Principles of C7 Signalling

CHAPTER 2THE SS7 NETWORK

CHAPTER 3SS7 4 LEVEL MODEL

CHAPTER 4SS7 NETWORK

ADDRESSING AND ROUTING

CHAPTER 5SS7 SIGNALLING UNITS

CHAPTER 1ROLE OF SIGNALLING

SYSTEM

CHAPTER 7TRANS. CAP’S. AP AND

MAP

CHAPTER 8GSM NETWORK OVERVIEW

TO SS7

CHAPTER 6SIGNALLING CONNECTION

CONTROL PART

Principles of C7

Training Manual

Version 1 Revision 0

FOR TRAININGPURPOSES ONLY

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FOR TRAININGPURPOSES ONLY


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CP03: Principles of C7

FOR TRAINING PURPOSES ONLY i


CP03Principles of C7

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




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.




FOR TRAINING PURPOSES ONLY iii

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Reporting safety issues 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Warnings and cautions 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General warnings 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Human exposure to radio frequency energy (PCS1900 only) 8. . . . . . . . . . . . . . . . . . . . . .

Beryllium health and safety precautions 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General cautions 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Devices sensitive to static 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 1Role of Signalling System No 7 in GSM i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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

SS7 in GSM 1–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GSM Network Overview 1–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Network Switching Subsystem 1–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Base Station System 1–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Network Management Centre (NMC) 1–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2Mbits PCM 1–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 Interfaces 1–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

GSM Interface Names 1–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interface Names 1–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 2The SS7 Network i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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

Main Requirements of SS7 2–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Elements in a Network 2–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Point/Signalling Transfer Point 2–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Point Code 2–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .




FOR TRAINING PURPOSES ONLYiv

Format of Signalling Point Code 2–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Numbering of International Signalling Points 2–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Link and Link Sets 2–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SS7 Signalling Link Types 2–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Route and Route Set 2–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Message Routing across a network 2–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Methods 2–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

E1 PCM 2–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCP Database 2–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service Switching Point (SSP) 2–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service Control Point (SCP) 2–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The SS7 Network 2–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 3SS7 4 Level Model i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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

Protocols 3–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Protocol Layers of the OSI 7 Model 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Protocol Comparison of OSI to SS7 3–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 to OSI Overview 3–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Layer 1 3–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Layer 2 3–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Layer 2 Functionality 3–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Layer 3 3–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Layer 3 Functionality 3–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Traffic Handling 3–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Signalling Network Management 3–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Functionality 3–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Message discrimination 3–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Message Transfer Part 3–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 layer 4 3–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 to OSI layers 3–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Connection Control Part 3–28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Transaction Capabilities Application Part 3–30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Mobile Application Part (MAP) 3–32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MAP services 3–34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MAP Services and Primitives 3–36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 4SS7 Network Addressing and Routing i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Network Addressing 4–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Point Codes 4–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .




FOR TRAINING PURPOSES ONLY v

Point Codes 4–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Global Title 4–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Subsystem Numbering 4–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 5SS7 Signalling Units i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Units Overview 5–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Circuit Switch 5–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Message Switch 5–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Packet Switch 5–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 Packet Switching 5–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signal Unit Packets (Generic) 5–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Flag 5–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Error Correction and Flow Control 5–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


FIB p BIB 5–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Retransmission of Signalling Units 5–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Length Indicator (LI) 5–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Field Check Sum 5–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Units Overview 5–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fill in Signal Unit 5–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Link Status Signal Unit 5–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LSSU Status Indication 5–28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Link Alignment 5–30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Link Alignment Test Duration 5–32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Message Signal Unit 5–34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Service Information Octet 5–36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Service Indicator (SI) 5–38. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sub-Service Field 5–40. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Information Field 5–42. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Routing Label 5–44. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 Management and Test Messages 5–46. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Header Fields 5–48. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 Network Management and Network Test Messages 5–50. . . . . . . . . . . . . . . . . . . . . . . . .


Chapter 6Signalling Connection Control Part i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 6–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


SCCP Signalling Services 6–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .




FOR TRAINING PURPOSES ONLYvi

SCCP Services 6–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Primitives 6–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Protocol Classes 6–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Embedded in MSU 6–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Message 6–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Routing Label 6–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Message type code. 6–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Parameters 6–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Message Structure 6–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Message Type Code 6–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Routing 6–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Routing Calling Party and Called Party 6–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Addressing for Routing 6–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Called Party Address 6–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Address information 6–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Functional Structure 6–28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 7Transaction Capabilities Application Part and Mobile Application Part i. .

Objectives 7–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Transaction Capabilities Application Part (TCAP) 7–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Purpose of TCAP 7–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Mobile Application Part 7–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MAP Application Entities 7–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP and MAP Interworking 7–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP and MAP in the OSI Model 7–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

AE Functionality 7–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Structure 7–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Component Sub Layer (CSL) 7–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Transaction Sub layer (TSL) 7–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Message Interfaces 7–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Embedded Message Structure 7–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Information Elements 7–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Primitives and Constructor IE 7–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Message Structure 7–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Transaction Procedures 7–28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MAP user Communication 7–30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP/MAP Transactions 7–32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 8GSM Network Overview to SS7 i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 8–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

GSM Network Components 8–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .




FOR TRAINING PURPOSES ONLY vii


A Interface Protocols 8–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A Interface between MSC and BSS 8–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

BSSAP Message Structure 8–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BSSMAP Message 8–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DTAP Message 8–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Interfaces Between BSC, BTS and MS 8–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LAPD frame Structure 8–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Address Field 8–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control field 8–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LAPDm Frames 8–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LAPDm Frame Structure 8–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A and B format Frame Structure 8–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Address Field 8–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control Field 8–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 Connection to GPRS 8–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .




FOR TRAINING PURPOSES ONLYviii

Version 1 Revision 0 General information



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

Version 1 Revision 0General information



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.

Version 1 Revision 0 First aid in case of electric shock




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

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.

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.

Version 1 Revision 0Reporting safety issues




Reporting safety issues

Introduction

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.

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 Customer Network Resolution Centre+44 (0)1793 430040 (telephone) and follow up with a written report by fax+44 (0)1793 430987 (fax).

4. Collect evidence from the equipment under the guidance of the Customer NetworkResolution Centre.

Version 1 Revision 0 Warnings and cautions




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

Version 1 Revision 0General warnings




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.

Version 1 Revision 0 General warnings




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.

Version 1 Revision 0Human exposure to radio frequency energy (PCS1900 only)




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 environmentControlled 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.

Version 1 Revision 0 Human exposure to radio frequency energy (PCS1900 only)




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.

Version 1 Revision 0Human exposure to radio frequency energy (PCS1900 only)




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.

Version 1 Revision 0 Beryllium health and safety precautions




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. Captive withinthe component it presents no health risk whatsoever. However, if the component shouldbe broken open and the Beryllium Oxide, which is in the form of dust, released, thereexists 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.

Version 1 Revision 0Beryllium health and safety precautions




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. The spatula/toolused to collect the paste is also to be placed in the container. The container is then to besealed and labelled. A suitable respirator is to be worn at all times during this 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.

Version 1 Revision 0 General cautions




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.

Version 1 Revision 0Devices sensitive to static




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.

Version 1 Revision 0 Motorola GSM manual set




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

Version 1 Revision 0Motorola GSM manual set




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

Version 1 Revision 0 Motorola GSM manual set




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.

Version 1 Revision 0Motorola GSM manual set







Chapter 1

Role of Signalling System

No 7 in GSM









Chapter 1Role of Signalling System No 7 in GSM i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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

SS7 in GSM 1–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GSM Network Overview 1–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Network Switching Subsystem 1–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Base Station System 1–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Network Management Centre (NMC) 1–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2Mbits PCM 1–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 Interfaces 1–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .






Version 1 Revision 0 Objectives



FOR TRAINING PURPOSES ONLY 1–1

Objectives

At the end of this chapter the student will be able to:

� Identify the two Subsystems and their components in GSM.

� Identify the components and interfaces of the GSM network and describe theirfunction.

Version 1 Revision 0SS7 in GSM



FOR TRAINING PURPOSES ONLY1–2

SS7 in GSMGSM network components

GSM NetworkOverview

The diagram opposite shows a simplified GSM network. Each network component isillustrated only once. However, many of the components will occur several timesthroughout a network.

Each network component is designed to communicate over an interface specified by theGSM standards. This provides flexibility and enables a network provider to utilizesystem components from different manufacturers. For example Motorola Base StationSystem (BSS) equipment may be coupled with an Ericsson Network Switching System.

The principle component groups of a GSM network are:

The Mobile Station (MS)

This consists of the mobile telephone, fax machine etc. This is the part of the networkthat the subscriber will see.

The Base Station System (BSS)

This BSS is the part of the network that provides the radio interconnection from the MSto the land-based switching equipment.

The Network Switching System (NSS)

The NSS consists of the Mobile services Switching Centre (MSC) and its associatedsystem-control databases and processors together with the required interfaces. This isthe part that provides for interconnection between the GSM network and the PublicSwitched Telephone Network (PSTN).

The Operations and Maintenance Centre (OMC)

This enables the network provider to configure and maintain the network from a centrallocation.

Version 1 Revision 0 SS7 in GSM




GSM Network Components

CP03_Ch1_01

NMC

OMC

Operations andMaintenance System

Network Switching System

Base Station System

Interface/Connection

Mobile Station

PSTN

VLR HLR

AUC

EIRMSC

IWFEC

BTS

BSC

ME

SIM

XCDR

Version 1 Revision 0The Network Switching Subsystem




The Network Switching Subsystem


The Network Switching System includes the main switching functions of the GSMnetwork. It also contains the databases required for subscriber data and mobilitymanagement. Its main function is to manage communications between the GSMnetwork and other telecommunications networks.

The components of the Network Switching System are listed below:

� Mobile Services Switching Centre (MSC)

� Home Location Register (HLR)

� Visitor Location Register (VLR)

� Equipment Identity Register (EIR)

� Authentication Centre (AUC)

� InterWorking Function (IWF)

� Echo Canceller (EC)

In addition to the more traditional elements of a cellular telephone system, GSM hasLocation Register network entities. These entities are the Home Location Register(HLR), Visitor Location Register (VLR), and the Equipment Identity Register (EIR). Thelocation registers are database-oriented processing nodes, which address the problemsof managing subscriber data and keeping track of a MS’s location as it roams around thenetwork.

Functionally, the Interworking Function and the Echo Cancellers may be considered asparts of the MSC, since their activities are inextricably linked with those of the switch as itconnects speech and data calls to and from the MSs.

Version 1 Revision 0 The Network Switching Subsystem




Networking Switching System

CP03_Ch1_02

VLR

EC IWF

MSC

HLR

AUC

EIR


VLR

EC IWF

MSC

HLR

AUC

EIR


PSTNPSTNPSTN

Operationsand

Maintenance System

Operationsand

Maintenance System

Operationsand

Maintenance System

BSSBSSBSS

Version 1 Revision 0The Base Station System




The Base Station SystemThe GSM Base Station System is the equipment located at a cell site. It comprises acombination of digital and RF equipment. The BSS provides the link between the MobileStation (MS) and the Mobile services Switching Centre (MSC).

The BSS communicates with the MS over the digital air interface and with the MSC via 2Mbit/s links.

The BSS consists of three major hardware components:

The Base Transceiver Station (BTS)

The BTS contains the RF components that provide the air interface for a particular cell.This is the part of the GSM network that communicates with the MS. The antenna isincluded as part of the BTS.

The Base Station Controller (BSC)

The BSC as its name implies provides the control for the BSS. The BSC communicatesdirectly with the MSC. The BSC may control single or multiple BTSs.

The Transcoder (XCDR)

The transcoder is used to compact the signals from the MS so that they are moreefficiently sent over the terrestrial interfaces. Although the transcoder is considered to bea part of the BSS, it is very often located closer to the MSC.

The transcoder is used to reduce the rate at which the traffic (voice/data) is transmittedover the air interface. Although the transcoder is part of the BSS, it is often foundphysically closer to the NSS to allow more efficient use of the terrestrial links.

Version 1 Revision 0 The Base Station System




Base Station System

CP03_Ch1_03

BSC

BSS

BTS

XCDR

BTS

BTSBTS

Version 1 Revision 0Network Management Centre (NMC)




Network Management Centre (NMC)The NMC offers the ability to provide hierarchical regionalized network management of acomplete GSM system.

It is responsible for operations and maintenance at the network level, supported by theOMCs which are responsible for regional network management.

The NMC is therefore a single logical facility at the top of the network managementhierarchy.

The NMC has a high level view of the network, as a series of network nodes andinterconnecting communications facilities.

The OMC, on the other hand, is used to filter information from the network equipment forforwarding to the NMC, thus allowing it to focus on issues requiring nationalco-ordination. The NMC can also co-ordinate issues regarding interconnection to othernetworks, for example the Public Switched Telephone Network (PSTN).

The NMC can take regional responsibility when an OMC is not manned, with the OMCacting as a transit point between the NMC and the network equipment. The NMCprovides operators with functions equivalent to those available at the OMC.

Functionality of the NMC

� Monitors node on the network.

� Monitors GSM Network Element Statistics.

� Monitors OMC regions and provides information to OMC staff.

� Passes on statistical information from one OMC region to another to improveproblem strategies.

Version 1 Revision 0 Network Management Centre (NMC)




Network Management Centre

CP03_Ch1_04

NMC

OMC

OMC

OMC

NETWORK

REGION 1

REGION 2 REGION 3

Q3 PROTOCOL(GSM 12 SERIES)

Version 1 Revision 02Mbits PCM




2Mbits PCM

2 Mbit/s Trunk 32-channel PCM

This diagram opposite shows the logical GSM system with the 2 Mbit/s interfaceshighlighted.

The interfaces carry traffic from the PSTN to the MSC, between MSCs, from an MSC toa BSC and from a BSC to remotely sited BTSs.

These links are also used between the MSC and IWF.

Each 2.048 Mbit/s link provides thirty-two 64 kbit/s channels available to carry speech,data, or control information. The control information may contain C7, LAPD or X.25formatted information.

These 2 Mbit/s links commonly act as the physical bearer for the interfaces usedbetween the GSM system entities.

Version 1 Revision 0 2Mbits PCM




2Mbit trunks

CP03_Ch1_05

NMC

OMC

VLR

MSC

ECIWFXC

XC

VLR

EC IWF XC

MSC

HLR

AUC

EIR

PSTN

BTS BSC

CO–LOCATED ENTITIES

BSS

BTS

BTS

BTS

BTS

BTS

BTS

BSC

BTS BTS BTS

MS

MS

MS

VLR

Version 1 Revision 0SS7 Interfaces




SS7 InterfacesThe term C7 and SS7 are describing the same function, they both describe the signallingfunction of the network, either term may be used

ITU-TS Signalling System #7

The diagram opposite illustrates the use of C7 in the GSM system; carrying signallingand control information between most major entities, and to and from the PSTN.

The following message protocols, which are part of C7, are used to communicatebetween the different GSM network entities:

Interfacing the PSTN, the MSC performs call-signalling functions using the TelephoneUser Part (TUP), or interfacing ISDN, the ISDN User Part (ISUP).

Between the MSC and the BSC, the Base Station System Management Application Part(BSSMAP) is used.

The Direct Transfer Application Part (DTAP) is used to send messages between theMSC and the mobile (MS).

MAP is used between the MSC and the VLR, EIR, and HLR.

Acronyms:

BSSAP Base Station System Application Part

BSSMAP Base Station System Management Application Part

DTAP Direct Transfer Application Part

ISUP ISDN User Part

MAP Mobile Application Part

SCCP Signalling connection Control Part

TUP Telephone User Part

TCAP Transaction Capabilities Application Part

Version 1 Revision 0 SS7 Interfaces




C7 Interfaces

CP03_Ch1_06

MAP

NMC

OMC

VLR

MSC

ECIWFXC

XC

VLR

EC IWF XC

MSC

HLR

AUC

EIR

PSTN

BTS BSC

BSS

BTS

BTS

BTS

BTS

BTS

BTS

BSC

BTS BTS BTS

MS

MS

MS

VLR

BSSMAP TUP

BSSAP

Version 1 Revision 0GSM Interface Names




GSM Interface Names

Interface Names

Each interface specified within the GSM system has a name associated with it. Thediagram opposite illustrates the names of all the interfaces specified by GSM.

Air-interface MS–BTS

A-bis(Mo-bis) BTS–BSC

A-interface BSS–MSC

B-Interface MSC–VLR

C-interface MSC–HLR

D-interface HLR–VLR

E-interface inter–MSC

F-interface MSC–EIR

G-interface VLR–VLR

R-interface MS–DTE (Data Terminating Equipment)

Version 1 Revision 0 GSM Interface Names




GSM interface names

CP03_Ch1_07

NMC

OMC

VLR

MSC

ECIWFXC

XC

VLR

EC IWF XC

MSC

HLR

AUC

EIR

PSTN

BTS BSC


BSS

BTS

BTS

BTS

BTS

BTS

BTS

BSC

BTS BTS BTS

MS

MS

MS

VLR

A

E

Abis

Um

G

B

D

BC

H

F








Chapter 2

The SS7 Network









Chapter 2The SS7 Network i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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

Main Requirements of SS7 2–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Elements in a Network 2–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Point/Signalling Transfer Point 2–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Point Code 2–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Format of Signalling Point Code 2–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Numbering of International Signalling Points 2–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Link and Link Sets 2–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SS7 Signalling Link Types 2–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Route and Route Set 2–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Message Routing across a network 2–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Methods 2–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

E1 PCM 2–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCP Database 2–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service Switching Point (SSP) 2–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service Control Point (SCP) 2–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The SS7 Network 2–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .









Objectives

At the end of this chapter you will be able to:

� Identify the different functions that make up a signalling network.

� Understand the functionality within an SS7 network.

Version 1 Revision 0Main Requirements of SS7




Main Requirements of SS7There are two main requirements of the signalling system.

� All calls must be set-up, monitored and broken down in a correct manner.

� The signalling system must be able to support all non-circuit applications such asdatabase enquires and supplementary services.

The SS7 network and protocol are used for:

� Basic call set-up, management, and tear down.

� Wireless services such as personal communications services (PCS), wirelessroaming, and mobile subscriber authentication.

� Local number portability (LNP).

� Toll-free (800/888) and toll (900) wire line services.

� Enhanced call features such as call forwarding, calling party name/number display,and three-way calling.

� Efficient and secure worldwide telecommunications.

Network management information must also be carried across the network. This enablesthe network to maintain itself during failures and then recover from them.

The network also needs to deal with load sharing and re-routing this is also achievedthrough the use of SS7

When looking at any signalling requirements within a telephone network it is important tounderstand that all voice calls breakdown into two separate components, the voicecomponent and the signalling component. All other calls are just seen by the network asdata that is signalling

Version 1 Revision 0 Main Requirements of SS7




Main Requirements of SS7

CP03_Ch2_01

Circuit related applications concerned with the connection anddisconnection of telephone calls

Non circuit related applications which support the circuit relatedapplications

To achieve call processing the different components in the network mustbe able to interact with each other.

A call is made up of two components:– The voice/data component.– The signalling component.

Version 1 Revision 0Signalling Elements in a Network




Signalling Elements in a NetworkSP/STP The basic blocks in the network

SPC An address of a single unit in the network

Signalling link The physical connection

Link set More than one physical connection between the same two points

Route The logical connection between two points in a network

Route set More than one logical connection between the same two points

Version 1 Revision 0 Signalling Elements in a Network




Signalling Elements

CP03_Ch2_02

SP/STP

SPC ( opc–dpc)

Signalling Link

Link set

Route

Route set

�

�

�

�

�

�

Version 1 Revision 0Signalling Point/Signalling Transfer Point




Signalling Point/Signalling Transfer Point

Signalling Point (SP)

A Signalling Point is any node in the network that is able to handle signalling messages.These signalling messages can either be generated or received

Signalling transfer Point (STP)

A Signalling Transfer Point is able to receive a message on one signalling link and thentransfer that message to another link, without processing the contents of the message.

STP is able to transfer in three dimensions, national, regional and international

Version 1 Revision 0 Signalling Point/Signalling Transfer Point




Signalling Point/STP

CP03_Ch2_03

SP is a processing node in a signalling network, which hasSS7 implemented

STP is a processing node where a message is received inone link and transferred to another.

SPSPSTPSTP

�

�

Version 1 Revision 0Signalling Point Code




Signalling Point Code

Signalling Point Code (SPC)

In the SS7 network all signalling points (SP) need to be identified in order to allow forcommunication between each other. All Signalling Points are identified by a unique codeknown as the Signalling Point Code (SPC)

The Signalling Point at which the signalling message is generated, or is the source userpart is known as the Originating Point Code (OPC)

The Signalling Point to which the signalling message is destined, or is the receiving userpart is known as the Destination Point Code (DPC)

In order to allow for multiplayer signalling there must be a method that allows forcommunication between different networks. It is the Network Indicator (NI) that must bedefined for this.

SP = NI – SPC

The SPC is normally 14 bits long in the binary form. This can be translated to either hexor various national presentations

Version 1 Revision 0 Signalling Point Code




Signalling Point Code

CP03_Ch2_04

All signalling points in a SS7 network are identified by a unique codeknown as a Signalling Point Code SPC

There are two components to a SPC

SP = NI –SPC

�

�

Version 1 Revision 0Format of Signalling Point Code




Format of Signalling Point Code

Numbering ofInternationalSignalling Points

A 14-bit binary code is used for the identification of signalling points (ITU-I Q708).

An international signalling point code (ISPC) should be assigned to each signalling point,which belongs to the international signalling network. For some network environment,one physical network node may serve as more than one signalling point, and maytherefore be assigned more than one signalling point code. All international signallingpoint codes (ISPC) should consist of three identification sub-fields as indicated. Thesub-field of 3 bits (NML) should identify a world geographical zone. The sub-field of 8 bits(K–D) should identify a geographical area or network in a specific zone. The sub-field of3 bits (CBA) should identify a signalling point in a specific geographical area or network.The combination of the first and second sub-fields could be regarded asa signallingarea/network code (SANC).

Each country (or geographical area) should be assigned at least one signallingarea/network code (SANC).

The system of International Signalling Point Codes (ISPC) will provide for 6�256�8(12288) ISPCs.

If a country (or geographical area) should require more than 8 international signallingpoints, one or more additional signalling area/network code(s) (SANC) would be assignedto it.

Version 1 Revision 0 Format of Signalling Point Code




Format of Signalling Point Code

CP03_Ch2_05

Version 1 Revision 0Signalling Link and Link Sets




Signalling Link and Link SetsA signalling link is the physical data link that connects two signalling points. It is abi-directional transmission path for signalling, comprising two data channels operatingtogether in opposite directions at the same data rate. It constitutes the lowest functionallevel (level 1) in the Signalling System No. 7 (SS7) functional hierarchy.

� A link set is a group of one to sixteen links between two nodes.

� All of the links must have the same attributes.

� Multiple link sets can be deployed between two nodes.

SS7 SignallingLink Types

Signalling links are logically organized by link type (“A” through “F”) according to their usein the SS7 signalling network.

A Link: An “A” (access) link connects a signalling end point (e.g., an SCP or SSP) to anSTP.

B Link: A “B” (bridge) link connects an STP to another STP. Typically, a quad of “B” linksinterconnect peer (or primary) STPs (e.g., the STPs from one network to the STPs ofanother network). The distinction between a “B” link and a “D” link is rather arbitrary. Forthis reason, such links may be referred to as “B/D” links.

C Link: A “C” (cross) link connects STPs performing identical functions into a mated pair.

D Link: A “D” (diagonal) link connects a secondary (e.g., local or regional) STP pair to aprimary (e.g., inter-network gateway) STP pair in a quad-link configuration. Thedistinction between a “B” link and a “D” link is rather arbitrary. For this reason, such linksmay be referred to as “B/D” links.

E Link: An “E” (extended) link connects an SSP to an alternate STP.

F Link: An “F” (fully associated) link connects two signalling end points.

Version 1 Revision 0 Signalling Link and Link Sets




Signalling link & Link Set

CP03_Ch2_06

The physical connection between two nodes (SP/STP) in theSS7 network

One or more links connected between the same two nodes inthe network Can be used for Load distribution

Link 2

SPSP

STPSTP

Link 1 Link Set

Link 2

SPSP

STPSTP

Link 1 Link Set

�

�

Version 1 Revision 0Signalling Route and Route Set




Signalling Route and Route SetA signalling route is the pre-determined path, consisting of a succession of STPs andinterconnecting SLs that take a message through the network between the originatingpoint to the destination point.

Each route carries traffic to only one destination, the route may be direct or over severalSTPs, the SLs in a route may belong to several routes and as such carry traffic toseveral destinations

SLs and data in STPs combine to form a signalling route.

All the signalling routes that may be used between an originating point and a destinationpoint are known as a Signalling Route Set.

Version 1 Revision 0 Signalling Route and Route Set




Signalling Route and Route Set

CP03_Ch2_07

A signalling route is a predetermined path that takes themessage through the signalling network

A route set is one or more routes linked together

SPSPSPSP

STPSTP

Link Set

STPSTP

Link Set

STPSTP

Link Set

STPSTP

Link Set

STPSTP

Link Set

Signalling route

�

�

Version 1 Revision 0Message Routing across a network




Message Routing across a networkThere are two signalling points that have a requirement to pass a message, the networkneeds to have various elements in order to pass the message.

If the two SPs are connected then the SL between them is the only network element.

If the SPs are in two different networks then all of the elements are required:

Signalling Route: Needs to be in place in order to pass the message

STP: Able to transfer message between networks

Signalling Link: Connects the SP to STP/SPs

SP: Start point and end point of message

Link Set: If more that one SL exists between SP and STP

Version 1 Revision 0 Message Routing across a network




Message Routing

CP03_Ch2_08

Link SetOPC 2 –2–2

SPSP

STPSTP

STPSTP

Link Set

STPSTP

Link Set

signallinglink

Link Set

OPC 1 –1–1

STPSTPSTPSTP

SPSP

Version 1 Revision 0Signalling Methods




Signalling MethodsThere are two methods of signalling that can be used to achieve call processing, theyare:

� Channel Associated Signalling (CAS), where the speech and signalling areassociated to each other and follow the same physical path.

� Common Channel Signalling (CCS), is a signalling method in which a singlechannel conveys in data packets signalling information that relates to userspecified connections – as a result, speech and voice do not need to be physicallyrelated. Also known as associated mode when voice and signalling take the samepath, if the path is different then the signalling mode is associated.

SS7 has two signalling types:

� Connection orientated signalling where two nodes establish a link to transferinformation

� Connectionless signalling where a node sends information that does not requireacknowledgement of receipt

Version 1 Revision 0 Signalling Methods




Signalling Methods

CP03_Ch2_09

Voice and Signalling Channel

Signalling Channel

Voice Channels

CAS

CCS

Version 1 Revision 0E1 PCM




E1 PCMAn E1 or 2.048Mbit/s PCM frame is made up of 32 eight-bit timeslots, numbered from 0to 31. Timeslot (T/S) 0 is always used for sync, this enables incoming slots to be read atthe correct time, timeslot 16 is normally used for signalling – this is not mandatory but itis widely accepted as the norm.

Sampling of the analogue signal is done at 8000 times per second. Each frame consistsof 8 bits from each timeslot. So, each timeslot is 8�8000=64,000 bits per second 64Kbit/sec

When referred to, the term E1 indicates both transmission and reception components.

Version 1 Revision 0 E1 PCM




E1 PCM

CP03_Ch2_10

VOICE

32 timeslots @64 kb/s

0 16 31

What is an E1 PCM?

VOICE

SYNC SIG

Version 1 Revision 0SCP Database




SCP DatabaseThe terms SSP and SCP are used in the Intelligent Network (IN), they explain theoperation of database enquiries.

ServiceSwitching Point(SSP)

SSPs are switches that originate, terminate, or tandem calls. An SSP sends signallingmessages to other SSPs to set-up, manage, and release voice circuits required tocomplete a call. An SSP may also send a query message to a centralized database (anSCP) to determine how to route a call (e.g., a toll-free 1-800/888 call in North America).

Service ControlPoint (SCP)

An SCP sends a response to the originating SSP containing the routing number(s)associated with the dialled number. An alternate routing number may be used by theSSP if the primary number is busy or the call is unanswered within a specified time.Actual call features vary from network to network and from service to service.

Databases may be either physically internal or external to the SCP, but must beconsidered a separate device. There are several types of database, which include:

� Call Management Service Database (CMSDB)

� Number Portability (NP)

� Line Information Database (LIDB)

� Home Location Register (HLR)

� Visitor Location Register (VLR)

Registers act as an interface to the telephone company database, and translate nongeographical numbers from a database to provide information for calling card, subscriberservices, fraud protection and intelligent networks

Version 1 Revision 0 SCP Database




Network Databases

CP03_Ch2_11

SCP

SSP

SSP

SCP

SS7 LINKS

SCPSCP

SSP

SSP

SCPSCP

SS7 LINKS

Version 1 Revision 0The SS7 Network




The SS7 NetworkThe SS7 network can be divided into two parts, Voice and Signalling. As alreadymentioned they do need to follow the same physical path, and the two components arerequired to achieve a completed call.

In the network the signalling can also be broken into separate parts, one for the control ofthe voice and a second that is involved with database access. The database queries areclose to register signalling, however they can also be from many User Parts (UP) orapplication parts (AP).

The first parts of the network that will be used are the SPs and the SSPs these willestablish the validity of the call and also prepare the voice circuit, behind these parts theother components in the network the STPs and the SSPs will be used in the set up, or toanswer database queries and send reponses.

Version 1 Revision 0 The SS7 Network




The SS7 Network

CP03_Ch2_12

STP

STP

SCP

SCP

SS7 Links

STP

STP

SCPSCP

SCPSCP

SS7 LinksVOICE CIRCUITS

SP

SP

SSP

SSP

VOICE CIRCUITS

SP

SP

SSP

SSP

Version 1 Revision 0The SS7 Network







Chapter 3

SS7 4 Level Model









Chapter 3SS7 4 Level Model i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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

Protocols 3–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Protocol Layers of the OSI 7 Model 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Protocol Comparison of OSI to SS7 3–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 to OSI Overview 3–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Layer 1 3–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Layer 2 3–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Layer 2 Functionality 3–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Layer 3 3–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Layer 3 Functionality 3–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Traffic Handling 3–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Signalling Network Management 3–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MTP Functionality 3–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Message discrimination 3–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Message Transfer Part 3–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 layer 4 3–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 to OSI layers 3–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Transaction Capabilities Application Part 3–30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Mobile Application Part (MAP) 3–32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MAP services 3–34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MAP Services and Primitives 3–36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .









Objectives


� State the rules of a protocol and identify the different layers that constitute aprotocol.

� Identify the different levels in SS7 and their function.

� Understand how SS7 relates to the OSI model.

Version 1 Revision 0Protocols




ProtocolsA Protocol is an agreed set of rules and procedures that if followed by all participants, willallow the orderly and controlled transfer of information between and among theseparticipants.

Or in simple terms a protocol:

� Allows unique physical addressing for separate entities

� Controls the flow of information between the network layers for guaranteeddelivery.

� Processor outages

� Error detection and correction

Protocols also define the rules for data exchange, using fixed or variable length packets,enables error free data transmission. It has the ability to append network managementinformation in predefined message structures using segmentation of data blocks fortransmission over established layers for different functions.

Version 1 Revision 0 Protocols




What is a Protocol?

�

CP03_Ch3_01

The Definition of a protocol is:

– A protocol is a set of definitions and agreements on how tocommunicate

Version 1 Revision 0Protocol Layers of the OSI 7 Model




Protocol Layers of the OSI 7 Model

Number Layer Description

1 Physical Is responsible for the actual transmission ofthe data and the provision of the necessaryfacilities, could be copper, wire, radio, satellite

2 Data Link Is responsible for the packaging of the data tobe transmitted. Also error detection andcorrection

3 Network Prescribes the path a message has to takeand who the message is routed to. Layer 3has all responsibility for all routing

4 Transport Guarantees the correct end–to–end orderingof message packets, also end–to–end datacontrol

5 Session Global synchronization, both parties use thislayer to co–ordinate the communicationprocess between themselves

6 Presentation Is responsible for the definition andpreparation of data before it is passed to theapplication layer, it is able to distinguishdifferent data types and perform datacompression and decompression

7 Application Is the interface of specific application to thetransmission medium

Version 1 Revision 0 Protocol Layers of the OSI 7 Model




Protocol Layers of the OSI Model

CP03_Ch3_02

Data Link

Network

Transport

Session

Presentation

Application

Physical

7

6

5

4

3

2

1

Data Link

Network

Transport

Session

Presentation

Application

Physical

7

6

5

4

3

2

1

OSI 7 Layer Model

Version 1 Revision 0Protocol Comparison of OSI to SS7




Protocol Comparison of OSI to SS7The model that is most often spoken about when referring to the SS7 network is the OSImodel, this covers all layers within the SS7 model but the OSI model is laid out over 7layers whilst the SS7 model is a 4 level one.

The major problem is that one can not then define directly across the two, the simpleview is that layers 1–3 in OSI are almost covered by level 1–3 in SS7, and that the Level4 in SS7 can be laid over the layers 4–7 in the OSI model

Version 1 Revision 0 Protocol Comparison of OSI to SS7




Protocol Comparison of OSI to SS7

CP03_Ch3_03

Level 1–3

Level 4Level 4

OSI SS7

Data Link

Network

Transport

Session

Presentation

Application

Physical

7

6

5

4

3

2

1

Data Link

Network

Transport

Session

Presentation

Application

Physical

7

6

5

4

3

2

1

Version 1 Revision 0SS7 to OSI Overview




SS7 to OSI OverviewThe layers in the SS7 model the three lowest levels form the message transfer part(MTP) and the fourth level contains the user parts (UP).

The OSI model uses layer 4–7 as the message handling part. In SS7 the messagehandling also uses part of what would be layer three in OSI, and as a consequence themessage transfer part layer 1–3 in OSI does not equate to level 1–3 in the SS7 model.

The layers 4–7 in OSI are known as User Parts in SS7, these can be a specific User Partsuch as the ISDN–User Part (ISUP) or can be comprised of different parts to make upthe signalling:

SCCP – Signalling Connection Control Part

TCAP – Transaction Capabilities Application Part

MAP – Mobile Application Part

ASE – Application Service Elements

Version 1 Revision 0 SS7 to OSI Overview




SS7 to OSI Overview

CP03_Ch3_04

MTP Level 1

MTP Level 2

MTP Level 3

SCCP

ISUP

TCAP

ASE

MTP Level 1

MTP Level 2

MTP Level 3

SCCP

ISUP

TCAP

ASE

OSI SS7

Data Link

Network

Transport

Session

Presentation

Application

Physical

7

6

5

4

3

2

1

Data Link

Network

Transport

Session

Presentation

Application

Physical

7

6

5

4

3

2

1

Version 1 Revision 0MTP Layer 1




MTP Layer 1The MTP Layer 1 is the physical level and it is virtually the same as the OSI model.Layer 1 defines the physical, electrical and functional characteristics of a signalling datalink and the means to access it. The Layer 1 element provides a bearer for a signallinglink.

In a digital environment, 64 kbit/s digital paths will normally be used for the signallingdata link. The signalling data link may be accessed via a switching function, providing apotential for automatic reconfiguration of signalling links.

� Provides the physical connection between two nodes.

� The protocol should be able to use any type of physical interface.

Version 1 Revision 0 MTP Layer 1




MTP layer 1

CP03_Ch3_05

MTP–L1

MAP ASE

TCAP

SCCP

MTP–L3

MTP–L2

MTP–L1

ISDN –UP

Physical Data Link





MTP Layer 2Level 2 defines the functions and procedures for, and relating to, the transfer of signallingmessages over one individual signalling data link. The layer 2 functions together with alayer 1 signalling data link as a bearer provide a signalling link for reliable transfer ofsignalling messages between two points.

A signalling message delivered by the higher levels is transferred over the signalling linkin variable length signal units. For proper operation of the signalling link, the signal unitcomprises transfer control information in addition to the information content of thesignalling message.

The signalling link functions include:

� Delimitation of signal unit by means of flags;

� Flag imitation prevention by bit stuffing;

� Error detection by means of check bits included in each signal unit;

� Error correction by retransmission and signal unit sequence control by means ofexplicit sequence numbers in each signal unit and explicit continuousacknowledgements;

� Signalling link failure detection by means of signal unit error rate monitoring andsignalling link recovery by means of special procedures.





MTP layer 2

CP03_Ch3_06

SPSP SPSP

MTPMTP––L1L1MTP–L1

MAP ASE

TCAP

SCCP

MTP–L3

MTP–L2

MTP–L1

ISDN–UP

SS7LINKSPSP SPSP

MTPMTP––L1L1MTP–L1

MAP ASE

TCAP

SCCP

MTP–L3

MTP–L2

MTP–L1

ISDN–UP

SS7LINK

Version 1 Revision 0MTP Layer 2 Functionality




MTP Layer 2 FunctionalityLayer 2 defines the functions and procedures for, and relating to the transfer of signallingmessages over one individual signalling data link. The function of Layer 2 is to ensuremessages are delivered in the correct sequence and without loss or error, it alsoperforms initial alignment of the link and to supervise the performance of the link.

Functions include:

Buffer functions : Three buffers are contained at both ends of the signallinglink, used to ensure the messages are transported correctly

Signalling Delimitation : This removes or adds the flag as required.

Signalling Alignment : This checks that the bit pattern corresponds to therules of bit stuffing.

Error Detection : this is performed by the Frame Check Sequence (FCS) ifthe checksum is different the Message Signalling Unit (MSU) is rejected

Delimitation, Alignment and error detection: perform acceptanceprocedure

Error Correction : operates to ensure the correct MSU stream, eachmessage is assigned a sequence number, the MSUs are retransmitted whenan error is detected, Link Status Signalling Units (LSSUs) and Fill In SignalUnits (FISUs) are not retransmitted.

Version 1 Revision 0 MTP Layer 2 Functionality




MTP Layer 2 Functionality

CP03_Ch3_07

Level 1

Level 3

TransmissionBufferTransmissionBuffer

ChecksumgenerationChecksumgenerationChecksumgeneration

Message LengthCheck

Message LengthCheck

RetransmissionBufferRetransmissionBuffer

ReceiveBufferReceiveBuffer

Sequence NumberCheckSequence NumberCheck

ChecksumDecodingChecksumDecoding

Bit destuffingFlag detectionBit destuffingFlag detection

Bit stuffingFlag generationBit stuffingFlag generation

Level 2

IncomingMSUs

IncomingMSUs outgoingMSUs

outgoing MSUs

Supervision(LSSU)

Sequence numbergeneration

Supervision(LSSU)

Supervision(LSSU)

Sequence numbergenerationSequence numbergeneration

DelimitationDelimitation

Error detectionError detection

Error correctionError correction





MTP Layer 3Layer 3 in principle defines those transport functions and procedures that are commonto, and independent of, the operation of individual signalling links.

These functions fall into two major categories:

1. Signalling message handling functions – These are functions that, at the actualtransfer of a message, direct the message to the proper signalling link or UserPart.

2. Signalling network management functions – These are functions that, on the basisof predetermined data and information about the status of the signalling network,control the current message routing and configuration of signalling networkfacilities. In the event of changes in the status, they also control reconfigurationsand other actions to preserve or restore the normal message transfer capability.

The different Layer 3 functions interact with each other and with the functions of otherlevels by means of indications and controls as well as the testing and maintenanceactions may include exchange of signalling messages with corresponding functionslocated at other signalling points. Although not User Parts, these parts of layer 3 can beseen as serving as “User Parts of the Message Transfer Part”. As a convention in thesespecifications, for each description, general references to User Parts as sources or sinksof a signalling message, implicitly include these parts of Layer 3 – unless the opposite isevident from the context or explicitly stated.





MTP Layer 3

CP03_Ch3_08

SCP

SSP SSP

STPSTP STPSTP

SCP

MTP–L1

MAP ASE

TCAP

SCCP

MTP–L3

MTP–L2

MTP–L1

ISDN–UP

NETWORKNETWORK

SCPSCP

SSP SSP

STPSTP STPSTP

SCPSCP

MTP–L1

MAP ASE

TCAP

SCCP

MTP–L3

MTP–L2

MTP–L1

ISDN–UP

NETWORKNETWORK

Version 1 Revision 0MTP Layer 3 Functionality




MTP Layer 3 FunctionalityThe Layer 3 function is signalling network, and can be divided into two basic categories,Traffic Handling and Signalling Network Management.

Traffic Handling

Traffic Handling has the purpose of ensuring that signalling messages from a User Partat a Signalling Point are delivered to the same user part at the destination indicated bythe sending User Part. The signalling message handling functions are divided into thethree areas detailed below.

Message Discrimination

This determines whether or not the received message is destined to the point itself

Message Distribution

This is used to deliver the received messages to the appropriate user part

Message Routing

This is used at each signalling point to determine the outgoing signalling link on which amessage is forwarded to the destination point.

SignallingNetworkManagement

The Signalling Network Management function is to provide reconfiguration of thesignalling network in the case of failures. The signalling network functions are divided intofour main areas:

Network flow control

The purpose of network flow control is to limit signalling traffic at source, this is done tocontrol congestion of a destination

Network control

This contains the rules and procedures for routing the traffic in both normal and abnormalstates. This provides all the necessary information to traffic handling to perform therouting.

Signalling link Management

This is used to restore failed links, activates idle links and to deactivate aligned signallinglinks, the function monitors and controls signalling resources.

Policing

This is a method by which operators are able to restrict the use of their signalling networkby external operators; this can be implemented in STPs and at the MTP level.

Version 1 Revision 0 MTP Layer 3 Functionality




MTP layer 3 Functionality

CP03_Ch3_09

Traffic Handling

MessageDistribution

MessageDiscrimination

MessageRouting

Traffic Handling

MessageDistributionMessageDistribution

MessageDiscriminationMessageDiscrimination

MessageRoutingMessageRouting

Signalling network management

Networkcontrol

Policing

Network flowcontrol

Signalling resourcemanagement

Signalling network management

NetworkcontrolNetworkcontrol

PolicingPolicing

Network flowcontrolNetwork flowcontrol

Signalling resourcemanagementSignalling resourcemanagement

IncomingMessage

OutgoingMessage

To UserPart

From UserPart

MTP Layer 2

Version 1 Revision 0MTP Functionality




MTP FunctionalitySince the Message Transfer Part forms the interface at a node with the rest of thesignalling network, the signalling network will have significant impact on the MTP. TheMTP must however be independent of the signalling network in that it has to be capableof performing its set functions and attaining its objectives, no matter what networkstructure or status prevails.

The MTP has therefore to contain the necessary functions to ensure any impact that thenetwork has does not impair MTP performance. The components that must beconsidered by the MTP are:

– Signalling points (including signalling transfer points);

– Signalling relations between two signalling points;

– Signalling links;

– Signalling link sets (including link groups);

– Signalling routes;

– Signalling route-sets.

The modes applicable to SS No. 7 MTP are:

– Associated mode;

– Quasi–associated mode.

The standard routing label is suitable for national applications. The signalling systemincludes the possibility for using different routing labels nationally.

Message routing is the process of selecting the signalling to be used, for each signallingmessage sent. Message routing is destination-code dependent with an additionalload-sharing element allowing different portions of the signalling traffic to a particulardestination to be distributed over two or more signalling links. This traffic distribution maybe limited to different links within a link set, or applied to links in different link sets.

Message distribution is the process, which, upon receipt of a message at its destinationpoint, determines to which User Part or Layer 3 function the message is to be delivered.

Messagediscrimination

Upon receipt of a message at a signalling point, message discrimination determineswhether or not that point is the destination point of that message. This decision is basedon analysis of the destination code in the routing label in the message. If the signallingpoint is the destination point, the message is delivered to the message distributionfunction. If it is not the destination point, and the signalling point has the transfercapability, the message is delivered to the routing function for further transfer on asignalling link.

Version 1 Revision 0 MTP Functionality




MTP Functionality

CP03_Ch3_10

Level 1Level 2Level 3Level 4 Level 1Level 2Level 3Level 4

Message Transfer PartMessage Transfer Part

Signalling NetworkFunctions

SignallingMessageHandling










Signalling LinkFunctions

Signalling LinkFunctions

TUP

ISUP

SCCP

TUP

ISUP

SCCP

Version 1 Revision 0 Message Transfer Part




Message Transfer PartMTP is responsible for the delivery of messages between switches

The MTP covers the first three levels of the SS7 protocol, the function of MTP is to serveas a common transport system that provides reliable transmission of signalling messagesbetween communicating users, SS7 network does not equate directly to the OSI model,for the SS7 model to match to the OSI first 3 layers some of the SCCP functionality mustbe included in the MTP, in SS7 the MTP and SCCP is known as the Network ServicePart.

The MTP will ensure that the messages are transferred

� Correctly, all the received messages will be checked before they are accepted

� Without loss or duplication

� In correct sequence

The MTP will also react to system and network features that will affect the reliabletransport of messages and will take the necessary action to ensure a high degree ofreliability.

Version 1 Revision 0 Message Transfer Part




Message transfer Part

CP03_Ch3_11

Data Link

Network

Physical

3

2

1 MTP Level 1

MTP Level 2

MTP Level 3

OSI SS7

Data Link

Network

Physical

3

2

1 MTP Level 1

MTP Level 2

MTP Level 3

OSI SS7

Version 1 Revision 0SS7 layer 4




SS7 layer 4The 4th level in SS7 equate to layers 4–7 in the OSI model, in SS7 the 4th level is knownas the User Parts (UP).

The user parts contain functions connected with the processing of signal information, theUPs generate and analyse signalling messages, they use the MTP as a transportfunction to carry the information to other user parts.

The combination of MTP 1–3 and SCCP is called the Network Services Part.

Version 1 Revision 0 SS7 layer 4




SS7 level 4

CP03_Ch3_12

This level is known as the user part and is made up ofseveral different applications.

These are split into two main functions.

Telephone user parts.

SS7 user parts.

�

�

�

�

Version 1 Revision 0SS7 to OSI layers




SS7 to OSI layersSS7 User Parts are

� ISDN User Part (ISUP)

� Telephone User Part (TUP)

� Data User Part (DUP)

� Signalling Connection Control Part (SCCP)

For some applications more complex signalling maybe required, in these casesApplication parts have been defined.

Application parts include

� Mobile Telephony Application Part (MAP)

� Intelligent Network Application Part (INAP)

� Transaction Capabilities Application Part (TCAP)

Version 1 Revision 0 SS7 to OSI layers




SS7 to OSI Overview

CP03_Ch3_13

Presentation

Transport

Session

Application7

6

5

4 SCCP

ISUP

TCAP

ASE

OSI SS7

Presentation

Transport

Session

Application7

6

5

4 SCCP

ISUP

TCAP

ASE

OSI SS7

SS7 Level 4

Version 1 Revision 0Signalling Connection Control Part




Signalling Connection Control PartSCCP sits at level 4 and is part of the SS7 protocol. It provides the following functions:

� Connectionless and connection oriented network services

� Tracking of application status.

� Transfer of messages between subsystems at the originating and destinationnodes

Version 1 Revision 0 Signalling Connection Control Part




Signalling Connection Control Part

CP03_Ch3_14

Data Link

Network

Transport

Physical

4

3

2

1 MTP Level 1

MTP Level 2

MTP Level 3

SCCP

Data Link

Network

Transport

Physical

4

3

2

1 MTP Level 1

MTP Level 2

MTP Level 3

SCCP

OSI SS7

Version 1 Revision 0Transaction Capabilities Application Part




Transaction Capabilities Application PartTCAP is an SS7 level 4 application and is part of the SS7 Protocol.

TCAP provides a common protocol which allows a large number of applications whichuse databases to operate. The protocol is independent of application.

TCAP is responsible for

� Maintaining the connection once it is established.

� Transferring information between nodes to allow applications to operate

� Containing a transaction portion and a component portion.

TCAP provides support for interactive applications in a distributed environment.

Version 1 Revision 0 Transaction Capabilities Application Part




Transaction Capabilities Application Part

CP03_Ch3_15

MTP Level 1

MTP Level 2

MTP Level 3

SCCP

TCAP

MTP Level 1

MTP Level 2

MTP Level 3

SCCP

TCAP

Data Link

Network

Transport

Session

Presentation

Application

Physical

7

6

5

4

3

2

1

Data Link

Network

Transport

Session

Presentation

Application

Physical

7

6

5

4

3

2

1

Version 1 Revision 0Mobile Application Part (MAP)




Mobile Application Part (MAP)For some applications more complex signalling maybe required, in these casesApplication Parts have been defined.

MAP’s functions are to perform signalling within the GSM network, SS7 signalling isrequired between the MSC and all the registers such as HLR, VLR, EIR and AUC.

MAP consists of all signalling messages on the SS7 network that are not call control(ISUP) messages (e.g. statistics, mobility, SMS)

MAP is the interface between TCAP and the application, because the MAP function iscontrol tasks and data exchange between subsystems MAP can be considered anapplication.

As the MAP services are seen as primitives it cannot really be considered to be withinthe OSI reference Model

Version 1 Revision 0 Mobile Application Part (MAP)




Mobile Application Part

CP03_Ch3_16

MTP Level 1

MTP Level 2

MTP Level 3

SCCP

TCAP

MAP

MTP Level 1

MTP Level 2

MTP Level 3

SCCP

TCAP

MAP

Data Link

Network

Transport

Session

Presentation

Application

Physical

7

6

5

4

3

2

1

Data Link

Network

Transport

Session

Presentation

Application

Physical

7

6

5

4

3

2

1

Version 1 Revision 0MAP services




MAP servicesMAP must be considered as both an application in its own right and part of the GSMsubsystems. This is because it uses the TCAP within the signalling system forpeer-to-peer communication and also has a functionality of its own for the applicationentities to allow them to operate in the GSM environment.

Because the function of MAP service is control and data exchange between theapplications and MAP, two functions are required.

– Common MAP services, for pure communication control

– Special MAP services, for carrying signalling data

MAP subsystems include MSC, BSC, HLR, VLR, AUC and SMSC.

Version 1 Revision 0 MAP services




MAP services

CP03_Ch3_17

MAP

TCAP

MAP

TCAP

MAP user MAP user

Peer to peer protocol

Peer to peer protocol

MAP

TCAP

MAP

TCAP

MAP user MAP user

Peer to peer protocolPeer to peer protocol

Peer to peer protocolPeer to peer protocol

MAP services(Primitives)

Primitives

Version 1 Revision 0MAP Services and Primitives




MAP Services and PrimitivesThe common MAP services can be used to control a communication between MAP andits application. Depending on the task of the service either all, or only some of theprimitives will be used.

The purpose of the special MAP services is to carry the data between MAP and theapplication. It is only a special MAP service that will contain the actual parameters.

Up to four of the primitives could be defined for the special MAP services

Included in the special MAP services are the message types, the local operation code,used to identify the special MAP services within MAP. The primitives used could be“request”, “indication”, “response” and “confirmation”.

It is only the special MAP message that will contain the actual parameter

Version 1 Revision 0 MAP Services and Primitives




Map Services (cont)

CP03_Ch3_18

There are six common MAP services, these are used to control acommunicationBetween Map and an application. Depending on the service beingusedeither all or only some of the primitives will be used.

Common MAP services

–MAP–DELIMITER–MAP–OPEN–MAP–CLOSE–MAP–U–ABORT (U=user)–MAP–P–ABORT (P=provider)–MAP–NOTICE

Version 1 Revision 0MAP Services and Primitives







Chapter 4

SS7 Network Addressing and

Routing









Chapter 4SS7 Network Addressing and Routing i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Network Addressing 4–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Point Codes 4–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Point Codes 4–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Global Title 4–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Subsystem Numbering 4–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .









Objectives


� Describe the different types of addressing and routing structures.

Version 1 Revision 0Network Addressing




Network AddressingIn an SS7 network the signalling information is not always exchanged between adjacentSPs or STPs

In a GSM system the exchange of information may involve several STPs, as aconsequence the network needs to understand how to each STP is addressed and howcan the system rout the signalling information to the correct point.

The addressing systems work on a national and international basis, with the services ofhigher layers being used for international addressing.

Version 1 Revision 0 Network Addressing




Network Addressing

CP03_Ch4_01

There are three types of network addressing information these are:

– Point code routing

– Sub system routing

– Global title translation

�

elements

Version 1 Revision 0Point Codes




Point CodesIn order to find the destination SP/STP certain signalling messages have routing labels.Contained in the routing label is the Originating Point Code (OPC) (that is the point codeof the sender) and the addressee or Destination Point Code (DPC).

Addressing using signalling point codes will only work on a national basis.

Version 1 Revision 0 Point Codes




Point Codes

CP03_Ch4_02

Point codes are a unique address of a signalling point within anetwork

Originating point code (OPC)

Destination point code (DPC)

Signalling point code (SPC)

�

�

�

�

Version 1 Revision 0Point Codes




Point CodesIf two SPs need to communicate with each other if they are part of the same network, allthat is required is a signalling link between the two SPs.

The key element is the Point Code, this will allow unique addressing of each individualelement within a network.

For example, if the two SPs 1–134 and 1–234, as part of the same networks, areenabled correctly they can communicate without requiring an STP, this would allow fullcommunication between the two points.

If two SPs that are not in the same network, SPs 1–134 and 4–234, which can be eitherdifferent layers or international networks, require to communicate they will require allelements of the signalling networks to be in place. Because the network needs to eithercross network layers or is accessing a different network there is a requirement to gothrough an STP. The STP is the only part of the signalling network that is able to changethe layer on which a network may communicate.

Version 1 Revision 0 Point Codes




Point Code Layers

CP03_Ch4_03

SPSTP

SS7 LINKS

Point Code = 1–334

SS7 LINKS

STP

SS7 LINKS

Point Code = 1–334

SS7 LINKS

SP SPVOICE CIRCUITS

Point Code = 1–134 Point Code = 1–234

SS7 LINKS

SP SPVOICE CIRCUITS

Point Code = 1–134 Point Code = 1–234

SS7 LINKSPoint Code = 4–234Point Code = 4–234

Version 1 Revision 0Global Title




Global TitleA Global Title (GT) is not an element within a signalling network that on its own is able toprovide routing within the network, a translation function is required to define the DPC.

A Global Title is an address such as a dialled digit.

The Global Title consists of a directory number and information on how to read thenumber in order to achieve a routing solution.

Version 1 Revision 0 Global Title




Global Title Translations

CP03_Ch4_04

Global title translation is performed by an STP to enable routinga message towards its final destination

The destination point code or subsystem number is determinedfrom the the dialled digits

�

�

of

Version 1 Revision 0Subsystem Numbering




Subsystem NumberingA Subsystem Number (SSN) is an identification of a specific User Part, each user partwill have its own specific number.

The subsystem is identified either directly as in SCCP or indirectly, using a layer to carrythe signalling MAP.

Subsystem Numbers

SSN (Hex) Subsystem

00 SSN not available

01 SCCP Management

02 Reserved

03 ISUP

04 OMAP

05 MAP

06 HLR

07 VLR

08 MSC

09 EIR

0A AuC

FE NSSAP

Version 1 Revision 0 Subsystem Numbering




Subsystem Numbering

CP03_Ch4_05

The Subsystem Number (SSN) specifies the user that either sent theSCCP message, or to which subsystem it is addressed.

The SSN is transmitted in the SCCP message and has a hex value

Subsystems might be

SCCP managementISUPOMAPMAP

Version 1 Revision 0Subsystem Numbering







Chapter 5

SS7 Signalling Units









Chapter 5SS7 Signalling Units i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Units Overview 5–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Circuit Switch 5–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Message Switch 5–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Packet Switch 5–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 Packet Switching 5–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signal Unit Packets (Generic) 5–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Flag 5–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .



FIB p BIB 5–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Retransmission of Signalling Units 5–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Length Indicator (LI) 5–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Field Check Sum 5–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Units Overview 5–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fill in Signal Unit 5–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Link Status Signal Unit 5–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LSSU Status Indication 5–28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Link Alignment 5–30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Link Alignment Test Duration 5–32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Message Signal Unit 5–34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Service Information Octet 5–36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Service Indicator (SI) 5–38. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sub-Service Field 5–40. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Signalling Information Field 5–42. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Routing Label 5–44. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 Management and Test Messages 5–46. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Header Fields 5–48. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .











Objectives


� Understand the different types of switching.

� Identify the SS7 signalling units and describe their function and composition.

Version 1 Revision 0Signalling Units Overview




Signalling Units OverviewIn all networks there are three types of switching, they can either be implementedtogether, working with and over each other, or a network could have one method ofswitching.

Circuit Switch

Where an open circuit is required at all times during the call, such as voice, this isexpensive and wasteful of resources. With the relationship to voice this is currently thebest option because open circuit reduces time delay.

Message Switch

With message switching the circuit is open for as long as each message takes to send.This is good for a point-to-point data transmission. The sending switch does not stayactive but once the message has been sent the circuit closes down

Packet Switch

With the packet switch the circuit is made up only to send the packet of data, the packetsare of a set size, this allows packets that are going to multiple points to be sent down thesame links. This allows a high connection rate to one link. A packet switch will switchuser data and control data.

Version 1 Revision 0 Signalling Units Overview




Signalling units overview

�

CP03_Ch5_01

There are three basic methods of switching within a network

– Circuit switching

– Message switching

– Packet switching

Version 1 Revision 0SS7 Packet Switching




SS7 Packet SwitchingThe SS7 network uses a packet switch to send the information around, this allows a lotof information to be sent and also allows for fewer links to control more points.

If switch A has data to send to switch B, using packet data it does not require the circuitA–B to be active all the time. This means it could be used as a signalling link within adifferent route.

Packets can be sent directly or via different signalling routes. The data arrives at itsdestination and can arrive in any order, this is because the destination is able toreassemble the data in the correct order by using the Packet Assembler/Dissembler(PAD).

Version 1 Revision 0 SS7 Packet Switching




Network using Packet

CP03_Ch5_02

1

1

1

2 2 2

1

1

1 11

11

11

22 22 22

412

3441122

33 3

3 3

333

33 33

33

4 4 444 44 44

21

34

2211

3344

Version 1 Revision 0Signal Unit Packets (Generic)




Signal Unit Packets (Generic)The definition of SS7 message types is a functionality of MTP 2. In level 2 of SS7 thereare three different message types. Each one has its own role.

All messages follow the same basic format, the frame structure is laid down by ITU-TQ.701.

All signalling messages are an assembly of information that is to be transferred as a datapacket by the MTP, the signalling information can be exchanged between User Parts,Application Parts or Message Transfer Parts.

The frame structure is as follows:

� A flag to indicate the start

� An acknowledgement field which houses sequence numbers

� A length indicator

� An optional information field the length varies with usage

� The field check sum field

� An end flag.

The end flag may also be used as the start flag for the next frame. Two flags should notbe sequenced.

Version 1 Revision 0 Signal Unit Packets (Generic)




Signal Packet Generic

CP03_Ch5_03

Length(Bits)

FirstTransmissionDirection

Last FirstTransmissionDirection

Last

Flag FlagFCS Information field Length AcknowledgmentFlag FlagFCS Information field Length Acknowledgment

Version 1 Revision 0Flag




FlagEach signalling unit is enclosed between two flags, the opening flag and closing flag. Theclosing flag may also be the opening flag of the next frame. As a consequence two flagsshould not be sequenced.

The flag is made up of 8 bits, this is a unique 8 bits pattern, 01111110 (zero-sixones-zero). As this is a unique pattern to stop it appearing elsewhere in the signal unit,bit stuffing is used. The sender is responsible for the stuffing and the receiver isresponsible for the removal or de-stuffing.

Version 1 Revision 0 Flag




Flag

CP03_Ch5_04

0 1 1 1 1 1 1 0

LI FlagBSNBIB

FSNFIB

SpareFCSFlag

0 1 1 1 1 1 1 00 1 1 1 1 1 1 0

LI FlagBSNBIB

FSNFIB

SpareFCSFlag

FLAG

FirstTransmission DirectionLast FirstTransmission DirectionLast

Version 1 Revision 0Error Correction and Flow Control




Error Correction and Flow ControlThe error correction field contains 16 bits and consists of the Forward Sequence Number(FSN), the Backward Sequence Number (BSN), the Forward Information Bit (FIB) andthe Backward Information Bit (BIB).

The error correction field ensures the reception of messages in the right order andrequests resending in case of any error.

Backward Sequence Number (BSN),

There are 7 bits reserved for sequence numbers. The BSN are used to acknowledge thecorrect transmission of a signalling unit.

Backward Information Bit (BIB)

The BIB marks the signalling unit as to the state of received signalling units.

Forward Sequence Number (FSN),

There are 7 bits reserved for a 128 modulo counter function, it is stepped up whenever asignalling unit is transmitted, FSN is used to recognise signalling units that are out ofsequence.

Forward Information Bit (FIB)

The FIB informs the receiver if the signalling unit is a retransmission or a first timetransmission.

Version 1 Revision 0 Error Correction and Flow Control




Error Correction Field

CP03_Ch5_05

LI FlagBSNBIB

FSNFIB

SpareFCSFlag

16 Bits

LI FlagBSNBIB

FSNFIB

SpareFCSFlag LI FlagBSNBIB

FSNFIB

SpareFCSFlag

16 Bits

Error Correction FieldError Correction Field


Version 1 Revision 0Error Correction and Flow Control




Error Correction and Flow ControlThere are two error correction methods, the Basic Error Correction Method (BASIC) andthe Preventive Cyclic Retransmission Error Correction (PCR).

The Basic Error Correction Method (BASIC)

The receiving terminal sends a negative acknowledgement in response to an incorrectlyreceived signal unit, this will initiate a retransmission of the incorrect message signallingunit and all those that follow.

The Preventive Cyclic Retransmission Error Correction (PCR)

In PCR, retransmission of not positively acknowledged message signal units is initiatedwhen there are no new message signal units to send from the transmission buffer. Thisleads on to the sending of FISUs when the transmission buffer is empty and there are nonew message signalling units to send. Also if a timer is used, once the time frame isover, retransmission takes place. During a period when there are no new signal units totransmit, all units, which have not been positively acknowledged, will be retransmittedcyclically.

Both methods are used in GSM. The PCR is easier to understand, when a timer has rundown or if no positive acknowledgement is received retransmission takes place.

With the BASIC method, the BSN and FSN use modulo 128 counters to indicate themessage signalling units numbers, the FIB and BIB are used to indicate if the messagesignalling units have been received or to indicate a transmission error.

If the link has just been brought into service all of the values for the FSN, BSN, BIB andFIB are 1, the return information will be of the same values if there are no errors or needto retransmit.

Because FIB= BIB this can be thought of as a positive acknowledgement and theoriginating signalling point will now remove the message from the buffer.

Version 1 Revision 0 Error Correction and Flow Control




Error Correction and flow control

CP03_Ch5_06

SP SPSP SP

FIB = 1, FSN = 50, BIB = 1, BSN= 0FIB = 1, FSN = 50, BIB = 1, BSN= 0

BSN = 50, BIB = 1, FSN = 1, FIB = 1BSN = 50, BIB = 1, FSN = 1, FIB = 1

Version 1 Revision 0FIB p BIB




FIB ≠ BIBThe value of the FIB and BIB are the keys to error correction. Both the FIB and BIB are 1bit symbols and can either be 1 or 0.

To indicate a transmission error the BIB is inverted either from 1 to 0 or from 0 to 1, it isthe sending of the inverted BIB that indicates an error.

The function of the FIB is to indicate if the message signalling unit is a retransmission.This is shown by the inversion of the FIB.

When the receiving point receives an incorrect message two actions are taken:

The BIB is inverted, and the FSN of the last correct received message will be insertedinto the BSN field, this will indicate an error to the sending point and which messagesignalling unit needs to be retransmitted.

When it is received at the sending point, the FIB will then be compared to the BIB,because FIB ≠ BIB, it means that it is a negative acknowledgement.

When a negative acknowledgement is received the sending of new signalling units isinterrupted, all signals in the buffer, which have not been positively acknowledged, willnow be retransmitted. Any message signalling units in the buffer that have sequencenumbers that are higher than the retransmitted signal unit will also be retransmitted.

If a signalling message has been lost completely, then because the sequencing numbersare not consecutive, the receiving point is able to ask for retransmission.

Version 1 Revision 0 FIB p BIB




FIB ≠ BIB

CP03_Ch5_06

SP SPSP SP


BSN = 50, BIB = 0, FSN= 2, FIB = 1,BSN = 50, BIB = 0, FSN= 2, FIB = 1,

Version 1 Revision 0Retransmission of Signalling Units




Retransmission of Signalling UnitsThe sending point on receipt of the indication of a signalling error will retransmit themessage signalling unit. On transmission the FIB will now be inverted to indicate that thisis a retransmission.

The sending point will then send the signalling unit, on receipt of a successfulre-transmission the receiving point will send message signalling units as normal. If theFIB = BIB then the signalling is correct.

Version 1 Revision 0 Retransmission of Signalling Units




Retransmission of Signalling Unit

CP03_Ch5_08

SP SPSP SP


BSN = 51, BIB = 0 , FSN= 3, FIB = 0,BSN = 51, BIB = 0 , FSN= 3, FIB = 0,

Version 1 Revision 0Length Indicator (LI)




Length Indicator (LI)The length indicator is used to distinguish between the types of signalling units, MSU,FISU and LSSU. The LI relates to the length of the optional Data Field.

The field consists of two parts, it is an 8 bit field, the first 6 bits are used to indicate avalue of between 0–63.

The final 2 bits are spare and not currently used.

Version 1 Revision 0 Length Indicator (LI)




Length Indicator

CP03_Ch5_09

LI FlagBSNBIB

FSNFIB


FSNFIB

SpareFCSFlag

8 bits

2 Bits 6 Bits

MSULI>2

LSSULI=1,2

FISULI=0

Signalling UnitLI

MSULI>2

LSSULI=1,2

FISULI=0

Signalling UnitLI


Version 1 Revision 0Field Check Sum




Field Check SumThe error detection function of the message signalling unit is performed by means of the16 bit Field Check Sum (FCS).

The sending terminal generates the check bits, the FCS consists of the preceding bits ofthe signalling unit being applied to a specified algorithm, and the FCS is opened at thereceiving terminal. The same algorithm is applied and the new check sum is compared tothe received. If an error occurs then the error correction operates.

Version 1 Revision 0 Field Check Sum




Field Check Sum

CP03_Ch5_10

LI FlagBSNBIB

FSNFIB


FSNFIB

SpareFCSFlag

16 Bits


Field used to check the signalling units for errors

Version 1 Revision 0Signalling Units Overview




Signalling Units OverviewThere are three different formats of messages. The message type is another functionalityof MTP 2, in SS7 level 2 the types of message are defined.

Although no field is available to determine what type the message is, it is possible to doso based on their different lengths, it is the LI that provides the information.

Version 1 Revision 0 Signalling Units Overview




Signalling Units Overview

CP03_Ch5_11

There are three different types of packets in the SS7 network anthese are:

Fill in signal unit (FISU)

Link status signal unit (LSSU)

Message signal unit (MSU)

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�

�

�

Version 1 Revision 0Fill in Signal Unit




Fill in Signal UnitWhen no data is being sent across the SS7 network Fill In Signal Units (FISU) aretransmitted

They contain no network information, but are used to monitor link quality

The frame check sequence field is used to determine if there are any errors on the link.When a FISU is sent the last sent FSN would be sent constantly. The FISU does not usethe sequence counter.

The length indicator is used to identify the type of message unit being sent.

As there is no information sent in an FISU, the length indicator is set to zero

Because the FISU is used in the idle state the BSN, FSN, FIB and BIB do not changetheir values. Both ends of the link poll each other in the idle state. The FISU can also beused to acknowledge receipt of an MSU.

Version 1 Revision 0 Fill in Signal Unit




Fill In Signal Unit

CP03_Ch5_12

Flag BSNBIB

FSNFIB

LISpareFCS

Length(Bits)

Flag BSNBIB

FSNFIB

LISpareFCS

Length(Bits)


Flag

8 71716216 88 71716216 8

Version 1 Revision 0Link Status Signal Unit




Link Status Signal UnitThe Link Status Signal Unit (LSSU) is used to transfer information dealing with thephysical state of the signalling link. The LSSUs are only used to bring a link into service,take a link out of service and during error situations, between two SPs/STPs.

Link Status Signal Units can also be used to align signalling links.

The status field of the LSSU can under ITU-T either be 1 or 2 octets long. This is reallyinconsequential because it is only the first 3 bits that carry actual status information.

The receiver of an LSSU does not confirm its receipt.

Version 1 Revision 0 Link Status Signal Unit




Link Status Signal Unit

CP03_Ch5_13


87171628 or 16

Length(Bits)

168

FCS Status FlagFlag Spare LIFIB

BIB

FSN BSNFCS Status FlagFlag Spare LIFIB

BIB

FSN BSN

Version 1 Revision 0LSSU Status Indication




LSSU Status IndicationThe term, Status Field, in the LSSU is not normally used and the term Status Informationis used to explain the data that the LSSU carries.

The SF (or status field) according to ITU-T is 1 or 2 octets long, only the first three bits ofthe first octet are used. All other bits are currently spare.

SI is the term STATUS INDICATION

Value Abbreviation Description

0 SIO Start of link alignment

1 SIN A link brought into service with anormal surveillance time of 8.2 secs

2 SIE A link brought into service with anemergency surveillance time of 500

msecs

3 SIOS An error situation or before a link isin service, no MSU’s can be sent or

received

4 SIPO When layer 2 of an SP detects aproblem within layer 3 within it’s ownnode it indicate the problem status to

the peer entity.

5 SIB Signals overload on the originatingside, acknowledgements will not be

sent, link failure usually follows

Version 1 Revision 0 LSSU Status Indication




LSSU Status Indication

CP03_Ch5_14


000 SIO Out of alignment001 SIN Normal Alignment010 SIE Emergency Alignment011 SIOS Out of Service100 SIPO Processor Outage101 SIB Busy

5 or 13 Spare Bits

000 SIO Out of alignment001 SIN Normal Alignment010 SIE Emergency Alignment011 SIOS Out of Service100 SIPO Processor Outage101 SIB Busy

5 or 13 Spare Bits

Status

8 or 16

Spare LIFCS Status

8 or 16

Spare LIFCS

Version 1 Revision 0Link Alignment




Link AlignmentThe operation of a signalling link is a duplex operation – that is the link must be createdin both directions. Both terminals are equal, and as such, both need to establish thecorrect link.

The first stage is the sending of SIOS indicating that the link is in error and out of service(OOS).

The second stage is the sending of the SIO, this is the link out of alignment and the startof alignment.

These steps are returned from the other SP involved in the link, to establish layer 2between the two SPs

Version 1 Revision 0 Link Alignment




Link Alignment

CP03_Ch5_15

LSSU OOS = SIOS

STPSP

STPSP

LSSU OOS = SIOS

LSSU OOS = SIO

LSSU OOS = SIO

Version 1 Revision 0Link Alignment Test Duration




Link Alignment Test DurationThe test period is started once the duplex link has been established in layer 2, the LSSUsent depends on the test duration, if the test duration is normal at 8.2 secs, then the SINis sent, the other option, Emergency, the time duration of test is 500 msecs, then the SIEis sent.

During this time all FISUs that are sent must demonstrate no errors.

The SIE or emergency alignment is only used if no alternative link exists and the linkneeds to be in service.

When the test time is over and layer 2 is in service layer 3 will then initiate further tests,an Signalling Link Test Message (SLTM)is sent for this purpose and it transmits a numberof test octets to layer 3 of the receiving end, if the test is correctly completed by thesending of a Signalling Link Test Acknowledgement (SLTA) message, layer 3 is alsoconsidered to be in traffic.

Version 1 Revision 0 Link Alignment Test Duration




Link Alignment Test

CP03_Ch5_16

STPSP

STPSP

1 LSSU = SIN/SIE

3 MSU = SLTM

2 LSSU =SIN/SIE

4 MSU = SLTM

Version 1 Revision 0Message Signal Unit




Message Signal UnitMessage Signalling Units (MSU) are the third type of signalling unit and they are themost diverse. The message signalling units are used for transmission of layer 3information or layer 4 signalling. Whenever an MSU is received it must be acknowledgedto the peer entity.

Layer 3 information includes Signalling Network Management messages (SNM) andSignalling Network Testing and Maintenance messages (SNT).

Layer 4 information is mainly User Parts or Application Parts signalling information.

In the Message Signal Unit the status field is divided into two parts – the ServiceInformation Octet (SIO) and the Signal Information Field (SIF). The Signal InformationOctet is used to associate signalling information with a User Part, while the SignalInformation Field contains the actual user data.

Version 1 Revision 0 Message Signal Unit




Message Signal Unit

CP03_Ch5_17

BIB

BIB


87171628n

N< 272

Length(Bits)

168 8

FCS SIF FlagFlag Spare LIFIB

FSN BSNSIOFCS SIF FlagFlag Spare LIFIB

FSN BSNSIO

Version 1 Revision 0Service Information Octet




Service Information OctetThe Service Information Octet (SIO) is 8 bits long and is divided in two parts, the ServiceIndicator (SI) and the Sub-Service Field (SSF). Both of these two sub fields are 4 bits inlength.

The Service Indicator is used to associate signalling information with a User Part and isonly used with MSU messages.

The Sub-Service Field allows for a distinction to be made between national andinternational signalling messages.

Version 1 Revision 0 Service Information Octet




Service Information Octet

CP03_Ch5_18


8 bits

FCS SIFFlag Spare LISIOFCS SIFFlag Spare LISIO

SF SISF SISF SI

Version 1 Revision 0Service Indicator (SI)




Service Indicator (SI)The Service Indicator (SI) is used to point out the recipient User Part of the message unitand is used by the distribution function of Level 3 in MTP to distribute the MSU to thecorrect User Part. The association of signalling to User Part is only used with MSUmessages.

Version 1 Revision 0 Service Indicator (SI)




Service Indicator

CP03_Ch5_19


8 bitsSF SISF SISF SI

Data User Part (DUP) (call admin)0110

Telephone User Part (TUP)0100

ISDN User Part (ISUP)0101

Service IndicatorDCBA

Signalling Network Testing and Maintenance0001

Data User Part (DUP) (Supp Services)0111

Signalling Connection Control Part (SCCP)0011

Operation and Maintenance Application Part (OMAP)0010

Signalling Network Management0000

Data User Part (DUP) (call admin)0110

Telephone User Part (TUP)0100

ISDN User Part (ISUP)0101

Service IndicatorDCBA

Signalling Network Testing and Maintenance0001

Data User Part (DUP) (Supp Services)0111

Signalling Connection Control Part (SCCP)0011

Operation and Maintenance Application Part (OMAP)0010

Signalling Network Management0000


Version 1 Revision 0Sub-Service Field




Sub-Service FieldThe Sub-Service Field indicates the type of signalling network used. Bits C and D areused to specify if the network is international or national. Bits A and B are used in theUSA for priority but are spare under ETSI.

Version 1 Revision 0 Sub-Service Field




Sub-Service Field

CP03_Ch5_20


8 bitsSF SISF SISF SI

International 10100

Network IndicatorDCBA

National 11100

National 01000

International 00000

International 10100

Network IndicatorDCBA

National 11100

National 01000

International 00000


Version 1 Revision 0Signalling Information Field




Signalling Information FieldThe Signalling Information Field (SIF) is the only part of the MSU that refers to the UserPart. The SIF consists of two sub fields, the user information with the contained messageelements and the label field.

The user information is all the information carried in the message-signalling unit thatrelates to the User Part of the message.

The label field refers to the transfer of the message through the signalling system.

MSUs do not need to be exchanged only between adjacent SP/STP. In a GSM systemthe information may involve several STPs.

As SS7 uses signalling Point Codes (SPC) each SP/STP has a unique identifier to map itin the GSM system.

MSUs can be exchanged through SP/STPs and as a result need a routing label withinthe signalling unit, because FISUs and LSSUs are only between adjacent SP/STPs theyhave no requirement for routing labels.

Each type of MSU within the SS7 network has its own label type.

Version 1 Revision 0 Signalling Information Field




Signalling Information Field

CP03_Ch5_21


LabelMessage elements

MTP Management

SCCP User Data

ISUP Information Elements

TUP Information Elements

MTP Management

SCCP User Data

ISUP Information Elements

TUP Information Elements


Version 1 Revision 0Routing Label




Routing LabelThe Routing Label is separately defined for each of the User Parts and this label is usedby the MTP to route the message to the correct destination. Each User Part within theSS7 system has its own label format.

Destination Point Code (DPC) indicates the Signalling Point Code of the receiver of thesignalling message

Originating Point Code (OPC) indicates the signalling point code of the sender of thesignalling message

Signalling Link Selection (SLS), these 12 bits have various uses depending on the userpart that the signalling message belongs to.

Depending on the user part the SLS may carry the Circuit Identification Code or it may bea separate field. The Signalling Link Selection (SLS), depending again on the user part,might have its own field or might be imposed in the CIC fields, as in TUP. The length ofthe SLS field allows for the definition of a maximum of 16 signalling links per link set, assuch it is used to determine which Signalling Link within a link set will be used to transferthe message.

If the user part is Signalling Network Management messages (SNM) or SignallingNetwork Testing and Maintenance messages (SNT), then the SLS is replaced bySignalling Link Code (SLC) again 12 bits long but only 4 are used, this indicates theSignalling Link Number.

Version 1 Revision 0 Routing Label




Routing Label

CP03_Ch5_21


Routing LabelRouting Label

Signalling Link Selection (SLS) OPC DPCSignalling Link Selection (SLS) OPC DPC

12/4 bit 14 bit 14 bit


Version 1 Revision 0SS7 Management and Test Messages




SS7 Management and Test MessagesThe core of a Message Signalling Unit (MSU) is generated on level 3 or 4. At level 3there are two kinds of MSU that are generated:

� Signalling Network Management messages (SNM-MSU) or

� Signalling Network Testing and Maintenance messages (SNT-MSU).

In the Service Information Octet (SIO) the Service Indicator (SI) identifies the MSU,

0000 for SNM-MSUs

0001 for SNT-MSUs

for these messages contained in the Service Information Field (SIF) after the label willbe the header and then the data field which is optional. This applies only to layer 3.

Version 1 Revision 0 SS7 Management and Test Messages




SS7 Management and Test Messages

CP03_Ch5_23


Routing LabelData Field Heading Code

8n (272 >n>3) bits

32 bits8 bitsData opt.


Version 1 Revision 0Header Fields




Header FieldsBecause this is a Layer 3 only, all of the signaling messages will relate to the signallingnetwork and not the user part. It is these dedicated user parts in layer 3 thatautomatically detects error situations.

Errors can be separated into one of three groups

� Overload on a single SS7 link

� Outage/bringing into service an SP/STP

� Outage/bringing into service an SS7 link between SPs/STPs

The SI will already define the MSUs and as such the SIF will be of a set nature.

Heading Code 0 (H0) defines a whole message group, whilst Heading Code 1 (H1) isused to define a single message within the group.

Version 1 Revision 0 Header Fields




Header Fields

CP03_Ch5_24

By using the SI field it is possible to differentiate between user partswithin the network, this is only a layer 3 function, it will indicates what iscontained in both the heading codes and how much of the data field willused.

The SI field and the Heading Code are necessary for message andmessage –group coding.

Heading code 0 (H0) defines the whole message group.

Heading code 1 (H1) identifies a single message in that group.

Version 1 Revision 0SS7 Network Management and Network Test Messages




SS7 Network Management and Network Test MessagesField H0 and H1 work together to give full message. H0 explains what is being appliedand H1 explains each task to achieve H0

The heading code (H0) is the 4-bit field following the label and identifies the messagegroup.

The different heading codes for message groups are allocated as follows:

0000 Spare

0001 Changeover and change back messages

0010 Emergency changeover message

0011 Transfer-controlled and signalling-route-set congestion messages

0100 Transfer-prohibited-allowed-restricted messages

0101 Signalling-route-set-test messages

0110 Management inhibit messages

0111 Traffic restart allowed message

1000 Signalling-data-link-connection messages

1001 Spare

1010 User part flow control messages

Version 1 Revision 0 SS7 Network Management and Network Test Messages




SS7 Network Management and Network Test Messages

CP03_Ch5_25


Heading Code Routing Label

H1 H0

4 bits 4 bits






SS7 Network Management and Network Test MessagesThe heading code (H1) is the 4-bit field following the label and identifies the messagegroup- message ITU-T Q.704

CBA Change back-acknowledgement signal

CBD Change back-declaration signal

CHM Changeover and change backmessages

CNP Connection-not-possible signal

CNS Connection-not-successful signal

COA Changeover-acknowledgement signal

COO Changeover-order signal

CSS Connection-successful signal

DLC Signalling-data-link-connection-ordersignal

DLM Signalling-data-link-connection-ordermessage

ECA Emergency-changeover-acknowledgement signal

ECM Emergency-changeover message

ECO Emergency-changeover-order signal

FCM Signalling-traffic-flow-controlmessages

LFU Link forced uninhibit signal

LIA Link inhibit acknowledgement signal

LID Link inhibit denied signal

LIN Link inhibit signal

LLT Link local inhibit test signal

LUA Link uninhibit acknowledgementsignal

LUN Link uninhibit signal

LRT Link remote inhibit test signal

MIM Management inhibit messages

RCT Signalling-route-set-congestion-testsignal

RSM Signalling-route-set-test message

RSR Signalling-route-set-test signal forrestricted destination (national option)

RST Signalling-route-set-test signal forprohibited destination

TFA Transfer-allowed signal

TFC Transfer-controlled signal

TFMTransfer-prohibited-transfer-allowed-transfer-restricted messages

TFP Transfer-prohibited signal

TFR Transfer-restricted signal (nationaloption)

TRA Traffic-restart-allowed signal

TRM Traffic-restart-allowed message

UFC User part flow control messages

UPU User part unavailable signal

With SNT the SI sub field in the SIO has the value 0001 to indicate that it is a MSU-SNTmessage, the H0 code is SLT indicating signalling link test messages, the two messagetypes are M, for message and A, for acknowledgement.

Version 1 Revision 0 SS7 Network Management and Network Test Messages




SS7 Network Mngt and Network Test Messages

CP03_Ch5_25


Heading Code Routing Label

H1 H0

4 bits 4 bits









Chapter 6










Chapter 6Signalling Connection Control Part i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 6–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


SCCP Signalling Services 6–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Services 6–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Primitives 6–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Protocol Classes 6–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Embedded in MSU 6–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Message 6–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Routing Label 6–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Message type code. 6–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Parameters 6–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Message Structure 6–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Message Type Code 6–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Routing 6–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Routing Calling Party and Called Party 6–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Addressing for Routing 6–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Called Party Address 6–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Address information 6–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCCP Functional Structure 6–28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .









Objectives


� Identify the SCCP protocol class and describe their functions.

� Explain the connection–oriented and commectionless processes.

� Explain SCCP routing and SCCP management methods.

Version 1 Revision 0Signalling Connection Control Part




Signalling Connection Control PartThe Signalling Connection Control Part (SCCP) is a functional entity, which is situatedabove the message transfer part (MTP). In SS7 the SCCP and MTP combine to form theNetwork Service Part (NSP). This then meets the requirements of the network layer –Layer 3 of the OSI model. SCCP is defined in ITU-T recommendation Q.711– Q.716.

SCCP was designed to communicate with databases without any speech connections. InGSM new protocols have been developed to handle the signalling between the MSC/VLRand BSC the protocol Base Station System Application Part (BSSAP), and for theMSC/VLR and HLR the protocol is Mobile Application Part (MAP). SCCP will work withboth the Transaction Capabilities Application Part (TCAP) and MAP on the interfaces thatare within the Network Switching Subsystem (NSS).

The SCCP maintains both Connection Orientated (CO) and Connection-less (CL)network services. CO services allow the transfer of signals via an established path. COservices are used normally when there are many messages to transfer or if the signallingmessages are so large they need to be segmented. In CL the address required to routethe information to its destination is included in each data packet, no logical connectionbetween the nodes is established in CL service.

SCCP has addressing capabilities that allow for end-to-end routing. This is possible asthe SCCP supplements the addressing found in MTP which is only possible to deliver amessage to a node by the use of a four bit code. In SCCP the addressing is enhanced bythe use of Destination Point Codes (DPC) and Subsystem Numbers (SSN). A secondfeature in SCCP addressing is the ability to translate Global Titles into DPC and SSN.

Although SCCP is considered a Layer 3 functionality it is able to provide features that areLayer 4, such as error detection and segmentation of data. SCCP also provides its ownmanagement for administrative tasks. These are independent from the SS7 signallingNetwork Management.

Version 1 Revision 0 Signalling Connection Control Part





�

CP03_Ch6_01

SCCP is used by the Base Station Subsystem Application Part(BSSAP) on the A–interface and by the TCAP and MAP on variousinterfaces within the Network Subsystem (NSS)

The SCCP can operate in either the connectionless or connection–orientated service. It also maintains circuit and non–circuit signalling

The SCCP offers end to end addressing even across networks,national or international.

SCCP also has it’s own management and administrative functions.

�

�

�

either

Version 1 Revision 0SCCP Signalling Services




SCCP Signalling ServicesThe SCCP protocol is able to provide two types of signalling service –Connection-orientated (CO) service and connection-less (CL). Distinguishing betweenconnection-oriented and connection-less service within the SCCP is done using aparameter called the protocol class.

Connection-orientated (CO) service is when a virtual connection is established betweennodes and identification of the connection is via reference numbers, these being theSource Local Reference (SLR) and the Destination Local Reference (DLR), when theconnection is active data can be exchanged not only between the nodes but also toaddress individual transactions, such as a location update in GSM or a mobile originatingcall.

Connection-less (CL) service is different, there is no referencing, and as a result thereceiver of the message must assign it to an active process, such as paging in theBSSAP.

The SCCP user is the functionality that determines if the connection for SCCP is CO orCL.

Version 1 Revision 0 SCCP Signalling Services




SCCP Signalling Services

CP03_Ch6_02

Connection–orientated services allow transfer of messages via anestablished path, this is used either for multiple messages or when thesignalling message needs to be segmented. BSSAP

Connection–less service is when no logical path is established and theSCCP message will contain the destination. MAP or BSSAP

MTP Level 3

SCCP

MAP

TCAP

BSSAP

CL CO

DTAPBSSMAP

MTP Level 3

SCCP

MAP

TCAP

BSSAP

CL CO

DTAPBSSMAP

�

�

Version 1 Revision 0SCCP Services




SCCP ServicesThe connection-oriented services enable the transfer of signalling over establishedsignalling connections. These connections are either temporary or permanent. If theconnection is a temporary connection the control of signalling can be divided into threephases.

1. Connection Establishment – this provides the method to establish the signallingconnection. At this stage both the reference numbers are assigned to the link andeach node.

2. Data transfer – this provides the transfer of data in Network Service Data Units(NSDU). The transfer can be in simultaneous directions or in answer responsemethod. The data transfer service is compiled of SCCP messages. the SCCPmessage contains two elements – Network Protocol Information (NPCI) andNetwork Service Data Unit (NSDU).

� Network Protocol Control Information (NPCI)

The NPCI contains a connection reference number that allocated themessage to a signalling connection.

� Network Service Data Unit (NSDU)

The NSDU contains the user data, if the data is too large for one SCCPmessage to be carried in the SIF of an SS7 message the protocol class willcontrol segmenting and reassembling

3. Connection release – this provides the method to breakdown the connection andrelease of the reference numbers.

The permanent connections have the same phases as temporary connection but mayhave additional safeguarding mechanisms at the end points to ensure re-establishment incase of processor outage.

In connectionless signalling all data for routing is carried in each data packet, so nological path is created in the network, the functions of the connectionless service are,mapping of the network address to signalling relations, sequence services andsegmenting.

Version 1 Revision 0 SCCP Services




SCCP services

CP03_Ch6_03

Connection orientated transfer mode can be divided into three phases

Establishing the connectionData transferRelease of the connection

Connection less orientated transfer all of the information required to routethe data to its destination is contained in each packet.

Version 1 Revision 0SCCP Primitives




SCCP PrimitivesSCCP is a layer within the SS7. Because SCCP is not a top layer or a base layer itmeans that it must be able to transfer information and communicate with the layersabove and below it in the protocol stack.

Layers either side of the SCCP are known as the service user and the SCCP is theservice provider, communication is achieved using Service Primitives.

Primitives consist of commands and responses that are associated with the servicesrequested of the layers. Service primitives are data units sent between layers to invoke adifferent procedure.

There is a general syntax applied to all primitives:-

Layer Identifier Generic Name Specific Name Parameter

The Layer Identifier specifies which layer is providing the service e.g. N=SCCP,MTP=MTP, TR=transaction sub layer TCAP, TC=service provider in TCAP

The Generic Name defines the action to be performed

The Specific Name indicates the purpose of the primitive, it also indicates the direction ofprimitive flow.

The parameter contains elements of information that will be transferred between layers.

Version 1 Revision 0 SCCP Primitives




Primitive Structure

CP03_Ch6_04

MTP Level 3

SCCP

ISUP

TCAPService

Primitives

ServicePrimitives

ServicePrimitives

Network Service Part

Service Access Point

Version 1 Revision 0SCCP Protocol Classes




SCCP Protocol ClassesThe protocol used by SCCP to provide network services is divided into four classes.

Two classes are defined for each signalling services, 0 and 1 represent theconnection-less service and 2 and 3 represent the connection-orientated services.

Class 0 and 2 form the basic version whilst 1 and 3 allow for additional data security andsegmentation.

In GSM protocol classes 0,1 and 2 are used, class 3 is never used in GSM

Over the A interface protocol classes, 0 and 2 are used.

When using GSM MAP protocol classes, 0 and 2 are used

Protocol class 0 – the NSDUs are transported independently of each other and may bedelivered out of sequence, this protocol class is a pure connection-less network service

Protocol class 1 – all the features of class 0 are included and added to. An additionalsequencing feature is added and the signalling link selection is encoded into the routinglabel. This is a connection-less network service.

Protocol class 2 – allows for bi-directional transfer of NSDUs and it ensures sequencingas in protocol class 1. This corresponds to a connection-oriented network service.

Version 1 Revision 0 SCCP Protocol Classes




SCCP Protocol Classes

CP03_Ch6_05

There are four Protocol classes defined within the SCCP protocol

Protocol Classes

Dataform2 packets DT2Flow Control Connection–orientated Class3

Dataform1 packets DT1Basic Connection–orientated Class2

Unit Data (UDT) or UnitData Service (UDTS)

Sequenced Connection–less class1


Basic Connection–less Class0

Dataform2 packets DT2Flow Control Connection–orientated Class3

Dataform1 packets DT1Basic Connection–orientated Class2


Sequenced Connection–less class1


Basic Connection–less Class0

Version 1 Revision 0SCCP Embedded in MSU




SCCP Embedded in MSUSCCP messages are carried on signalling links by means of MSUs.

The Service Indicator (SI) in the Service Information Octet (SIO) is coded to 0011 toindicate that the payload of the Signalling Information Field (SIF) is an SCCP. The maxsize of the SCCP message is 272 octets.

Version 1 Revision 0 SCCP Embedded in MSU




SCCP embedded in MSU

CP03_Ch6_06


87171628n

n< 272

168 8


BIB

FSN BSNSIO

SCCP Message

87171628n

n< 272

168 8


BIB

FSN BSNSIO

SCCP Message

87171628n

n< 272

168 8


BIB

FSN BSNSIOFCS SIF FlagFlag Spare LIFIB

BIB

FSN BSNSIO

SCCP MessageSCCP Message

Version 1 Revision 0SCCP Message




SCCP MessageAn SCCP message consists of the following parts,

Routing Label

This contains the DPC, OPC and SLS.

Message typecode.

This is a 1 octet field and defines the function and format of the SCCP message.

Parameters

This field is variable and depends on the information that needs to be carried. The SCCPmay contain a number of parameters with the signalling information. These parameterscan be of either a fixed or variable length and can also be mandatory or optional.

Version 1 Revision 0 SCCP Message




Signalling Connection Control Part Msg

CP03_Ch6_07


Routing LabelMandatory variable Part Message type Code

8n (272 >n>3) bits

Mandatory Fixed Part

Parameters


Version 1 Revision 0SCCP Message Structure




SCCP Message StructureThe complete message is hosted by the MSU. The SCCP breaks down into various partsand the SCCP message that is sent will have three types of fields filled as laid out byITU-T.

Message TypeCode

This is the protocol class, it is using the message type code that the SCCP includes inthe MSU. The message type will also indicate if it is a CO or CL service. For CL themessage is either Unit Data (UDT) or Unit Data Service (UDTS). For CO the messagewill be Data form 1 (DT1).

The parameters are further broken down into two sub fields.

� Mandatory fixed Part

� Mandatory variable Part

The contents of these two sub fields are specific for each SCCP message. This isbecause each SCCP message has its specific number and type of parameters. Thelength of these can be fixed or variable.

The Mandatory Part includes segmentation information, Destination/Source LocationRegister DLR/SLR, or calling party and called party address.

Version 1 Revision 0 SCCP Message Structure




SCCP Message Structure

CP03_Ch6_08


Routing LabelMandatory variable Part Message type CodeMandatory Fixed Part

Msg.typeCode

Param

. A

Param

. B

Pointer A

Pointer O

pt

Pointer B

LengthParam. ALength

Param. B

Param

. N

Length

NA

ME

EndOptParm.

Version 1 Revision 0SCCP Routing




SCCP RoutingThe SCCP messages are carried in the SIF of the MSU. The only identifier is carried inthe SIO. The routing label carries information about the correct routing of the message

In the Parameter field there is a division of parameter groups. It is here that the protocolclass for service is indicated. Also included in the parameters is the Called Partyaddress, this is for SCCP routing. The information carried here will identify the type ofaddress and the address itself.

This information, being SCCP routing and addressing must be carried in both CO and CLservices.

Version 1 Revision 0 SCCP Routing




SCCP routing

CP03_Ch6_09

When SCCP is used to transfer a message, two parameters are used toroute it to the next node

– Called Party Address

– Calling Party Address

Both parts are included in connection–less Unidata and Unidata services.

Version 1 Revision 0SCCP Routing Calling Party and Called Party




SCCP Routing Calling Party and Called PartyWithin the SCCP message structure there must be parameters that enable non-circuitrelated signalling for point-to-point communication between two users.

These address parameters are Called Party Address (CdPA) and Calling Party Address(CaPA). The format of these two sub fields is the same and they identify the type ofaddress and the address itself.

An address may consist of any combination the following,

� SPC

� SSN

� Global Title

The parameters CaPA and CdPA are necessary for end-to-end addressing of SCCPmessages

MAP uses all possible combinations for addressing, while BSSAP requires only the SPCand SSN.

Version 1 Revision 0 SCCP Routing Calling Party and Called Party




SCCP Routing Calling Party and Called Party

CP03_Ch6_10

The calling –party address ( CaPA) and the called–party address (CdPA)have the same format and also identify the type of address beingused.

The address may consist of any combination of the following

– SPC

– SSN

– Global title

�

�

Version 1 Revision 0SCCP Addressing for Routing




SCCP Addressing for RoutingWithin SCCP there must be a method by which the addressing of node across thenetwork can be carried and understood. These addresses would be used to resolve therouting to enable the transfer of SCCP message to the destination node throughout thenetwork.

The Addressing within SCCP has two basic categories:

1. Global Title (GT), a global title consists of a regular directory number andinformation as to how to interpret the number, only the SCCP layer in differentnodes is able to use the GT

2. Destination Point Code (DPC) and Sub System Number (SSN), this system allowsdirect routing, it bypasses the SCCP, the sub system number (SSN) is used by theSCCP to identify different applications in a node, this is to identify the part of anode and establish if it uses SCCP directly or indirectly.

Sub Systems of the SCCP

SSN (Hex) Sub System

00 SSN not known oravailable

01 SCCP management

02 Reserved

03 ISUP

04 OMAP

05 MAP

06 HLR

07 VLR

08 MSC

09 EIR

0A AuC

FE BSSAP

Version 1 Revision 0 SCCP Addressing for Routing




SCCP Addressing for Routing

CP03_Ch6_11

There are two methods of addresses for SCCP routing

– Global title (GT), is a destination address, it is used by differentnodes to solve routing

– DPC and SSN, this allows direct routing, as a result no

translation is required by the SCCP

Version 1 Revision 0SCCP Called Party Address




SCCP Called Party AddressThe format of the Called Party Address (CdPA) and the Calling Party Address (CaPA)are the same, so by looking at one it is possible to explain both.

The Called Party Address field breaks down into three sub fields:

Address Length. This indicates the amount of information in the SCCP address subfield.

Address Indicator . Because address information handled by the SCCP can appear indifferent variants, it is then practical to have a sub field that defines the structure of theaddress related information.

SCCP address . This is made up from the Sub-System Number (SSN), Signaling PointCode (SPC) and Global Title (GT) (which is defined by lower level parameters).

Version 1 Revision 0 SCCP Called Party Address




SCCP Called Party Addressing

CP03_Ch6_12

Address LengthSSN Address IndicatorSPCGT Address LengthSSN Address IndicatorSPCGT

FirstTransmission DirectionLast

SCCP Address


SCCP Address

Point Code IndicatorGT Indicator SSN IndicatorRouting IndicatorSpare Point Code IndicatorGT Indicator SSN IndicatorRouting IndicatorSpare Point Code IndicatorGT Indicator SSN IndicatorRouting IndicatorSpare

0=SPC not included1=SPC included0=SPC not included1=SPC included0=SPC not included1=SPC included

0=SSN not included1=SSN included0=SSN not included1=SSN included0=SSN not included1=SSN included

0000=GT not included00010010

=GT included00110100





Routing based on0=GT1=DPC+SSN



Version 1 Revision 0SCCP Address information




SCCP Address informationAs the SCCP is embedded in MTP layer 3 using the MSU to transport the user data, inthe routing label of the MTP the DPC and OPC for the link being used to transfer theinformation is enclosed. This information is only between two SP/STP’s and is notend-to-end addressing.

Within the SCCP the subdivisions of address field includes the Calling Party Address(CaPA) and the Called Party Address (CdPA), because SCCP can provide end-to-endrouting these address are used to achieve it.

The Called Party Address and Calling Party Address are of the same format and as bylooking at one in detail it is possible to understand either.

The Called Party Address field breaks down into three sub fields, the SCCP address, thisis made up from the SPC, SSN and GT (which is defined by lower level parameters).

SPC, this indicates the SPC of the Called/Calling Party SCCP node

SSN, this is the SCCP sub system number

GT, this is the Global Title, which is a sub parameter that is defined by lower level subparameters:

� Address Information

this indicates the called or calling party’s number

� Nature of Address

defines the type of number contained in the GT – National number or InternationalNumber

� Numbering Plan

indicates the numbering plan – PLMN, ISDN/Mobile

� Translation type

defines the routing table – GSM or Short Message Centre

The format of the information is laid out in ITU-T Q713

Version 1 Revision 0 SCCP Address information




SCCP Address Information

CP03_Ch6_13

MTP

SCCP

MAP

TCAP

MTP

SCCP

MAP

TCAP

Routing Label

Calling Address

Called Address

Routing LabelRouting Label

Calling AddressCalling Address

Called AddressCalled Address

DPC

OPC

DPCDPC

OPCOPC

Translation type

Numbering Plan

Nature of Address

Address Information

Translation typeTranslation type

Numbering PlanNumbering Plan

Nature of AddressNature of Address

Address InformationAddress Information

Global Title

SSN

SPC

Global TitleGlobal Title

SSNSSN

SPCSPC

Version 1 Revision 0SCCP Functional Structure




SCCP Functional StructureThe SCCP is able to transfer messages both to higher layers, SCCP Users and aroundthe network using MTP, in order to do so it must have separate functionality within theSCCP to achieve this

The SCCP function consists of the following main sub functions:

SCCP Connection-Oriented Control (SCOC). The function of the SCOC is to control theestablishment and release of signalling connection and to provide for data transfer onsignalling connections.

SCCP Connectionless Control (SSLC). This sub function is responsible for theconnectionless transfer of data units.

SCCP Management (SCM). The purpose of the SCCP Management is to providecapabilities to handle the congestion or failure of the SCCP, the SCCP user or thesignalling route to the SCCP/SCCP user. These are in addition to the MTPs signallingroute management and flow control.

SCCP Routing Control. On receipt of a message from the MTP or any of the above subfunctions, the SCCP Routing Control provides the necessary routing functions to forwardthe message. If the called party is a local user then the message is passed to eitherSCOC, SSLC or SCM. If the called party is not a local user, then it is passed to MTP fortransfer to a distant SCCP user.

Version 1 Revision 0 SCCP Functional Structure




SCCP Functional Structure

CP03_Ch6_14

SCCP MTPSCCP MTP

SCCPManagement

(SCM)

SCCPConnectionless

Control(SCLC)

SCCPConnection

OrientedControl(SCOC) SCCP

RoutingControl(SCRC)

MTPSCCP

USERS

Version 1 Revision 0SCCP Functional Structure







Chapter 7

Transaction Capabilities

Application Part and Mobile

Application Part









Chapter 7Transaction Capabilities Application Part and Mobile Application Part i. .

Objectives 7–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Transaction Capabilities Application Part (TCAP) 7–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Purpose of TCAP 7–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Mobile Application Part 7–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MAP Application Entities 7–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP and MAP Interworking 7–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP and MAP in the OSI Model 7–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

AE Functionality 7–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Structure 7–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Component Sub Layer (CSL) 7–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Transaction Sub layer (TSL) 7–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Message Interfaces 7–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Embedded Message Structure 7–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Information Elements 7–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Primitives and Constructor IE 7–24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Message Structure 7–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP Transaction Procedures 7–28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MAP user Communication 7–30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TCAP/MAP Transactions 7–32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .









Objectives


� Describe the functionality of TCAP and MAP.

� Identify the portions of the TCAP and MAP environment.

� Identify the TCAP message structure and explain the function of the elements.

� Describe the procedure for a TCP transaction.

Version 1 Revision 0Transaction Capabilities Application Part (TCAP)




Transaction Capabilities Application Part (TCAP)Transaction Capabilities Application Part (TCAP) was introduced above the SCCP andMTP as a reaction for the need to deal with increasing Database-to-Databasecommunication. TCAP uses SCCP to carry the information throughout the signallingnetwork and it is TCAP that provides the core functionality to support roaming.

TCAP is the serving interface between SCCP and the functionality that sits above TCAPproviding GSM with a lot of dialogues running concurrently with a wide variety ofmessages carrying numerous parameters. These communications are now not onlyconcerned with data transfer but are now able to invoke operations at the remote end.The element named Transaction Capabilities (TC) provides general standardised protocolfunctions.

TCAP information is carried within SCCP messages as user data. This is known asembedded data, allowing the TCAP message through the SS7 levels. It relies on theNSP for physically transporting the messages over the network.

TCAP defines an end-to-end protocol between TC users. This means that in acommunication link between two TCAP nodes, the TCAP is not processed in anyintermediate node.

Version 1 Revision 0 Transaction Capabilities Application Part (TCAP)




Transaction Capabilities Application Part

CP03_Ch7_01

TCAP and MAP sit over SCCP and MTP 1–3

TCAP is routed using the SCCP routing function, this provides logicalrouting through the MTP layers

TCAP defines an end–to–end protocol between TC users, this means thaa communication link between two TCAP nodes is not processed byTCAP in any intermediate node

�

�

�

Version 1 Revision 0Purpose of TCAP




Purpose of TCAPThe purpose of TCAP is to provide means for the transfer of information between nodes,which will enable generic services for applications in mobile telephony and different typesof Intelligent Network services.

The main purpose of TCAP is to support interactive applications. This allows for transferof information and interactive applications. This element is called Transaction Capabilities(TC) and are defined in ITU-T Q.771-775.

TC provides the means to establish non-circuit related communications between twonodes in a TC enabled signalling network.

Examples of interactive applications are:

� Mobile service applications

� 0800 service applications

� HLR/VLR communication

� Credit Card Calling

An important function of TCAP is that the information obtained is able to be acted on inthe receiving node.

Version 1 Revision 0 Purpose of TCAP




Purpose of TCAP

�

�

�

CP03_Ch7_02

TCAP provides the capability for an application to invoke an operation inanother node and provides a means for the transfer of informationbetween nodes

TCAP information flow between two nodes is known as dialogue

It can also receive the results of the operation and act upon them

It was developed to support interactive applications, both in GSM anddatabase access. E.g. HLR/VLR communication, 0800 services and IN

�

Version 1 Revision 0Mobile Application Part




Mobile Application PartMobile Application Part (MAP) is a protocol that is designed to support GSMrequirements. This protocol is required between the MSC and all registers in the GSMsystem, the protocol is installed in the MSC, VLR, HLR, EIR and AUC to allow thesenode communication. A second application part is required from the MSC to the BSC,this has been designed and is known as the Base Station System Application Part(BSSAP).

MAP is a TC user and it utilises the dialogue and component-handling facilities forpeer-to-peer communication offered by TCAP. It uses the services of the NSP (SCCPand MTP) for the transmission of messages.

Because most of the applications that use MAP are not part of the OSI, MAP servicesare required for control tasks and data exchanges between the different applications andMAP. The MAP services are primitives.

Version 1 Revision 0 Mobile Application Part




Mobile Application Part

�

�

�

CP03_Ch7_03

MAP is a protocol that was designed to support GSM requirements, awith TCAP, MAP resides above level 4 in the SS7 model

MAP is installed in the GSM network entities. HLR/VLR, MSC, EIR

MAP is a TC user utilising the dialogue and component handling ofTCAP in an end–to–end solution

Version 1 Revision 0MAP Application Entities




MAP Application EntitiesIn order for MAP to communicate with the applications that sit outside the OSI modelthere needs to be a method within MAP to establish a link with these applications.

MAP is divided into five Application Entities (AE)

MAP-MSCMAP-VLRMAP-HLRMAP-EIRMAP-AUC

Each AE consists of a number of Application Service Elements (ASEs). There are twotypes of ASE – common and specific. Common ASEs are required by all AEs in order tooperate, and specific ASEs are dependant on each AE.

Application Service Elements (ASE) support the interworking of AEs and will consist ofone or several operations with their associated parameters. Any entity using the MAPprotocol can communicate with several other entities simultaneously.

Version 1 Revision 0 MAP Application Entities




TCAP and MAP

�

CP03_Ch7_04

MAP is divided into five Application Entities (AE)

MAP–MSC

MAP–VLR

MAP–HLR

MAP–EIR

MAP–AUC

� Each AE is divided into Application Service Elements (ASE). These are grouped as common and specific. ESEssupport the interwork of the AEs, they may be combined to perform a certain task.

Version 1 Revision 0TCAP and MAP Interworking




TCAP and MAP InterworkingEach of the AEs are assigned a Sub System Number (SSN). These are the same SSNsthat are used by the SCCP to address certain GSM network entities.

The functionality of AEs are subdivided into Application Service Elements (ASE). ASEsare grouped as common ASEs and specific ASEs. ASEs support the interworking ofAEs. ASEs consist of one or more operations and these operations can be combined toperform a certain task. E.g. in handover a system may require interaction with severalother systems at once and any entity using MAP protocol can communicate with severalothers simultaneously.

TCAP is common to all ASEs and is always included in the MAP-AEs

Version 1 Revision 0 TCAP and MAP Interworking




TCAP and MAP Interworking

CP03_Ch7_05

MTP

SCCP

MAPHLR

MAPAuC

SSN SSN

TCAPASE common

MTP

SCCP

MAPHLR

MAPAuC

SSN SSN

TCAPASE common

MAP MSC

ASE 1 ASE 2

MAP MSC

ASE 1 ASE 2

Version 1 Revision 0TCAP and MAP in the OSI Model




TCAP and MAP in the OSI ModelWhen looking at the OSI model compared to the SS7 levels it is important to rememberthat the OSI model is only used as a guide to explain the functionality of a signallingnetwork.

SCCP sits both on the functionality of MTP-3 and layer 4. Layers 5 and 6 are transparentto the SS7 4 level system – this does not mean that they are not in place but are coveredby TCCP. It is also possible to show TCAP as being spread across Layers 4 to 7. Thebiggest problem is that SS7 does not cross directly to the OSI.

MAP protocol is designed to support GSM requirements. In the OSI model, MAP residesabove TCAP, both are thought of as belonging to layer 7. As MAP does not requireconnected signalling links it uses the connection-less service of the SCCP.

The Application Entities (AE) are logically part of the MAP protocol within a signallingnetwork but are physically outside the SS7 model – they are thought of as MAP users.

Version 1 Revision 0 TCAP and MAP in the OSI Model




TCAP and MAP in the OSI Model

CP03_Ch7_06

SCCP

MAP

TCAP

SCCP

MAP

TCAP

OSI Layer

Transport

Session

Presentation

Application7

6

5

4

OSI Layer

Transport

Session

Presentation

Application7

6

5

4

EIRMSCVLRHLR AUCEIRMSCVLRHLR AUC AE’s

Version 1 Revision 0AE Functionality




AE FunctionalityThere are five Application Entities (AE) within the GSM architecture and all operate in thesame manner. However their functions supported within the GSM network are different.

All application entities (AE) consist of a number of Application Service Elements (ASEs).ASEs are grouped as common ASEs and specific ASEs. TCAP is a common ASE to allAEs – this is because it is always included in all MAP-AEs.

Common ASEs

Common ASEs control communication between MAP and the application

MAP-OPEN – allows MAP to establish a dialogueMAP-CLOSE – terminates the existing processMAP-U-ABORT – indicates that an application wishes to interrupt a dialogueMAP-P-ABORT – indicates that TCAP wishes to interrupt a dialogueMAP-NOTICE – provides an application with information about problems on the peersideMAP-DELIMITER – this indicates that a data packet is ready to be passed.

Specific ASEs

Specific ASEs contain and transfer the actual data. The common service only containsthe applications context name and establishes the requested protocol for the dialogue tobe established. The specific ASE’s depend on the MAP application entity

Version 1 Revision 0 AE Functionality




AE Functionality

CP03_Ch7_07

OTHER ASE OTHER ASE

TCAP(common ASE)

APPLICATION ENTITY

OTHER ASE OTHER ASE

TCAP(common ASE)

APPLICATION ENTITY

Version 1 Revision 0TCAP Structure




TCAP StructureThe TCAP is divided into two main parts – The Component Sub Layer (CSL) and theTransaction Sub Layer (TSL).

The ComponentSub Layer (CSL)

The CSL is responsible for individual actions or data requested, and is concerned withthe exchange of information between the TC user and TCAP. The component layerequates to Layers 5 and 6 in the OSI model. The CSL also provides the TC user with thecapabilities of invoking remote operations and receiving replies. The CSL provides auniform data interface to its users, represented by the Application Protocol Data Unit(APDU). These transport the payload which MAP and the application uses. The CSLallows many dialogues to be run concurrently between TC users.

The TransactionSub layer (TSL)

The TSL deals with the actual exchange of messages between two TC users, containingthe components from the CSL. The term “transaction” is used because the dialoguecontrol is translated to transaction control with one-to-one mapping.

TCAP packages a message with all its parameters and components in a special format,before it is handed over to the NSP. Because there is a transaction id, dialogue id, invokeid and operation code included in the message, the destination TCAP is able to handlemulti dialogues and transactions concurrently between two nodes without mixing themessages.

� “Dialogue” is between TC users

� “Transaction” is between TCAP

Version 1 Revision 0 TCAP Structure




TCAP Structure

�

CP03_Ch7_08

TCAP has two main parts

– Component Sub layer, which is responsible for individual actions ordata requests, it is concerned with the exchange of informationbetween the TC user and TCAP

– Transaction Sub layer, this deals with the actual exchange ofmessages. The term transaction is used because each TCAPmessage is associated with one transaction.

Version 1 Revision 0TCAP Message Interfaces




TCAP Message InterfacesThe TCAP resides between SCCP and MAP and as such it has the requirement tofunction in both directions.

The Transaction Sub Layer (TSL) defines the transaction ID that is comparable to theSLR/DLR in SCCP to invoke addressing. This is used with the invoke ID, it is possible tohave several dialogues open at once. TCAP allows for the dialogues to run concurrentlybetween two users. The TSL provides the capability for the exchange of componentsbetween TC users and it is the TSL that interfaces with the SCCP.

The Component Sub Layer (CSL) is responsible for the synchronisation andco-ordination of a communication. The CSL consists of two functions:

� Dialogue Handling (DHA)

� Component Handling (CHA)

There are two dialogue facilities provided – unstructured and structured. The differencebetween unstructured and structured is that in unstructured the dialogue is terminated assoon as the component is transferred. In structured dialogue several flows ofcomponents are allowed to co-exist between two TC users. The component handling isrelated to the request to perform an operation or a reply and it is the CHA which isresponsible for the correct component.

Version 1 Revision 0 TCAP Message Interfaces




TCAP Message Interfaces

CP03_Ch7_09

Network Service e.g SCCPNSP

Network Service e.g SCCPNSP

APDUTransfer

AddressingInformation

MAP TC–user

Actions or dataAPDUTransfer


APDUTransfer

AddressingInformationAddressingInformation

MAP TC–user

Actions or dataActions or data

TCAP Transaction Sublayer

TCAP Component SublayerTCAP

Exchange of components

Network ServiceAccess Point


TCAP Component SublayerTCAP

Exchange of componentsExchange of components

Network ServiceAccess PointNetwork ServiceAccess Point

Version 1 Revision 0TCAP Embedded Message Structure




TCAP Embedded Message StructureThe TCAP message is carried as a payload of an SCCP message, this in turn is hostedby the MSU.

The SCCP breaks down into various parts

Label is a type D this is the routing label which is of standard format,

| sig info | SLS | OPC | DPC .

Message type indicates what the SCCP message is carried.

The SCCP message header carries the protocol class and the standard SCCPinformation, such as CaPA and CdPA

The User data within the message will indicate it is a TCAP message, this is broken intothe transaction portion and the component portion.

EOP = end of optional part

Version 1 Revision 0 TCAP Embedded Message Structure




TCAP Embedded Message Structure

CP03_Ch7_10


LabelMessage TypeSCCP message HeaderUser message/dataEOP LabelMessage TypeSCCP message HeaderUser message/dataEOP

Transactionportion

Component Portion

Component n Component 2 Component 1

Transactionportion

Component Portion

Component n Component 2 Component 1

Transactionportion

Component Portion

Component n Component 2 Component 1TCAP


Version 1 Revision 0TCAP Information Elements




TCAP Information ElementsAll types of information in a TCAP message are divided into modules. These are calledinformation elements.

All information elements have the same structure and they consist of three fields whichwill always appear in a set order:

1. TAG, this distinguishes one information element from another, and controls theinterpretation of the contents.

2. LENGTH specifies the length of the contents of an information element.

3. CONTENTS, this is the substance of an information element.

Version 1 Revision 0 TCAP Information Elements




TCAP Information Elements

CP03_Ch7_11

Information in TCAP messages are divided into modules calledinformation elements, all information elements have the same structure

– TAG

– Length

– Contents

�

Version 1 Revision 0Primitives and Constructor IE




Primitives and Constructor IEThe content of each element is either one Information Element (primitive) or multipleInformation Elements (constructor)

If primitives are used the information elements are always Tag, Length and thenContents.

If it is more than one information element it is a constructor and the Tag will then be usedto distinguish between one information element and another.

The first Field indicators will indicate the information in the Constructor InformationElement.

The length of content is coded to indicate the number of octets. The Length does notinclude the Tag or the length of the Contents octets.

Version 1 Revision 0 Primitives and Constructor IE




Primitives and Constructor IE

CP03_Ch7_12

Tag

Length

Tag

Length

Contents

Contents

Contents

Tag

Length

Tag

Length

Tag

Length

Contents

Tag

Length

Tag

Length

Tag

Length

Contents

ContentsPrimitive

Constructor

Version 1 Revision 0TCAP Message Structure




TCAP Message StructureA TC user invoking an operation creates the structure of a TCAP message. It consists ofa Dialogue portion part, Transaction portion part and a Component portion part.

Message Type Tag

There are five types of messages defined for the transaction portion

� Unidirectional

� Begin

� End

� Continue

� Abort

Message length

The message length indicates the total length of the message.

Transaction portion information element

The Transaction portion information element carries the transaction ID. It will carry eitherthe destination and/or originating ID.

Dialogue portion information element

The Dialogue portion information element consists of two elements – the applicationcontext and the user information.

Component portion

The Component portion is a constructor and consists of two elements, the invoke ID andOperation code information element. The Invoke ID distinguishes between differentoperations invoked within one dialogue. The Operation code information element,identifies the operation that is to be invoked at the far end. The number of parametersand constructors included in the Operation code constructor is not limited, so a numberof constructors may be included in the same message.

Version 1 Revision 0 TCAP Message Structure




TCAP Message Structure

CP03_Ch7_13

Total Message LengthMessage Type Tag

TransactionPortion

ComponentPortion

Transaction Portion Information Element

Dialogue Portion Information Element

Component Portion TagComponent Portion Length

Component Portion Contents



Component Information Element





Version 1 Revision 0TCAP Transaction Procedures




TCAP Transaction ProceduresThe operation of TCAP is logical.

The originating TC user will send a dialogue request (this is a BEG message – BEGin)for TCAP to open a dialogue for one user with another. The BEG message comprises ofthe transaction ID and identifies a dialogue within the transaction layer.

The second TC user will either send a CON (CONtinue) or END message. If it is a CONmessage it means that the transport of information may take place. The first CONmessage confirms that the requested protocol and application context are accepted. Ifthe message is an END it means that the process is to be terminated.

The only other message is the ABT (AborT) message and this can be sent by either TCuser and the reason for termination does not need to be provided. There is, however adistinction between the user abort, U-ABT and the service provider abort, P-ABT.

Version 1 Revision 0 TCAP Transaction Procedures




TCAP transaction Procedures

CP03_Ch7_14

BEGIN [OTID = x, Invoke (#1, provide dialled freephone number)]

CONTINUE [OTID = y DTID = x,Invoke(#2, play announcement and collect digits)]

CONTINUE [OTID = x DTID = y,Return result (#2 collected digits)}

END [DTID = x, Return result (#1, routing number)]

ORIGINATINGEXCHANGE

DATABASE

BEGIN [OTID = x, Invoke (#1, provide dialled freephone number)]

CONTINUE [OTID = y DTID = x,Invoke(#2, play announcement and collect digits)]

CONTINUE [OTID = x DTID = y,Return result (#2 collected digits)}

END [DTID = x, Return result (#1, routing number)]

ORIGINATINGEXCHANGE

DATABASE

Version 1 Revision 0MAP user Communication




MAP user CommunicationAs can be seen, all of the Application Parts interact using primitives. A primitive is acommunication between layers.

Service primitives are data units, or functional signals that are sent between adjacentlayers in order to invoke different procedures. The data units contain parameters withinformation that is used in the interaction between the two users.

TCAP primitives contain the portions of information that make up a TCAP message

Primitives can be sent in both directions

The virtual communication is the apparent communication that is seen by the user.

Primitives are used to access the different layers and levels. This is done through accesspoints and each layer has its own service access point. A service access point is anentry/exit point between two protocols and each service access point has a designatedfunction.

Version 1 Revision 0 MAP user Communication




MAP user Communication

CP03_Ch7_15

MAP

TCAP

MAP User

MAP

TCAP

MAP User

MAP ServicePrimitives

Primitives

Virtual Peer to Peercommunication

To/From SCCP To/From SCCP



Primitives

PrimitivesPrimitives

MAP

TCAP

MAP User

MAP

TCAP

MAP User


Primitives





Primitives

PrimitivesPrimitives

Version 1 Revision 0TCAP/MAP Transactions




TCAP/MAP TransactionsIn MAP there is an important need for the direction of the services to be known. Thereare four variants defined for every MAP service.

Initiating MAP user will start with a request (REQ), this translates itself as an indication(IND) at the responding MAP user.

When the responding MAP user replies the MAP service will respond with the response(RSP). This indicates that the message being sent, although known that it is leaving theresponding MAP user, it is in response to an already sent REQ. The RSP when it isreceived at the initiating MAP user it translated to a Confirmation (CNF) message.

These actions are important to understand the operation of direction control in MAP.

Version 1 Revision 0 TCAP/MAP Transactions




TCAP/MAP transactions

CP03_Ch7_16

Initiating MAP User Responding MAP UserInitiating MAP User Responding MAP User

ConfirmationCNF

RequestREQ

IndicationIND

ResponseRES

APDU Transfer

MAP MAP



APDU Transfer


TCAP ComponentSublayer




ConfirmationCNF

RequestREQ

IndicationIND

ResponseRES

ConfirmationCNF

RequestREQ

IndicationIND

ResponseRES

APDU Transfer

MAP MAP



APDU Transfer






APDU Transfer

MAP MAP



APDU Transfer











Version 1 Revision 0TCAP/MAP Transactions







Chapter 8

GSM Network Overview to SS7









Chapter 8GSM Network Overview to SS7 i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Objectives 8–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

GSM Network Components 8–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


A Interface Protocols 8–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A Interface between MSC and BSS 8–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

BSSAP Message Structure 8–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BSSMAP Message 8–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DTAP Message 8–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Interfaces Between BSC, BTS and MS 8–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LAPD frame Structure 8–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Address Field 8–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control field 8–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LAPDm Frames 8–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LAPDm Frame Structure 8–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A and B format Frame Structure 8–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Address Field 8–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control Field 8–20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SS7 Connection to GPRS 8–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .









Objectives

At the end of this chapter the student will be able to:

� Identify the two Subsystems and their components in GSM.

� Identify the components and interfaces of the GSM network and describe theirfunction.

� Understand the A interface, LApD and LApdM message formats.

Version 1 Revision 0GSM Network Components




GSM Network ComponentsEach network component is illustrated only once, however, many of the components willoccur several times throughout a network.

Each network component is designed to communicate over an interface specified by theGSM standards. This provides flexibility and enables a network provider to utilize systemcomponents from different manufacturers. For example Motorola Base Station System(BSS) equipment may be coupled with an Ericsson Network Switching System.

The principle component groups of a GSM network are:

The Mobile Station (MS)

This consists of the mobile telephone, fax machine etc. This is the part of the networkthat the subscriber will see.

The Base Station System (BSS)

This is the part of the network that provides the radio interconnection from the MS to theland-based switching equipment.

The Network Switching System

This consists of the Mobile services Switching Centre (MSC) and its associatedsystem-control databases and processors together with the required interfaces. This isthe part that provides for interconnection between the GSM network and the PublicSwitched Telephone Network (PSTN).

The Operations and Maintenance System

This enables the network provider to configure and maintain the network from a centrallocation.

Version 1 Revision 0 GSM Network Components




GSM Network Components

CP03_Ch8_01

NMC

OMC

Operations andMaintenance System


Base Station System

Interface/Connection

Mobile Station

PSTN

VLR HLR

AUC

EIRMSC

IWFEC

BTS

BSC

ME

SIM

XCDR





GSM Interface Names

Interface Names

Each interface specified within the GSM system has a name associated with it. Thediagram opposite illustrates the names of all the interfaces specified by GSM.

Air-interface MS-BTS

A-bis(Mo-bis) BTS-BSC

A-interface BSS-MSC

B-Interface MSC-VLR

C-interface MSC-HLR

D-interface HLR-VLR

E-interface inter-MSC

F-interface MSC-EIR

G-interface VLR-VLR

R-interface MS-DTE (Data Terminating Equipment)

Version 1 Revision 0 GSM Interface Names




GSM Interface Names

CP03_Ch8_02

NMC

OMC

VLR

MSC

ECIWFXC

XC

VLR

EC IWF XC

MSC

HLR

AUC

EIR

PSTN

BTS BSC


BSS

BTS

BTS

BTS

BTS

BTS

BTS

BSC

BTS BTS BTS

MS

MS

MS

VLR

A

E

Abis

Um

G

B

D

BC

H

F

Version 1 Revision 0A Interface Protocols




A Interface ProtocolsThe A interface is the interface between the BSS and the MSC. The protocol usedacross the A interface is called Base Station System Application Part (BSSAP). TheBSSAP sends messages associated with specific MS in the SCCP connection-orientatedmode.

The BSSAP is used for signalling between MSC and BSS and it is made up of threetypes of signalling messages

� DTAP

� BSSMAP

� Initial MS message

DTAP and Initial signalling can be looked at as one as they are both transparent to theBSS, both of these messages carry user information.

Version 1 Revision 0 A Interface Protocols




A Interface Protocols

CP03_Ch8_03

DTAP

MTP Level 1

MTP Level 2

MTP Level 3

SCCP

BSSMAP

BSSAPDTAP

MTP Level 1

MTP Level 2

MTP Level 3

SCCP

BSSMAP

BSSAP

MSC

BSS

BSC/BTS

Transparent to BSS

DTAP

BSSAP LAPDm

Initial MSMSC

BSS

BSC/BTS

Transparent to BSS

DTAP

BSSAP LAPDm

Initial MS

Version 1 Revision 0A Interface between MSC and BSS




A Interface between MSC and BSSThe signalling channel between the MSC and BSS is able to serve one or more basetransceiver stations. Motorola’s feature is 100 BTSs supported by one BSC.

The protocols used for signalling between the MSC and BSS are BSSAP, SCCP andMTP.

The distribution sub layer performs the distribution of BSSAP messages to eitherBSSMAP or DTAP. It is able to do this by reading the distribution data unit which iscontained in the header of the message. This information is used to determine if themessage is BSSMAP or DTAP.

Version 1 Revision 0 A Interface between MSC and BSS




A Interface between MSC and BSS

CP03_Ch8_04

MTP

SCCP

Distribution Sublayer

BSSAP

MTP

SCCP


BSSAP

MTP

SCCP


BSSAP

MTP

SCCP


MTP

SCCP


BSSAP

DTAPBSSMAP DTAPBSSMAP DTAPBSSMAP DTAPBSSMAP

A–InterfaceMSC BSS

A–InterfaceMSC BSS

Version 1 Revision 0BSSAP Message Structure




BSSAP Message StructureThe entire BSSAP message is embedded in an SCCP message. The first 8 or 16 bits ofthe BSSAP indicate if the message is either a BSSMAP or a DTAP. This is thediscrimination field.

BSSMAP, the 8-bit header discriminates the message as a BSSMAP.

DTAP, the 16 bits break into the first 8 bits indicate a DTAP and the second 8 bitsindicate the data link connection identifier (DLCI).

A length indicator, indicates the length of the information/data field.

BSSMAPMessage

Message type is an 8-bit field indicating the code of the message.

Information field consists of the information element identifier (IEI), a length indicator anda data field.

DTAP Message

Data Link Connection Identification (DLCI), part of the distribution data unit, is used toidentify the radio channel and also specifies which SAPI value used on the radio link:

� SAPI 0= call control signalling

� SAPI 1= short message service

Message type is an 8-bit field indicating the code of the message

TI/PD

The purpose of Transaction Identifier (TI) is to distinguish between multiple parallelactivities within one MS.

Protocol Discriminator (PD) is to distinguish between messages belonging to following:

� Call control

� Mobility management

� Radio resource management

� Supplementary service control

� Other signalling procedures

Version 1 Revision 0 BSSAP Message Structure




BSSAP Message Structure

CP03_Ch8_05

BSSMAP

Discrimination

Length

Message Type

Info

BSSMAP

Discrimination

Length

Message Type

Info

DTAP

Discrimination

Length

Message Type

Info

DLCI

TI / PD

DTAP

Discrimination

Length

Message Type

Info

DLCI

TI / PD

Version 1 Revision 0Interfaces Between BSC, BTS and MS




Interfaces Between BSC, BTS and MSBetween the BSC and the BTS one 64 kbit/sec channel is used for sending all thesignalling information. This requires a special protocol and this is the link accessprocedure on D channel (LAPD).

The sending portion constructs a LAPD frame, which is then transmitted octet by octetover the PCM link. At the receiving end the octets are put back into the LAPD frame andthe information data is extracted and then delivered to the user.

LAPD supports both unacknowledged and acknowledged information transfer.

Between the BTS and the MS which is the Air interface, it is not possible to use TDMA tosend a signalling frame that is the length of LAPD. As a result the message needs to bedivided into segments. To meet the radio requirements the LAPD functionality has beenused to create the LAPDm.

LAPD and LAPDm are Layer 2 in the OSI protocol Stack.

Version 1 Revision 0 Interfaces Between BSC, BTS and MS




Interfaces Between BSC, BTS and MS

Between the BSC and the BTS the protocol for transporting signallingmessages is Link Access Procedure on D–channel (LAPD)

Between the BTS and the MS, which is viewed as the air interface, amodified LAPD protocol is used. (LAPDm). This protocol is based onLAPD functionality but has been adapted to match radio requirements.Due to the length of LAPD frame, sending the frame over the air interfacerequires that frame to be segmented.

�

�

CP03_Ch8_06

Version 1 Revision 0LAPD frame Structure




LAPD frame StructureThe LAPD frame follows the same format as all signalling frames, the fields are outlinedbelow.

Address Field

EA Extension Address – one EA per octet, first ia always set to 0 indicating that thefollowing octet is part of the address field, the second one is set to 1, meaning it is thelast octet of the address

SAPI Service Access Point Identifier – this address is used to access differentfunctions. GSM uses 3 SAPI

� 0–Radio signalling/traffic management, call control

� 62–operational and maintenance

� 63–layer 2 management

C/R command or response – is the message a command or an answer/response

TEI Terminal Endpoint Identifier – this allows for distinction among identical functionentities, e.g. transceivers

Control field

There are 3 types of Control Field, either 8 bits or 16 bits long, depending on the frametype.

� Information frame – I

� Supervision frame – S

� Unnumbered frame – U

N (S) (R) Number send and receive – used for modulo counting used in I frame only

P/F polling bit final bit – used for forcing a response to a frame by setting p=1 in acommand frame, f bit is the response.

The P/F bit varies with frame type and is dependant on the frame requiringacknowledgement.

Version 1 Revision 0 LAPD frame Structure




LAPD Frame Structure

CP03_Ch8_07

C/RTEI SAPIEA EAC/RTEI SAPIEA EA


Flag FlagFCSInformation field

Layer 3Control Address

8 816 0–260 octets 16 16

Flag FlagFCSInformation field

Layer 3Control AddressFlag FlagFCS

Information fieldLayer 3

Control Address

8 816 0–260 octets 16 16

N(S)PFN(R) 0N(S)PFN(R) 0N(S)PFN(R) 0

Version 1 Revision 0LAPDm Frames




LAPDm FramesThere are two operation modes in LAPDm

Unacknowledged

Messages that do not need to be acknowledged are sent in Unnumbered Informationframes (UI), there is no error correction or flow control for these frames.

Acknowledged

These are sent when it is necessary to obtain an answer. The frame is a NumberedInformation Frame (I-frame). They require acknowledgement before the next frame issent.

There are three formats of the LAPDm frame:

� A-format

� B-format

� Bbis format

A and B formats are used in both directions. Bbis format is used in downlink only.

Version 1 Revision 0 LAPDm Frames




LAPDm Frames

CP03_Ch8_08

There are two type of frame, Unacknowledged (UI) and Acknowledged (and three formats for the LAPDm frame, which one is sent depends onthe type of information to be sent

– A–format, sent with no payload but has addressing information

– B–format, used to transport signalling information

– Bbis –format, used for broadcast when no addressing information isneeded

– All formats are of identical length 23 octets

�

Version 1 Revision 0LAPDm Frame Structure




LAPDm Frame StructureThe three frame types that are used can be separated into two frame structures – theA-format and B-format can be viewed as the same format and the Bbis format isdifferent.

The Bbis format is the easiest structure to view. It consists of an information field, whichis the signalling data which takes the frame length to 23 octets.

The A-format and B-format frame length sub field contains more information.

EL Extension Length bit, is always set to 0 unless another length indicator field followswhen it is set to 1.

M More data bit this bit indicates segmentation if the layer 3 message.

� M=1 part of a segmented message

� M=0 last segment of message

The last bits 2–7 are used in all three frames to indicate the length of the informationfield.

Version 1 Revision 0 LAPDm Frame Structure




LAPDm Frame Structure

CP03_Ch8_09

Bbis format

Signalling Data

Bbis format

Signalling Data

B–format

Fill–in octet Signalling Data Frame Length Control Field Address FieldFill–in octet Signalling Data Frame Length Control Field Address Field

Fill octets Frame Length Control Field Address FieldFill octets Frame Length Control Field Address Field

A–format

Length MLengthLength M EL

Version 1 Revision 0A and B format Frame Structure




A and B format Frame StructureThe A-format and B-format have the same structure – the only difference being after theframe length sub field.

Address Field

EA Extension Address – one EA per octet, the first EA is permanently set to 0indicating following octet is part of the address field.

C/R command or response – is the message a command or an answer/response.

SAPI Service Access Point Identifier – this address is used to access differentfunctions. LAPDm uses different SAPI on the air interface.

� SAPI 0= Radio Resources, Mobility Management, Call Control.

� SAPI 3= Short Message Service, Supplementary Services.

LPD Link Protocol Discriminator – a 2-bit field always coded 00, unless Cell Broadcastservice is used then it is coded 01.

X is a fill bit.

Control Field

The MT message Type bit – indicates what the frame is being used for,

� 0 = Information Frame

� 1 = Supervisory frame

In unnumbered frames the N(S) field is not used and becomes part of the MT field, theMT field then is a 2bit field.

11 = Unnumbered frame.

N (S) (R) Number send and receive – used for modulo counting used in I frame only.

P/F polling bit final bit – used for forcing a response to a frame by setting p=1 in acommand frame, f bit is the response.

The P/F bit varies with frame type and is dependant on the frame requiringacknowledgement.

In the B-format, if the information to be transmitted requires less space than thesignalling data field, the space is filled in with fill-in octets.

Version 1 Revision 0 A and B format Frame Structure




A and B format Frame Structure

CP03_Ch8_10

B–format

Fill–in octet Signalling Data Frame Length Control Field Address FieldFill–in octet Signalling Data Frame Length Control Field Address Field

Fill octets Frame Length Control Field Address FieldFill octets Frame Length Control Field Address Field

A–format

N(S)P/FN(R) MTN(S)P/FN(R) MTN(S)P/FN(R) MT

SAPIX C/RLPD EASAPIX C/RLPD EASAPIX C/RLPD EA

Version 1 Revision 0SS7 Connection to GPRS




SS7 Connection to GPRSGPRS is a new set of GSM bearer services that provide packet mode transmission withinthe PLMN.

There remains a requirement to interface with certain components within the GSMnetwork over SS7 interfaces.

The interfaces that are used are:

Gs – the interface between the MSC/VLR and the SGSN

Gr – the interface between the SGSN and the HLR.

The Gs is the interface that is used to establish what state the subscriber is in – if thesubscriber has initialised the GPRS services or not (IMSI attached). The Gs is also usedfor circuit switching paging messages.

The Gr is the interface that is used to establish if the subscriber has the servicesenabled.

Version 1 Revision 0 SS7 Connection to GPRS




SS7 Connections to GPRS

CP03_Ch8_11

External Gateway

IP Routers

Gateway IP Router

Gateway GSN

Comm Hub ISS

SF

Serving GSN

FR access

BSC

PCU

BTS

MSC – VLRs

SMS – SC

SS7 Network

Signaling Transfer Points

HLRs

Gr Gs Gd

Gn

FR access

Frame Relay Network

IP host

IP host

IP host

IP host IP

host

IP host IP

host External IP Network

External Gateway

IP Routers

Gateway IP Router

Gateway GSN

Serving GSN

FR access

FR access

MS MS MS MS MS MS MS MS MS MS MS MS

MS MS MS MS MS MS MS MS MS MS

Gn

Gn Gn

Gi Gi

BSC

PCU

BTS

BSC

PCU

BTS

BSC

PCU

BTS

cell

External IP Network External IP Network

MS

Version 1 Revision 0SS7 Connection to GPRS




Documents

Principles of C7 Signalling