The 3G IP Multimedia Subsystem (IMS) Merging the Internet and the Cellular Worlds Gonzalo Camarillo and Miguel A. Garcia-Martin Both of Ericsson, Finland John Wiley & Sons, Ltd
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The 3G IP Multimedia Subsystem (IMS) Merging the Internet and the Cellular Worlds
Gonzalo Camarillo and Miguel A. Garcia-Martin
Both of Ericsson, Finland
John Wiley & Sons, Ltd
Contents
Foreword by Stephen Hayes xv
Foreword by Allison Mankin and Jon Peterson xvii
About the Authors xix
Preface xxi
Acknowledgements xxiii
I Introduction to the IMS 1
1 IMS Vision: Where Do We Want to Go? 5 1.1 The Internet 5 1.2 The Cellular World 6 1.3 Why Do We Need the IMS? 6 1.4 Relation between IMS and non-IMS Services 8
2 The History of the IMS Standardization 11 2.1 Relations between IMS-related Standardization Bodies 11 2.2 Internet Engineering Task Force (IETF) 12
2.2.1 Structure of IETF 12 2.2.2 Working Group Operations 13 2.2.3 TypesofRFCs 14
2.3 Third Generation Partnership Project (3GPP) 15 2.3.1 3GPP Structure 16 2.3.2 3GPP Deliverables 17
2.4 Third Generation Partnership Project 2 (3GPP2) 18 2.4.1 3GPP2 Structure 18 2.4.2 3GPP2 Deliverables 18
2.5 IETF-3GPP/3GPP2 Collaboration 19 2.5.1 Internet Area 20 2.5.2 Operations and Management Area 20 2.5.3 Transport Area 21
vn
viii CONTENTS
3 General Principles of the IMS Architecture 23 3.1 From Circuit-switched to Packet-switched 23
3.1.1 GSM Circuit-switched 23 3.1.2 GSM Packet-switched 24
3.2 IMS Requirements 24 3.2.1 IP Multimedia Sessions 25 3.2.2 QoS 26 3.2.3 Interworking 26 3.2.4 Roaming 26 3.2.5 Service Control 26 3.2.6 Rapid Service Creation 27 3.2.7 Multiple Access 27
3.3 Overview of Protocols Used in the IMS 27 3.3.1 Session Control Protocol 28 3.3.2 The AAA Protocol 29 3.3.3 Other Protocols 29
3.4 Overview of IMS Architecture 29 3.4.1 The Databases: the HSS and the SLF 31 3.4.2 The CSCF 31 3.4.3 The AS 34 3.4.4 The MRF 36 3.4.5 The BGCF 36 3.4.6 The PSTN/CS Gateway 36 3.4.7 Home and Visited Networks 37
3.5 Identification in the IMS 39 3.5.1 Public User Identities 40 3.5.2 Private User Identities 40 3.5.3 The Relation between Public and Private User Identities . . . 41 3.5.4 Public Service Identities ( 42
3.6 SIM, USIM, and ISIM in 3GPP 42 3.6.1 SIM 43 3.6.2 USIM 43 3.6.3 ISIM 44
II The Signaling Plane in the IMS 47
4 Session Control on the Internet 51 4.1 SIP Functionality * 51
4.1.1 Session Descriptions and SDP 51 4.1.2 The Offer/Answer Model 53 4.1.3 SIP and SIPS URIs 54 4.1.4 User Location 54
4.2 SIP Entities 55 4.2.1 Forking Proxies 58 4.2.2 Redirect Servers 59
4.3 Message Format 59
CONTENTS ix
4.4 The Start Line in SIP Responses: the Status Line 60
4.5 The Start Line in SIP Requests: the Request Line 60
4.6 Header Fields 62 4.7 Message Body 63 4.8 SIP Transactions 63 4.9 Message Fl«w for Session Establishment 66 4.10 SIP Dialogs 71
4.10.1 Record-Route, Route, and Contact Header Fields 71 4.11 Extending SIP 72
4.11.1 New Methods 73 4.12 Caller Preferences and
User Agent Capabilities 73 4.13 Reliability of Provisional Responses 75 4.14 Preconditions 77 4.15 Event Notifikation 80
4.15.1 High Notifikation Rates 80 4.16 Signaling Compression 82
4.16.1 SigComp Extended Operations 83 4.16.2 Static SIP/SDP Dictionary 83
4.17 Content Indirection 84 4.18 URI Lists 87
5 Session Control in the IMS 91 5.1 Prerequisites for Operation in the IMS 92 5.2 IP Connectivity Access Network 93 5.3 P-CSCF Discovery 94 5.4 IMS-level Registration 96
5.4.1 IMS Registration with an ISIM 97 5.4.2 IMS registration with a USIM 105
5.5 Subscription to the reg Event State 110 5.6 Basic Session Setup 115 5.7 Application Servers: Providing Services to Users 146
5.7.1 Generalities About Application Servers 148 5.7.2 Types of Application Servers 150 5.7.3 The Session Setup Model through Application Servers . . . . 153 5.7.4 Filter Criteria 161 5.7.5 An Example of Service Execution 165
5.8 Interworking 169 5.8.1 SIP-PSTN Interworking 169 5.8.2 Interworking with Non-IMS SIP-based Networks 172
5.9 Emergency Sessions 176
X CONTENTS
6 A A A on the Internet 179 6.1 Authentication, Authorization, and Accounting 179 6.2 AAA Framework on the Internet 180 6.3 The Diameter Protocol 181
6.3.1 Diameter Sessions 182 6.3.2 The Format of a Diameter Message 183 6.3.3 Attribute Value Pairs 184 6.3.4 The AAA and AAAS UPJs 186 6.3.5 Diameter Base Protocol Commands 186 6.3.6 Diameter Base Protocol AVPs 188
7 AAA in the IMS 191 7.1 Authentication and Authorization in the IMS 191 7.2 The Cx and Dx Interfaces 191
7.2.1 Command Codes Defined in the Diameter Application for the Cx Interface 193
7.2.2 AVPs Defined in the Diameter Application for the Cx Interface 198
7.2.3 The User Profile 201 7.3 The Sh Interface 201
7.3.1 Command Codes Defined in the Diameter Application for the Sh interface 203
7.3.2 AVPs Defined in the Diameter Application for the Sh Interface 205
7.4 Accounting 206 7.5 Charging Architecture 207 7.6 Offline Charging 208
7.6.1 IMS Terminal in a Visited Network ' 209 7.6.2 IMS Terminal in Its Home Network 211 7.6.3 The Rf Interface 214
7.7 Online Charging 215 7.7.1 S-CSCF 215 7.7.2 Application Servers and the MRFC 216
8 Security on the Internet 221 8.1 HTTP Digest 221
8.1.1 Security Properties of Digest 223 8.2 Certificates 224 8.3 TLS 224
8.3.1 SIP Usage 226 8.4 S/MIME 226
8.4.1 Self-signed Certificates 229 8.5 Authenticated Identity Body 231 8.6 IPsec 231
8.6.1 ESP and AH 233 8.6.2 Tunnel and Transport Modes 234 8.6.3 Internet Key Exchange 234
CONTENTS xi
8.7 Privacy 236 8.8 Encrypting Media Streams 236
8.8.1 MIKEY 237
9 Security in the IMS 239 9.1 Access Security 239
9.1.1 Authentication and Authorization 239 9.1.2 Authentication and Authorization with ISIM 240 9.1.3 Authentication and Authorization with USIM 243 9.1.4 Security Association Establishment 243
9.2 Network Security 245
10 Policy on the Internet 247 10.1 The COPS Protocol 247 10.2 The Outsourcing Model 249 10.3 The ConfigurStion Model 250
11 Policy in the IMS 253 11.1 SIP Procedures 253 11.2 Media Authorization 254
11.2.1 The Policy Decision Function 255 11.2.2 Media Authorization Token 255
11.3 Proxy Access to SDP Bodies 258 11.4 Initialization Procedure 258
12 Quality of Service on the Internet 259 12.1 Integrated Services 259
12.1.1 RSVP 260 12.1.2 State in the Network 261
12.2 Differentiated Services 261
13 Quality of Service in the IMS 263 13.1 Instructions to Perform Resource
Reservations 263 13.1.1 Proxy Modifying Bodies 264
13.2 Reservations by the Terminals 266 13.3 Network Authorization 266 13.4 QoS in the Network 268
III The Media Plane in the IMS 269
14 Media Encoding 273 14.1 Speech Encoding 273
14.1.1 Pulse Code Modulation 274 14.1.2 Linear Prediction 275 14.1.3 GSM-FR 277 14.1.4 AMR 278
xii CONTENTS
14.1.5 AMR-WB 281 14.1.6 SMV 285
14.2 Video Encoding 286 14.2.1 Common Video Codecs 287 14.2.2 H.263 287 14.2.3 Image Encoding 288 14.2.4 Temporal Correlation 289 14.2.5 Spatial Correlation 289
14.3 Text Encoding 289 14.4 Mandatory Codecs in the IMS 289
15 Media Transport 291 15.1 Reliable Media Transport 291 15.2 Unreliable Media Transport 292
15.2.1 DCCP 293 15.2.2 RTP 293 15.2.3 RTCP 295 15.2.4 SRTP 297
15.3 Media Transport in the IMS 297
IV Building Services with the IMS 299
16 The Presence Service on the Internet 303 16.1 Overview of the Presence Service 303 16.2 Presence Information Data Format 305 16.3 Rieh Presence Information Data Format 306 16.4 Contact Information in Presence Information Data Format 308 16.5 Timed Presence Extension to the PIDF 308 16.6 Presence Capabilities ' 311 16.7 Presence Publication 311 16.8 Presence Subscription and Notification 313 16.9 Watcher Information 313 16.10 SIP Exploders and Resource Lists 316 16.11 XML Configuration Access Protocol 318
16.11.1 XCAP Application Usage 319 16.12 Presence Optimizations 320
16.12.1 Partial Notification of Presence Information. 321 16.12.2 Event Notification Filtering 321
17 The Presence Service in the IMS 323 17.1 The Foundation of Services 323 17.2 Presence Architecture in the IMS 324 17.3 Watcher Subscription 325 17.4 Subscription to Watcher Information 326 17.5 Presence Publication 327 17.6 Presence Optimizations 328 17.7 The Ut Interface 328
CONTENTS xiii
18 Instant Messaging on the Internet 331 18.1 Modes of Instant Messages 332 18.2 Pager-mode Instant Messaging 332
18.2.1 Congestion Control with MESSAGE 333 18.3 Session-based Instant Messaging 334
18.3.1 The MSRP and MSRPS URLs 334 18.3.2 A Closer Look at MSRP 334
19 The Instant Messaging Service in the IMS 339 19.1 Pager-mode Instant Messaging in the IMS 339 19.2 Session-based Instant Messaging in the IMS 340
20 Push-To-Talk 345 20.1 Push-To-Talk Standardization 345 20.2 Architecture 346 20.3 Interoperator Sessions 348
A The 3GPP2 IMS 349 A.l An Introduction to 3GPP2 349 A.2 The Multimedia Domain (MMD) 349 A.3 Architecture of the 3GPP2 IMS 350
B List of IMS-related Specifications 353 B.l Introduction 353 B.2 3GPP Specifications 353 B.3 3GPP2 Specifications 354
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