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Chapter 1
Overview
ATM Adaptation Layer (AAL)
Ethernet frames can be between 64 and 1514 bytes in length. ATM transmits data in
fixed length cells. Each cell contains 48 bytes of user data. The ATM Adaptation Layer
(AAL) converts data between the Ethernet and ATM formats.
The AAL has a Segmentation and Reassembly (SAR) sub-layer that does the
conversion.
In the sending device the LEC passes the Ethernet frames to the SAR. The SAR
converts the user data into fixed length cells, and passes these cells to the ATM
Layer for transmission across the ATM network.
In the receiving device, the SAR converts the ATM cells back into the appropriate
user data again, and passes this data to the LEC.
As ATM can carry different traffic types (for example, voice, video, and other data),
several Adaptation Layer protocols have been defined. These protocols operate
simultaneously within the Adaptation Layer, and allow the ATM Layer to support
different applications and traffic types.
Note: The M-ACC module uses the AAL5 ATM Adaptation Layer protocol, which
is a data-oriented protocol. The ATM access module will only work with other
devices using the AAL5 ATM adaptation layer protocol.
Asynchronous Transfer Mode (ATM) Layer
Asynchronous Transfer Mode (ATM) is a connection-oriented transmission protocol
that has the following features:
•
ATM uses the Signalling Protocol (Q.2931) to dynamically create, maintain and
clear ATM connections between end-systems.
•
ATM uses fixed length packets known as cells, and each cell identifies the
connection to be used.
•
ATM is transparent to the multiple services it supports and can carry cells from
different applications over the same physical connection.
•
ATM has well-defined user and network interfaces.
ATM Basics
Asynchronous Transfer Mode (ATM) technology transfers network traffic,
including voice, video, and data, at high speed. Using this connection-oriented
networking technology, centered by a switch, you can set up a great number of
virtual connections to support multiple applications through the same physical
connection. The switching technology enables dedicated bandwidth for each
application, overcoming the problems that exist in a shared-media networking
technology, like Ethernet, Token Ring, and FDDI. ATM allows different types of
16
Avaya M770 M-ACCF/SF ATM Access Modules User's Guide
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Table of Contents
Troubleshooting
