frame relay

CHAPTER 2FRAME RELAYTERMINOLOGY

CHAPTER 3FRAME RELAY

CHAPTER 4FRAME RELAYMANAGEMENT

CHAPTER 5VOICE OVER FRAME RELAY

CHAPTER 1 INTRODUCTION TO FRAME

RELAY

CHAPTER 6 FRAME RELAY TO ATM

Frame Relay

Training Manual

Issue 3 Revision 2

FOR TRAININGPURPOSES ONLY

CP08

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�MOTOROLA LTD. 2000

CP08: Frame Relay

FOR TRAINING PURPOSES ONLY i

Issue 3 Revision 2

CP08Frame Relay

� Motorola 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001All Rights ReservedPrinted in the U.K.

Issue 3 Revision 2


CP08: Frame Relay

FOR TRAINING PURPOSES ONLYii

Copyrights, notices and trademarks

CopyrightsThe Motorola products described in this document may include copyrighted Motorola computerprograms stored in semiconductor memories or other media. Laws in the United States and othercountries preserve for Motorola certain exclusive rights for copyright computer programs, including theexclusive right to copy or reproduce in any form the copyright computer program. Accordingly, anycopyright Motorola computer programs contained in the Motorola products described in this documentmay not be copied or reproduced in any manner without the express written permission of Motorola.Furthermore, the purchase of Motorola products shall not be deemed to grant either directly or byimplication, estoppel or otherwise, any license under the copyrights, patents or patent applications ofMotorola, except for the rights that arise by operation of law in the sale of a product.

RestrictionsThe software described in this document is the property of Motorola. It is furnished under a licenseagreement and may be used and/or disclosed only in accordance with the terms of the agreement.Software and documentation are copyright materials. Making unauthorized copies is prohibited bylaw. No part of the software or documentation may be reproduced, transmitted, transcribed, storedin a retrieval system, or translated into any language or computer language, in any form or by anymeans, without prior written permission of Motorola.

AccuracyWhile reasonable efforts have been made to assure the accuracy of this document, Motorolaassumes no liability resulting from any inaccuracies or omissions in this document, or from the useof the information obtained herein. Motorola reserves the right to make changes to any productsdescribed herein to improve reliability, function, or design, and reserves the right to revise thisdocument and to make changes from time to time in content hereof with no obligation to notify anyperson of revisions or changes. Motorola does not assume any liability arising out of the applicationor use of any product or circuit described herein; neither does it convey license under its patentrights of others.

Trademarks

and MOTOROLA are trademarks of Motorola Inc.UNIX is a registered trademark in the United States and other countries, licensed exclusively throughX/Open Company Limited.Tandem , Integrity , Integrity S2 , and Non-Stop-UX are trademarks of Tandem ComputersIncorporated.X Window System , X and X11 are trademarks of the Massachusetts Institute of Technology.Looking Glass is a registered trademark of Visix Software Ltd.OSF/Motif is a trademark of the Open Software Foundation.Ethernet is a trademark of the Xerox Corporation.Wingz is a trademark and INFORMIX is a registered trademark of Informix Software Ltd.SUN, SPARC, and SPARCStation are trademarks of Sun Microsystems Computer Corporation.IBM is a registered trademark of International Business Machines Corporation.HP is a registered trademark of Hewlett Packard Inc.

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General information 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Important notice 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Purpose 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . About this manual 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross references 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Text conventions 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

First aid in case of electric shock 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Warning 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Artificial respiration 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Burns treatment 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Reporting safety issues 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Procedure 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Warnings and cautions 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Warnings 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cautions 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General warnings 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Warning labels 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Specific warnings 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . High voltage 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RF radiation 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Laser radiation 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lifting equipment 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Do not ... 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Battery supplies 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Toxic material 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Human exposure to radio frequency energy (PCS1900 only) 8. . . . . . . . . . . . . . . . . . . . . . Introduction 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Definitions 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum permitted exposures 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximum permitted exposure ceilings 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example calculation 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Power density measurements 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other equipment 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Beryllium health and safety precautions 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Health issues 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inhalation 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Skin contact 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Eye contact 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Handling procedures 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Disposal methods 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Product life cycle implications 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General cautions 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Caution labels 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Specific cautions 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fibre optics 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Static discharge 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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FOR TRAINING PURPOSES ONLYiv

Devices sensitive to static 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Special handling techniques 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Motorola GSM manual set 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Generic manuals 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tandem OMC 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scaleable OMC 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Related manuals 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service manuals 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Category number 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Catalogue number 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ordering manuals 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 1Introduction to Frame Relay i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 1–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Wide Area Networks 1–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Public Data Networks 1–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Circuit Switching 1–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Packet Switching 1–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Circuit Switching vs Packet Switching 1–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

X.25 1–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

X.25 Layers 1–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay 1–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Standards 1–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 2Frame Relay Terminology i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 2–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Network Components 2–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Physical and Logical Connections 2–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Switches 2–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Access Devices - FRAD 2–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Permanent Virtual Connection - PVC 2–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Data Link Connection Identifier - DLCI 2–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Internodal DLCIs 2–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

User to Network Interface - UNI 2–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

UNI Signalling Protocols 2–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Network to Network Interface - NNI 2–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Internodal Signalling Protocols 2–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 3Frame Relay i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 3–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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CP08: Frame Relay

FOR TRAINING PURPOSES ONLY v

Concepts of Frame Relay 3–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outline Operation 3–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Frame Format 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flag 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Address Header Field 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Information/User Data Field 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Frame Check Sequence, FCS 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Header Address Field 3–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Local Management Interface - LMI 3–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Link Integrity Verification (LIV) 3–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Counters and Timers 3–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Consolidated Link Layer Management - CLLM 3–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Bandwidth Admission 3–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Committed Information Rate - CIR 3–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Traffic Parameters 3–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Switched Virtual Circuit - SVC 3–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 4Frame Relay Management i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Management 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objectives 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Discard Eligibility 4–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Congestion Control 4–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Network Congestion 4–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Network Management 4–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Port Statistics Example 4–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

PVC Statistics Example 4–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 5Voice Over Frame Relay i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Voice Over Frame Relay 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objectives 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Voice Over Frame Relay 5–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fragmentation and Prioritisation 5–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Voice Compression 5–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Silence Detection and Suppression 5–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 6Frame Relay to ATM i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay to ATM 6–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objectives 6–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay and ATM 6–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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CP08: Frame Relay

FOR TRAINING PURPOSES ONLYvi

Frame Relay to ATM Service Interworking - FRASI 6–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame-Based User Network Interface - FUNI 6–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . High-Speed Frame Relay 6–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Issue 3 Revision 2 General information


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FOR TRAINING PURPOSES ONLY 1

General information

Important notice

If this manual was obtained when you attended a Motorola training course, it will not beupdated or amended by Motorola. It is intended for TRAINING PURPOSES ONLY. If itwas supplied under normal operational circumstances, to support a major softwarerelease, then corrections will be supplied automatically by Motorola in the form ofGeneral Manual Revisions (GMRs).

Purpose

Motorola Global System for Mobile Communications (GSM) Technical Education manualsare intended to support the delivery of Technical Education only and are not intended toreplace the use of Customer Product Documentation.

Failure to comply with Motorola’s operation, installation and maintenanceinstructions may, in exceptional circumstances, lead to serious injury or death.

WARNING

These manuals are not intended to replace the system and equipment training offered byMotorola, although they can be used to supplement and enhance the knowledge gainedthrough such training.

About thismanual

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FOR TRAINING PURPOSES ONLY2

Cross references

Throughout this manual, cross references are made to the chapter numbers and sectionnames. The section name cross references are printed bold in text.

This manual is divided into uniquely identified and numbered chapters that, in turn, aredivided into sections. Sections are not numbered, but are individually named at the topof each page, and are listed in the table of contents.

Text conventions

The following conventions are used in the Motorola GSM manuals to represent keyboardinput text, screen output text and special key sequences.

Input

Characters typed in at the keyboard are shown like this.

Output

Messages, prompts, file listings, directories, utilities, and environmentalvariables that appear on the screen are shown like this.

Special key sequences

Special key sequences are represented as follows:

CTRL-c Press the Control and c keys at the same time.

ALT-f Press the Alt and f keys at the same time.

| Press the pipe symbol key.

CR or RETURN Press the Return (Enter) key. The Return key isidentified with the ↵ symbol on both the X terminal andthe SPARCstation keyboards. The SPARCstationkeyboard Return key is also identified with the wordReturn.

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First aid in case of electric shock

Warning

Do not touch the victim with your bare hands until the electric circuit isbroken.Switch off. If this is not possible, protect yourself with dry insulatingmaterial and pull or push the victim clear of the conductor.

WARNING

Artificialrespiration

In the event of an electric shock it may be necessary to carry out artificial respiration.Send for medical assistance immediately.

Burns treatment

If the patient is also suffering from burns, then, without hindrance to artificial respiration,carry out the following:

1. Do not attempt to remove clothing adhering to the burn.

2. If help is available, or as soon as artificial respiration is no longer required, coverthe wound with a dry dressing.

3. Do not apply oil or grease in any form.

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Reporting safety issues

Introduction

Whenever a safety issue arises, carry out the following procedure in all instances.Ensure that all site personnel are familiar with this procedure.

Procedure

Whenever a safety issue arises:

1. Make the equipment concerned safe, for example, by removing power.

2. Make no further attempt to tamper with the equipment.

3. Report the problem directly to GSM MCSC +44 (0)1793 430040 (telephone) andfollow up with a written report by fax +44 (0)1793 430987 (fax).

4. Collect evidence from the equipment under the guidance of the MCSC.

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Warnings and cautions

Introduction

The following describes how warnings and cautions are used in this manual and in allmanuals of the Motorola GSM manual set.

Warnings

Definition

A warning is used to alert the reader to possible hazards that could cause loss of life,physical injury, or ill health. This includes hazards introduced during maintenance, forexample, the use of adhesives and solvents, as well as those inherent in the equipment.

Example and format

Do not look directly into fibre optic cables or optical data in/out connectors.Laser radiation can come from either the data in/out connectors orunterminated fibre optic cables connected to data in/out connectors.

WARNING

Cautions

Definition

A caution means that there is a possibility of damage to systems, or individual items ofequipment within a system. However, this presents no danger to personnel.

Example and format

Do not use test equipment that is beyond its calibration due date when testingMotorola base stations.

CAUTION

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General warnings

Introduction

Observe the following warnings during all phases of operation, installation andmaintenance of the equipment described in the Motorola GSM manuals. Failure tocomply with these warnings, or with specific warnings elsewhere in the Motorola GSMmanuals, violates safety standards of design, manufacture and intended use of theequipment. Motorola assumes no liability for the customer’s failure to comply with theserequirements.

Warning labelsPersonnel working with or operating Motorola equipment must comply with any warninglabels fitted to the equipment. Warning labels must not be removed, painted over orobscured in any way.

Specificwarnings

Warnings particularly applicable to the equipment are positioned on the equipment andwithin the text of this manual. These must be observed by all personnel at all times whenworking with the equipment, as must any other warnings given in text, on the illustrationsand on the equipment.

High voltageCertain Motorola equipment operates from a dangerous high voltage of 230 V ac singlephase or 415 V ac three phase mains which is potentially lethal. Therefore, the areaswhere the ac mains power is present must not be approached until the warnings andcautions in the text and on the equipment have been complied with.

To achieve isolation of the equipment from the ac supply, the mains input isolator mustbe set to off and locked.

Within the United Kingdom (UK) regard must be paid to the requirements of theElectricity at Work Regulations 1989. There may also be specific country legislationwhich need to be complied with, depending on where the equipment is used.

RF radiationHigh RF potentials and electromagnetic fields are present in the base station equipmentwhen in operation. Ensure that all transmitters are switched off when any antennaconnections have to be changed. Do not key transmitters connected to unterminatedcavities or feeders.

Refer to the following standards:

� ANSI IEEE C95.1-1991, IEEE Standard for Safety Levels with Respect to HumanExposure to Radio Frequency Electromagnetic Fields, 3kHz to 300GHz.

� CENELEC 95 ENV 50166-2, Human Exposure to Electromagnetic Fields HighFrequency (10kHz to 300GHz).

Laser radiationDo not look directly into fibre optic cables or optical data in/out connectors. Laserradiation can come from either the data in/out connectors or unterminated fibre opticcables connected to data in/out connectors.

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Liftingequipment

When dismantling heavy assemblies, or removing or replacing equipment, the competentresponsible person must ensure that adequate lifting facilities are available. Whereprovided, lifting frames must be used for these operations. When equipments have to bemanhandled, reference must be made to the Manual Handling of Loads Regulations1992 (UK) or to the relevant manual handling of loads legislation for the country in whichthe equipment is used.

Do not ...... substitute parts or modify equipment.

Because of the danger of introducing additional hazards, do not install substitute parts orperform any unauthorized modification of equipment. Contact Motorola if in doubt toensure that safety features are maintained.

Battery supplies

Do not wear earth straps when working with standby battery supplies.

Toxic material

Certain Motorola equipment incorporates components containing the highly toxic materialBeryllium or its oxide Beryllia or both. These materials are especially hazardous if:

� Beryllium materials are absorbed into the body tissues through the skin, mouth, ora wound.

� The dust created by breakage of Beryllia is inhaled.

� Toxic fumes are inhaled from Beryllium or Beryllia involved in a fire.

See the Beryllium health and safety precautions section for further information.

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Human exposure to radio frequency energy (PCS1900 only)

IntroductionThis equipment is designed to generate and radiate radio frequency (RF) energy. Itshould be installed and maintained only by trained technicians. Licensees of the FederalCommunications Commission (FCC) using this equipment are responsible for insuringthat its installation and operation comply with FCC regulations designed to limit humanexposure to RF radiation in accordance with the American National Standards InstituteIEEE Standard C95.1-1991, IEEE Standard for Safety Levels with Respect to HumanExposure to Radio Frequency Electromagnetic Fields, 3kHz to 300GHz.

DefinitionsThis standard establishes two sets of maximum permitted exposure limits, one forcontrolled environments and another, that allows less exposure, for uncontrolledenvironments. These terms are defined by the standard, as follows:

Uncontrolled environment

Uncontrolled environments are locations where there is the exposure of individuals whohave no knowledge or control of their exposure. The exposures may occur in livingquarters or workplaces where there are no expectations that the exposure levels mayexceed those shown for uncontrolled environments in the table of maximum permittedexposure ceilings.

Controlled environment

Controlled environments are locations where there is exposure that may be incurred bypersons who are aware of the potential for exposure as a concomitant of employment, byother cognizant persons, or as the incidental result of transient passage through areaswhere analysis shows the exposure levels may be above those shown for uncontrolledenvironments but do not exceed the values shown for controlled environments in thetable of maximum permitted exposure ceilings.

Maximumpermittedexposures

The maximum permitted exposures prescribed by the standard are set in terms ofdifferent parameters of effects, depending on the frequency generated by the equipmentin question. At the frequency range of this Personal Communication System equipment,1930-1970MHz, the maximum permitted exposure levels are set in terms of powerdensity, whose definition and relationship to electric field and magnetic field strengths aredescribed by the standard as follows:

Power density (S)

Power per unit area normal to the direction of propagation, usually expressed in units ofwatts per square metre (W/m2) or, for convenience, units such as milliwatts per squarecentimetre (mW/cm2). For plane waves, power density, electric field strength (E) andmagnetic field strength (H) are related by the impedance of free space, 377 ohms. Inparticular,

� ��

��

where E and H are expressed in units of V/m and A/m, respectively, and S in units ofW/m2. Although many survey instruments indicate power density units, the actualquantities measured are E or E2 or H or H2.

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Maximumpermittedexposureceilings

Within the frequency range, the maximum permitted exposure ceiling for uncontrolledenvironments is a power density (mW/cm2) that equals f/1500, where f is the frequencyexpressed in MHz, and measurements are averaged over a period of 30 minutes. Themaximum permitted exposure ceiling for controlled environments, also expressed inmW/cm2, is f/300 where measurements are averaged over 6 minutes. Applying theseprinciples to the minimum and maximum frequencies for which this equipment is intendedto be used yields the following maximum permitted exposure levels:

Uncontrolled Environment Controlled Environment

1930MHz 1970MHz 1930MHz 1970MHz

Ceiling 1.287mW/cm2 1.313mW/cm2 6.433mW/cm2 6.567mW/cm2

If you plan to operate the equipment at more than one frequency, compliance should beassured at the frequency which produces the lowest exposure ceiling (among thefrequencies at which operation will occur).

Licensees must be able to certify to the FCC that their facilities meet the above ceilings.Some lower power PCS devices, 100 milliwatts or less, are excluded from demonstratingcompliance, but this equipment operates at power levels orders of magnitude higher, andthe exclusion is not applicable.

Whether a given installation meets the maximum permitted exposure ceilings depends, inpart, upon antenna type, antenna placement and the output power to which thisequipment is adjusted. The following example sets forth the distances from the antennato which access should be prevented in order to comply with the uncontrolled andcontrolled environment exposure limits as set forth in the ANSI IEEE standards andcomputed above.

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Examplecalculation

For a base station with the following characteristics, what is the minimum distance fromthe antenna necessary to meet the requirements of an uncontrolled environment?

Transmit frequency 1930MHz

Base station cabinet output power, P +39.0dBm (8 watts)

Antenna feeder cable loss, CL 2.0dB

Antenna input power Pin P–CL = +39.0–2.0 = +37.0dB (5watts)

Antenna gain, G 16.4dBi (43.65)

Using the following relationship:

� ��

��

Where W is the maximum permissible power density in W/m2 and r is the safe distancefrom the antenna in metres, the desired distance can be calculated as follows:

� ��

��

��

��

where W = 12.87 W/m2 was obtained from table listed above and converting frommW/cm2 to W/m2.

The above result applies only in the direction of maximum radiation of theantenna. Actual installations may employ antennas that have defined radiationpatterns and gains that differ from the example set forth above. The distancescalculated can vary depending on the actual antenna pattern and gain.

NOTE

Power densitymeasurements

While installation calculations such as the above are useful and essential in planning anddesign, validation that the operating facility using this equipment actually complies willrequire making power density measurements. For information on measuring RF fields fordetermining compliance with ANSI IEEE C95.1-1991, see IEEE Recommended Practicefor the Measure of Potentially Hazardous Electromagnetic Fields - RF and Microwave,IEEE Std C95.3-1991. Copies of IEEE C95.1-1991 and IEEE C95.3-1991 may bepurchased from the Institute of Electrical and Electronics Engineers, Inc., Attn:Publication Sales, 445 Hoes Lane, P.O. Box 1331, Piscattaway, NJ 08855-1331,(800) 678-IEEE or from ANSI, (212) 642-4900. Persons responsible for installation of thisequipment are urged to consult these standards in determining whether a giveninstallation complies with the applicable limits.

Other equipmentWhether a given installation meets ANSI standards for human exposure to radiofrequency radiation may depend not only on this equipment but also on whether theenvironments being assessed are being affected by radio frequency fields from otherequipment, the effects of which may add to the level of exposure. Accordingly, the overallexposure may be affected by radio frequency generating facilities that exist at the timethe licensee’s equipment is being installed or even by equipment installed later.Therefore, the effects of any such facilities must be considered in site selection and indetermining whether a particular installation meets the FCC requirements.

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Beryllium health and safety precautions

Introduction

Beryllium (Be), is a hard silver/white metal. It is stable in air, but burns brilliantly inOxygen.

With the exception of the naturally occurring Beryl ore (Beryllium Silicate), all Berylliumcompounds and Beryllium metal are potentially highly toxic.

Health issues

Beryllium Oxide is used within some components as an electrical insulator. Captivewithin the component it presents no health risk whatsoever. However, if the componentshould be broken open and the Beryllium Oxide, which is in the form of dust, released,there exists the potential for harm.

Inhalation

Inhalation of Beryllium Oxide can lead to a condition known as Berylliosis, the symptomsof Berylliosis are similar to Pneumonia and may be identified by all or any of thefollowing:

Mild poisoning causes fever, shortness of breath, and a cough that producesyellow/green sputum, or occasionally bloodstained sputum. Inflammation of the mucousmembranes of the nose, throat, and chest with discomfort, possibly pain, and difficultywith swallowing and breathing.

Severe poisoning causes chest pain and wheezing which may progress to severeshortness of breath due to congestion of the lungs. Incubation period for lung symptomsis 2–20 days.

Exposure to moderately high concentrations of Beryllium in air may produce a veryserious condition of the lungs. The injured person may become blue, feverish with rapidbreathing and raised pulse rate. Recovery is usual but may take several months. Therehave been deaths in the acute stage.

Chronic response. This condition is more truly a general one although the lungs aremainly affected. There may be lesions in the kidneys and the skin. Certain featuressupport the view that the condition is allergic. There is no relationship between thedegree of exposure and the severity of response and there is usually a time lag of up to10 years between exposure and the onset of the illness. Both sexes are equallysusceptible. The onset of the illness is insidious but only a small number of exposedpersons develop this reaction.

First aid

Seek immediate medical assistance. The casualty should be removed immediately fromthe exposure area and placed in a fresh air environment with breathing supported withOxygen where required. Any contaminated clothing should be removed. The casualtyshould be kept warm and at rest until medical aid arrives.

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Skin contact

Possible irritation and redness at the contact area. Persistent itching and blisterformations can occur which usually resolve on removal from exposure.

First aid

Wash area thoroughly with soap and water. If skin is broken seek immediate medicalassistance.

Eye contact

May cause severe irritation, redness and swelling of eyelid(s) and inflammation of themucous membranes of the eyes.

First aid

Flush eyes with running water for at least 15 minutes. Seek medical assistance as soonas possible.

Handlingprocedures

Removal of components from printed circuit boards (PCBs) is to take place only atMotorola approved repair centres.

The removal station will be equipped with extraction equipment and all other protectiveequipment necessary for the safe removal of components containing Beryllium Oxide.

If during removal a component is accidently opened, the Beryllium Oxide dust is to bewetted into a paste and put into a container with a spatula or similar tool. Thespatula/tool used to collect the paste is also to be placed in the container. The containeris then to be sealed and labelled. A suitable respirator is to be worn at all times duringthis operation.

Components which are successfully removed are to be placed in a separate bag, sealedand labelled.

Disposalmethods

Beryllium Oxide or components containing Beryllium Oxide are to be treated ashazardous waste. All components must be removed where possible from boards and putinto sealed bags labelled Beryllium Oxide components. These bags must be given to thesafety and environmental adviser for disposal.

Under no circumstances are boards or components containing Beryllium Oxide to be putinto the general waste skips or incinerated.

Product life cycleimplications

Motorola GSM and analogue equipment includes components containing Beryllium Oxide(identified in text as appropriate and indicated by warning labels on the equipment).These components require specific disposal measures as indicated in the preceding(Disposal methods) paragraph. Motorola will arrange for the disposal of all suchhazardous waste as part of its Total Customer Satisfaction philosophy and will arrangefor the most environmentally “friendly” disposal available at that time.

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General cautions

Introduction

Observe the following cautions during operation, installation and maintenance of theequipment described in the Motorola GSM manuals. Failure to comply with thesecautions or with specific cautions elsewhere in the Motorola GSM manuals may result indamage to the equipment. Motorola assumes no liability for the customer’s failure tocomply with these requirements.

Caution labels

Personnel working with or operating Motorola equipment must comply with any cautionlabels fitted to the equipment. Caution labels must not be removed, painted over orobscured in any way.

Specific cautions

Cautions particularly applicable to the equipment are positioned within the text of thismanual. These must be observed by all personnel at all times when working with theequipment, as must any other cautions given in text, on the illustrations and on theequipment.

Fibre optics

The bending radius of all fibre optic cables must not be less than 30 mm.

Static discharge

Motorola equipment contains CMOS devices that are vulnerable to static discharge.Although the damage caused by static discharge may not be immediately apparent,CMOS devices may be damaged in the long term due to static discharge caused bymishandling. Wear an approved earth strap when adjusting or handling digital boards.

See Devices sensitive to static for further information.

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Devices sensitive to static

Introduction

Certain metal oxide semiconductor (MOS) devices embody in their design a thin layer ofinsulation that is susceptible to damage from electrostatic charge. Such a charge appliedto the leads of the device could cause irreparable damage.

These charges can be built up on nylon overalls, by friction, by pushing the hands intohigh insulation packing material or by use of unearthed soldering irons.

MOS devices are normally despatched from the manufacturers with the leads shortedtogether, for example, by metal foil eyelets, wire strapping, or by inserting the leads intoconductive plastic foam. Provided the leads are shorted it is safe to handle the device.

Special handlingtechniques

In the event of one of these devices having to be replaced observe the followingprecautions when handling the replacement:

� Always wear an earth strap which must be connected to the electrostatic point(ESP) on the equipment.

� Leave the short circuit on the leads until the last moment. It may be necessary toreplace the conductive foam by a piece of wire to enable the device to be fitted.

� Do not wear outer clothing made of nylon or similar man made material. A cottonoverall is preferable.

� If possible work on an earthed metal surface. Wipe insulated plastic work surfaceswith an anti-static cloth before starting the operation.

� All metal tools should be used and when not in use they should be placed on anearthed surface.

� Take care when removing components connected to electrostatic sensitivedevices. These components may be providing protection to the device.

When mounted onto printed circuit boards (PCBs), MOS devices are normally lesssusceptible to electrostatic damage. However PCBs should be handled with care,preferably by their edges and not by their tracks and pins, they should be transferreddirectly from their packing to the equipment (or the other way around) and never leftexposed on the workbench.

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Motorola GSM manual set

Introduction

The following manuals provide the information needed to operate, install and maintain theMotorola GSM equipment.

Generic manuals

The following are the generic manuals in the GSM manual set, these manuals arerelease dependent:

Categorynumber

Name Cataloguenumber

GSM-100-101 System Information: General 68P02901W01

GSM-100-201 Operating Information: GSM System Operation 68P02901W14

GSM-100-311 Technical Description: OMC in a GSM System 68P02901W31

GSM-100-313 Technical Description: OMC Database Schema 68P02901W34

GSM-100-320 Technical Description: BSS Implementation 68P02901W36

GSM-100-321 Technical Description: BSS CommandReference

68P02901W23

GSM-100-403 Installation & Configuration: GSM SystemConfiguration

68P02901W17

GSM-100-423 Installation & Configuration: BSS Optimization 68P02901W43

GSM-100-501 Maintenance Information: Alarm Handling atthe OMC

68P02901W26

GSM-100-521 Maintenance Information: Device StateTransitions

68P02901W57

GSM-100-523 Maintenance Information: BSS FieldTroubleshooting

68P02901W51

GSM-100-503 Maintenance Information: GSM StatisticsApplication

68P02901W56

GSM-100-721 Software Release Notes: BSS/RXCDR 68P02901W72

Tandem OMC

The following Tandem OMC manuals are part of the GSM manual set for systemsdeploying Tandem S300 and 1475:

Categorynumber


GSM-100-202 Operating Information: OMC SystemAdministration

68P02901W13

GSM-100-712 Software Release Notes: OMC System 68P02901W71

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Scaleable OMC

The following Scaleable OMC manuals replace the equivalent Tandem OMC manuals inthe GSM manual set:

Categorynumber


GSM-100-202 Operating Information: Scaleable OMC SystemAdministration

68P02901W19

GSM-100-413 Installation & Configuration: Scaleable OMCClean Install

68P02901W47

GSM-100-712 Software Release Notes: Scaleable OMCSystem

68P02901W74

Related manuals

The following are related Motorola GSM manuals:

Categorynumber


GSM-001-103 System Information: BSS Equipment Planning 68P02900W21

GSM-002-103 System Information: DataGen 68P02900W22

GSM-005-103 System Information: Advance OperationalImpact

68P02900W25

GSM-008-403 Installation & Configuration: Expert Adviser 68P02900W36

Service manuals

The following are the service manuals in the GSM manual set, these manuals are notrelease dependent. The internal organization and makeup of service manual sets mayvary, they may consist of from one to four separate manuals, but they can all be orderedusing the overall catalogue number shown below:

Categorynumber


GSM-100-020 Service Manual: BTS 68P02901W37

GSM-100-030 Service Manual: BSC/RXCDR 68P02901W38

GSM-105-020 Service Manual: M-Cell2 68P02901W75

GSM-106-020 Service Manual: M-Cell6 68P02901W85

GSM-201-020 Service Manual: M-Cellcity 68P02901W95

GSM-202-020 Service Manual: M-Cellaccess 68P02901W65

GSM-101-SERIES ExCell4 Documentation Set 68P02900W50

GSM-103-SERIES ExCell6 Documentation Set 68P02900W70

GSM-102-SERIES TopCell Documentation Set 68P02901W80

GSM-200-SERIES M-Cellmicro Documentation Set 68P02901W90

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Category number

The category number is used to identify the type and level of a manual. For example,manuals with the category number GSM-100-2xx contain operating information.

Cataloguenumber

The Motorola 68P catalogue number is used to order manuals.

Orderingmanuals

All orders for Motorola manuals must be placed with your Motorola Local Office orRepresentative. Manuals are ordered using the catalogue number. Remember, specifythe manual issue required by quoting the correct suffix letter.

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Chapter 1

Introduction to Frame Relay

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Chapter 1Introduction to Frame Relay i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction to Frame Relay 1–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objectives 1–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Wide Area Networks 1–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Public Data Networks 1–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Circuit Switching 1–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Packet Switching 1–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Circuit Switching vs Packet Switching 1–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

X.25 1–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

X.25 Layers 1–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay 1–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Standards 1–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Standards 1–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Issue 3 Revision 2 Objectives


CP08: Frame Relay

FOR TRAINING PURPOSES ONLY 1–1

ObjectivesOn completion of this chapter the student should be able to:

� Appreciate the development of Public Data Networks

� Explain the differences in Packet and Circuit switched networks

� Describe the function and difference of X.25 and Frame Relay

Issue 3 Revision 2Wide Area Networks


CP08: Frame Relay

FOR TRAINING PURPOSES ONLY1–2

Wide Area NetworksThe first WAN’s were designed to carry voice communications and used circuit switchingtechnology to connect end users. These were the PSTN networks. They used analoguelines and the bandwidth was limited to approximately 4Khz.

Initially computer systems tended to be host centric and many terminals were directlyconnected to the host, but there was a need to be able to access hosts from remoteterminals.

This was achieved by the use of modems (modulator / demodulator) either using dial upfacilities or leased lines.

As computer technology advanced the data processing moved towards a network centricmodel. This change gave rise to LOCAL AREA NETWORKS (LAN’s) which allowedmany users in a small area to access expensive resources such as printers and servers.Again leased lines were used to interconnect LAN’s but these were less than ideal asthey were costly and a separate line was required for each connection. The LAN’sthemselves operated initially at speeds of 4 Mbps, 10M bps and 16 Mbps with low errorrates, WAN’s on the other hand were very slow and tended to have high error rates. Therequirement was for a Public Data Network that could transport error free data end toend.

Issue 3 Revision 2 Wide Area Networks


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WANS and LANS

CP08_Ch1_01

Router

WAN

LAN

Leased LineLeased Line

Modem access

Modem access

Remote User

Remote User

Leased LineMainframe

Router

Issue 3 Revision 2Public Data Networks


CP08: Frame Relay


Public Data NetworksAlthough early PDNs were proprietary, the specification of the X.25 interface resulted in aglobally standard Packet Switched Public Data Network (PSPDN) . Its services havebeen widely used for LAN interconnection and other forms of computer communication,and is still in widespread use today.

Packet Switching guaranteed that whatever data was input to the network would bedelivered error free. X.25 is an access protocol and uses the bottom three layers of theOSI 7 layer model, both the packet layer and the link layer carried out error detection andcorrection. Because all packets and frames are acknowledged there is a high overhead(delay), and typically X.25 uses relatively low speed analogue lines (up to 2.048 Mbps)the network tends to be slow.

When interconnecting LAN’s over X.25 the network tends to be a bottleneck as thespeed of the WAN is much slower than even the slowest LAN.

The simplest form of data connection over the PSTN requires a modem to modulatedata as voice frequency tones over the analogue local loop. However, the introduction ofdigital technology to switching and transmission within the PSTN has led to thedevelopment of the Integrated Services Digital Network (ISDN) - providing digitalaccess on customer premises - and digital leased lines - providing high-speedpoint-to-point connections. Calls are established within the PSTN by signalling - themodern PSTN employs a sophisticated signalling system that facilitates the provision ofvalue-added services within Advanced Intelligent Networks (AIN).

Issue 3 Revision 2 Public Data Networks


CP08: Frame Relay


Public Networks

PSPDN

PSTN

CP08_Ch1_02

Analogue access

Digital access

Modem

ISDN Device

Private Packet Network

LELE

LE

PSEPSE

Analogue access

Digital access

LE

PBX

Issue 3 Revision 2Circuit Switching


CP08: Frame Relay


Circuit SwitchingThe two main switching techniques used in WANs are circuit and packet switching.

The PSTN is a circuit switched network that provides fixed-bandwidth channels for voiceor data communication. A connection is established using a call set-up procedure, andthe channel is then dedicated to the circuit for the entire duration of the call.

This method of networking is not efficient for many data applications in which data istransferred in one direction, with only acknowledgements being returned. Thecharacteristics of packet switched networks render them more suitable for this type ofapplication.

Circuit Switching

The diagram shows separate paths (circuits) A-B and A-C that are created through aCircuit Switched Data Network (CSDN) . In this example, the paths are 64kb/schannels (timeslots) provided within an E1 TDM frame that operates at 2.048 Mb/s; thetimeslots are switched at the switching nodes in order to create the required paths.

The circuits are permanently provisioned and operate at fixed data rates (64kb/s);Nx64kb/s circuits could also be provisioned for higher bandwidth applications. Note thata duplex path (i.e. A/B and B/A) is provided.

Circuit switching takes place at the OSI physical layer, and there is no provision for errorcontrol or flow control. However, circuit switched paths are protocol transparent - theyprovide basic pipes for transmission.

Circuit switched paths are generally suitable for applications that require a fixed, shortdelay e.g. voice and video. The bandwidth available is permanently dedicated to thecircuit and the paths are non-blocking. However, this is wasteful for many dataapplications which are bursty by nature, or which involve a short request / long response.

Issue 3 Revision 2 Circuit Switching


CP08: Frame Relay


Circuit Switching

CSDN S

CP08_Ch1_03

B

C

S

S

S – Switching Node

A

Higher Layers

Physical

Higher Layers

PhysicalPhysical Physical Physical

Issue 3 Revision 2Packet Switching


CP08: Frame Relay


Packet SwitchingIn a Packet Switched Data Network (PSDN ), data to be transmitted is first segmentedby the source DTE into message units called packets . Each packet includes thenetwork addresses of the source and destination DTE’s. On receipt of each packet, thePacket Switch Exchange (PSE) stores it while inspecting the destination address; eachPSE has a routing table specifying the outgoing link(s) to be used for each destinationnetwork address. The PSE then forwards the packet on the appropriate link at the rate ofthat link. This method of working is known as store-and-forward.

A number of packets may arrive simultaneously at a PSE on different incoming links forforwarding on the same outgoing link. Packets may therefore experience unpredictablylong delays (To prevent this, a maximum length is specified for each packet).

The PSDN has a meshed topology that offers multiple alternate routes for packets. Inthe diagram, there are two alternate routes between any pair of PSEs. The PSDNtherefore provides a resilient networking service.

As packet networks use store-and-forward, the two communicating DTEs can havedifferent access speeds to the network. The transmission links between PSEs are betterutilised because users only occupy bandwidth when data is being sent and a number ofsuch users can therefore “share” the available transmission bandwidth. This technique isknown as statistical multiplexing - a statistical gain is achieved because it is unlikelythat all users will be transmitting at the same time.

On packet switched networks, error control and flow control are performed on each link.Error control ensures that packets are delivered error-free and in sequence, and flowcontrol provides a method of reducing congestion during busy periods. Overheads forthese functions are carried by each packet and employed by each PSE at OSI Layers 2and 3.

Packet switching can achieve equipment economies because many DTE’s can beconnected to a single PSDN access equipment.

Packet switching matches the characteristics of many data applications (occasional,bursty transfer of data). Its statistical nature means that it is efficient. It does not offer aconstant, low-delay performance and is not therefore ideal for delay sensitiveapplications e.g. voice and video.

Issue 3 Revision 2 Packet Switching


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Packet Switching

CP08_Ch1_04

PSDN

B

CA

D

PSE

PSE

PSE

PSE

a b

a ca c

b c

a d

Higher Layers

Physical LAP–B X.25

Higher Layers




Physical LAP–B X.25 L3

L2 L1

Issue 3 Revision 2Circuit Switching vs Packet Switching


CP08: Frame Relay


Circuit Switching vs Packet Switching

Circuit Switching

The advantages are that there is a direct low delay path point to point, and that circuitswitching is suited to near real time applications.

The major disadvantage is that if a circuit is not in use then the bandwidth is not availableto any other user, also the user may only require a portion of the available bandwidth theremainder being wasted. Another disadvantage is that each user requires a dedicatedaccess port, so large TDM switches may have many physical ports, which increasescost.

Packet Switching

The advantages are that when a user wants to send something he has use of all theavailable bandwidth for short periods of time. When the user is not sending anything thebandwidth is available to other users.

The disadvantage is that delivery is non-deterministic in time. Because traffic is bufferedone users traffic may be held up by other users. Packet switching is not ideally suited todelay sensitive applications.

Issue 3 Revision 2 Circuit Switching vs Packet Switching


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Circuit Switching vs Packet Switching

CP08_Ch1_05

C ABCDABCDAB

Terminals A and C workingTerminals B and D offline

C ACACCAAC

TDM Switch

Packet Switch

Issue 3 Revision 2X.25


CP08: Frame Relay


X.25X.25 is a WAN access protocol that operates over the bottom three layers of the ISO 7Layer model. The interface protocol describes the procedures between a DTE and aDCE, where the DTE is a Packet Assembler Disassembler (PAD) and the DCE is thenetwork. X.25 does not define what happens in the network, but in practice the networkoperates in a similar way to the access protocol

The advantage of X.25 was that it guaranteed that what was put into the network wouldbe delivered error free at the destination point. The operating principal was store andforward, when the next device acknowledged the error free receipt of a packet / framethe sending device could discard the stored copy.

X.25 is used where there are mainly analogue lines that are prone to line hits that giverise to errors in the frames. The Frame format that is used is HDLC that uses a 16 bitCRC. Many vendors of X.25 equipment used not only layer 2 acknowledgement, theyalso acknowledged layer 3. The end result was a high overhead as layer 3acknowledgement was carried in layer two frames.

Three types of frame are used in X.25. For the end user data I frames (information) areused. For flow control S Frames (supervisory) are used, and for link set up U Frames(Un-numbered). The end user data is contained in a Packet, the header contains variousbits of information including, called and calling addresses (X.121 Format), LogicalChannel Number and length of the packet. The link set up uses LAP B (link accessprocedures Balanced).

X.25 predates the ISO 7 layer model. The diagram opposite shows the X.25 layernames.

Issue 3 Revision 2 X.25


CP08: Frame Relay


X.25

CP08_Ch1_06

X.25 Switch

DCE DTE

PAD

Frame

Packet

Physical

Frame

Packet

Physical

Issue 3 Revision 2X.25 Layers


CP08: Frame Relay


X.25 LayersThe physical interface between DTE and DCE is defined as X.21. It is common to seevendors using RS232 (V.24) interfaces.

The link layer protocol between DTE and DCE is a version of High-level Data LinkControl (HDLC) protocol that provides the packet level with an error-free packet transportservice.

The packet layer between DTE and DCE deals with the reliable transfer of data from thehigher levels. In addition it statistically multiplexes virtual calls across a single physicallink.

Issue 3 Revision 2 X.25 Layers


CP08: Frame Relay


X.25 Layers

CP08_Ch1_07

Physical

Frame (Data Link)

Packet (Network)

Transport

Session

Presentation

Application

Virtual Circuits

Serial Bit Stream DCE

DTE

Data

Packet Header

Frame Header

Packet Header Data

Data

7E CRC 7E

Issue 3 Revision 2Frame Relay


CP08: Frame Relay


Frame RelayFrame Relay is a WAN Access Protocol that operates at the physical and data linklayers of the OSI reference model. Frame Relay combines two well-establishedtechnologies, those of time division multiplexing (TDM) and statistical multiplexing. Highspeed and low delay from TDM technology and bandwidth sharing and packetinterleaving from statistical multiplexing. Frame Relay was targeted at bursty LAN traffic.

Packet-switched networks enable end users to dynamically share the network mediumand the available bandwidth. Variable-length packets are used for more efficient andflexible transfers. These packets then are switched between the various networksegments until the destination is reached.

Frame Relay requires digital links that offer a high degree of reliability and low errorrates. As a replacement for X.25 it was an ideal solution. X.25 which operates over thebottom 3 layers of the OSI model has a heavy overhead both at frame and packet level,in that packets and frames are acknowledged and any missing or corrupt frames areretransmitted between network nodes. Frame Relay on the other hand error checksframes and any frames that are errored are discarded without notification. The end userapplications identify missing data and carry out the recovery for lost data.

The diagram opposite shows the relationship of X.25 and Frame Relay to the OSI 7 layermodel.

For an efficient Frame Relay network to operate it is normal for the switches to bemeshed together. If Layer 1 is TDM technology then any re-routing capabilities, if any,are disabled so that re-routing can take place at Layer 2. This allows the PVC’s toreroute which is much faster than any routing that can be done at Layer 1.

Care should be taken with the term Frame Relay. The standards cover the interfaceprotocol, but Frame Relay is also applied as a general term for a network that runsFrame Relay interface protocol - the standard does not define what goes on in thenetwork.

Issue 3 Revision 2 Frame Relay


CP08: Frame Relay


Comparison of X.25 and Frame Relay

CP08_Ch1_08

1. Physical

2. Data Link

1. Physical

2. Link

3. Packet

1. Physical

2. Data Link

4. Transport

3. Network

5. Session

6. Presentation

7. Application

X.25 OSI Model Frame Relay

Issue 3 Revision 2Frame Relay Standards


CP08: Frame Relay


Frame Relay StandardsThere are three standards organisations that cover Frame Relay:

ITU-T : International Telecommunications Union (Formally the CCITT)

ANSI : American National Standards Institute

FRF : Frame Relay Forum

To understand how frame relay standards developed, we need to go back to 1988. Thatyear, ITU-T (then called CCITT) approved Recommendation I.122, ”Framework foradditional packet mode bearer services.”

I.122 was part of a series of ISDN-related specifications. ISDN developers had beenusing a protocol known as Link Access Protocol - D channel (LAPD) to carry thesignaling information on the ”D channel” of ISDN. (LAPD is defined in ITURecommendation Q.921.)

Developers recognized that LAPD had characteristics that could be very useful in otherapplications. One of these characteristics is that it has provisions for multiplexing virtualcircuits at level 2, the frame level (instead of level 3, the packet level as in X.25).Therefore, I.122 was written to provide a general framework outlining how such aprotocol might be used in applications other than ISDN signaling.

Initial proposals for the standardization of Frame Relay were presented to theConsultative Committee on International Telephone and Telegraph (CCITT) in 1984. Dueto lack of interoperability and lack of complete standardization, however, Frame Relay didnot experience significant deployment during the late 1980s. In 1990, four companies,namely Cisco, Digital Equipment, Northern Telecom, and StrataCom collaborated torefine the frame relay specification. ”The Gang of Four,” as they were known, laterformed the Frame Relay Forum, which was incorporated in 1991. Since its inception, theFrame Relay Forum has grown to more than 300 members, evidence of widespreadacceptance of frame relay as the method of choice for high-speed networks.

This group of four developed a specification that conformed to the basic Frame Relayprotocol that was being discussed in CCITT(now ITU-T) but extended the protocol withfeatures that provide additional capabilities for complex internetworking environments.These Frame Relay extensions are referred to collectively as the Local ManagementInterface (LMI).

ANSI and ITU standards are essentially the same.

ANSI standards include :

T1.606 SERVICE DESCRIPTION

T1.617 ANNEX D ACCESS SIGNALLING

T1.618 CORE ASPECTS

Further information on standards may be found at:

http://www.frforum.com

http://www.itu.ch

http://web.ansi.org

Issue 3 Revision 2 Frame Relay Standards


CP08: Frame Relay


ITU-T Recommendations and FRF ImplementationAgreements

CP08_Ch1_10

I.122 Structure of a Frame Mode Bearer Service

I.233 Frame Mode Bearer Services

I.233.1 ISDN Frame Relaying Bearer Service

I.233.2 ISDN Frame Switching Bearer Service

I.370 Congestion Management for the ISDNFrame Relaying Bearer Service

I.372 Frame Relaying Bearer Service Network–to–NetworkInterface Requirements

Q.922 ISDN Data Link Layer Specification for FrameMode Bearer Services

Q.933 Layer 3 Signalling Specification for FrameMode Bearer Services

CP08_Ch1_11

FRF.1.2 User–to–Network (UNI) Implementation Agreement

FRF.2.1 Frame Relay Network–to–Network (NNI) I A

FRF.3.2 Multiprotocol Encapsulation I A (MEI)

FRF.4.1 Switched Virtual Circuit I A

FRF.5 Frame Relay/ATM PVC Network Interworking I A

FRF.6 Frame Relay Service Customer Network ManagmentI A (MIB)

FRF.7 Frame Relay PVC Multicast Service and ProtocolDescription I A

FRF.8.1 Frame Relay/ATM PVC Service Interworking I A

FRF.9

FRF.10

FRF.11.1

FRF.12 Frame Relay Fragmentation I A

Voice over Frame Relay I A

Frame Relay Network–to–Network Interface SVC I A

Data Compression over Frame Relay I A

Issue 3 Revision 2Frame Relay Standards


CP08: Frame Relay



CP08: Frame Relay


Chapter 2

Frame Relay Terminology

Issue 3 Revision 2


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Issue 3 Revision 2


CP08: Frame Relay


Chapter 2Frame Relay Terminology i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Terminology 2–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objectives 2–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Network Components 2–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Physical and Logical Connections 2–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Switches 2–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Access Devices - FRAD 2–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Permanent Virtual Connection - PVC 2–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Internodal DLCIs 2–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

User to Network Interface - UNI 2–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

UNI Signalling Protocols 2–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Internodal Signalling Protocols 2–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Issue 3 Revision 2


CP08: Frame Relay




CP08: Frame Relay



� Understand the function of Frame Relay Components.

� Describe the interaction of the logical and physical components.

� Describe the circuit types and interfaces within Frame Relay.

Issue 3 Revision 2Frame Relay Network Components


CP08: Frame Relay


Frame Relay Network ComponentsA Frame Relay network requires both physical and software components.

The physical requirements are access devices, switches and physical connectionsbetween access devices and switches, and between switches.

The software components comprise of PVC’s, SVC’s, DLCI’s and the interface protocolsUNI and NNI.

It should be noted that until recently few vendors implemented SVC’s.

Issue 3 Revision 2 Frame Relay Network Components


CP08: Frame Relay


Frame Relay Network Components

CP08_Ch2_01

The physical components that comprise a frame relay:

Frame Relay Nodes/Switches (DCE)

Frame Relay Access Equipment (DTE)

Access Line

The software components that comprise a frame relay network are:

PVC’s (Permanent Virtual Circuits), SVC’s (Switched Virtual Circuits)

DLCI’s (Data Link Communication Identifiers)

Interface Protocols:

UNI

NNI

Frame Relay Switch

Access Device

Frame Relay Switch

Frame Relay Switch

Frame Relay Switch

Access Device

Access Device

Access Line

End Users

End Users

Issue 3 Revision 2Physical and Logical Connections


CP08: Frame Relay


Physical and Logical Connections

Layer 1

Physical connections are the access lines and the trunks between the nodes. The endusers will need a connection to the access device.

Layer 2

The logical connections are virtual ”pipes” between end points. These are the PVC’s.

Issue 3 Revision 2 Physical and Logical Connections


CP08: Frame Relay


Frame Relay Network

CP08_Ch2_02

SwitchAccess Device

Switch

Switch

Switch

Access Device

Access Device

Physical ConnectionLayer 1

Logical ConnectionLayer 2

SwitchAccess Device

Switch

Switch

Access Device

Access Device

Many logical connections overone physical interface

Switch

Issue 3 Revision 2Frame Relay Switches


CP08: Frame Relay


Frame Relay SwitchesThe switches or nodes provide the backbone of the network. They typically are SNMPmanaged devices and are capable of providing port, PVC and DLCI usage statistics.

They can reroute PVC’s in the event of a network failure.

Issue 3 Revision 2 Frame Relay Switches


CP08: Frame Relay


Frame Relay Switches

CP08_Ch2_03

Frame Relay Switch

Frame Relay Switch

Frame Relay Switch

Frame Relay Switch

The Switches (also known as nodes) form the backbone of the network

Frame Relay Switch:

Issue 3 Revision 2Frame Relay Access Devices - FRAD


CP08: Frame Relay


Frame Relay Access Devices - FRADThere are many types of access device. The most common FRAD is probably therouters, but any device that runs the Frame Relay software and outputs Frame Relayframes can be a FRAD.

� ROUTERS

� DEDICATED FRADS

� PC’s

� FRONT END PROCESSORS

When purchasing FRADS it is important to check the vendor specifications to ensurethey comply with the standards. Not all vendors support all the Frame Relay standards.For example a vendor may only support the FRF standards. Most switch vendors supportITU, ANSI and FRF but there are many old switches and FRAD’s in use now which donot have compliance with the latest standards. E.G. few FRADS in use support voiceover Frame Relay.

Issue 3 Revision 2 Frame Relay Access Devices - FRAD


CP08: Frame Relay


Frame Relay Access Devices - FRADs

CP08_Ch2_04

SwitchAccess Device

Switch

Switch

Switch

Access Device

Access Device

FRAD

FRAD FRAD

Issue 3 Revision 2Permanent Virtual Connection - PVC


CP08: Frame Relay


Permanent Virtual Connection - PVCPVC’s establish the path a Frame Relay frame will take through the network. A PVC is avirtual connection between endpoints.

The path is normally allocated by the switches dynamically, but may be defined by theoperator. If allocated by the switch, the switch usually will select the shortest path (theleast hop path).

It should be noted that a single physical access line can support many PVC’s.

Switches can re-route PVC’s in the event of a network failure.

SVC’s will be covered later in the course.

Issue 3 Revision 2 Permanent Virtual Connection - PVC


CP08: Frame Relay


Permanent Virtual Circuits - PVC

CP08_Ch2_05

SwitchAccess Device

Switch

Switch

Switch

Access Device

Logical Connection

PVC

Access Device

Issue 3 Revision 2Data Link Connection Identifier - DLCI


CP08: Frame Relay


Data Link Connection Identifier - DLCIThe DLCI is a unique number that identifies a PVC endpoint within the users accesschannel. It is up to the network planners to decide the DLCI numbering scheme to beused in the network. It should be noted that the DLCI has local significance only,therefore another interface in the network may use the same DLCI.

Issue 3 Revision 2 Data Link Connection Identifier - DLCI


CP08: Frame Relay


Data Link Connection Identifier - DLCI

CP08_Ch2_06

SwitchAccess Device

Switch

Switch

Switch

Access Device

PVC

Access Device

Physical Path

550 55

The DLCI has local significance only

Access DLCI’s: 16 – 991 ITU and ANSI

16 – 1007 LMI

Issue 3 Revision 2Internodal DLCIs


CP08: Frame Relay


Internodal DLCIsFor each hop in the network the DLCI will change. The DLCI may have to be configuredor the switches may assign the DLCI dynamically. How DLCI’s are assigned will dependon the vendor equipment.

Issue 3 Revision 2 Internodal DLCIs


CP08: Frame Relay


Internodal DLCIs

CP08_Ch2_07

SwitchAccess Device

Switch

Switch

Switch

Access Device

PVC

Access Device

55055

765 81

Issue 3 Revision 2User to Network Interface - UNI


CP08: Frame Relay


User to Network Interface - UNIUNI signalling protocols are designed to allow the FRAD to communicate with theattached switch. Signalling frames are sent between the FRAD and its local switch tocheck the interface status and PVC status.

The checking process is called Link Integrity Verification (LIV).

There are three standards that cover the UNI.

� ITU – Network

� LMI – Network

� ANSI – Network

Issue 3 Revision 2 User to Network Interface - UNI


CP08: Frame Relay


User to Network Interface - UNI

CP08_Ch2_08

SwitchAccess Device

Switch

Switch

Switch

Access Device

PVC

Access Device

55055

765 81

UNI

UNIUNI

Issue 3 Revision 2UNI Signalling Protocols


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UNI Signalling ProtocolsThe UNI was developed by what is now known as the ITU-T. ANSI followed most of therecommendation. The FRF founded in 1991 developed additions to the core functions.There are differences in the original standards, for example the DLCI allocations,although the FRF has subsequently made changes to align with ITU and ANSI.

Different vendors support one or more of the UNI protocols. Some vendors support allprotocols.

Issue 3 Revision 2 UNI Signalling Protocols


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UNI Signalling Protocols

CP08_Ch2_09

Access Device

Access Device

Access Device

Access Device

Frame Relay Switch

DCE

UNI – ITU (CCITT)

UNI – LMI

Status Request Status Response

UNI – ANSI

UNI – None (No Protocol)

DTE

Issue 3 Revision 2Network to Network Interface - NNI


CP08: Frame Relay


Network to Network Interface - NNIThe NNI allows for two way messages across the interface between two networks. Thisallows each network to have updates on PVC status in the other network.

The FRF do not as such specify the NNI, but FRF2.1 point’s to the ITU and ANSIrecommendations.

Issue 3 Revision 2 Network to Network Interface - NNI


CP08: Frame Relay


Network to Network Interface - NNI

CP08_Ch2_10

Access Device

Access Device

Access Device

Public Frame Relay

Network

Public Frame Relay

Network

Private Frame Relay

Network

UNI

ITU – NNI

UNI

UNI

LMI – User ITU – User

ANSI – User

ITU (CCITT) – NNI (ITU Network to Network Interface Procedures) ANSI – NNI (ANSI Network to Network Interface Procedures)

ANSI – NNI

Issue 3 Revision 2Internodal Signalling Protocols


CP08: Frame Relay


Internodal Signalling ProtocolsThe internodal protocols are not standards based and are usually vendor specific.

The protocols tend to be similar to the NNI protocols, and are designed to allow switchesto send proprietary signalling frames to update other switches about status andconnectivity.

Issue 3 Revision 2 Internodal Signalling Protocols


CP08: Frame Relay


Internodal Signalling Protocols

CP08_Ch2_11

Frame Relay Switch

Frame Relay Switch

Frame Relay Switch

Frame Relay Switch

Internodal Protocols are not defined

Issue 3 Revision 2Internodal Signalling Protocols


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CP08: Frame Relay


Chapter 3

Frame Relay

Issue 3 Revision 2


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Issue 3 Revision 2


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Chapter 3Frame Relay i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 3–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Concepts of Frame Relay 3–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outline Operation 3–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Frame Format 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flag 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Address Header Field 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Information/User Data Field 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Frame Check Sequence, FCS 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Header Address Field 3–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Local Management Interface - LMI 3–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Link Integrity Verification (LIV) 3–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Counters and Timers 3–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Consolidated Link Layer Management - CLLM 3–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Bandwidth Admission 3–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Committed Information Rate - CIR 3–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Traffic Parameters 3–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Switched Virtual Circuit - SVC 3–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Issue 3 Revision 2


CP08: Frame Relay




CP08: Frame Relay



�

Issue 3 Revision 2Concepts of Frame Relay


CP08: Frame Relay


Concepts of Frame Relay

OutlineOperation

A Frame Relay network is made up of Frame Relay compatible devices (e.g. routers,FRAD’s) and Frame Relay switching equipment, which is meshed together.

Connectivity between switches is generally accomplished through TDM circuits where allor a portion of the available bandwidth is assigned for Frame Relay services.

Permanent Virtual Circuits (PVC’s) are carried within this bandwidth; a PVC is a logicalend point to end point connection between two access devices. A Data Link ConnectionIdentifier (DLCI) identifies a PVC end point through which appropriate traffic is routed.

In outline, the principle of Frame Relay operation requires physical bandwidth to beassigned to the Frame Relay service -

this is sometimes referred to as a Frame Stream.

As devices send data frames, the PVC can use the entire allocated Frame Relaybandwidth for its transmission. If the bandwidth is in use, the frames will be queued in abuffer until the bandwidth becomes available.

Frame Relay does not look at the contents of the frame (the end user data) and does notmake any changes to that data. For each hop in the network the header is stripped offand a new header is added (DLCI changes on every hop). Because the header changesthe CRC is recalculated at every step through the network, at any switch if a CRC error isfound then the frame is discarded without notifying the end user.

Issue 3 Revision 2 Concepts of Frame Relay


CP08: Frame Relay


Frame Relay Network

CP08_Ch3_01

Switch Switch

Switch Switch

Frad Frad

Frad Frad 256 Kbps

256 Kbps

64 Kbps

128 Kbps

File Server Host

Issue 3 Revision 2Frame Relay Frame Format


CP08: Frame Relay


Frame Relay Frame FormatThe ITU-T Q.922 recommendation describes the format of the layer two frames that areexchanged on the UNI. The HDLC frame (see diagram) comprises of a pair of flags, aheader, the user data field and the frame check sequence field. A description of thesefields is given below.

Flag

The flag is a unique marker used to delimit the frame and consists of a single octet withthe value hex 7E (Binary 01111110). All frames must start and end with this flag. If theuser data contains the same bit sequence as the flag, a process known as bit (de)stuffing is applied. This involves the addition of a zero inserted by the originator after asequence of five ones to avoid the receiver confusing user data with the flag. Thereceiver removes each zero bit after five consecutive 1 bits. The end flag may also markthe start of the next frame.

Address HeaderField

The address header field can either be two, three or four octets in length; the defaultused by most implementations is two bytes. The bytes within this header are describedwithin the following pages.

Information/UserData Field

The user data field contains the data to be transported and should contain an integralnumber of octets before/after bit (de) stuffing. The maximum size for this field is 4096octets (The standard specifies a maximum of 8192 octets, however a 16 bit CRC will notwork with frames greater than 4096 octets). The user data field is passed transparentlyacross the network and is not changed or interpreted by the frame relay protocol. Theuser data may contain various types of Protocol Data Units (PDU) which are utilised bythe access devices. This field may also include ”multi-protocol encapsulation” accordingto IETF RFC-1294; an industry-standard mechanism for specifying which particularprotocol is in this field.

Frame CheckSequence, FCS

Error detection is performed using the frame check sequence (FCS) ensuring that datahas been received without errors. The two octets contain a cyclic redundancy check,CRC, which operates using a defined ITU-T error checking polynomial. The FCS checksall bits within the frame apart from the flags. A frame containing an incorrect FCS will bediscarded requiring retransmission from the host. Each time the address field changes,the FCS is recalculated.

Issue 3 Revision 2 Frame Relay Frame Format


CP08: Frame Relay


Frame Relay Frame Format

CP08_Ch3_02

Flag Header Information FCS Flag

1 12 – 4 2Variable 1 – 4096 octets

Issue 3 Revision 2Header Address Field


CP08: Frame Relay


Header Address FieldThe header field within the frame is shown in the diagram contains the followinginformation:

The Data Link Connection Identifier (DLCI)

Used to uniquely identify a virtual circuit (VC). As Frame Relay is a packet switchingtechnology, the virtual circuits are used to maintain connections between end stations ona single user-network interface concurrently. DLCI’s have only local significance as theychange for each hop comprising the path of a VC. The two-byte header provides theDLCI with 10 bits, permitting 1024 VC addresses on every interface. However, some ofthe addresses are reserved for management purposes.

Command/Response Indication (CR)

The Frame Relay protocol does not define its use and values are passed transparentlyacross the network.

Extended Address (EA)

Used to indicate whether the header has an extended length to include additionaladdress bits. The one bit field is set to a one in the last octet and zero in the precedingoctet(s) of the address field. By increasing the header size to three or four octets, manymore circuits are available - about 268 million using two additional address octets. (Notnormally used).

Forward Explicit Congestion Notification Bit (FECN)

This one-bit field is used to indicate to the frames destination access device that it haspassed through a congested node or port. It is assumed that the users will take action torelieve the congestion, although no obligation exists.

Backward Explicit Congestion Notification Bit (BECN)

This one-bit field is used to indicate to the access device that the network is experiencingcongestion for frames travelling in the opposite direction of the BECN-marked frame onthat PVC. It is assumed that the users will take action to relieve the congestion, althoughagain, no obligation exists.

Discard Eligibility (DE)

This one-bit field is used to indicate to the network whether this frame may be discardedin the event of congestion (DE=1).

Issue 3 Revision 2 Header Address Field


CP08: Frame Relay


Frame Relay Header

CP08_Ch3_03

Flag Header Information FCS Flag

1 octet n

DLCI (MSB) C/R

DLCI (LSB) FECN BECN DE EA 0

EA 0

8 7 6 5 4 3 2 1

Issue 3 Revision 2Data Link Connection Identifier - DLCI


CP08: Frame Relay


Data Link Connection Identifier - DLCIAs already seen the DLCI is used to identify which PVC a frame should use. It isimportant to remember that a DLCI has local significance only, on another interface thesame DLCI number may be used.

Most vendors do not support extended addressing, but many support ITU, ANSI andFRF standards. The 10 bits allow for 1024 values (0 - 1023) but not all are allocated touser channels, some numbers are reserved for other use.

The table opposite shows the number allocations for the ITU and ANSI standard, whichare the same, and for the FRF standard which uses different allocations.

Issue 3 Revision 2 Data Link Connection Identifier - DLCI


CP08: Frame Relay


Data Link Connection Identifier - DLCI

CP08_Ch3_04

ITU/ANSI LMI

0

1 – 15

16 – 991

992 – 1007

1008 – 1023

Signalling

Reserved

Assigned to PVC’s

Reserved

Reserved

0 – 15

16 – 1007

1008 – 1018

1019 – 1022

1023

Reserved

Assigned to PVC’s

Reserved

Multicast

Signalling

Issue 3 Revision 2Local Management Interface - LMI


CP08: Frame Relay


Local Management Interface - LMIThe LMI enables communication between the access device and the network. The LMIhas two functions:

1. A keep alive signal between FRAD and network.

2. To provide health information on the network.

The FRAD polls the network at regular intervals and expects a response from thenetwork. If the response is received then the interface is up. These polls are sometimescalled short polls. After a number of short polls the FRAD will send a status requestasking the network for details on active, inactive and removed DLCI’s. This process isknown as Link Integrity Verification (LIV).

The LIV is carried out on DLCI 0 in the ITU and ANSI standards and on DLCI 1023 in theFRF standard.

Issue 3 Revision 2 Local Management Interface - LMI


CP08: Frame Relay


Local Management Interface - LMI

CP08_Ch3_05

Access Device

DTE

Frame Relay Switch

DCE

DLCI 0 (ITU/ANSI) or 1023 (LMI)

Status Request

Status Response

Issue 3 Revision 2Link Integrity Verification (LIV)


CP08: Frame Relay


Link Integrity Verification (LIV)The LIV is controlled by a number of configurable counters and timers which are shownopposite.

It is possible that on older access devices they do not provide LIV, or that they may beerratic in polling the network. Under these circumstances the switch can be configured sothat it will not expect to be polled. The problem that then exists is that the updates on thenetwork must be carried out manually.

Another option is that the switch can be set to asynchronous operation, which lets theswitch update the access device on PVC status without being polled.

The Timers (T) and counters (N) are:

T392 How often the frame relay node expects to see a short status enquiry from the user equipment.

N392 The node measurement for the number of times the access equipment can misssending a status enquiry (T391). If the node dose not hear from the accessdevice in the designated number of sequential intervales, it declares the interface down.

N393 The number of good sequential status requests the node must receive before declaring the interface up.

N391 The total number of intervals (how many T391’s) the access device counts before requesting a full status from the frame relay node.

T391 The frame relay “keep alive” interval that has been set on the access device.T391 must be less than the node timming interval, T392. Nodes may be busydoing some other process and may need a few more seconds to respond to anaccess equipment poll.

Issue 3 Revision 2 Link Integrity Verification (LIV)


CP08: Frame Relay


Link Integrity Verification – LIV

CP08_Ch3_06

Access Device

DTE

Frame Relay Switch

DCE

DLCI 0 (ITU/ANSI) or 1023 (LMI)

T391 = 10N391 = 6 T392 = 15

N392 = 3N393 = 4

Issue 3 Revision 2Counters and Timers


CP08: Frame Relay


Counters and TimersThe counters are configurable to customer requirements, but vendors tend to use thedefault values shown opposite. Most vendors do not recommend changing the countervalues unless there is a specific reason to do so.

Issue 3 Revision 2 Counters and Timers


CP08: Frame Relay


System Parameters - Counters

CP08_Ch3_07

Counter Description Range Default Usage

N392

N393

N391 Full Status (all PVC’s)polling counter

Error threshold

Monitored events

1 – 255

1 – 10

1 – 10

6

3

4

Polling cycles

Errors

Events

N392 should be less than or equal to N393.1.

If N393 is set to a value much less than N391, then the linkcould go in and out of error condition without the userequipment or network being notified.

2.

N391 always applies to the user equipment. It applies to theuser and network if the optional bidirectional networkprocedures are invoked.

3.

System Parameters - Timers

CP08_Ch3_08

T392 should be greater than T391.1.

T391 always applies to the user. It applies to the user and network if the optionalbi–directional network procedures are invoked.

2.

T392 always applies to the network. It applies to the network and user equipment ifthe optional bi–directional network procedures are invoked.

3.

Timer Description Range(seconds)

Default(seconds)

Started Stopped Actions takenwhen expired

T391

T392

Link IntegrityVerification

PollingVerification

5 – 30

5 – 30

10

15

TransmitStatusEnquiry

TransmitStatus

ReceiveStatusEnquiry

Transmit StatusEnquiry. Recorderror if Statusmessage is notreceived

Record error byincrementing N392Timer Restart

Issue 3 Revision 2Consolidated Link Layer Management - CLLM


CP08: Frame Relay


Consolidated Link Layer Management - CLLMThe network may send Consolidated Link Layer Management (CLLM) messagesgenerated in the presence of congestion. ANSI defines DLCI 1023 as reserved for theCLLM. Few vendors have implemented CLLM as its use is optional in the standards. Itshould be noticed that the FRF specify DLCI 1023 for the LMI.

Issue 3 Revision 2 Consolidated Link Layer Management - CLLM


CP08: Frame Relay


Consolidated Link Layer Management - CLLM

CP08_Ch3_09

CLLM message Indicating congestion

(ITU/ANSI on DLCI 1023)

Frame Relay Network

Congestion Control

Issue 3 Revision 2Network to Network Interface - NNI


CP08: Frame Relay


Network to Network Interface - NNIThe NNI operates in a similar way to the UNI except that the polls are in both directionsallowing each network to get DLCI status from the other. The NNI operates betweenswitches and allows traffic to pass from one network to the other.

The FRF do not define the NNI but they point to the ITU and ANSI standards for the NNI.

Typically, a PVC that crosses from one network to another will have the DLCI allocatedby the carrier. On the private network the terminating DLCI will be set to match the carrierDLCI. The PVC will then be passed across the interface between the two networks.

Issue 3 Revision 2 Network to Network Interface - NNI


CP08: Frame Relay


Network to Network Interface - NNI

CP08_Ch3_10

Access Device

Access Device

NNI

DLCI 456

DLCI 123 DLCI 777DLCI 777

ITU – T Standard Q933ANSI Standard T1.618

Private Frame Relay

NetworkPublic

Frame Relay Network

Vendor BVendor A UNI

UNI ITU – T NNI

ITU – T User

LMI – User

Issue 3 Revision 2Bandwidth Admission


CP08: Frame Relay


Bandwidth AdmissionService providers charge customers to access and use the frame relay network. Theyneed some method of determining which user is getting what percentage of thebandwidth.

Frame relay service providers use bandwidth admission and prioritisation as a Class ofService mechanism - per PVC.

Customer pays for a Committed Information Rate (CIR) in bps.

Issue 3 Revision 2 Bandwidth Admission


CP08: Frame Relay


Bandwidth Admission

CP08_Ch3_11

Access Device

Public

Frame Relay Network

What traffic am i sending?

How much am i sending? Is it the same in both directions? What access line speed is it?

What CIR’s do i need? How much does it cost?

Access Device

Access Device

Issue 3 Revision 2Committed Information Rate - CIR


CP08: Frame Relay


Committed Information Rate - CIRThe CIR provides a quality of service mechanism for the customer, in that with anappropriate CIR the service provider would guarantee the throughput without loss.

The initial CIR setting may not be easy to estimate, as the speed should reflect theaverage throughput expected, and this may be unknown on a new network. Rememberthat the sum of the CIR’s may exceed the access line speed. Oversubscription can go ashigh as five to one, but may be as low as one to one, and depends on the type of trafficflow.

There are some loose rules that can help decide what CIR to use. In the diagramopposite the PVC from FRAD A to FRAD D should not exceed the lowest access linespeed - in this example 64Kbps. A starting value for oversubscription of about 120%allows for fine tuning the network later, without running into congestion immediately. Byusing the statistics generated by the switches the CIR’s can be adjusted up or down asappropriate.

It is possible to allocate a CIR of 0 to a PVC, but this is normally only done with lowpriority traffic. With a CIR of 0 all frames would be marked DE=1 on the ingress switch.

Issue 3 Revision 2 Committed Information Rate - CIR


CP08: Frame Relay


Committed Information Rate

CP08_Ch3_12

Switch Switch

Switch

Frad DFrad B

Frad A Frad C

256 Kbps

64 Kbps

128 Kbps

File Server Host

Switch 64 Kbps

All CIR’s on this interface would be

64 Kbps or less

Issue 3 Revision 2Frame Relay Traffic Parameters


CP08: Frame Relay


Frame Relay Traffic ParametersThe switch checks each PVC to police the customer, that is to check the customer doesnot exceed the agreed contract limits. Without policing the customer could burstexcessively to the extent that other users could not have access.

There are three key parameters to the policing :

TC - Time constant. A calculated value in seconds

BC - Burst committed. Measured in bits per TC

CIR - Committed Information Rate Measured in Bits per second

TC is calculated by the formula

��

��

If Bc was 64,000 bits and the CIR was 32 Kbps then TC would equal 2 seconds

Other values are:

BE - Burst excess measured in bits per TC

If a customer has a burst excess he can exceed his BC into BE, but frames that startabove the BC in TC will be marked DE 1. If frames go over BC+BE they may be passedthrough the network but the customer may loose a token. If the frame starts aboveBC+BE then the frame will be discarded.

Tokens or credits are vendor specific, the customer may loose all his tokens if he keepsbursting over BC+BE, and then he may loose additional frames.

Issue 3 Revision 2 Frame Relay Traffic Parameters


CP08: Frame Relay


Frame Relay Traffic Parameters

CP08_Ch3_13

Bits

Be

Bc

Discard Frame

CIR

DLCI 98 Frame 1 Frame 2 Frame 3 F4 F5DE=0 DE=0 DE=1 DE=1 X..

TC

Access Rate

Discard all frames that start

above BE

May discard frames

Send frames

Issue 3 Revision 2Switched Virtual Circuit - SVC


CP08: Frame Relay


Switched Virtual Circuit - SVCUp until recently few vendors have supported SVC’s either in switches or FRAD’s, butthere is now more interest in providing SVC’s.

PVC’s are defined at subscription time, and provides a permanent path (A to B) at alltimes even though there may be no traffic flow for part of the time. With an SVCbandwidth is dynamically established (ANY to ANY) when there is a need to make a call,and on completion of the call bandwidth is released, thus saving money and resource.

The SVC is well suited to many intermittent applications such as voice calls, trafficoverflow, video conferencing and remote access, to name a few.

Costing can be carried out on a call by call basis, and various elements can be chargedfor:

� call duration

� bandwidth

� number of frames sent / received

However, distance is not an issue.

SVC’s require call set up, information transfer and call release stages. The standardshave specified that the addressing will be either E.164 ( ISDN / Telephony numberingplan ) or x.121 ( data numbering plan ). The basic procedures are shown opposite.

It will be appreciated that the Frame Relay frame header will contain additionalinformation and will therefore be larger.

Issue 3 Revision 2 Switched Virtual Circuit - SVC


CP08: Frame Relay


Switched Virtual Circuit - SVC

CP08_Ch3_14

Switch Access Device Switch

Switch

Access Device

Access DeviceSwitchE.164 or X.121

Addressing

FRAD

FRAD

FRADSVC

SVC

SVC

T2 Call Setup

Connect T3

T6 Disconnect

Release T7

T1 Call Setup

Call Proceeding T2

T5 Disconnect

T7 Release Complete

Connect

Information

T4

Information

T8 Release Release complete T8

T9 Release complete

Issue 3 Revision 2Switched Virtual Circuit - SVC


CP08: Frame Relay



CP08: Frame Relay


Chapter 4

Frame Relay Management

Issue 3 Revision 2


CP08: Frame Relay


Issue 3 Revision 2


CP08: Frame Relay


Chapter 4Frame Relay Management i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay Management 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objectives 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Discard Eligibility 4–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Congestion Control 4–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Network Congestion 4–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Network Management 4–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Port Statistics Example 4–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

PVC Statistics Example 4–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Issue 3 Revision 2


CP08: Frame Relay


Issue 3 Revision 2 Frame Relay Management


CP08: Frame Relay


Frame Relay Management

Objectives

On completion of this chapter the student should be able to:

�

Issue 3 Revision 2Discard Eligibility


CP08: Frame Relay


Discard EligibilityIf the access device A is exceeding his CIR and bursting into BE, then the ingress switchwill mark the frames starting in burst excess (BE) as discard eligible by setting the DE bitto one.

If the network is not congested then the network may pass all the frames to the egresspoint.

If the end user had been given a CIR of 0 Kbps then all his frames would be marked asDE=1.

Issue 3 Revision 2 Discard Eligibility


CP08: Frame Relay


Discard Eligibility

CP08_Ch4_01

Frame Relay

Switch

DE=1

DE=1 DE=1

Access Device A

Access Device B

Issue 3 Revision 2Congestion Control


CP08: Frame Relay


Congestion ControlCongestion control is a mechanism incorporated within Frame Relay to attain certainnetwork performance objectives (especially during peak traffic periods) by optimising andimproving the network resources. The aim is to limit the number of times that the userperceives congestion, and to prevent a single user monopolising network resources atthe expense of other users. Congestion control uses mechanisms to both avoid andrecover from network congestion.

The frame relay service provides the transparent and unacknowledged transport offrames across the network. The network will only modify the address and FCS fields,ensuring the user data received is identical to that which was sent. However, thenetwork does not guarantee message delivery, and frames may have to be dropped (ordiscarded) by the network. If a frame relay switch is approaching congestion, then it willinform the access devices at either end of this congestion using the FECN / BECN bits.This assumes that the users will take the appropriate action to limit the flow of data sentto the network, although this is not detailed within the frame relay standards.

Network congestion can occur in the following ways:

� Switch failure within the network.

� Layer one failure within the network.

� Switch Congestion - a network switch will indicate a status of congestion if thepackets delivered to it for switching exceed a specified threshold set in the switch.

� Port congestion - if the number of frames within the input or output buffers of aswitch exceed specified threshold values, the buffers will indicate a status ofcongestion.

Vendors usually define the degree of congestion as a percentage of buffer utilisation, thiscan vary between vendors, but tends to be when the buffer is about 70% full.

Issue 3 Revision 2 Congestion Control


CP08: Frame Relay


Congestion Control

CP08_Ch4_02

Frame Relay

Switch

FECN FECN

Access Device A

Access Device B

Buffers start to fillbecause of extratraffic

FECNFECN

BECN

DE=1

BECN

FECN

Issue 3 Revision 2Network Congestion


CP08: Frame Relay


Network CongestionIf the access device ignores the BECN/ FECN and continues to excess burst bringing theport on the switch to a congested state, then the switch will start to discard frames withthe DE=1.

The problem then arises that the end user application re-transmits discarded frames.This action could lead to the switch becoming more congested. If discards do not easethe congestion and the situation becomes more congested, then the node may startdiscarding non DE frames. Again, how the switch does this is vendor specific. Anexample of what may happen is that the switch will discard 1 in 4 frames, then 1 in 3frames, then 1 in 2 after that the switch may clear all buffers and restart.

Issue 3 Revision 2 Network Congestion


CP08: Frame Relay


Network Congestion

CP08_Ch4_03

Frame Relay

SwitchAccess Device A

Access Device B

Discard Frames markedDE=1 when switch is ina congested condition

DE=1

DE=1

Issue 3 Revision 2Network Management


CP08: Frame Relay


Network ManagementMost networks are managed by some form of management, and where required anaccounting package.

The management system is more often than not using Simple Network ManagementProtocol (SNMP). This allows the network to be monitored for faults and failures.

The accounting packages vary as it depends on how charges are made for use of thenetwork.

There may be a standing charge per PVC, or there may be a charge based on framecount.

The switches generate a large amount of statistics that can be used for grooming thenetwork, and for checking network utilisation. From the statistics it may be found thatadditional PVC’s may be added or that CIR’s may be increased or decreased.

Issue 3 Revision 2 Network Management


CP08: Frame Relay


Network Management

CP08_Ch4_04

Frame Relay

Switch

Access Device

Access DeviceManager

Issue 3 Revision 2Port Statistics Example


CP08: Frame Relay


Port Statistics ExampleThe network management and operations centre can monitor all ports in the network andfrom statistics gathered will make any necessary adjustments to the ports. For example ifa large number of frames are being discarded because of bad CRC errors, then it mayindicate a problem with the physical layer.

In many cases a fault condition may produce several indications. Statistics should not belooked at in isolation.

Remember that a port may have many PVC’s / SVC’s configured on it.

Issue 3 Revision 2 Port Statistics Example


CP08: Frame Relay


Port Statistics Example

CP08_Ch4_05

Port 0 Statistics (last cleared 0 days, 0 hours, 25 minutes, 30 seconds ago)––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Frames In Frames Out Bytes In Bytes OutAll: 177 183 5713 6079Non–DE: 177 183 5713 6079DE: 0 0 0 0BECN: 0 0FECN: 0 0––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– ––– Last 5 minutes ––––– ––– Max since clear –––– ––– In ––– ––– Out –– ––– In ––– ––– Out ––Frames/sec: 0 0 0 0Bytes/sec: 3 3 6 10Maximum Queue depth: 1 1 1 2––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– *** Priority Queueing *** –– Current –– –– Since clear ––Priority Av.Queue Max Usage: P_1 0% 0 [183] P_2 0% 0 [0] P_3 0% 0 [0]–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––Dropped: BW Admission:0 In Congest:0 Out congest:0 frames: Unknown DLCI:0 DE:0 Frame Error:0 PVC inactive:0 Other:0 Last Unknown DLCI: N/ADevice Errors: Short frames: 0 Bad CRC/Non–octet: 0 Long frames: 0 Receiver overruns: 0 Missed frames: 0 Transmitter underruns: 0(RETURN to continue ...) >

Issue 3 Revision 2PVC Statistics Example


CP08: Frame Relay


PVC Statistics ExampleBy checking individual PVC’s the network management and operations centre can see ifa customer is over or under utilising the PVC.

If DLCI accounting is enabled then the customer can be charged for the use of the PVC.

If a DLCI was showing large numbers of frames being dropped (>Bc+Be) and with a highnumber of frames being marked DE, and the burst excess was high it may indicate thatthe current CIR is too low.

A customer pays for a CIR, the higher the CIR the more the customer pays.

Issue 3 Revision 2 PVC Statistics Example


CP08: Frame Relay


PVC Statistics Example

CP08_Ch4_06

Port 2 DLCI 100 PVC Status–––––––––––––––––––––––––––

Data Base State ActivatedPVC State CompleteLast Disconnect Reason Operator RequestPVC Route N13C42–N12C42Path Towards Destination P0 –> N12C42P0 using DLCI 988Window Length (Tc) 1.0 secondsDropped Frames (> Bc + Be) 0Frames Marked DE 0DE frames Received 0Burst Bits this Tc 0Excess Bits this Tc 0Maximum Bc (during Tc) 0Maximum Be (during Tc) 0Average Bc Bits (past 5 Tc) 0Average Be Bits (past 5 Tc) 0PVC Status Active

DLCI Counters are not available because Full PVC Accounting is disabled.

Issue 3 Revision 2PVC Statistics Example


CP08: Frame Relay



CP08: Frame Relay


Chapter 5

Voice Over Frame Relay

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CP08: Frame Relay


Issue 3 Revision 2


CP08: Frame Relay


Chapter 5Voice Over Frame Relay i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Voice Over Frame Relay 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objectives 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Voice Over Frame Relay 5–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fragmentation and Prioritisation 5–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Voice Compression 5–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Silence Detection and Suppression 5–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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CP08: Frame Relay


Issue 3 Revision 2 Voice Over Frame Relay


CP08: Frame Relay



Objectives


�

Issue 3 Revision 2Voice Over Frame Relay


CP08: Frame Relay


Voice Over Frame RelayWhy voice over Frame Relay?

There are probably three main reasons for putting voice over Frame Relay:

Cost - By deploying voice over Frame Relay companies, in particularmultinational groups can make substantial savings on international calls.

Simplified Network - Voice and data over a single network makes for easiermanagement and maintenance. A failure in the network is not a majorproblem as Frame Relay networks have inherent automatic rerouting.

Network utilization - It is rare that data transmission is prolonged to theextent that the full bandwidth is used. A file transfer may need the full CIRand some additional bandwidth (burst excess), but when complete otherapplications can use the bandwidth.

Voice quality over Frame Relay was quite poor in the early days, but with careful networkdesign quality has been vastly improved.

Delay is a potential problem for voice traffic. To overcome the problem voice traffic isgiven a higher priority than data traffic, and data frames are also fragmented into muchsmaller frames. Fragmentation may be carried out in the access device or the switch.Many vendors have supported traffic prioritisation, originally for delay sensitive dataapplications. Vendors are now introducing voice FRAD’s that have a number of featuresto improve the quality of the voice traffic, these include:

� Voice compression - reduces bandwidth required

� Fragmentation - reduces delay

� Jitter buffering - smoothes delivery

� Prioritisation - reduces delay

� Silence detection and suppression - reduces bandwidth required

Implementation Agreement FRF.11 covers voice over Frame Relay standards, but doesnot, for example, address fragmentation or silence suppression, and only offer guidelinesfor compression. Vendors are offering features over and above the standard, so careneeds to be taken in a multi vendor environment.

Issue 3 Revision 2 Voice Over Frame Relay


CP08: Frame Relay



CP08_Ch5_01

Voice Compression

Fragmentation

Jitter Buffering

Prioritization

Silence Detection and Suppression

VFRAD

Frame Relay Network

PVC SVC

Fax

Voice

Data

File Server

Host Computer

Issue 3 Revision 2Fragmentation and Prioritisation


CP08: Frame Relay


Fragmentation and Prioritisation

Fragmentation

Fragmentation is used to reduce the size of data frames down to a nominal frame ofaround 160 octets (vendor dependent). This minimizes the chances of large data framesdelaying time sensitive voice frames. Some vendors also fragment voice frames, theadvantage being that any lost frames will have the minimum impact on the end user.

The downside of fragmentation is that the overhead is increased in that there are moreframes for a given amount of traffic, and as a result, more headers and trailers.

Fragmentation is normally carried out by the FRAD, but some vendors provide the facilityto fragment traffic in the switches. This is to allow the use of older FRAD’s that do notsupport fragmentation to be used.

Prioritisation

PVC’s may be prioritised on the switches or traffic may be prioritised in the FRAD. Manyvendors use three priorities (high, medium and low) but there are some who use more.There are various ways to give fairness of service, it may be a fairly simple round robinsystem or a system that spends varying amounts of time on working on the queues.

Issue 3 Revision 2 Fragmentation and Prioritisation


CP08: Frame Relay


Fragmentation and Prioritisation

CP08_Ch5_02

Voice

Fragmentation Output Buffer

Data

SwitchVFRAD

High

Med

Low

Issue 3 Revision 2Voice Compression


CP08: Frame Relay


Voice CompressionVoice at PCM rate occupies a full 64 Kbps of bandwidth, by compressing the voice downto 32 Kbps would effectively double the number of calls that could be supported on thenetwork. Today there are many compression algorithms which vendor’s use, some whichcan compress calls down to 8 Kbps or less.

The Frame Relay Forum specify two ITU–T algorithms in FRF 11.1:-

G.727 - Adaptive Differential Pulse Code Modulation (ADPCM) 32Kbps.

G.729 - Conjugate Structure Algebraic Code Explicit Linear Prediction (CS-ACELP) 8Kbps.

It should be noted that an 8 Kbps compressed call may take up more bandwidth than the8 Kbps because of the framing overhead.

Silence Detectionand Suppression

Speech is not a constant flow, it has pauses and moments of silence. In a normaltelephone conversation around 50% of the time there is silence. Most voice applicationstransmit the silence that uses as much bandwidth as speech. To free up bandwidth voiceFRAD’s do not send silence, but send a small packet to the destination voice FRADindicating when, and for how long it needs to reinsert the silence. This process savesmore bandwidth.

Issue 3 Revision 2 Voice Compression


CP08: Frame Relay


Voice Compression and Silence Suppression

CP08_Ch4_03

PCM Voice

64 Kbps

G.729 CS–ACELP

8 Kbps

Silence Suppression

3.5 Kbps

CS–ACELP – Conjugate structure algebraic code explicit linear predictionPCM – Pulse code modulation

Issue 3 Revision 2Voice Compression


CP08: Frame Relay



CP08: Frame Relay


Chapter 6

Frame Relay to ATM

Issue 3 Revision 2


CP08: Frame Relay


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CP08: Frame Relay


Chapter 6Frame Relay to ATM i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay to ATM 6–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objectives 6–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay and ATM 6–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame Relay to ATM Service Interworking - FRASI 6–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Frame-Based User Network Interface - FUNI 6–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . High-Speed Frame Relay 6–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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CP08: Frame Relay


Issue 3 Revision 2 Frame Relay to ATM


CP08: Frame Relay


Frame Relay to ATM

Objectives


�

Issue 3 Revision 2Frame Relay and ATM


CP08: Frame Relay


Frame Relay and ATMToday there are an increasing number of ATM networks. It is not uncommon to have anATM backbone in a Frame Relay network. Remember that Frame Relay is an interfaceprotocol and that what happens in the network is not defined.

Customers have a number of options that can be taken:

1. They can maintain and expand, if required, their current Frame Relay Network.

2. They can migrate to an ATM network - which can be very costly.

3. Customers can use Frame Relay on some sites, and on other sites that carry muchmore traffic, ATM can be installed.

It is worthwhile to note that Frame Relay and ATM have a number of similarities:

� Both Frame Relay and ATM are connection-orientated technologies.

� Both technologies use packets, with Frame Relay using variable length packets(frames) and ATM using fixed length packets (cells) which are 53 bytes long.

� The base technology for both is statistical multiplexing which allows only activeapplications to access the resource.

� Frame Relay and ATM have inherent automatic rerouting capabilities (assuming amesh network).

� Logical virtual circuits connect endpoints.

� Both services allow end users to oversubscribe ports.

Issue 3 Revision 2 Frame Relay and ATM


CP08: Frame Relay


Frame Relay/ATM Common Features

CP08_Ch6_01

Connection orientated technologies

Packet based

Statistical multiplexing

Automatic rerouting capabilities

Logical virtual circuits connect endpoints (PVC)

Oversubscribe on ports

Frame Relay

ATM

Y

Frame

Y

Y

Y

DLCI

Y

Cell

Y

Y

VPI/VCI

Y

VPI = Virtual Path IdentifierVCI = Virtual Channel Identifier

Issue 3 Revision 2Frame Relay to ATM Service Interworking - FRASI


CP08: Frame Relay


Frame Relay to ATM Service Interworking - FRASIFRASI provides a way to connect a Frame Relay site to an ATM site. The two (or more)sites can communicate seamlessly with each other without the need to install a newAccess Device or software. The translations and protocol conversion are carried out inthe network. From the end user point of view FRASI would provide a logical migrationpath from Frame Relay to ATM.

FRASI has been defined in FRF 8.1. To allow Frame Relay to communicate with ATMrequires a protocol conversion and translation device known as the Inter WorkingFunction (IWF). The IWF can be a standalone equipment or it can be integrated into aFrame Relay or ATM switch.

In the diagram opposite, as well as showing examples of service interworking there is anexample of network interworking (FRF 5). Traffic from FRAD A to FRAD B would passthrough the ATM network effectively using it as a high–speed backbone. The frames aretunneled through the ATM network as cells, the end users protocol is preserved and thedata is unaltered. As the cells leave the ATM network the frames are reconstructed anddelivered to the Frame Relay network.

Issue 3 Revision 2 Frame Relay to ATM Service Interworking - FRASI


CP08: Frame Relay


Inter Working Function

CP08_Ch6_02

FRAD A

FRAD

FRAD B

IWF

B CPE

B CPE

IWF

IWF

IWF

UNI

UNI

UNI Frame Relay

Network

Frame Relay

Network

ATM Network

ATM UNI

ATM UNI

B = Broadband

Issue 3 Revision 2Frame-Based User Network Interface - FUNI


CP08: Frame Relay


Frame-Based User Network Interface - FUNIThere are other alternatives to FRASI which have benefits and drawbacks. Frame-BasedUNI sends frames to the ATM network that has a FUNI interface. The ATM switchprovides segmentation and reassembly services, in that frames are switched into 53 bytecells and sent over the ATM network.

FUNI has a similar structure to frame relay frames, but not the same, which means theFRAD would require a software upgrade and a FUNI interface.

The disadvantages are that SVC’s are not supported and, at the moment, supports VBRonly.

There are limited standards, and few vendors support FUNI

Similar to the FUNI is the Data eXchange Interface ( DXI ). The main difference is thatsegmentation and reassembly are carried out at the customer premises.

High-SpeedFrame Relay

Many frame relay ports run up to 2.048 Mbps, but some vendors, and thus serviceproviders, run ports in excess of 2.048 Mbps for Frame Relay. A major issue is the costof the lines, as the customer may need an E2 or E3 interface.

Issue 3 Revision 2 Frame-Based User Network Interface - FUNI


CP08: Frame Relay


Frame-Based UNI - FUNI

CP08_Ch6_03

FRAD B CPE

ATM Network

FUNIATM UNI

Cells

ATM FUNI

Frames

Segmentation and

Reassembly

B = Broadband

Issue 3 Revision 2Frame-Based User Network Interface - FUNI


CP08: Frame Relay


frame relay

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