bandwidth. This feature makes ATM the ideal technology for transferring voice, video, and data through private networks and across public networks.

ATM is a connection-oriented, cell-switching and multiplexing technology. Cells transit ATM networks by passing through ATM switches, which analyze information in the header to switch the cell to the output interface that connects the cell to the next appropriate switch as the cell proceeds to its destination.

The ATM switch acts as a hub in the ATM network. All devices are attached to an ATM switch, either directly or indirectly.

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