Cabletron Systems BRIM-A6 B.2 THE ATM CELL

Appendix B: ATM Overview

Page B-2 BRIM-A6 User’s Guide

B.2 THE ATM CELL

One major difference between ATM and current transmission methods is

that instead of using variable-length packets, ATM transmits ﬁxed-size

cells. (See Figure B-1.)

Figure B-1 ATM Cells

ATM uses three types of cells – Assigned, Unassigned, and Idle. Assigned

cells carry actual trafﬁc. Unassigned cells are free and waiting to be

assigned trafﬁc. Idle cells are used to separate cells, provide receiver

synchronization (byte alignment), and reserve bandwidth for another

channel (i.e., occupy bandwidth between transmissions). Idle cells do not

receive trafﬁc.

ATM cells total 53 bytes long and consist of two general parts: the Header

ﬁeld and the Data ﬁeld. The Header ﬁeld consists of 5 bytes and contains

management/control information for the cell. The Data ﬁeld contains 48

bytes of information. Figure B-2 shows the additional components of the

Header ﬁeld.

Header Data

5 Bytes 48 Bytes

book Page 2 Thursday, April 18, 1996 2:18 PM

Contents

Main BRIM-A6 Users Guide i NOTICE ii BRIM-A6 Users Guide VCCI NOTICE DOC NOTICE FCC NOTICE BRIM-A6 Users Guide iii EXCLUSION OF WARRANTY AND DISCLAIMER OF LIABILITY CABLETRON SOFTWARE PROGRAM LICENSE CABLETRON SYSTEMS, INC. PROGRAM LICENSE AGREEMENT Page BRIM-A6 Users Guide v DECLARATION OF CONFORMITY BRIM-A6 Users Guide vii CONTENTS Contents viii BRIM-A6 Users Guide CHAPTER 1 INTRODUCTION 1.1 USING THIS MANUAL 1.2 DOCUMENT CONVENTIONS 1.3 BRIM-A6 OVERVIEW 1.4 BRIM-A6 FEATURES 1.5 BRIM-A6 SPECIFICATIONS 1.6 RELATED MANUALS 1.7 GETTING HELP CHAPTER 2 INSTALLATION 2.1 UNPACKING THE BRIM 2.2 INSTALLING APIMS 2.3 INSTALLING BRIMS 2.3.1 Installing a BRIM in a MIM Chapter 2: Installation Page 2-4 BRIM-A6 Users Guide Figure 2-2 Removing the BRIM Coverplate Figure 2-3 Installing the BRIM 2.3.2 Installing a BRIM in a Hub Page CHAPTER 3 LOCAL MANAGEMENT Chapter 3: Local Management Page 3-2 BRIM-A6 Users Guide 3.1 LOCAL MANAGEMENT KEYBOARD CONVENTIONS 3.2 USING LIM TO CREATE PVCs 3.2.1 ATM Connection Tables Screen Fields 3.2.2 ATM Connection Tables Screen Commands 3.2.3 Using ATM Connection Tables Screen Commands 3.2.4 Adding PVCs to the Connection Tables Screen 3.2.5 Deleting PVCs from the Connection Tables Screen 3.3 USING LM TO CREATE PVCS 3.3.1 BRIM-A6 Setup Screen Fields 3.3.2 BRIM-A6 Setup Screen Commands 3.3.3 Using BRIM-A6 Setup Screen Commands 3.3.4 Accessing the BRIM-A6 Add/Delete Entry Screen 3.3.5 BRIM-A6 Add/Delete Entry Screen Fields 3.3.6 BRIM-A6 Add/Delete Entry Screen Commands 3.3.7 Adding a PVC 3.3.8 Modifying a PVC 3.3.9 Deleting a PVC BRIM-A6 Users Guide Page 4-1 CHAPTER 4 LANVIEW LEDs 4.1 BRIM-A6 LEDs Table 4-1 describes each of the BRIM-A6 LEDs. BRIM-A6 Chapter 4: LANVIEW LEDs 4.2 APIM LEDs Table 4-2 describes each of the APIM LEDs. APPENDIX A APIM SPECIFICATIONS A.1 APIM-11 SPECIFICATIONS A.2 APIM-21 SPECIFICATIONS A.3 APIM-22 SPECIFICATIONS A.4 APIM-29 SPECIFICATIONS A.5 APIM-67 SPECIFICATIONS APPENDIX B ATM OVERVIEW B.1 ATM BASICS B.2 THE ATM CELL Page B.3 THE ATM NETWORK B.3.1 VIRTUAL CHANNELS AND VIRTUAL PATHS B.3.2 PERMANENT AND SWITCHED VIRTUAL CHANNELS B.4 ATM PROTOCOL