Tài liệu IMS Application Developer’s Handbook Creating and Deploying Innovative IMS Applications ppt

IMS Application

Developer’s Handbook

Creating and Deploying

Innovative IMS Applications

Rogier Noldus

Ulf Olsson

Catherine Mulligan

Ioannis Fikouras

Anders Ryde

Mats Stille

AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD

PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO

Academic Press is an imprint of Elsevier

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First published 2011

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11 12 13 14 10 9 8 7 6 5 4 3 2 1

iii

Contents

Foreword ................................................................................................................................................ xi

Preface ................................................................................................................................................. xiii

Acknowledgements .............................................................................................................................. xvi

About the Authors ............................................................................................................................... xvii

CHAPTER 1 Introduction ................................................................................. 1

1.1 Why Was IMS Developed? .......................................................................................... 1

1.2 Observations ................................................................................................................ 2

1.3 Network Vision: Enable and Simplify ......................................................................... 2

1.3.1 Billions of Mobile Handsets ............................................................................... 4

1.3.2 The Multi-Talented Mobile Handset ................................................................... 5

1.3.3 Extending Existing Behavior .............................................................................. 6

1.3.4 Voice-Over IP Over Broadband .......................................................................... 6

1.3.5 The Mobile Phone, Boosted................................................................................ 8

1.4 IMS Architecture for Those That Don’t Need to Know ..............................................9

1.4.1 Services ............................................................................................................. 12

1.4.2 The Home Network Concept ............................................................................ 12

1.4.3 The Residential Opportunity ............................................................................. 13

1.4.4 The Enterprise Opportunity .............................................................................. 13

1.5 Setting the Scene: The Story So Far .......................................................................... 14

1.5.1 IMS VoIP on Existing IP Networks .................................................................. 14

1.5.2 Rich Communication Suite (RCS) .................................................................... 14

1.5.3 Push-to-Talk ...................................................................................................... 15

1.6 Doing Useful Work: The Service Story .....................................................................15

1.6.1 The Communication Service Layer .................................................................. 17

1.6.2 IMS and Web 2.0 .............................................................................................. 20

1.7 The Concept Applied ................................................................................................. 21

1.8 Multimedia Telephony ............................................................................................... 21

1.8.1 Multimedia Telephony: What Is It? .................................................................. 22

1.8.2 Why MMTel – What are the Driving Requirements? ....................................... 23

1.8.3 Multimedia Telephony: The Origins ................................................................. 25

1.9 Summary .................................................................................................................... 26

CHAPTER 2 Business Modeling for a Digital Planet ........................................ 27

2.1 Introduction ................................................................................................................ 27

2.2 Basic Economic Concepts for Developers ................................................................. 27

2.2.1 Economies of Scale ........................................................................................... 27

2.2.2 Transaction Costs .............................................................................................. 28

2.2.3 Open APIs and Transaction Costs ..................................................................... 28

2.2.4 Factors of Production ........................................................................................32

iv Contents

2.2.5 Capital Goods Software .................................................................................... 32

2.2.6 Consumer Goods Software ............................................................................... 33

2.3 Value Creation and Capture in Modern Communications Industries ........................ 33

2.3.1 The Role of the Individual in a Digital World .................................................. 35

2.3.2 The Mobile Broadband Platform ......................................................................37

2.4 The Business Case for IMS ....................................................................................... 38

2.4.1 Global Interoperable Standards – a Developer’s View ..................................... 39

2.4.2 Regulation and the Right to Private Communications ...................................... 41

2.5 Business Models for a Digital Planet ......................................................................... 42

2.6 Toward a Diagramming Technique ............................................................................ 44

2.7 Practical Examples – Application to IMS .................................................................. 47

2.8 Conclusions ................................................................................................................ 48

CHAPTER 3 Service Deployment Patterns ....................................................... 49

3.1 Introduction ................................................................................................................ 49

3.2 Back to Basics ............................................................................................................50

3.3 Client-Side Application ............................................................................................. 51

3.4 Server-Side End-Point Application ............................................................................ 51

3.5 Web Server-Side End-Point Application ................................................................... 52

3.6 Web Client-Side End-Point Application .................................................................... 53

3.7 Mid-Point Application ............................................................................................... 55

3.8 Client-Side Application, Building on a Standardized Service ...................................56

3.9 To-Do List .................................................................................................................. 57

3.10 Summary .................................................................................................................... 58

CHAPTER 4 Applications in the IP Multimedia Subsystem ............................... 59

4.1 Introduction ................................................................................................................ 59

4.2 IMS Service Creation ................................................................................................ 60

4.2.1 Service Composition ........................................................................................60

4.2.2 Composition Through Chaining ....................................................................... 61

4.2.3 IMS Service Chaining Architecture .................................................................. 62

4.3 IMS Service Composition .......................................................................................... 64

4.3.1 Initial Filter Criteria .......................................................................................... 64

4.3.2 Two-Tier Composition and the Service Capability Interaction Manager ......... 65

4.3.3 Unifi ed Web Services and IMS Composition ................................................... 67

4.3.4 Next-Generation Intelligent Networks and Migration to IMS ......................... 68

4.4 IMS Application Servers ............................................................................................ 69

4.4.1 The Converged SIP Servlet Container .............................................................. 69

4.4.2 SIP Application Types ......................................................................................75

4.4.3 SIP Application Composition in JSR116 .........................................................77

4.5 Conclusions ................................................................................................................ 80

Contents v

CHAPTER 5 Service Development .................................................................. 81

5.1 Virtual Call Center Use-Case .....................................................................................82

5.1.1 Use-Case Architecture ...................................................................................... 83

5.1.2 Use-Case Business Logic .................................................................................83

5.1.3 Constituent SIP Applications ............................................................................ 87

5.2 Web-Based Do-Not-Disturb Use-Case ...................................................................... 93

5.2.1 Use-Case Architecture ...................................................................................... 93

5.2.2 Constituent Components ..................................................................................95

5.2.3 Use-Case Business Logic ................................................................................. 98

5.2.4 AJAX/SIP Interaction ..................................................................................... 102

5.3 Conclusions ..............................................................................................................104

CHAPTER 6 Introduction to IP-Based Real-Time Communications .................. 105

6.1 Introduction .............................................................................................................. 105

6.2 Basics of Voice Over IP ........................................................................................... 105

6.2.1 Digital Speech Transmission .......................................................................... 105

6.2.2 OSI Reference Model .....................................................................................109

6.2.3 Data Transmission Using the Real-time Transport Protocol .......................... 111

6.2.4 Real-time Transport Control Protocol ............................................................ 118

6.2.5 Control Plane Versus User Plane .................................................................... 118

6.2.6 Multi-Party Communication Session .............................................................. 129

6.3 Registration .............................................................................................................. 130

6.3.1 Initial Registration and Call Establishment .................................................... 133

6.3.2 De-registration ................................................................................................ 136

6.3.3 Re-registration ................................................................................................ 136

6.3.4 Mobility Versus Nomadicity ........................................................................... 137

6.4 Locating the Registrar .............................................................................................. 137

6.5 Registration Relationships .......................................................................................141

6.5.1 Subscriber Administered in VoIP Network, but Currently not Registered ..... 141

6.5.2 Subscriber Administered in VoIP Network and Currently Registered............ 142

6.6 Network Domains .................................................................................................... 142

CHAPTER 7 Introduction to Session Initiation Protocol ................................. 145

7.1 Introduction .............................................................................................................. 145

7.2 The SIP Standard ..................................................................................................... 145

7.3 SIP Session Versus Media Session .......................................................................... 145

7.4 SIP Transaction Model ............................................................................................ 147

7.4.1 Command Sequence .......................................................................................152

7.5 SIP Transaction State Models .................................................................................. 154

7.6 Proxy Roles ..............................................................................................................157

7.6.1 Stateless Proxy ................................................................................................ 158

vi Contents

7.6.2 Stateful Proxy ................................................................................................. 158

7.6.3 Back-to-Back User Agent ............................................................................... 160

7.7 SIP Session Establishment ....................................................................................... 161

7.7.1 Request Message ............................................................................................ 162

7.7.2 Response Message .......................................................................................... 163

7.7.3 Initial Request Message Routing .................................................................... 163

7.7.4 Response Message Routing ............................................................................ 168

7.7.5 Building an SIP Routing Path for Subsequent SIP Requests ......................... 173

7.7.6 Exchanging Contact Addresses for Subsequent SIP Requests ....................... 179

7.7.7 Subsequent Request Message Routing ........................................................... 181

7.8 SIP Transport Considerations .................................................................................. 183

7.8.1 Internal DNS Versus External DNS ................................................................ 185

7.8.2 Reliability of SIP Requests and SIP Responses ............................................. 185

7.9 Canceling a SIP Transaction Request ...................................................................... 194

7.10 SIP Dialogs .............................................................................................................. 197

7.10.1 Multiple Early Dialogs ................................................................................. 201

7.10.2 Target Set ...................................................................................................... 205

7.10.3 Early Media .................................................................................................. 206

7.11 Media Transmission: Offer–Answer Model ............................................................ 209

7.11.1 A Closer Look at the SDP Structure ............................................................. 215

7.11.2 Some SDP Examples .................................................................................... 219

CHAPTER 8 Introduction to the IMS Network ................................................ 223

8.1 Introduction .............................................................................................................. 223

8.2 Overview of IMS Standards and Releases ............................................................... 223

8.3 IMS Network Architecture – A Global View ........................................................... 224

8.3.1 IMS Core Network ......................................................................................... 227

8.3.2 IMS Access Network ...................................................................................... 229

8.4 IMS Network Architecture – A Closer Look ........................................................... 232

8.4.1 Core Network Entities .................................................................................... 232

8.4.2 Network Border Gateway Nodes ....................................................................242

8.5 Registration ..............................................................................................................249

8.5.1 Registration Relationships .............................................................................. 259

8.5.2 Periodic Re-Registration and De-Registration ............................................... 260

8.5.3 Implicit Registration Set ................................................................................. 262

8.5.4 Third-party Registration ................................................................................. 266

8.5.5 Application-initiated Registration ................................................................... 268

8.6 Session Establishment ............................................................................................. 270

8.6.1 Media Gating .................................................................................................. 284

8.7 Using Phone Numbers ............................................................................................. 285

8.7.1 Number Normalization ................................................................................... 286

8.7.2 ENUM Query ................................................................................................. 288

Contents vii

8.7.3 Public ENUM versus Carrier ENUM ............................................................. 290

8.7.4 Phone Number Representation Through SIP URI .......................................... 291

8.8 Application Servers in IMS ..................................................................................... 292

8.8.1 Introduction and Concept ............................................................................... 292

8.8.2 The ISC Reference Point ................................................................................ 294

8.8.3 Service Chaining ............................................................................................ 298

8.8.4 SIP-AS as Proxy, B2BUA, UAC, or UAS ...................................................... 300

8.8.5 Public Services ............................................................................................... 304

8.8.6 Service-initiated Session Establishment ......................................................... 312

8.8.7 User Interaction .............................................................................................. 316

8.8.8 Unregistered Service Invocation ..................................................................... 320

8.9 Messaging in IMS .................................................................................................... 324

8.9.1 Instant Message .............................................................................................. 325

8.9.2 Messaging Session .......................................................................................... 328

CHAPTER 9 MMTel and Other IMS Enablers ................................................. 329

9.1 Introduction .............................................................................................................. 329

9.2 A More In-Depth Look into MMTel........................................................................ 329

9.3 Basic MMTel Architecture ....................................................................................... 330

9.4 Going Deeper and Wider ......................................................................................... 331

9.5 Adding to MMTel ....................................................................................................334

9.5.1 ISC Chaining .................................................................................................. 334

9.5.2 Northbound Interface ...................................................................................... 335

9.5.3 Forwarding to Extension Logic ...................................................................... 335

9.5.4 Web Interfaces on the Client Side ................................................................... 336

9.6 Use-Case: Calendar-Based Routing ......................................................................... 336

9.7 IMS Presence ...........................................................................................................337

9.7.1 Presence as Defi ned by OMA ......................................................................... 338

9.7.2 Interacting with the Presence System ............................................................. 340

9.7.3 The Presentity Data Model ............................................................................. 343

9.7.4 XDM Data Management ................................................................................345

9.8 Finding the right devices .......................................................................................... 346

9.9 Conclusion ............................................................................................................... 349

CHAPTER 10 Charging .................................................................................. 351

10.1 Introduction .............................................................................................................. 351

10.2 Obvious and Not So Obvious Ways of Getting Paid ............................................... 352

10.3 Money Makes the App Go Around ..........................................................................352

10.3.1 Selling to the End-user Through a Store ...................................................... 352

10.3.2 Selling Over and Over Again ........................................................................ 353

10.3.3 Pay-per-use ................................................................................................... 354

10.3.4 Advertising .................................................................................................... 354

viii Contents

10.3.5 Letting Someone Else do the Heavy Lifting ................................................355

10.3.6 Sell Something Else ...................................................................................... 356

10.3.7 Count on your Fellow Man ........................................................................... 356

10.3.8 Benefi t in an Entirely Different Dimension .................................................. 356

10.4 The Mechanics of Charging ..................................................................................... 357

10.4.1 Offl ine Charging ........................................................................................... 358

10.4.2 Online Charging ........................................................................................... 359

10.5 Summary .................................................................................................................. 362

CHAPTER 11 Interworking with Legacy Networks ........................................... 363

11.1 Introduction .............................................................................................................. 363

11.2 The Bigger Picture – Connecting IMS to the Outside World ..................................363

11.3 Interworking Through MGCF and IM-MGW ......................................................... 365

11.3.1 General ......................................................................................................... 365

11.3.2 Protocol Mapping ......................................................................................... 367

11.3.3 MGCF SIP Signaling Capability .................................................................. 371

11.3.4 User-plane Interworking ............................................................................... 376

11.4 Video Interworking .................................................................................................. 378

11.5 Supplementary Service Interworking ...................................................................... 380

11.5.1 Calling Line Presentation and Calling Line Presentation Restriction .......... 382

11.5.2 Connected Line Presentation and Connected Line Presentation

Restriction .....................................................................................................383

11.5.3 Call Hold and Resume ..................................................................................386

11.5.4 Call Forwarding ............................................................................................ 388

11.6 Applying Legacy VAS in the IMS Network ............................................................ 389

11.6.1 The Starting Point: VAS in the CS Network and VAS in the

IMS Network ................................................................................................ 389

11.6.2 The Challenge: Safeguarding Legacy VAS Investment ................................393

11.6.3 Service Capability Interaction Manager ....................................................... 399

CHAPTER 12 Rich Communication Suite ........................................................ 401

12.1 Introduction .............................................................................................................. 401

12.2 The Basics of RCS ................................................................................................... 402

12.2.1 What is RCS? ................................................................................................ 402

12.2.2 Why RCS? .................................................................................................... 402

12.3 Overview of RCS Release Functionality ................................................................. 404

12.4 RCS Release 1 ......................................................................................................... 405

12.4.1 Enriched Call ................................................................................................ 406

12.4.2 Enhanced Messaging .................................................................................... 414

12.4.3 Enriched Phone Book ................................................................................... 417

12.5 RCS Release 2 .........................................................................................................418

12.5.1 Broadband Access ........................................................................................ 418

12.5.2 Multi-Device Environment ........................................................................... 419

Contents ix

12.5.3 Enriched Call – Multi-Device ....................................................................... 419

12.5.4 Network Address Book ................................................................................. 420

12.5.5 RCS Provisioning ......................................................................................... 420

12.6 RCS Release 3 .........................................................................................................421

12.7 RCS Release 4 ......................................................................................................... 422

12.8 RCS-e ....................................................................................................................... 423

12.8.1 Capability Discovery in RCS-e ....................................................................424

12.9 Using RCS Applications to Capture Value .............................................................. 425

12.10 Conclusions .............................................................................................................. 430

CHAPTER 13 Evolved IP Multimedia Architecture and Services ....................... 431

13.1 Introduction .............................................................................................................. 431

13.2 Overview of the Evolved IMS Architecture ............................................................ 431

13.3 GSMA VoLTE – IMS Profi le for Voice and SMS .................................................... 432

13.4 VoLTE Considerations for Service Designers ......................................................... 436

13.5 Single Radio Voice Call Continuity (SRVCC) ........................................................ 436

13.5.1 SRVCC Architecture in 3GPP Release 9 ...................................................... 437

13.5.2 SRVCC High-Level Use-case Explained ..................................................... 438

13.5.3 SRVCC Architecture in 3GPP Release 10 .................................................... 440

13.6 IMS Centralized Services (ICS) ..............................................................................441

13.6.1 ICS Solution with Evolved MSC .................................................................. 443

13.6.2 ICS Solution Using Existing ISUP/Mg and CAMEL .................................. 444

13.6.3 Terminating Access Domain Selection (T-ADS) .......................................... 445

13.7 SRVCC and ICS Considerations for Service Designers .......................................... 445

CHAPTER 14 Future Outlook: Market and Technology ..................................... 449

14.1 What is Next in Store for IMS? ............................................................................... 449

14.2 TV ............................................................................................................................ 449

14.3 Smart Pipes .............................................................................................................. 449

14.4 Home Networks ....................................................................................................... 450

14.5 Web Clients .............................................................................................................. 450

14.6 Machine to Machine (M2M) ................................................................................... 450

14.7 Vehicle Automation ................................................................................................. 450

14.8 WAC and Other App Stores ..................................................................................... 450

14.9 Secure, Non-Anonymous Comms: The Alternative Network .................................451

14.10 Conclusion ............................................................................................................... 451

References ........................................................................................................................................... 453

Abbreviations ...................................................................................................................................... 455

Index ...................................................................................................................................................463

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xi

Foreword

IMS – the IP Multimedia Subsystem of the 3GPP family of telecommunication standards –

may very well be at the same time the worst and the best kept secret of the telecom world.

“Secret” because it is essentially designed to be invisible – the modern version of the infra￾structure that delivers communication to the world. “Worst kept” because it has dominated

the strategies for communication evolution in the past years, and has thus been very vis￾ible, at least to those in the industry. And fi nally “best kept”, as it is right now sneaking

up to become the key technology it was built to be, with the advent of new personal com￾munication concepts like RCS (Rich Communication Suite) and the way IMS will provide

telephony services to the emerging LTE radio standard (the VoLTE initiative). Thus, tel￾ecommunication is now fully transforming itself into IP-based technology. In order to do

this, some basic capabilities from the classical technology space needed to be provided, such

as interoperability between peer communications providers. IMS was designed to ensure

such interoperability, hinting that the “M” in IMS could just as well be interpreted as multi￾operator. It doesn’t stop there: IMS is also multi-access and multi-device. Interestingly, as

this book shows, it is also multi-service: IMS provides the infrastructure to build and deliver

all kinds of interesting, useful user features, with the added benefi t of potential worldwide

interoperability.

Traditionally, the focus of technology vendors has been on how to build the actual net￾works and the standard services that run in and on them. The view from the outside, as seen

by a software developer or service provider, has been harder to fi nd. The time has come to

change this, as the industry – and essentially not just the telecom industry, but the whole

converging information and communication technology space – is going through a game￾changing phase. With the advent of open APIs and the new way of creating software that we

see emerging, where it is natural to build new capabilities by creatively using and com bining

existing assets, a new way of approaching IMS is becoming apparent. With this developer￾oriented mindset, the important issues are not so much how you go about building an effi -

cient IMS network, but rather how you can use what it provides with minimum effort and

maximum effi ciency; i.e. the things a developer should have to know in order to build some￾thing useful and profi table should be exactly what he or she needs to know – hiding the

details and providing the right abstractions is the key property here, in addition to all the

classical attributes like performance, availability, and robustness.

Therefore, the book you have before you right now is a very timely contribution to the

IMS community, aiming to give the developer an outside-in view: how applications interact

with the IMS network, which of the inner workings you need to know about, how IMS can

support your business model, and also – unusually for this kind of text, but very interesting

reading for those of us who do not spend much of our time thinking about what we do in the

language of economics – how IMS and the application ecosystem around it can be described

in terms that business school graduates might want to use.

xii Foreword

To summarize: in the following pages you will hopefully fi nd information that will help

you design your services and bring them to market. I look forward to being amazed and

amused by your creative new IMS-based applications!

Håkan Eriksson, CTO Ericsson Group

San Jose, February 2011

Telephony has been with us for over a century and we have been awaiting the dawn of a

new age of multimedia communications for many years. That wait is fi nally over. IMS,

the IP Multimedia Subsystem defi ned by 3GPP, is set to revolutionize the communications

world. Originally defi ned almost a decade ago, we are fi nally seeing a broader deployment

from fi xed and cable operators and of course mobile operators, spurred on by the commer￾cial launch of LTE and by initiatives such as the GSMA’s own Rich Communication Suite

(RCS). Not only will RCS provide a wealth of interoperable multimedia capabilities for per￾son-to-person communication across device and network boundaries, but it will also provide

a range of new APIs to developers, to embed those capabilities into their own applications.

This is a multifaceted and complex topic, covering protocols, devices, and of course the

all-important applications. Getting to grips with IMS is not for the faint hearted and that

is why a book such as this one is essential. Written by seasoned industry professionals, it

serves as an accessible introduction to the subject for beginners, as well as a reference work,

for those already engaged in the development of multimedia services and applications.

Alex Sinclair, CTO GSM Association

London, UK, February 2011

xiii

Preface

THE REASONING BEHIND THIS BOOK

Many books have been written about IMS, so why do we think another is needed? Most of

the existing books are written from the perspective of those who implement the technology,

either network vendors or operators. There is no such focus for developers. The standards

that form the basis of IMS are complex – as they are designed to solve complex problems –

and require specialized knowledge to understand. Developing services and applications on

IMS requires a different set of skills and knowledge, however, and these are generally over￾looked in existing books. This book covers these aspects, from creating small applications to

utilizing the full features of IMS Communication Services and RCS.

This is a unique IMS book, therefore, written not from the perspective of building an

IMS system, but from using it to create new and interesting services. We base this on many

years of practical engineering experience, pointing out the important bits as we go along so

you can avoid getting lost in the detail. This includes a walk-through of the IMS infrastruc￾ture, but in a novel way: starting from fi rst principles, then gradually introducing the core

concepts. We also provide examples of how services are built: general service composition

principles as well as standard services like Multimedia Telephony, and industry standard

service profi les like Rich Communication Suite (RCS).

READER’S GUIDE

In order to help you focus on your particular interests, this list of chapters describes what

subjects are respectively covered:

Block 1: The Context

1. Introduction. Some of the background and the basic concepts. Includes a brief intro￾duction to what is potentially the most commercially important IMS service: Multimedia

Telephony.

2. IMS and business modeling for a digital planet. The business context. This is a rather

unorthodox chapter for a book like this, but the value it brings is that it provides some eco￾nomic theory and practice. This is very useful in building more understanding of IMS as a

way of supporting – and sometimes driving – current changes in the business landscape.

Block 2: The Service Developer View

3. Service delivery deployment patterns. Describes a number of answers to the question,

“Where does an application connect to the IMS infrastructure?” Applications attach to

the IMS at different points; APIs and platforms depend heavily on where your app is.

xiv Preface

4. Applications in the multimedia subsystem. Basic principles for server-side applica￾tion creation. This section gives an overview of modern service composition as applied

to IMS/SIP-based applications.

5. Service development. Some concrete examples of how applications can be structured,

applying the principles from Chapter 4 in practice.

Block 3: How IMS Works

6. Introduction to IP-based real-time communications. Building the architecture from

the ground up. The chapters in this block are a bit more technical; in Chapter 6 we dis￾cuss the general technologies needed to deliver media streams over digital networks.

7. Introduction to Session Initiation Protocol. What you need to know about SIP.

Building on Chapter 6, it discusses how SIP provides the necessary control capabilities.

8. Introduction to IP Multimedia Subsystem. How IMS puts SIP and other protocols into

an architecture. This is where it all comes together: the logical entities in an IMS net￾work, why they are there, and what they do.

9. Multimedia Telephony and other IMS enablers. A brief description of some of the

key services that IMS supports. Part of the chapter describes how the IMS service archi￾tecture is applied to produce standardized services; another part shows how those stand￾ardized services can be extended.

10. Charging. How to make money out of IMS-based services. The basic scenarios are laid

out, and an overview is given of how IMS charging mechanisms work.

Block 4: IMS Deployment and Evolution

11. Interworking with legacy networks and services. How does IMS interconnect with

the existing telecom world? This is one of the key differentiating properties of IMS; it is

designed from the ground up to work with existing networks.

12. Rich Communication Suite. RCS packages a set of IMS-based services to provide a

rich user experience. RCS terminals and systems are being deployed as this is written;

thus, it provides a good starting point for the introduction of new services building on

the same enablers as for RCS.

13. Evolved IP multimedia architecture and services. This chapter is aimed at explaining

the main new concepts and evolution of IMS supporting mobile telephony evolution.

The intent is that it should provide background and create awareness of how value￾added service developers need to understand this evolution.

14. Future outlook: Market and technology. Some fi nal notes on where IMS might be going.

Depending on your viewpoint and needs, you may want to approach this book from dif￾ferent angles. Feel free to read it as you please, but we would like to suggest a couple of

selections from the menu. If you are interested in:

● A general overview of the technology, see Chapters 1, 3, 4, and 12.

● Mainly the business aspects, see Chapters 1, 2, 3, and 10.