Cabletron Systems BRIM-A6 - page 41

The ATM Cell

BRIM-A6 User’s Guide Page B-3

Figure B-2 ATM Header Field Breakdown

The Header ﬁeld is made up of several sub-ﬁelds which provide

management/control information relating to a cell. Brief descriptions of

each header ﬁeld are as follows:

• Generic Flow Control (GFC) – provides the ability to control the

trafﬁc ﬂow for different grades of service.

• Virtual Path Identiﬁer (VPI) – identiﬁes the virtual path to which the

cell belongs.

• Virtual Channel Identiﬁer (VCI) – identiﬁes the virtual channel to

which the cell belongs.

• Payload Type Indicator (PTI) – describes whether the information is

user information, network information, or management information.

• Header Check Sequence (HCS) – detects bit errors; corrects single bit

errors.

This method of ﬁxed-cell length has many advantages over conventional

packet transfer technologies; one major advantage is time. Since ATM

cells are ﬁxed in length, and all of the header data is the same, processing

them is dramatically simpliﬁed. This eliminates the need for buffers and

processors that tend to slow down transmission. By contrast, other LAN

packets vary in length, making it necessary to check each incoming

packet to ensure that it is complete and contains no errors.

Header Data

Generic Flow Control (GFC) Virtual Path Identiﬁer (VPI)

VPI VCI/VPI

Virtual Channel Identiﬁer (VCI)

VCI Payload Type Reserved

Header Check Sequence

book Page 3 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