The 3G IP Multimedia Subsystem (IMS) E-Book

Gonzalo Camarillo

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 952

Veröffentlichungsjahr: 2011

Beschreibung

Third edition of this best-selling guide to IMS: fully revised, and updated with brand new material

The IMS (IP Multimedia Subsystem) is the technology that merges the Internet with the cellular world. It makes Internet technologies such as the web, email, instant messaging, presence, and videoconferencing available nearly everywhere at any time.

The third edition of this bestselling book is fully updated and provides comprehensively expanded content, including new chapters on emergency calls and on Voice Call Continuity (VCC). As well as this, The 3G IP Multimedia Subsystem (IMS) presents updated material including a comprehensive picture of Session Initiation Protocol (SIP) as well as its applicability to IMS. As most of the protocols have been designed in the IETF, this book explains how the IETF developed these protocols and describes how these protocols are used in the IMS architecture.

This is an indispensable guide for engineers, programmers, business managers, marketing representatives and technically aware users who want to understand how the IMS works and explore the business model behind it.

• New chapters on emergency calls, Voice Call Continuity (VCC), service configuration (XCAP, XDM), and conferencing
• Fully updated throughout, including Policy and Charging Control (PCC), QoS, Presence, Instant Messaging, Multimedia Telephony Services, and Push-to-talk over Cellular (PoC)
• Describes the IP Multimedia Subsystem from two different perspectives: from the IETF perspective, and from the 3GPP perspective.
• Provides details on the latest policy technology and security architecture
• Written by experienced professionals in the field.

Leseprobe

Contents

Foreword by Stephen Hayes

Foreword by Allison Mankin and Jon Peterson

About the Authors

Preface to the Third Edition

Preface to the Second Edition

Preface to the First Edition

Acknowledgements

Part I Introduction to the IMS

Chapter 1 IMS Vision: Where Do We Want to Go?

1.1 The Internet

1.2 The Cellular World

1.3 Why do we need the IMS?

1.4 Relation between IMS and non-IMS Services

Chapter 2 The History of the IMS Standardization

2.1 Relations between IMS-related Standardization Bodies

2.2 Internet Engineering Task Force

2.3 Third Generation Partnership Project

2.4 Third Generation Partnership Project 2

2.5 IETF-3GPP/3GPP2 Collaboration

2.6 Open Mobile Alliance

Chapter 3 General Principles of the IMS Architecture

3.1 From Circuit-switched to Packet-switched

3.2 IMS Requirements

3.3 Overview of Protocols used in the IMS

3.4 Overview of IMS Architecture

3.5 Identification in the IMS

3.6 SIM, USIM, and ISIM in 3GPP

3.7 Next Generation Networks (NGN)

Part II The Signaling Plane in the IMS

Chapter 4 Session Control on the Internet

4.1 SIP Functionality

4.2 SIP Entities

4.3 Message Format

4.4 The Start Line in SIP Responses: the Status Line

4.5 The Start Line in SIP Requests: the Request Line

4.6 Header Fields

4.7 Message Body

4.8 SIP Transactions

4.9 Message Flow for Session Establishment

4.10 SIP Dialogs

4.11 Extending SIP

4.12 Caller Preferences and User Agent Capabilities

4.13 Reliability of Provisional Responses

4.14 Preconditions

4.15 Event Notification

4.16 Signaling Compression

4.17 Content Indirection

4.18 The REFER Method

4.19 Globally Routable User Agent URIs (GRUU)

4.20 NAT Traversal

Chapter 5 Session Control in the IMS

5.1 Prerequisites for Operation in the IMS

5.2 IPv4 and IPv6 in the IMS

5.3 IP Connectivity Access Network

5.4 P-CSCF Discovery

5.5 IMS-level Registration

5.6 Subscription to the reg Event State

5.7 Basic Session Setup

5.8 Application Servers: Providing Services to Users

5.9 Changes due to Next Generation Networks (NGN)

5.10 Interworking

5.11 Combinational Services

5.12 Basic Sessions Not Requiring Resource Reservation

5.13 Globally Routable User Agent URIs (GRUU) in IMS

5.14 IMS Communication Service Identifier (ICSI)

5.15 IMS Application Reference Identifier (IARI)

5.16 NAT Traversal in the IMS

Chapter 6 AAA on the Internet

6.1 Authentication, Authorization, and Accounting

6.2 AAA Framework on the Internet

6.3 The Diameter Protocol

Chapter 7 AAA in the IMS

7.1 Authentication and Authorization in the IMS

7.2 The Cx and Dx Interfaces

7.3 The Sh Interface

7.4 Accounting

Chapter 8 Policy and Charging Control in the IMS

8.1 PCC Architecture

8.2 Charging Architecture

8.3 Offline Charging Architecture

8.4 Online Charging Architecture

Chapter 9 Quality of Service on the Internet

9.1 Integrated Services

9.2 Differentiated Services

Chapter 10 Quality of Service in the IMS

10.1 Policy Control and QoS

10.2 Instructions to Perform Resource Reservations

10.3 Reservations by the Terminals

10.4 QoS in the Network

Chapter 11 Security on the Internet

11.1 HTTP Digest Access Authentication

11.2 Certificates

11.3 TLS

11.4 S/MIME

11.5 Authenticated Identity Body

11.6 IPsec

11.7 Privacy

11.8 Encrypting Media Streams

Chapter 12 Security in the IMS

12.1 Access Security

12.2 Network Security

Chapter 13 Emergency Calls on the Internet

13.1 Introduction

13.2 Location Acquisition

13.3 Identifying Emergency Calls

13.4 Locating the Closest PSAP

13.5 Issuing the Emergency Call

Chapter 14 Emergency Calls in the IMS

14.1 Architecture for Supporting Emergency Calls in IMS

14.2 Establishing an Emergency Call in IMS

14.3 IMS Registration for Emergency Calls

14.4 Call Back from the PSAP to a User

14.5 Anonymous Calls

14.6 Emergency Calls in Fixed Broadband Accesses

Part III The Media Plane in the IMS

Chapter 15 Media Encoding

15.1 Speech Encoding

15.2 Video Encoding

15.3 Text Encoding

15.4 Mandatory Codecs in the IMS

Chapter 16 Media Transport

16.1 Reliable Media Transport

16.2 Unreliable Media Transport

16.3 Media Transport in the IMS

Part IV Building Services with the IMS

Chapter 17 Service Configuration on the Internet

17.1 The XML Configuration Access Protocol (XCAP)

17.2 An Overview of XML

17.3 HTTP URIs that Identify XCAP Resources

17.4 XCAP Operations

17.5 Entity Tags and Conditional Operations

17.6 Subscriptions to Changes in XML Documents

17.7 XML Patch Operations

Chapter 18 Service Configuration in the IMS

18.1 XDM architecture

18.2 Downloading an XML Document, Attribute, or Element

18.3 Directory Retrieval

18.4 Data Search with XDM

18.5 Subscribing to Changes in XML Documents

Chapter 19 The Presence Service on the Internet

19.1 Overview of the Presence Service

19.2 The Presence Life Cycle

19.3 Presence Subscriptions and Notifications

19.4 Presence Publication

19.5 Presence Information Data Format (PIDF)

19.6 The Presence Data Model for SIP

19.7 Mapping the SIP Presence Data Model to the PIDF

19.8 Rich PIDF

19.9 CIPID

19.10 Timed Presence Extension to the PIDF

19.11 Presence Capabilities

19.12 Geographical Location in Presence

19.13 Watcher Information

19.14 Watcher Authorization: Presence Authorization Rules

19.15 URI-list Services and Resource Lists

19.16 Presence Optimizations

Chapter 20 The Presence Service in the IMS

20.1 The Foundation of Services

20.2 Presence Architecture in the IMS

20.3 Presence Publication

20.4 Watcher Subscription

20.5 Watcher Information and Authorization of Watchers

20.6 Presence Optimizations

20.7 OMA Extensions to PIDF

Chapter 21 Instant Messaging on the Internet

21.1 The im URI

21.2 Modes of Instant Messages

21.3 Pager-mode Instant Messaging

21.4 Session-based Instant Messaging

21.5 The “isComposing” Indication

21.6 Messaging Multiple Parties

21.7 File Transfer

Chapter 22 The Instant Messaging Service in the IMS

22.1 Pager-mode Instant Messaging in the IMS

22.2 Pager-mode Instant Messaging to Multiple Recipients

22.3 Session-based Instant Messaging in the IMS

22.4 File Transfer

Chapter 23 Conferencing on the Internet

23.1 Conferencing Standardization at the IETF

23.2 The SIPPING Conferencing Framework

23.3 The XCON Conferencing Framework

23.4 The Binary Floor Control Protocol (BFCP)

Chapter 24 Conferencing in the IMS

24.1 The IMS Conferencing Service

24.2 Relation with the Work in TISPAN and OMA

Chapter 25 Push-to-talk over Cellular

25.1 PoC Standardization

25.2 IETF Work Relevant to PoC

25.3 Architecture

25.4 Registration

25.5 PoC Server Roles

25.6 PoC Session Types

25.7 Adding Users to a PoC Session

25.8 Group Advertisements

25.9 Session Establishment Types

25.10 Answer Modes

25.11 Right-to-send-media Indication Types

25.12 Participant Information

25.13 Barring and Instant Personal Alerts

25.14 Full Duplex Call Follow On

25.15 The User Plane

25.16 Simultaneous PoC Sessions

25.17 Charging in PoC

Chapter 26 Multimedia Telephony Services: PSTN/ISDN Simulation Services

26.1 Providing Audible Announcements

26.2 Communication Diversion (CDIV) and Communication Forwarding

26.3 Communication Diversion Notification (CDIVN)

26.4 Conference (CONF)

26.5 Message Waiting Indication (MWI)

26.6 Originating Identification Presentation/Restriction (OIP, OIR)

26.7 Terminating Identification Presentation/Restriction (TIP, TIR)

26.8 Anonymous Communication Rejection (ACR) and Communication Barring (CB)

26.9 Advice of Charge (AoC)

26.10 Completion of Communications to Busy Subscriber (CCBS) and Completion of Communications on No Reply (CCNR)

26.11 Malicious Communication Identification (MCID)

26.12 Communication Hold (HOLD)

26.13 Explicit Communication Transfer (ECT)

26.14 User Settings in PSTN/ISDN Simulation Services

Chapter 27 Voice Call Continuity

27.1 Overview of Voice Call Continuity

27.2 VCC Architecture

27.3 Registration

27.4 Call Origination and Anchoring

27.5 Call Termination and Anchoring

27.6 Domain Transfer

Appendix A List of IMS-related Specifications

A.1 Introduction

A.2 3GPP Specifications

A.3 ETSI NGN Specifications

A.4 OMA Specifications

References

Index

This edition first published 2008

© 2008 John Wiley & Sons Ltd

First edition first published 2004 © 2004 John Wiley & Sons Ltd

Second edition first published 2005 © 2005 John Wiley & Sons Ltd

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Library of Congress Cataloging-in-Publication Data

Camarillo, Gonzalo.

The 3G IP multimedia subsystem (IMS): merging the Internet and the cellular worlds/Gonzalo Camarillo, Miguel A. García-Martín. – 3rd ed.

p. cm.

Includes bibliographical reference and index.

ISBN 978-0-470-51662-1 (cloth)

1. Wireless communication systems. 2. Mobile communication systems. 3.

Multimedia communications. 4. Internet Protocol multimedia subsystem. I.

García-Martín, Miguel A. II. Title.

TK5103.2.C35 2008

621.384–dc22

2008022139

To my parents, Anselmo and Isabel; my brothers, Alvaro, Daniel, and Ignacio; and Viviana. They all are a source of energy and motivation in everything I do.

Gonzalo

To my daughter Maria Elizabeth, who was born at the time I started writing this book ­ she is the sunshine of my life; my wife Jelena, who provided me with all the support and love I needed; my parents, José and Mari-Luz, my aunt Feli, my brother Javier José who, through the distance, encouraged and supported me during this project.

Miguel Angel

Foreword by Stephen Hayes

3GPP, or the Third Generation Partnership Project, was formed in late 1998 to specify the evolution of GSM into a third generation cellular system. Although much focus was placed on new higher bandwidth radio access methods, it was realized that the network infrastructure must also evolve in order to provide the rich services capable of taking advantage of higher bandwidths. The original GSM network infrastructure was very much circuit- and voice-centric. Although data capabilities were added over time the system retained much of its circuit-switched heritage and its inherent limitations. A new approach was needed.

IMS, or the IP Multimedia Subsystem, represented that new approach. The development of IMS was very much a collaborative effort between the leading cellular standards organization (3GPP) and the leading Internet standards organization (IETF). IETF provided the base technology and protocol specifications, while 3GPP developed the architectural framework and protocol integration required to provide the capabilities expected of a world-class mobile system, such as inter-operator roaming, differentiated QoS, and robust charging.

Since the initial specification of IMS, IMS has been adopted by 3GPP2 (the other major cellular standards organization) and it is the leading contender as the base of the ITU work on Next Generation Networks. In the upcoming decades an understanding of IMS will be as important and fundamental for the well-rounded telecom engineer as ISUP knowledge was in previous decades.

IMS is a system. It is designed to provide robust multimedia services across roaming boundaries and over diverse access technologies. To understand IMS, you must understand the underlying protocols and how IMS uses them within its architectural framework. This book facilitates that understanding by explaining first the underlying protocols, such as SIP, and then explaining how IMS makes use of those protocols. This approach allows the user to easily grasp the complex relationship between the protocols and entities as developed in the IETF and their usage and extensions as defined in IMS.

The two authors are uniquely qualified to explain not just the inner workings of IMS but also the rationale and tradeoffs behind the various design choices. Miguel Angel García-Martín was and still is a key contributor within 3GPP. He was one of the principal designers of IMS and authored the initial protocol requirements draft as well as other 3GPP-specific SIP drafts and RFCs. Gonzalo Camarillo was similarly a key contributor within IETF, where he is currently a SIPPING WG co-chair. He has written many RFCs that are key components of IMS. Both authors have been involved with IMS since its inception and do a good job of explaining not only what IMS is but also how it came to be.

Stephen Hayes

Chair – 3GPP Core Network

Foreword by Allison Mankin and Jon Peterson

The Session Initiation Protocol (SIP) is one of the most active initiatives underway in the Internet Engineering Task Force (IETF) today. While the IETF has standardized a number of Internet applications that have turned out to be quite successful (notably, email and the web), few efforts in the IETF have been as ambitious as SIP. Unlike previous attempts to bring telephony over the Internet, which relied extensively on the existing protocols and operational models of the Public Switched Telephone Network (PSTN), SIP elected to use the best parts of email and web technology as its building blocks, and to construct a framework for establishing real-time communication – be it voice, video, instant messaging, or what have you – that is truly native to the Internet.

SIP is a rendezvous protocol – a protocol that allows endpoints on the Internet to discover one another and negotiate the characteristics of a session they would like to share. It converges on the best way for users to communicate, given their preferences, and the capabilities of devices they have at their disposal. Even though it establishes sessions over numerous communications media, it allows policies and services to be provided at the rendezvous level, which greatly simplifies the way end-users and operators manage their needs.

This approach has garnered the attention of almost all of the major vendors and service providers interested in telephony today. But the adoption of SIP by 3GPP has been a special, definitive success for SIP in the global marketplace. 3GPP promises to place SIP firmly in the hands of millions of consumers worldwide, ushering in a whole new paradigm of Internet-based mobile multimedia communications. The IP Multimedia Subsystem (IMS) of 3GPP is the core of this strategy, and it is a SIP-based core.

The IETF has created and continues to develop SIP, and the other protocols for real-time communication and infrastructure: RTP, SDP, DNS, Diameter, . . . As 3GPP builds its successive IMS releases, towards a SIP-based multimedia Internet, IETF and 3GPP have grown into a close, working partnership, initiated by our liaison (RFC3113). Both committed to the Internet style afforded by SIP, two worlds with very different perspectives, the 3GPP world of mobile wireless telephony, and the IETF world of the packet Internet, have learned each other’s considerations. There remain some differences, in the security models, in some aspects of network control. It’s a tribute to the communications, the design work, and not least, to work by the authors of the present volume, that such differences have nonetheless resulted in interoperable SIP, SIP with a coherent character.

Gonzalo Camarillo has been one of the protagonists in SIP’s development. In addition to his work editing the core SIP specification (RFC3261) within the IETF, Gonzalo has chaired the SIPPING Working Group of the IETF (which studies new applications of SIP) and authored numerous documents related to interworking SIP with the traditional telephone network, ensuring that SIP is IPv6 compliant, and using SIP in a wireless context.

Miguel A. García-Martín is one of the principal designers of the IMS, and has also somehow found the time to be one of the main voices for 3GPP within the IETF SIP community. The application of SIP to the mobile handset domain gave rise to numerous new requirements for SIP functionality, many of which would not be obvious to designers unfamiliar with the intricacies of wireless roaming, bandwidth constraints, and so on. As such, Miguel provided some very valuable guidance to the IETF which ensured that SIP is well-tooled to one of its most promising applications.

This book is a milestone presenting the first in-depth coverage of the 3GPP SIP architecture. It is difficult to overestimate the importance of the 3GPP deployment, and this book will position readers to participate in the engineering of that network.

Allison Mankin

Jon Peterson

Directors of the Transport Area of the IETF

About the Authors

Gonzalo Camarillo

Gonzalo Camarillo leads the Multimedia Signaling Research Laboratory of Ericsson in Helsinki, Finland. He is an active participant in the IETF, where he has authored and co-authored several specifications used in the IMS. In particular, he is a co-author of the main SIP specification, RFC 3261. Gonzalo is a member of the IAB (Internet Architecture Board) and the IETF liaison manager to 3GPP. In addition, he co-chairs the IETF SIPPING working group, which handles the requirements from 3GPP and 3GPP2 related to SIP, and the IETF HIP (Host Identity Protocol) working group, which deals with lower-layer mobility and security. He is the Ericsson representative in the SIP Forum and is a regular speaker at different industry conferences. During his stay as a visitor researcher at Columbia University in New York, USA, he published a book entitled “SIP Demystified”. Gonzalo received an M.Sc. degree in Electrical Engineering from Universidad Politecnica de Madrid, Spain, and another M.Sc. degree (also in Electrical Engineering) from the Royal Institute of Technology in Stockholm, Sweden. He is currently continuing his studies as a Ph.D. candidate at Helsinki University of Technology, in Finland.

Miguel A. García-Martín

Miguel A. García-Martín is a System Expert of Ericsson in Madrid, Spain. In the past he has been a Senior Standardization Specialist in the Industry Environment unit of Nokia Siemens Networks in Espoo, Finland and a Principal Research Engineer in the Networking Technologies Laboratory of Nokia Research Center in Helsinki, Finland. Before joining Nokia, Miguel held several positions with Ericsson Finland and Ericsson Spain related to the development of IMS. Miguel is an active participant of the IETF, and for a number of years has been a key contributor in 3GPP. For some time he has also been participating in the specification of NGN in ETSI. In the IETF, he has authored and co-authored several specifications related to the IMS. In 3GPP, he has been a key contributor to the development of the IMS standard. Miguel is also a regular speaker at different industry conferences. Miguel received a B. Eng. degree in Telecommunications Engineering from Universidad de Valladolid, Spain.

Preface to the First Edition

The IMS (IP Multimedia Subsystem) is the technology that will merge the Internet with the cellular world. It will make Internet technologies, such as the web, email, instant messaging, presence, and videoconferencing available nearly everywhere. We have written this book to help engineers, programmers, business managers, marketing representatives, and technically aware users understand how the IMS works and the business model behind it.

We have distributed the topics in this book into four parts: an introduction, the signaling plane in the IMS, the media plane in the IMS, and IMS service examples. All four parts follow a similar structure; they provide both Internet and IMS perspectives on each topic.

First, we describe how each technology works on the Internet. Then, we see how the same technology is adapted to work in the IMS. Following these two steps for each technology provides the reader with a wider perspective. So, this book is not a commented version of the IMS specifications. It covers a much broader field.

Reading this book will improve anyone’s understanding of the Internet technologies used in the IMS. You will know how each technology is used on the Internet and which modifications are needed to make it work in the IMS. This way you will understand how the use of Internet technologies in the IMS will make it easy to take advantage of any current and future Internet service. Finally, you will appreciate how operators can reduce the operational cost of providing new services.

Engineers who are already familiar with the IMS or with any of the IMS-related Internet protocols will also benefit substantially from this book. This way, engineers from the IETF (Internet Engineering Task Force) will understand which special characteristics of the IMS makes it necessary to add or remove certain features from a few Internet protocols so that they can be used in the IMS. On the other hand, engineers from 3GPP (Third Generation Partnership Project) and 3GPP2 will gain a wider perspective on IMS technologies. In addition, any engineer who focuses on a specific technology will gain a better understanding of the system as a whole.

Readers who want to expand their knowledge of any particular topic will find multiple references to 3GPP and 3GPP2 specifications, ITU recommendations, and IETF RFCs and Internet-Drafts in the text. Moreover, Appendix A contains a list with all the 3GPP and 3GPP2 specifications that are relevant to the IMS.

Now, let us look at each part of this book. Part I provides an introduction to the IMS: its goals, its history, and its architecture. We highlight the gains the operators obtain from the IMS. Besides, we discuss what the user can expect from the IMS. In addition, we describe how existing services, such as GPRS, WAP, SMS, MMS, and video-telephony over circuits relate to the IMS.

Part II deals with the signaling plane of the IMS, which includes protocols, such as SIP (Session Initiation Protocol), SDP (Session Description Protocol), Diameter, IPsec, and COPS (Common Open Policy Service). As we said earlier, we describe each protocol as it is used on the Internet and, then, as it is used in the IMS.

Part III describes the media plane of the IMS. We describe how to convert audio and video into a digital form and how to transport it using protocols, such as RTP (Real-Time Transport Protocol) and RTCP (RTP Control Protocol). Furthermore, we introduce Internet protocols such as DCCP (Datagram Congestion Control Protocol) and SRTP (Secure RTP) that are not currently used in the IMS, but might be in the future.

Finally, Part IV provides IMS service examples, such as presence, instant messaging, and Push-to-talk. These examples illustrate how to build meaningful services using the technologies described in Parts II and III.

Essentially, this book is useful to a wide range of technical and business professionals because it provides a thorough overview of the IMS and its related technologies.

Preface to the Second Edition

The pace at which new IMS-related technologies have been developed in the last year has been impressive. Based on the deployment experiences of their members and on feedback from several organizations, 3GPP and 3GPP2 have worked extensively to update the IMS architecture so that it supports a wide range of new services.

While many of these updates consist of extensions to provide more functionality, some of them consist of simplifications to the IMS architecture. These simplifications make the IMS architecture more robust and reliable, or increase the performance of services implemented on top of it.

Examples of organizations that provide feedback to 3GPP and 3GPP2 on how to evolve the IMS are the OMA (Open Mobile Alliance) and the standardization bodies involved in the developing of NGN (Next Generation Networks). These organizations use the IMS as a base to provide different types of services.

The second edition of this book, in addition to describing updates to the IMS architecture, includes extensive discussions on the NGN architecture and the services it provides, and on the OMA PoC (Push-to-talk over Cellular) service. We are confident that the reader will find the chapters on these IMS-based services useful.

From the feedback received on the first edition, it seems that many readers found the structure of the book novel and useful. Readers agreed that first describing how a technology works on the Internet before discussing how it applies to the IMS provides a wider perspective than studying the technology in the IMS context alone.

Of course, we have also updated the sections dealing with Internet technologies. These sections include some of the latest protocol extensions developed in the IETF.

Based on the feedback received during the IMS seminars we have given around the world, we have clarified those concepts which were difficult to understand in the first edition.

Finally, also new to the second edition is a companion website on which instructors and lecturers can find electronic versions of the figures. Please go to

http://www.wiley.com/go/camarillo

Preface to the Third Edition

When 3GPP started standardizing the IMS a few years ago, most analysts expected the number of IMS deployments to grow dramatically as soon the initial IMS specifications were ready (3GPP Release 5 was functionally frozen in the first half of 2002 and completed shortly after that). While those predictions have proven to be too aggressive owing to a number of upheavals hitting the ICT (Information and Communications Technologies) sector, we are now seeing more and more commercial IMS-based service offerings in the market. At the time of writing (May 2008), there are over 30 commercial IMS networks running live traffic, adding up to over 10 million IMS users around the world; the IMS is being deployed globally. In addition, there are plenty of ongoing market activities; it is estimated that over 130 IMS contracts have been awarded to all IMS manufacturers. The number of IMS users will grow substantially as these awarded contracts are launched commercially. At the same time, the number of IMS users in presently deployed networks is steadily increasing as new services are introduced and operators running these networks migrate their non-IMS users to their IMS networks.

On the terminal side, estimations indicate that more than 100 million mobile terminals with support for at least one IMS service will be shipped in 2008. In addition, the fixed version of IMS has made a big effort to be compatible with any standard off-the-shelf SIP-based phone, making the number of available fixed terminals suitable for IMS close to unlimited.

The most common applications running on IMS commercial deployments are IP telephony in fixed and mobile networks, IP centrex, messaging (including text, pictures, and videos), Push-to-talk, video sharing, and presence. However, there is much ongoing work on additional IMS applications. In particular, applications involving machine-to-machine communications (e.g., in sensor networks) are getting much attention. At present, most of the already deployed IMS networks run a specific service instead of using the IMS as the service delivery platform, as the IMS was once envisioned. We expect the market to evolve towards multi-service IMS networks in the following years.

When it comes to current standardization activities in the IMS area, the most relevant activities have to do with multi-access networks. Current IMS networks provide service to endpoints that use several different types of fixed and mobile access technologies, such as WCDMA, WLAN, ADSL and PacketCable. In order to have all these different accesses seemlessly integrated in the IMS architecture, there is still some work to be done to coordinate the specifications coming from 3GPP, 3GPP2, TISPAN, and PacketCable. In the past, there have been a few overlaps between specifications from different organizations. The idea is to minimize those overlaps by clarifying which parts of the architecture each organization should be working on. Additional standardization work includes simplifications of the IMS architecture and the development of new extensions to implement new services or provide new functionality.

The third edition of this book includes a great deal of new material. We have added new chapters discussing emergency calls, service configuration (XCAP and OMA XDM 2.0), conferencing, and Voice Call Continuity (VCC). We have updated the description of the PCC (Policy and Charging Control) architecture to 3GPP Release 7, OMA Presence 2.0, and PoC (Push-to-talk over Cellular) to OMA PoC 2.0. We have added detailed flow descriptions to each multimedia telephony service (or PSTN/ISDN simulation services). We have included discussions on GRUUs (Globally Routable User agent URIs) and their use in the IMS. We have described new NAT traversal techniques such as ICE (Interactive Connectivity Establishment), protocols such as STUN and TURN, and how they apply to the IMS. We have introduced new service and application identification concepts such as ICSI (IMS Communication Services Identification) and IARI (IMS Application Reference Identifier). We have included a description of combinational services. The Security in the IMS chapter has been updated with HTTP Digest Access Authentication and TLS, Early IMS Security Solution, NASS-IMS bundled authentication, and TLS for Network Security. The Instant Messaging on the Internet chapter now discusses the ‘isComposing’ feature, MESSAGE URI-list services, chat rooms, and file transfer operations with SIP and SDP.

Based on feedback from instructors and lecturers, we have also improved the companion website to this book. We have made all the figures of this book available to our readers in a high-quality format, so that they can be easily imported to slide shows and presentations. Please refer to the companion web site at:

http://www.wiley.com/go/camarillo

Overall, we have put a considerable amount of effort into updating the book and creating this third edition. We hope our readers find the new material interesting and easy to understand, and continue finding the book a valuable reference on the IMS and its related Internet technologies.

Acknowledgements

Without the encouragement we received from Stephen Hayes we would not have written this book. He was the first to see the need for a book on the IMS that provided the IETF perspective in addition to the 3GPP and 3GPP2 perspectives. In addition, he and Allison Mankin did an outstanding job coordinating the IMS standardization from 3GPP and from the IETF, respectively.

Once we decided, pushed by Stephen, to start writing this book, our management in Ericsson Finland fully supported us in this endeavor. In particular, Stefan Von Schantz, Christian Engblom, Jussi Haapakangas, Rolf Svanback, and Markku Korpi understood from the beginning the importance of the IMS and of spreading knowledge about it.

Our technical reviewers helped us fix technical errors in early versions of the manuscript. Andrew Allen provided useful comments on the whole manuscript. Harri Hakala, Arto Mahkonen, Miguel Angel Pallares, Janne Suotula, Vesa Torvinen, Magnus Westerlund, Brian Williams, Oscar Novo, Jari Urpalainen, Joël Repiquet, Mari Melander, Hannes Tschofenig, Javier Pastor, Jan Holm, Ari Keränen, and Vesa Lehtovirta provided suggestions on different parts of the book. Takuya Sawada and Takuya Kashima performed a thorough review of the manuscript during its translation to Japanese. Anna Reiter provided guidance on language and writing style.

Our editor at John Wiley & Sons, Ltd, Mark Hammond, believed in this book from day one and supported us at every moment.

Part I

Introduction to the IMS

Before we look at how the IMS works in Parts II and III of this book we need to provide some background information on the IMS. This part (Part I) of the book will answer questions on, for example, what the IMS is, why it was created, what it provides, and which organizations are involved in its standardization. In addition, we will describe the IMS architecture and the design principles behind it

Chapter 1

IMS Vision: Where Do We Want to Go?

Third generation (3G) networks aim to merge two of the most successful paradigms in communications: cellular networks and the Internet. The IP (Internet Protocol) Multimedia Subsystem (IMS) is the key element in the 3G architecture that makes it possible to provide ubiquitous cellular access to all the services that the Internet provides. Picture yourself accessing your favorite web pages, reading your email, watching a movie, or taking part in a videoconference wherever you are by simply pulling a 3G hand-held device out of your pocket. This is the IMS vision.

1.1 The Internet

The Internet has experienced dramatic growth over the last few years. It has evolved from a small network linking a few research sites to a massive worldwide network. The main reason for this growth has been the ability to provide a number of extremely useful services that millions of users like. The best known examples are the World Wide Web and email, but there are many more, such as instant messaging, presence, VoIP (Voice Over IP), videoconferencing, and shared whiteboards.

The Internet is able to provide so many new services because it uses open protocols that are available on the web for any service developer. Moreover, the tools needed to create Internet services are taught at university and are described in large numbers of books.

A widespread knowledge of Internet protocols has an important implication: people who develop new services are the ones who are going to use them. Let us say that a user is interested in chess and would like to play chess over the Internet. This user will be able to program a chess application and make it work over the Internet using an existing transport protocol.

On the other hand, if the protocols were not open and there were few individuals who had access to them, the person programming the chess application would be somebody with deep knowledge of the protocol but little of chess. It is not difficult to guess who would come up with the best chess program: the chess player who understands what to expect from a chess program or the protocol expert. In fact, this is what the Internet has achieved. The number of protocol experts is so high that there is always somebody within a given community (e.g., the chess community) who understands the requirement of the community and the protocols that need to be involved.

1.2 The Cellular World

At present, cellular telephone networks provide services to over one billion users worldwide. These services include, of course, telephone calls, but are not limited to them. Modern cellular networks provide messaging services ranging from simple text messages (e.g., SMS (Short Messaging Service)) to fancy multimedia messages that include video, audio, and text (e.g., MMS (Multimedia Messaging Service)). Cellular users are able to surf the Internet and read email using data connections, and some operators even offer location services which notify users when a friend or colleague is nearby.

Still, cellular networks did not become so attractive to users only for the services they offered. Their main strength is that users have coverage virtually everywhere. Within a country, users can use their terminals not only in cities, but also in the countryside. In addition, there exist international roaming agreements between operators that allow users to access cellular services when they are abroad.

Reduction in terminal size also helped the spread of cellular networks. Old brick-like terminals gave way to modern small terminals that work for several days without having their batteries recharged. This allows people to carry their terminals everywhere with little difficulty.

1.3 Why do we need the IMS?

On the one hand, we have mentioned that the idea of the IMS is to offer Internet services everywhere and at any time using cellular technologies. On the other hand, we have also said that cellular networks already provide a wide range of services, which include some of the most successful Internet services, such as instant messaging. In fact, any cellular user can access the Internet using a data connection and in this way access any services the Internet may provide. So, what do we need the IMS for?

We need to further clarify what we mean by merging the Internet and the cellular worlds and what the real advantages of doing so are. To do that, we need to introduce the different domains in 3G networks, namely the circuit-switched domain and the packet-switched domain.

The circuit-switched domain is an evolution of the technology used in second generation (2G) networks. The circuits in this domain are optimized to transport voice and video, although they can also be used to transport instant messages.

Although circuit-switched technology has been in use since the birth of the telephone, the current trend is to substitute it with more efficient packet-switched technology. Cellular networks follow this trend and, as we said earlier, 3G networks have a packet-switched domain.

The packet-switched domain provides IP access to the Internet. While 2G terminals can act as a modem to transmit IP packets over a circuit, 3G terminals use native packet-switched technology to perform data communications. This way, data transmissions are much faster and the available bandwidth for Internet access increases dramatically. Users can surf the web, read email, download videos, and do virtually everything they can do over any other Internet connection, such as ISDN (Integrated Services Digital Network) or DSL (Digital Subscriber Line). This means that any given user can install a VoIP client in their 3G terminal and establish VoIP calls over the packet-switched domain. Such a user can take advantage of all the services that service providers on the Internet offer, such as voicemail or conferencing services.

So, again the same question: why do we need the IMS, if all the power of the Internet is already available for 3G users through the packet-switched domain? The answer is threefold: QoS (Quality of Service), charging, and integration of different services.

The main issue with using the packet-switched domain to provide real-time multimedia services is that it provides a best-effort service without QoS; that is, the network offers no guarantees about the amount of bandwidth a user gets for a particular connection or about the delay the packets experience. Consequently, the quality of a VoIP conversation can vary dramatically throughout its duration. At a certain point the voice of the person at the other end of the phone may sound perfectly clear and instants later it can become impossible to understand. Trying to maintain a conversation (or a videoconference) with poor QoS can soon become a nightmare.

So, one of the reasons for creating the IMS was to provide the QoS required for enjoying, rather than suffering, real-time multimedia sessions. The IMS takes care of synchronizing session establishment with QoS provision so that users have a predictable experience.

Another reason for creating the IMS was being able to charge multimedia sessions appropriately. A user involved in a videoconference over the packet-switched domain usually transfers a large amount of information (which consists mainly of encoded audio and video). Depending on the 3G operator, the transfer of such an amount of data may generate large expenses for the user, since operators typically charge by the number of bytes transferred. The user’s operator cannot follow a different business model to charge the user because the operator is not aware of the contents of those bytes: they could belong to a VoIP session, to an instant message, to a web page, or to an email.

On the other hand, if the operator is aware of the actual service that the user is using, the operator can provide an alternative charging scheme that may be more beneficial for the user. For instance, the operator might be able to charge a fixed amount for every instant message, regardless of its size. In addition, the operator may charge for a multimedia session based on its duration, independently of the number of bytes transferred.

The IMS does not mandate any particular business model. Instead, it lets operators charge as they think most appropriate. The IMS provides information about the service being invoked by the user, and with this information the operator decides whether to use a flat rate for the service, apply traditional time-based charging, apply QoS-based charging, or perform any new type of charging. As a clarification, by service, in this charging context, we refer to any value offered to the user (e.g., a voice session, an audio/video session, a conference bridge, an instant message, or the provision of presence information about co-workers).

Providing integrated services to users is the third main reason for the existence of the IMS. Although large equipment vendors and operators will develop some multimedia services, operators do not want to restrict themselves to these services. Operators want to be able to use services developed by third parties, combine them, integrate them with services they already have, and provide the user with a completely new service. For example, an operator may have a voicemail service able to store voice messages and a third party develops a text-to-speech conversion service. If the operator buys the text-to-speech service from the third party, it can provide voice versions of incoming text messages for blind users.

The IMS defines the standard interfaces to be used by service developers. This way, operators can take advantage of a powerful multi-vendor service creation industry, avoiding sticking to a single vendor to obtain new services.

Furthermore, the aim of the IMS is not only to provide new services but to provide all the services, current and future, that the Internet provides. In addition, users have to be able to execute all their services when roaming as well as from their home networks. To achieve these goals the IMS uses Internet technologies and Internet protocols. So, a multimedia session between two IMS users, between an IMS user and a user on the Internet, and between two users on the Internet is established using exactly the same protocol. Moreover, the interfaces for service developers we mentioned above are also based on Internet protocols. This is why the IMS truly merges the Internet with the cellular world; it uses cellular technologies to provide ubiquitous access and Internet technologies to provide appealing services.

1.4 Relation between IMS and non-IMS Services

We have just explained that the IMS is needed to provide Internet services (including real-time multimedia services) with an acceptable QoS at an acceptable price. Yet many such services can be provided outside the IMS as well. Two users can establish a videoconference over the circuit-switched domain and send each other multimedia messages using MMS. At the same time they can surf the web and check email over the packet-switched domain (e.g., GPRS (General Packet Radio Service)). They can even access a presence server on the Internet to check the availability of more people who may want to join the videoconference.

Given that all the services just described can be provided with an excellent QoS with no IMS at all, then what does the IMS really provide?

First of all, the IMS provides all the services using packet-switched technology, which is generally more efficient than circuit-switched technology. Nevertheless, the real strength of the IMS when compared with the situation above is that the IMS creates a service environment where any service can access any aspect of the session. This allows service providers to create far richer services than in an environment where all the services are independent of one another.

For example, a service could insert an announcement in a conference based on an event that happens on the Internet, like the change of the presence state of a colleague from busy to available. Another service could, for instance, display on the user’s screen the web page of the person who is calling every time a call is received. Moreover, the same service could automatically set the user’s presence status to busy and divert incoming calls to an email address instead of to the typical voicemail.

When services in the network can access all the aspects of a session, they can perform many operations (e.g., changing the presence status of the user) without sending any data over the air to the terminal. Spare radio capacity can be used to provide a higher QoS to existing users or to accommodate more users with the same QoS.

Another important advantage of the IMS is that it does not depend on the circuit-switched domain. This way, interworking with devices with no access to this domain, such as laptops connected to the Internet using any videoconferencing software, becomes trivial. This increments dramatically the number of people IMS users are able to communicate with using all types of media.

Chapter 2

The History of the IMS Standardization

In Chapter 1 we mentioned that the IMS (IP Multimedia Subsystem) uses Internet protocols. When the IMS needs a protocol to perform a particular task (e.g., to establish a multimedia session), the standardization bodies standardizing the IMS take the Internet protocol intended for that task and specify its use in the IMS. Still, no matter how simple this may sound, the process of choosing protocols to be used in the IMS can sometimes get tricky. Sometimes, the Internet protocol that is chosen lacks some essential functionality, or does not even exist at all. When this happens the IMS standardization bodies contact the standardization body developing Internet protocols to work together on a solution. We will cover this collaboration in Section 2.5. Nevertheless, before jumping into that we will introduce in Section 2.1 all the standardization bodies involved in IMS development. We need to know who is who and which functions of the IMS each of them performs.

2.1 Relations between IMS-related Standardization Bodies

The ITU (International Telecommunication Union) IMT-2000 (International Mobile Telecommunications-2000) is the global standard for 3G networks. IMT-2000 is the result of the collaboration between different standards bodies. It aims to provide access to telecommunication services using radio links, which include satellite and terrestrial networks.

We will focus on two of the standard bodies involved in IMT-2000: 3GPP (Third Generation Partnership Project) and 3GPP2 (Third Generation Partnership Project 2). However, they are not the only ones working within IMT-2000. Other bodies, such as the ITU-R (ITU-Radiocommunication Sector), for instance, are also involved in IMT-2000 but in different areas from the IMS.