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Chapter 6 Interface Configuration
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Configuring ATM
Asynchronous transfer mode (ATM) is a high-performance, cell-
oriented switching and multiplexing technology that utilizes
fixed-length packets to carry different types of traffic. Networks
that have been primarily focused on providing better voice
services are evolving to meet new multimedia communications
challenges and competitive pressures.
Services based on asynchronous transfer mode (ATM) and
synchronous digital hierarchy (SDH)/synchronous optical
network (SONET) architectures provide flexibility essential for
success in this market. The most basic service building block is
ATM virtual circuit, which is an end-to-end connection that has
defined end points and routes.
In ATM networks, all information is formatted into fixed-length
cells consisting of 48 bytes (8 bits per byte) of payload and 5
bytes of cell header. The fixed cell size ensures that time-critical
information such as voice or video is not adversely affected by
long data frames or packets. The header is organized for
efficient switching in high-speed hardware implementations and
carries payload-type information, virtual-circuit identifiers, and
header error check.
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ATM standards defined two types of ATM connections: virtual
path connections (VPCs), which contain virtual channel
connections (VCCs). A virtual channel connection (or virtual
circuit) is the basic unit, which carries a single stream of cells, in
order, from user to user.
A collection of virtual circuits can be bundled together into a
virtual path connection. A virtual path connection can be created
from end-to-end across an ATM network. In this case, the ATM
Background
Service Based
ATM Cells
VPI/VCI
Virtual
Connection