WILEY CAMEL User Manual
CAMEL
CAMEL
INTELLIGENT NETWORKS FOR THE
GSM, GPRS AND UMTS NETWORK
Rogier Noldus
Ericsson Telecommunications,
The Netherlands
Copyright 2006 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester,
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Library of Congress Cataloging-in-Publication Data:
Noldus, Rogier.
CAMEL : intelligent networks for the GSM, GPSR and UMTS
network / Rogier Noldus.
p. cm.
Includes bibliographical references and index.
ISBN-13: 978-0-470-01694-7 (cloth : alk. paper)
ISBN-10: 0-470-01694-9 (cloth : alk. paper)
1. Computer networks. 2. Artificial intelligence. 3. Global
system for mobile communications. I. Title.
TK5105.84.N65 2006
′
1 – dc22
621.382
2005032765
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
ISBN-13: 978-0-470-01694-7
ISBN-10: 0-470-01694-9
Typeset in 9/11pt Times by Laserwords Private Limited, Chennai, India
Printed and bound in Great Britain by Antony Rowe Ltd, Chippenham, Wiltshire
This book is printed on acid-free paper responsibly manufactured from sustainable forestry
in which at least two trees are planted for each one used for paper production.
to Ren´ee, Marc and Robyn
Contents
Foreword by Keijo Palviainen xiii
Foreword by Gerry Christensen xv
Preface xvii
1 Introduction to GSM Networks 1
1.1 Signalling in GSM 3
1.2 GSM Mobility 3
1.3 Mobile Station 4
1.4 Identifiers in the GSM Network 4
1.4.1 International Mobile Subscriber Identity 4
1.4.2 Mobile Station Integrated Services Digital Network Number
(MSISDN Number) 5
1.4.3 International Mobile Equipment Identifier 6
1.4.4 Mobile Station Roaming Number 6
1.5 Basic Services 6
1.5.1 Tele Services 7
1.5.2 Bearer Services 7
1.5.3 Circuit Bearer Description 7
1.6 Supplementary Services 9
2 Introduction to Intelligent Networks 11
2.1 History of Intelligent Networks 11
2.2 Principles of Intelligent Networks 12
2.3 Service Switching Function 14
2.4 Service Control Function 15
2.5 Basic Call State Model 15
2.6 Dialogue Handling 17
2.6.1 DP Arming/Disarming Rules 17
2.6.2 Control vs Monitor Relationship 18
2.7 Evolution of the CAMEL Standard 19
2.7.1 Third-generation Partnership Project 19
2.7.2 CAMEL Standards and Specifications 21
2.8 Principles of CAMEL 22
2.8.1 Location Update Procedure 22
2.8.2 CAMEL Application Part 24
2.8.3 Abstract Syntax Notation 26
2.8.4 Application Context 28
2.9 Signalling for CAMEL 28
2.9.1 Message Transfer Part 29
viii Contents
2.9.2 Signalling Connection Control Part 29
2.9.3 Transaction Capabilities 32
2.10 Dynamic Load Sharing 34
2.11 Using Signalling Point Code for Addressing in HPLMN 35
3 CAMEL Phase 1 37
3.1 Architecture for CAMEL Phase 1 37
3.1.1 Functional Entities 37
3.1.2 Information Flows 42
3.2 Feature Description 45
3.2.1 Mobile-originated Calls 46
3.2.2 Mobile-terminated Calls 49
3.2.3 Mobile-forwarded Calls 55
3.2.4 Any-time Interrogation 62
3.3 Subscription Data 65
3.3.1 Originating CSI and Terminating CSI 66
3.4 Basic Call State Model 69
3.4.1 Originating Basic Call State Model 69
3.4.2 Terminating Basic Call State Model 70
3.4.3 Detection Points 70
3.4.4 Points in Call 72
3.4.5 BCSM State Transitions 73
3.4.6 gsmSSF Process 73
3.4.7 Tssf Timer 74
3.5 CAMEL Application Part 75
3.5.1 Initial DP 75
3.5.2 Request Report BCSM 76
3.5.3 Event Report BCSM 76
3.5.4 Continue 76
3.5.5 Connect 77
3.5.6 Release Call 78
3.5.7 Activity Test 79
3.6 Service Examples 79
3.6.1 Virtual Private Network 79
3.6.2 Pre-paid Route Home 80
3.6.3 Short Number Dialling with CLI Guarantee 82
4 CAMEL Phase 2 85
4.1 Introduction 85
4.2 Architecture 87
4.2.1 Functional Entities 87
4.2.2 Information Flows 89
4.3 Feature Description 92
4.3.1 On-line Charging Control 92
4.3.2 Call Forwarding Notifications 112
4.3.3 Follow-on Calls 117
4.3.4 User Interaction 123
4.3.5 Equal Access 139
4.3.6 Enhancement of Call Control 141
Contents ix
4.3.7 Supplementary Service Invocation Notification 144
4.3.8 Short Forwarded-to Numbers 146
4.3.9 Conditional Triggering 149
4.3.10 USSD control 154
4.4 Subscription Data 160
4.4.1 Originating CSI 161
4.4.2 Terminating CSI 161
4.4.3 Supplementary Service CSI 161
4.4.4 Translation Information Flag CSI 162
4.4.5 Unstructured Supplementary Service Data CSI 162
4.4.6 USSD Generic CSI 162
4.5 Basic Call State Model 162
4.5.1 Originating Basic Call State Model 162
4.5.2 Terminating Basic Call State Model 169
4.6 CAMEL Phase 2 Relationship 173
4.6.1 CAP v2 operations 173
4.7 Interaction with GSM Supplementary Services 174
4.7.1 Line Identification 174
4.7.2 Call Forwarding 176
4.7.3 Explicit Call Transfer 177
4.7.4 Call Waiting 178
4.7.5 Call Hold 178
4.7.6 Completion of Calls to Busy Subscribers 179
4.7.7 Multi-party 179
4.7.8 Closed User Group 180
4.7.9 Call Barring 180
4.7.10 User-to-user Signalling 181
4.7.11 Call Deflection 181
4.8 Interaction with Network Services 182
4.8.1 Basic Optimal Routing 182
4.8.2 Immediate Service Termination 184
4.8.3 Operator-determined Barring 185
4.8.4 High-speed Circuit-switched Data 185
4.8.5 Multiple Subscriber Profile 186
5 CAMEL Phase 3 187
5.1 General Third-generation Networks 187
5.1.1 UMTS Network Architecture 187
5.1.2 2G Cell Planning vs 3G Cell Planning 188
5.1.3 Location Information 189
5.1.4 Split-MSC Architecture 194
5.1.5 CAMEL Phase 3 Features 196
5.2 Call Control 196
5.2.1 Subscribed Dialled Services 196
5.2.2 Serving Network-based Dialled Services 202
5.2.3 CAMEL Control of Mobile Terminated Calls in VMSC 203
5.2.4 CAMEL Service Invocation at Call Failure 206
5.2.5 Service Interaction Control 207
5.2.6 Call Gapping 211
x Contents
5.2.7 Support of Long Forwarded-to numbers 213
5.2.8 On-line Charging Enhancements 215
5.2.9 Multiple Subscriber Profile 219
5.2.10 Other Enhancements to CAP 223
5.3 CAMEL Control of GPRS 224
5.3.1 Network Architecture 224
5.3.2 Subscription Data 228
5.3.3 GPRS State Models 229
5.3.4 CAP v3 Operations for GPRS 247
5.3.5 On-line Charging for GPRS 247
5.3.6 Quality of Service 252
5.3.7 Routing Area Update 254
5.3.8 Network-initiated PDP Context Establishment 256
5.3.9 Secondary PDP Context 256
5.3.10 Impact on CDRs 257
5.3.11 Operator-determined Barring 259
5.3.12 GPRS Roaming Scenarios 259
5.3.13 Enhanced Data Rates for GSM Evolution 260
5.4 CAMEL Control of MO-SMS 260
5.4.1 Network Architecture 261
5.4.2 CAMEL Control of MO-SMS 263
5.4.3 Subscription Data 265
5.4.4 SMS State Model 265
5.4.5 Information Flows 266
5.4.6 Information Reporting and SMS Steering 267
5.4.7 Charging and Call Detail Records 269
5.4.8 Supplementary Services and Operator-determined Barring 270
5.4.9 Service Examples 271
5.4.10 International Roaming 271
5.5 Mobility Management 273
5.5.1 Description 273
5.5.2 Subscription Data 274
5.5.3 Information Flows 275
5.5.4 Service Examples 275
5.6 CAMEL Interaction with Location Services 277
5.6.1 Description 277
5.7 Active Location Retrieval 278
5.8 Subscription Data Control 280
5.8.1 Network Architecture 281
5.8.2 Any-time Subscription Interrogation 281
5.8.3 Any-time Modification 281
5.8.4 Notify Subscriber Data Change 283
5.9 Enhancement to USSD 283
5.10 Pre-paging 284
6 CAMEL Phase 4 285
6.1 General 285
6.1.1 Specifications Used for CAMEL Phase 4 285
6.1.2 Partial CAMEL Phase 4 Support 286
Contents xi
6.2 Call Control 289
6.2.1 Basic Call State Models 290
6.2.2 Call Party Handling 290
6.2.3 Network-initiated Call Establishment 305
6.2.4 Optimal Routing of Basic Mobile-to-mobile Calls 309
6.2.5 Alerting Detection Point 310
6.2.6 Mid-call Detection Point 312
6.2.7 Change of Position Detection Point 314
6.2.8 Flexible Warning Tone 316
6.2.9 Tone Injection 317
6.2.10 Enhancement to Call Forwarding Notification 318
6.2.11 Control of Video Telephony Calls 319
6.2.12 Control of SCUDIF Calls 321
6.2.13 Reporting IMEI and MS Classmark 323
6.3 GPRS Control 324
6.4 SMS Control 325
6.4.1 Mobile-originated SMS Control 325
6.4.2 Mobile-terminated SMS Control 326
6.5 Mobility Management 331
6.5.1 Subscription Data 332
6.6 Any-time Interrogation 334
6.6.1 ATI for CS Domain 334
6.6.2 ATI for PS Domain 335
6.7 Subscription Data Control 336
6.8 Mobile Number Portability 336
6.8.1 Call Routing 337
6.8.2 MNP SRF Query by gsmSCF 340
6.8.3 Non-standard MNP Solutions 341
6.9 Control of IP Multimedia Calls 342
6.9.1 Rationale of CAMEL Control of IMS 345
6.9.2 The IM-SSF 346
6.9.3 Registration 347
6.9.4 IMS Call Control 348
6.9.5 CAMEL Application Part for IMS Control 350
6.9.6 Supported Call Cases for IMS Control 353
6.9.7 Service Example 353
7 Charging and Accounting 355
7.1 Architecture 355
7.2 Call Detail Records 355
7.2.1 Overview of Call Detail Records 356
7.2.2 CAMEL-related Parameters in CDRs 358
7.2.3 Composite CDRs 359
7.3 Transfer Account Procedure Files 359
7.4 Inter-operator Accounting of CAMEL Calls 361
7.4.1 Clearing House 365
7.4.2 CAMEL Invocation Fee 366
7.5 Correlation of Call Detail Records 366
7.5.1 Call Reference Number 367
xii Contents
7.5.2 MF Calls 368
7.5.3 SCP-initiated Calls 369
7.6 Global Call Reference 369
7.7 Call Party Handling CDRs 370
8 3GPP Rel-6 and Beyond 371
8.1 General 371
8.1.1 Capability Negotiation 372
8.2 Enhancements to 3GPP Rel-6 373
8.2.1 Enhanced Dialled Service 373
8.2.2 Handover Notification Criteria 375
8.2.3 Enhancement to SCUDIF Control 376
8.2.4 Reporting User-to-user Information 376
8.2.5 Enhancement to User Interaction 378
8.3 Enhancements to 3GPP Rel-7 379
8.3.1 Trunk-originated Triggering 379
Appendix 383
A.1 Overview of CAP Operations 383
A.2 Overview of MAP Operations 384
A.3 Overview of ISUP Messages 386
A.4 Overview of CAMEL Subscription Information 386
References 389
Abbreviations 395
Index 401
Foreword by Keijo Palviainen
In the 1990’s the INAP (Intelligent Network Application Part) protocol was the dominant IN
protocol. The INAP was mainly used in the fixed network environment and it worked well. However,
the main issue was that the INAP deployments were vendor- and operator-specific since the INAP
specification was lacking in some details. For example, many parameters are octet strings – leaving
it up to the vendor to specify the precise encoding.
The other key functionality missing from INAP was mobility. The GSM system was becoming
the dominant mobile network, and allowed for mobility between countries. The mobile operators
were now seeing a real need to provide services to their subscribers when they were roaming.
To address these needs, ETSI started a project called CAMEL in late 1995. First, someone
invented a distinctive name and then the words were filled in later. In fact, very few people
actually remember what the ‘abbreviation’ actually stands for, including myself. As a result of this
activity, CAMEL phase 1 was developed. CAMEL phase 1 is a very simple standard, but is tailored
to the GSM-based core networks. One could claim that CAMEL is a child of INAP.
The CAMEL phase 2 extended CAMEL phase 1, the main focus being prepaid services. Then
CAMEL and other GSM/UMTS works were moved to 3GPP responsibility, as the development of
the 3G network was starting to become a global exercise. CAMEL phase 3 expands the service
to include Short Message Service (SMS) as well as GPRS. Leading the pack, CAMEL phase 4 is
the most advanced of the phases. It has about the same level of functionality as the Core INAP
CS2 for fixed networks. The CAMEL phase 4 is the last CAMEL phase but it is extensible for
any enhancements. In particular, the CAMEL phase 4 Call Party Handling has raised much interest
among operators.
The original scope of CAMEL was the mobility but CAMEL has also been deployed for intranetwork use in multi-vendor cases. Its deployment has begun in the large countries, such as India,
China and the USA.
The main principle of CAMEL is that it is a toolkit that will enable many services. For example,
when standardization was working on prepaid service, it was ensured that we have toolkits for
online charging. However, nothing will now prevent us from using these tools for other services
as well.
Much effort has been put into specification and testing specification work. However, the effort
has proven to be money well spent, as CAMEL will continue to serve the circuit switched networks
for many years to come.
Keijo Palviainen
Former ETSI SMG3 WPC and 3GPP CN2 chairman.
Nokia
Foreword by Gerry Christensen
When I started my career almost 18 years ago, I never envisioned the impact that mobile communications would have on telecom, IT, and for that matter, consumer lifestyles and business as
a whole. The Yankee Group recently predicted that worldwide mobile operator revenue will reach
$698 billion by 2009 with a unique user base of 2.4 billion individuals.
The exceptional growth of the customer base and usage of mobile communications raises some
very important questions including “how will operators most cost effectively and efficiently deliver
services?” and “how will service providers leverage common infrastructure to deploy new and
innovative value-added services (VAS)?” In addition, IP Multimedia Subsystem (IMS) will have a
profound effect on service creation and delivery for all service and content providers. While not the
only answer, utilization of intelligent network technologies such as CAMEL will gain increasing
importance as a tool in the mobile operator toolkit for voice and data applications.
While most consumers’ top reasons for owning and using a cellular phone continue to be convenience and safety, most people will at least investigate new features if they add value to their daily
lives. This is critical. Service providers must create and deliver VAS that generates incremental revenue as basic voice service becomes increasingly marginalized. In addition, momentum is gaining
for wireless to be more than a medium for voice communications. The success in recent years of
mobile personalization and entertainment applications and content such as ringtones, graphics, and
games has proven the importance of non-voice applications to meet customer interests and derived
new revenue for network operators.
In the book Wireless Intelligent Networking, I predicted five years ago that the future of CAMEL
(and WIN) would be largely determined by its ability to evolve to support wireless data. The
introduction of CAMEL phase III into mobile networks is beginning to make this a reality through
its support of triggering and signalling within the core network infrastructure for SMS and GPRS
control. However, there are also many emerging voice and voice/data hybrid services. A partial
listing includes:
• Calling Name Presentation: The ability to provide the name of the calling party to the called
party, allowing the called party to decide how to handle the call (e.g. the subscriber decides
either to answer the call or let it go to voice mail). CAMEL is used to query a database that
contains name information, which allows for a network-based service rather than programming
the GSM phone to recognize caller names.
• Prepay and Account Spending Limit (ASL): Prepay and ASL utilize CAMEL to allow for
metering usage on a prepaid basis and post-paid basis respectively. ASL has applications for
those markets that are not debit based or credit-challenged but rather want to just manage usage.
Markets include parental controls and corporate resource management.
• Incoming Call Management (ICM): CAMEL is leveraged to manage call termination
attempts to customize subscriber’s inbound calling experience. The subscriber can decide how
inbound calls will be automatically managed. Features include automatic call handling (example:
route all calls except boss to voice mail for the next hour) fixed-to-mobile convergence capabilities
such as routing to mobile when a fixed network number is called.
xvi Foreword by Gerry Christensen
• Virtual Private Network (VPN): CAMEL enables a mobile VPN that replicates PBX-like
dialling in a mobile environment. For example, this (typically) group-based feature allows one to
hit the digits “2706” and then SEND to actually place a call to Gerry Christensen at 650-798-2706.
• Call Redirect Services (CRS): CAMEL is utilized to provide a variety of CRS services includ-
ing redirecting international roamers to their own customer care when they dial “611”
• Location-based Services (LBS): CAMEL has been used in the United States to support FCC
mandates for wireless emergency calling (e.g. dialling 9-1-1) from a mobile phone. CAMEL
thus allows for call control, information to be passed to databases, call assistance for routing
to a Public Safety Answer Point, and for query of LBS infrastructure such as the Gateway
Mobile Location Center (GMLC) for more precise positioning data based on A-GPS or TDOA.
Commercial (non-regulatory) LBS applications are emerging that will rely on CAMEL include
directory services and location-based search and information.
CAMEL also enables hybrid applications that allow for both voice and data interaction. For
example, CAMEL is utilized in Teleractive mobile direct response marketing applications to allow
the end-user to obtain information about products and services and to interact with brand and
advertising agencies using data, voice, or both. CAMEL enables a simple and standard user interface
for the end-user to engage in wireless data including SMS, MMS, and WAP.
An interesting thing to note is that the majority of the aforementioned services are subscriberbased and a few are group-based. This means that an end-user or group must subscribe in advance
to be able to use the service. The mobile operator customer care department processes the request
and instructs the engineering and operations department to provision the Home Location Register
(HLR). The HLR is configured to utilize CAMEL functionality to recognize triggering events that
occur typically on a per-subscriber/group, per-call basis.
CAMEL services may also be office-based, which means that any mobile phone user may use
the service, whether in their home system or while roaming, without pre-subscription. CAMEL
application triggering is based on events recognized by the Mobile Switching Center (MSC) rather
than relying on communication and instruction from the HLR/VLR to arm a trigger detection point.
For example, the Teleractive mobile direct response marketing applications are accessible to anyone
with a mobile phone that dials a particular sequence of digits that follow “**“ (example: **12345).
The MSC recognizes “**” as a trigger to formulate a CAMEL message to be sent to a Service
Control Point (SCP) for more information.
I have only scratched the surface with the few reference voice, data, and hybrid applications
discussed in this foreward. The market for voice and data services for mobile is large and growing
dramatically. Network operators, developers, service and content providers must focus on both
market needs and the most effective and efficient creation and delivery mechanisms. The importance
of CAMEL to fulfill this role cannot be ignored.
Until the availability of CAMEL: Intelligent Networks for the GSM, GPRS, and UMTS Network,
there has been no book focused specifically on CAMEL. Rogier Noldus has really nailed the
subject matter. I expect that, through use of this book, there will be more effective implementation
of CAMEL-based applications and a lot more discussion about services heretofore unimagined.
CAMEL: Intelligent Networks for the GSM, GPRS, and UMTS Network is simply a must-have
reference and instructional resource for anyone involved in planning and/or engineering applications
and services within GSM voice and data networks. We use CAMEL in our mobile direct response
marketing applications at Teleractive. I have declared Rogier’s book to be must-reading for our
engineering team.
Gerry Christensen
Chief Technology Officer
Teleractive, Inc.
Preface
This book provides an in-depth description of CAMEL. CAMEL is the embodiment of the Intelligent Networks (IN) concept, for the mobile network. The mobile networks for which CAMEL is
specified, includes the GSM Network, the GPRS Network and the UMTS Network. This book is
based mainly on the ETSI standards and the 3GPP specifications. Where appropriate, references to
input document from other organizations, such as ITU-T, ISO, IETF are also included.
This book is not a GSM tutorial. However, since CAMEL is an integral part of GSM, the first
chapter provides a rudimentary introduction into GSM. The remainder of the book will regularly
fall back on the principles presented in that chapter. It will become clear, in the subsequent chapters
of this book that CAMEL interacts mainly with the GSM Core Network (the Network Switching
Subsystem). The entities that are part of the GSM Core Network, such as MSC, HLR, will be
dealt with in detail. It should be emphasised that for general and in-depth background on GSM, a
plethora of other text books are available.
This book is meant as reference material. For people who are new to IN, chapter two provides
an introduction into IN. A brief history of IN is also included in that chapter. Chapters three to
six describe the individual CAMEL Phases, i.e. CAMEL Phase 1 up to CAMEL Phase 4. Chapter
seven describes some of the main charging principles related to CAMEL. And finally, chapter eight
gives the reader a preview of the CAMEL features that are developed in 3GPP releases Rel-6 and
Rel-7.
Few people will know the exact expansion of CAMEL: Customized Applications for Mobile
networks Enhanced Logic. The concept that CAMEL stands for, on the other hand, is now widely
known within the telecommunications industry.
The present book has grown partly out of a personal desire to spread the knowledge about
CAMEL, to those who work in the fields of Mobile Networks (GSM, GPRS, UMTS) and Intelligent
Networks. The main drive, however, is a response to the question, “Where can I read up about
CAMEL?” Hopefully, this book puts that question to rest! The present book aids those who are
busy implementing CAMEL, developing CAMEL services, evaluating CAMEL etc.
CAMEL is the result of years of standardization work by ETSI and 3GPP. CAMEL development
started in 1996, in the ETSI working groups SMG3-WPB and SMG1. I started participating in the
SMG3-WPB meetings in September 1998. At that stage, development of the CAMEL Phase 2
standard was nearing completion. A “feet first” approach to the standardization work has resulted
in years of active involvement in CAMEL development. A time which I thoroughly enjoyed.
With the finalizing of CAMEL Phase 4 in 3GPP Rel-7, the work on CAMEL may be considered
complete. CAMEL is now deployed in most regions in the world, for pre-paid, VPN and many
other services. It is expected that CAMEL will continue to serve mobile network operators for a
vast number of years.
The IP Multimedia System (IMS) is currently gaining momentum. Whereas CAMEL is grafted on
principles of the Circuit Switched (CS) technology (the “old world”), IMS is based on the Internet
Protocol (IP) and is considered to represent the “new world”. IP-based communication technology
will eventually replace CS-based communication technology, both for wireline networks and for
mobile networks. Full-scale IMS deployment within the UMTS network for speech services, will,
however, take a couple of years to materialise. There are various estimates of the exact number of
xviii Preface
years that CS will remain the dominant technology for mobile speech services. IMS and CAMEL
will co-exist for this transition period.
As goes for all major standards world wide, CAMEL is the product of a group of enthusiastic
professionals. Without the commitment of the colleagues in ETSI and 3GPP, CAMEL would not
have seen the light. It is therefore appropriate to thank those who have helped create CAMEL,
both “the workers of the first hour” and those who continued to develop the later CAMEL phases.
This group includes, in random order, Paul Martlew, Ian Park, Keijo Palviainen, Stanislav Dzuban,
Jeremy Fuller, Noel Crespi, Michel Grech, Christian Homann, Sumio Miyagawa, Ruth Jones (nee
Hewson), Veronique Belfort, Georg Wegmann, Nick Russell, Andrijana Jurisic, Angelica Remoquillo, Steffen Habermann, Isabelle Lantelme, Iris Moilanen, Kazuhiko Nakada and David Smith.
Each person brought in his or her own expertise to the group. Especially those colleagues that
were linked through the “humps” discussion group deserve special credit for their hard work on
CAMEL. The above list does not pretend to be exhaustive. Hence, credit is due also to those whose
names are not mentioned, but who have nevertheless contributed to the CAMEL standard. I also
thank Gerry Christensen for supporting me during the initial stages of this book and during the
process of writing the text. Richard Davies, from Wiley, has provided useful comments on style,
grammar and layout for the book. I also thank my Ericsson colleagues of the “CAMEL team” for
their support, expertise and commitment.
It further goes without saying that main credit is due to my wife Renee as well as to Marc
and Robyn for being without husband and dad during the many hours, days and weeks spent on
travelling and writing.
Rogier Noldus
February 2006
About the author
Rogier Noldus is senior specialist at Ericsson Telecommunicatie B.V. in Rijen, The Netherlands.
He has been actively involved in Intelligent Networks (IN) standardization for six years and has
driven the development of CAMEL within Ericsson. He advises customers worldwide about the
implementation of CAMEL and about CAMEL service development.
Rogier is currently working in the area of Service Layer (for GSM, UMTS and IMS) system
development. He has filed a large number of patent applications in the area of GSM and IN.
He holds a B.Sc. degree (electronics) from the Institute of Technology in Utrecht (The Netherlands) and a M.Sc. degree (telecommunications) from the University of The Witwatersrand (Johannesburg, South Africa). He joined Ericsson in 1996. Prior to that, he has worked for several
companies in South Africa, in the area of telecommunications.
1
Introduction to GSM Networks
Figure 1.1 is a schematic overview of the main components in a GSM network. The various
interface labels are the formal names given to these interfaces. More details about these interfaces
are found in GSM TS 03.02 [26].
The GSM network consists mainly of the following functional parts:
• MSC – the mobile service switching centre (MSC) is the core switching entity in the network.
The MSC is connected to the radio access network (RAN); the RAN is formed by the BSCs and
BTSs within the Public Land Mobile Network (PLMN). Users of the GSM network are registered
with an MSC; all calls to and from the user are controlled by the MSC. A GSM network has
one or more MSCs, geographically distributed.
• VLR – the visitor location register (VLR) contains subscriber data for subscribers registered in
an MSC. Every MSC contains a VLR. Although MSC and VLR are individually addressable,
they are always contained in one integrated node.
• GMSC – the gateway MSC (GMSC) is the switching entity that controls mobile terminating
calls. When a call is established towards a GSM subscriber, a GMSC contacts the HLR of that
subscriber, to obtain the address of the MSC where that subscriber is currently registered. That
MSC address is used to route the call to that subscriber.
• HLR – the home location register (HLR) is the database that contains a subscription record for
each subscriber of the network. A GSM subscriber is normally associated with one particular
HLR. The HLR is responsible for the sending of subscription data to the VLR (during registration)
or GMSC (during mobile terminating call handling).
• CN – the core network (CN) consists of, amongst other things, MSC(s), GMSC(s) and HLR(s).
These entities are the main components for call handling and subscriber management. Other
main entities in the CN are the equipment identification register (EIR) and authentication centre
(AUC). CAMEL has no interaction with the EIR and AUC; hence EIR and AUC are not further
discussed.
• BSS – the base station system (BSS) is composed of one or more base station controllers (BSC)
and one or more base transceiver stations (BTS). The BTS contains one or more transceivers
(TRX). The TRX is responsible for radio signal transmission and reception. BTS and BSC are
connected through the Abis interface. The BSS is connected to the MSC through the A interface.
• MS – the mobile station (MS) is the GSM handset. The structure of the MS will be described in
more detail in a next section.
A GSM network is a public land mobile network (PLMN). Other types of PLMN are the time
division multiple access (TDMA) network or code division multiple access (CDMA) network. GSM
uses the following sub-division of the PLMN:
CAMEL: Intelligent Networks for the GSM, GPRS and UMTS Network Rogier Noldus
2006 John Wiley & Sons, Ltd
2 CAMEL: Intelligent Networks for the GSM, GPRS and UMTS Network
To HLR from
other PLMN
MSC ISUP
E
HLR
D C
D
MSC
A
BSC
Abis Abis
BTS BTS
Um Um
Figure 1.1 GSM network architecture
ISUP ISUP
A
BSC
Um Um
MSMSMS
GMSC
Core
network
To/from other
network
Base station
system
Air interface
MS
• Home PLMN (HPLMN) – the HPLMN is the GSM network that a GSM user is a subscriber of.
That implies that GSM user’s subscription data resides in the HLR in that PLMN. The HLR
may transfer the subscription data to a VLR (during registration in a PLMN) or a GMSC (during
mobile terminating call handling). The HPLMN may also contain various service nodes, such as
a short message service centre (SMSC), service control point (SCP), etc.
• Visited PLMN (VPLMN) – the VPLMN is the GSM network where a subscriber is currently
registered. The subscriber may be registered in her HPLMN or in another PLMN. In the latter
case, the subscriber is outbound roaming (from HPLMN’s perspective) and inbound roaming
(from VPLMN’s perspective). When the subscriber is currently registered in her HPLMN, then
the HPLMN is at the same time VPLMN.
1
• Interrogating PLMN (IPLMN) – the IPLMN is the PLMN containing the GMSC that handles
mobile terminating (MT) calls. MT calls are always handled by a GMSC in the PLMN, regardless
of the origin of the call. For most operators, MT call handling is done by a GMSC in the HPLMN;
in that case, the HPLMN is at the same time IPLMN. This implies that calls destined for a GSM
subscriber are always routed to the HPLMN of that GSM subscriber. Once the call has arrived in
the HPLMN, the HPLMN acts as IPLMN. MT call handling will be described in more detail in
subsequent sections. When basic optimal routing (BOR) is applied, the IPLMN is not the same
PLMN as the HPLMN.
The user of a GSM network is referred to as the served subscriber ; the MSC that is serving that
subscriber is known as the serving MSC.Examplesare:
• mobile originated call – the MSC that is handling the call is the serving MSC for this call; the
calling subscriber is the served subscriber;
• mobile terminated call – the GMSC that is handling the call is the serving GMSC for this call;
the called subscriber is the served subscriber.
1
The CAMEL service requirement, GSM TS 02.78 [12] uses this strict definition. The term VPLMN is,
however, commonly used to denote any network other than the HPLMN.
Introduction to GSM Networks 3
1.1 Signalling in GSM
The various entities in the GSM network are connected to one another through signalling networks.
Signalling is used for example, for subscriber mobility, subscriber registration, call establishment,
etc. The connections to the various entities are known as ‘reference points’. Examples include:
• A interface – the connection between MSC and BSC;
• Abis interface – the connection between BSC and BTS;
• D interface – the connection between MSC and HLR;
• Um interface – the radio connection between MS and BTS.
Various signalling protocols are used over the reference points. Some of these protocols for GSM
are the following:
• mobile application part (MAP) – MAP is used for call control, subscriber registration, short
message service, etc.; MAP is used over many of the GSM network interfaces;
• base station system application part (BSSAP) – BSSAP is used over the A interface;
• direct transfer application part (DTAP) – DTAP is used between MS and MSC; DTAP is carried
over the Abis and the A interface. DTAP is specified in GSM TS 04.08 [49];
• ISDN user part (ISUP) – ISUP is the protocol for establishing and releasing circuit switched
calls. ISUP is also used in landline Integrated Services Digital Network (ISDN). A circuit is the
data channel that is established between two users in the network. Within ISDN, the data channel
is generally a 64 kbit/s channel. The circuit is used for the transfer of the encoded speech or
other data. ISUP is specified in ITU-T Q.763 [137].
When it comes to call establishment, GSM makes a distinction between signalling and payload.
Signalling refers to the exchange of information for call set up; payload refers to the data that is
transferred within a call, i.e. voice, video, fax etc. For a mobile terminated GSM call, the signalling
consists of exchange of MAP messages between GMSC, HLR and visited MSC (VMSC). The
payload is transferred by the ISUP connection between GMSC and VMSC. It is a continual aim
to optimize the payload transfer through the network, as payload transfer has a direct cost aspect
associated with it. Some network services are designed to optimize the payload transfer. One
example is optimal routing.
1.2 GSM Mobility
Roaming with GSM is made possible through the separation of switching capability and subscription
data. A GSM subscriber has her subscription data, including CAMEL data, permanently registered
in the HLR in her HPLMN. The GSM operator is responsible for provisioning this data in the HLR.
The MSC and GMSC in a PLMN, on the other hand, are not specific for one subscriber group.
The switching capability of the MSC in a PLMN may be used by that PLMN’s own subscribers,
but also by inbound roaming subscribers; see Figure 1.2.
In Figure 1.2, the GSM user who is a subscriber of PLMN-A roams to PLMN-B. The HLR in
PLMN-A transfers the user’s subscription data to the MSC in PLMN-B. The subscriber’s subscription data remains in the MSC/VLR as long as she is served by a BSS that is connected to that
MSC. Even when the user switches her MS off and then on again, the subscription data remains
in the MSC. After an extended period of the MS being switched off, the subscription data will
be purged from the MSC. When the subscriber switches her MS on again, the subscriber has to
re-register with the MSC, which entails the MSC asking the HLR in the HPLMN to re-send the
subscription data for that subscriber.
4 CAMEL: Intelligent Networks for the GSM, GPRS and UMTS Network
Transfer of subscription
data to MSC/VLR
HLR
PLMN-A
PLMN-B
MSC
MS
Subscriber roams to
other PLMN
Figure 1.2 Transfer of GSM subscription data for a roaming subscriber
MSC
When the subscriber moves from one MSC service area (MSC-1) to another MSC service area
(MSC-2), the HLR will instruct MSC-1 to purge the subscription data of this subscriber and will
send the subscription data to MSC-2.
1.3 Mobile Station
The MS, i.e. the GSM handset, is logically built up from the following components:
• mobile equipment (ME) – this is the GSM terminal, excluding the SIM card;
• subscriber identification module (SIM) – this is the chip embedded in the SIM card that identifies
a subscriber of a GSM network; the SIM is embedded in the SIM card. When the SIM card is
inserted in the ME, the subscriber may register with a GSM network. The ME is now effectively
personalized for this GSM subscriber; see Figure 1.3. The characteristics of the SIM are specified
in GSM TS 11.11. The SIM card contains information such as IMSI, advice of charge parameters,
operator-specific emergency number, etc. For the UMTS network an enhanced SIM is specified,
the universal subscriber identity module (USIM); refer 3GPP TS 31.102.
1.4 Identifiers in the GSM Network
GSM uses several identifiers for the routing of calls, identifying subscribers (e.g. for charging),
locating the HLR, identifying equipment, etc. Some of these identifiers play an important role for
CAMEL.
1.4.1 International Mobile Subscriber Identity
The international mobile subscriber identity (IMSI) is embedded on the SIM card and is used to
identify a subscriber. The IMSI is also contained in the subscription data in the HLR. The IMSI is
used for identifying a subscriber for various processes in the GSM network. Some of these are:
KPN
SIM + ME = MS
Figure 1.3 Components of the mobile station
Introduction to GSM Networks 5
Maximum 15 digits
3 digits
MCC MNC MSIN
Figure 1.4 Structure of the IMSI
2 or 3 digits
• location update – when attaching to a network, the MS reports the IMSI to the MSC, which uses
the IMSI to derive the global title (GT) of the HLR associated with the subscriber;
• terminating call – when the GSM network handles a call to a GSM subscriber, the HLR uses
the IMSI to identify the subscriber in the MSC/VLR, to start a process for delivering the call to
that subscriber in that MSC/VLR.
• roaming charging – a VPLMN uses the IMSI to send billing records to the HPLMN of
a subscriber.
Figure 1.4 shows the format of the IMSI.
• mobile country code (MCC) – the MCC identifies the country for mobile networks. The MCC is
not used for call establishment. The usage of MCC is defined in ITU-T E.212 [129]. The MCC
values are allocated and published by the ITU-T.
• mobile network code (MNC) – the MNC identifies the mobile network within a mobile country
(as identified by MCC). MCC and MNC together identify a PLMN. Refer to ITU-T E.212 [129]
for MNC usage. The MNC may be two or three digits in length. Common practice is that, within
a country (as identified by MCC), all MNCs are either two or three digits.
• mobile subscriber identification number (MSIN) – the MSIN is the subscriber identifier within
aPLMN.
The IMSI is reported to the SCP during CAMEL service invocation. The IMSI may be needed,
for example, when identifying a country; countries in North America have equal country code
(country code = 1), but different MCC (e.g. Canada = 303; Mexico = 334).
1.4.2 Mobile Station Integrated Services Digital Network Number (MSISDN Number)
The MSISDN is used to identify the subscriber when, among other things, establishing a call to that
subscriber or sending an SMS to that subscriber. Hence, the MSISDN is used for routing purposes.
Figure 1.5 shows the structure of the MSISDN.
• country code (CC) – the CC identifies the country or group of countries of the subscriber;
• national destination code (NDC) – each PLMN in a country has one or more NDCs allocated to
it; the NDC may be used to route a call to the appropriate network;
• subscriber number (SN) – the SN identifies the subscriber within the number plan of a PLMN.
CC NDC SN
1, 2 or 3 digits
Maximum 15 digits
Figure 1.5 Structure of the MSISDN
6 CAMEL: Intelligent Networks for the GSM, GPRS and UMTS Network
IMEI
IMEISV
The MSISDN is not stored on the subscriber’s SIM card and is normally not available in the
2
The MSISDN is provisioned in the HLR, as part of the subscriber’s profile, and is sent to
MS.
TAC FAC SNR
6 digits 2 digits 6 digits
TAC FAC SNR
6 digits 2 digits 6 digits 2 digits
Figure 1.6 Structure of IMEI and IMEISV
spare
igit
1d
SV
MSC during registration. The MSISDN is also reported to SCP when a CAMEL service is invoked.
One subscriber may have multiple MSISDNs. These MSISDNs are provisioned in the HLR. At
any one moment, only a single MSISDN is available in the MSC/VLR for the subscriber.
1.4.3 International Mobile Equipment Identifier
The international mobile equipment identifier (IMEI) is used to identify the ME [or user equipment
(UE) in UMTS network]. Each ME has a unique IMEI. The IMEI is hard-coded in the ME and
cannot be modified. Figure 1.6 shows the structure of the IMEI. The IMEI is not used for routing
or subscriber identification.
Refer to GSM TS 03.03 [27] for the type approval code (TAC), final assembly code (FAC)
and serial number (SNR). The software version (SV) may be included in the IMEI (‘IMEISV’) to
indicate the version of software embedded in the ME. The IMEI is always encoded as an eight-octet
string. As from CAMEL Phase 4, the IMEI(SV) may be reported to the SCP.
1.4.4 Mobile Station Roaming Number
The mobile station roaming number (MSRN) is used in the GSM network for routing a call to a
MS. The need for the MSRN stems from the fact that the MSISDN identifies a subscriber, but not
the current location of that subscriber in a telecommunications network. The MSRN is allocated to
a subscriber during MT call handling and is released when the call to that subscriber is established.
Each MSC in a PLMN has a (limited) range of MSRNs allocated to it. An MSRN may be allocated
to any subscriber registered in that MSC. The MSRN has the form of an E.164 number and can
be used by the GMSC for establishing a call to a GSM subscriber. An MSRN is part of a GSM
operator’s number plan. The MSRN indicates the GSM network a subscriber is registered in, but
not the GSM network the subscriber belongs to. Figure 1.7 shows how the MSRN is used for call
routing. The MSRN is not meant for call initiation. GSM operators may configure their MSC such
that subscribers cannot dial numbers that fall within the MSRN range of that operator.
1.5 Basic Services
All activities that may be done in the GSM network, such as establishing a voice call, establishing
a data call, sending a short message, etc., are classified as basic services. In order for a subscriber
to use a GSM basic service, she must have a subscription to that service.
2
GSM subscribers may program their MSISDN into the phone; this has, however, no significance for the
network.
3
Exceptions are Tele Service 12 (emergency call establishment) and Tele Service 23 (Cell Broadcast).
Subscribers do not need a subscription to these Tele Services to use them.
3
The handling of a basic
Introduction to GSM Networks 7
GMSCVMSC
request MSRN
incoming call
return MSRN
Figure 1.7 Usage of MSRN during call establishment to a GSM subscriber
HLR
MSRN MSISDN
service is fully standardized. Hence, a subscriber may use a basic service in any GSM network
she roams to, provided that that basic service is supported in that network. The HLR will send
a list of subscribed basic services to the MSC/VLR, during registration. When a GSM subscriber
initiates a call, the MS supplies the serving MSC with a set of parameters describing the circuitswitched connection that is requested. These parameters are the bearer capability (BC), low-layer
compatibility (LLC) and high-layer compatibility (HLC), as will be described below. The MSC
uses the BC, LLC and HLC to derive the basic service for this call. The rules for deriving the basic
service from LLC, HLC and BC are specified in GSM TS 09.07 [55]. The MSC then checks whether
the subscriber has a subscription to the requested basic service, i.e. whether the subscription data
in the VLR contains that basic service. If the service is not subscribed to, then the MSC disallows
the call. The basic service is not transported over ISUP.
When a CAMEL service is invoked, the MSC reports the requested basic service to the SCP. The
SCP may use the indication of the requested basic service for call service processing. Examples
include:
• video calls may be charged at a higher rate than speech calls;
• for data calls and fax calls, the CAMEL service shall not play any announcements or tones.
Basic services are divided into two groups: tele services and bearer services.
1.5.1 Tele Services
Table 1.1 provides an overview of the available tele services (TS); see also GSM TS 02.03 [3].
1.5.2 Bearer Services
Table 1.2 provides an overview of the available bearer services (BS). The two bearer service groups
are sub-divided into a variety of bearer services with different characteristics. Refer to GSM TS
02.02 [2].
1.5.3 Circuit Bearer Description
Bearer capability, low-layer compatibility and high-layer compatibility are descriptors of a circuitswitched (CS) connection. When a GSM subscriber initiates a call, the BC, LLC and HLC are
transported from MS to MSC over DTAP. The MSC includes the parameters in the ISUP signal to
the destination. These parameters are also reported to the SCP during CAMEL service invocation.
That enables a CAMEL service to adapt the service logic processing to the type of call. Figure 1.8
shows the relation between LLC, HLC and BC on the DTAP and the corresponding parameters
on ISUP.
8 CAMEL: Intelligent Networks for the GSM, GPRS and UMTS Network
Ta bl e 1 . 1 Tele services
Tele service Description Comment
11 Telephony This TS represents the normal speech call
12 Emergency calls The emergency call uses the characteristics of telephony
(TS11), but may be established without subscription
and bypasses various checks in the MS and in the MSC
21 Short message MT This TS relates to receiving an SMS. This TS is not sent
to the MSC/VLR. When an SMS is sent to the
subscriber, the HLR checks whether the destination
subscriber has a subscription to TS 21
22 Short message MO This TS relates to the sending of an SMS
23 Cell broadcast This TS relates to the capability of an SMS that is sent as
a broadcast SMS
61 Alternate speech and fax
group 3
This TS relates to the capability to establish a speech and
fax (group 3) call
62 Automatic fax group 3 This TS relates to the capability to establish a fax (group
3) call
91 Voice group call This TS relates to the capability to participate in a group
call as specified in GSM TS 03.68 [35]
92 Voice broadcast This TS relates to the capability to receive a voice
broadcast as specified in GSM TS 03.68 [35]
Ta bl e 1 . 2 Bearer services
Tele service Description Comment
20 Asynchronous data
bearer services
30 Synchronous data
bearer services
DTAP
(GSM TS 04.08)
Low layer compatibility
High layer compatibility
Bearer capability
May be used for asynchronous services from 300 bit/s
to 64 kbit/s.
May be used for synchronous services from 1.2 to
64 kbit/s. This BS may be used, amongst other things,
for multimedia services such as video telephony.
MSC
Access transport [low l ayer compatibility]
User teleservice information
User service information
ISUP
(ITU-T Q.763)
4
Figure 1.8 Transfer of LLC, HLC and BC through DTAP and ISUP
• Low-layer compatibility – the LLC is transported transparently between the calling entity and
called entity; it may be used by the respective entities to adapt codecs for interworking purposes.
LLC describes mainly characteristics related to the data transfer.
4
3GPP Rel-7 may include a dedicated bearer service for video telephony.
Introduction to GSM Networks 9
• High-layer compatibility – the HLC is also transported transparently between the calling entity
and called entity; it is used to describe the requested service, such as telephony, Fax, video
telephony, etc.
• Bearer capability – the BC describes the characteristics of the 64 kbit/s circuit requested for
the call.
1.6 Supplementary Services
Supplementary services (SS) in GSM are a means of enriching the user experience. An SS may,
for example, forward a call in the case of no reply from the called party, bar certain outgoing or
incoming calls, show the number of the calling party to the called party, etc. In order to use an
SS, a GSM user needs a subscription to that SS. The subscription to supplementary services is
contained in the HLR and is sent to the MSC/VLR during registration. The supplementary services
are fully standardized. A GSM subscriber can therefore use her supplementary services in any GSM
network, provided that the network supports these supplementary services, and have the same user
experience.
Ta bl e 1 . 3 GSM supplementary services
SS group Supplementary services GSM TS
Line identification Calling line identification presentation (CLIP) 02.81 [13]
Calling line identification restriction (CLIR)
Connected line presentation (COLP)
Name identification Calling name presentation (CNAP) 02.96 [24]
Call forwarding Call forwarding – unconditional (CFU) 02.82 [14],
Call offering Explicit call transfer (ECT) 02.91 [22]
Call completion Call waiting (CW) 02.83 [15],
Multi-party Multi-party call (MPTY) 02.84 [16]
Community of interest Closed user group (CUG) 02.85 [17]
Charging Advice of charge – information (AOCI) 02.86 [18]
Additional information transfer User-to-user signalling – service 1 (UUS1) 02.87 [19]
Call barring Barring of all outgoing calls (BAOC) 02.88 [20]
Call priority enhanced multi-level precedence and pre-emption
Connected line restriction (COLR)
Call forwarding – busy (CFB)
Call forwarding – no reply (CFNRY)
Call forwarding – not reachable (CFNRC)
Call deflection (CD) 02.72 [11]
Call hold (CH)
Call completion to busy subscriber (CCBS) 02.93 [23],
Multi-call (MC) 22.135 [69]
Advice of charge – charge (AOCC)
User-to-user signalling – service 2 (UUS2)
User-to-user signalling – service 3 (UUS3)
Barring of outgoing international calls (BOIC)
Barring of outgoing international calls except to the
home country (BOIC-exHc)
Barring of all incoming calls (BAIC)
Barring of all incoming calls when roaming
(BICROAM)
02.67 [10]
(eMLPP)
a
a
For the multi-call service, there is no GSM TS available, but only a 3GPP TS (22.135).
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