Voice over LTE
EPS and IMS Networks

Voice over LTE (Long Term Evolution) presents the mechanisms put in place in 4G mobile networks for the transportation of IP packets containing voice data and telephone signaling, as well as the technologies used to provide a telephone service in the IMS (IP Multimedia Sub-system) network.
Despite the difficulty connected to the handover of the 4G network to the 2G/3G network, a telephone communication will not be established on the 4G network. This book analyzes the technologies that have been put in place, such as CSFB (Circuit Service FallBack), an interim solution that enables a mobile connected to the 4G network to receive an alert transmitted by the 2G/3G network.
The book also goes on to develop the SIP (Session Information Protocol) on which the telephone signaling transferred by the 4G network is based, the IMS network that provides the service and defines the routing, the SRVCC (Single Radio Voice Call Continuity) mechanism that maintains communication and the TAS (Telephony Application Server) that supplies supplementary services.

Contents

1. The EPS Network.
2. The LTE Interface.
3. The CSFB Function.
4. SIP and SDP Protocols.
5. The IMS Network.
6. Telephone Services.
7. The SRVCC Function.

About the Authors

André Perez is a consultant and teacher in networks and telecommunications. He works with industrialists and operators regarding architecture studies and leads training on the 4G and IMS networks for NEXCOM.

Preface ix

Acronyms xiii

Chapter 1. The EPS Network 1

1.1. Architecture 1

1.1.1. Access network 2

1.1.2. Core network 3

1.1.3. Protocol architecture 7

1.2. Signaling protocols 11

1.2.1. NAS protocol 11

1.2.2. RRC protocol 16

1.2.3. S1-AP protocol 21

1.2.4. X2-AP protocol 24

1.2.5. GTPv2-C protocol 27

1.3. Procedures 30

1.3.1. Attachment procedure 30

1.3.2. Location update 34

1.3.3. Bearer activation 36

1.3.4. Handover procedure 39

Chapter 2. The LTE Interface 47

2.1. Structure of the radioelectric interface 47

2.2. Data link layer 48

2.2.1. PDCP protocol 48

2.2.2. RLC protocol 50

2.2.3. MAC protocol 56

2.3. Physical layer 59

2.3.1. Frequency range 60

2.3.2. Spatial multiplexing 62

2.3.3. Time multiplexing 63

2.3.4. Physical signals and channels 68

2.4. Procedures 80

2.4.1. Cell searching 80

2.4.2. System information 80

2.4.3. Random access 80

2.4.4. Data scheduling 82

2.4.5. Re-transmission in the case of error 84

Chapter 3. The CSFB Function 89

3.1. Reminder about NGN 89

3.1.1. Architecture of NGN 89

3.1.2. Signaling transport 91

3.1.3. Transport of voice data 93

3.2. The CSFB function 94

3.3. Procedures 95

3.3.1. Attachment 95

3.3.2. Tracking area update 96

3.3.3. Outgoing call 98

3.3.4. Incoming call 99

Chapter 4. SIP and SDP Protocols  103

4.1. Entities 103

4.2. Identities 104

4.3. Structure of SIP 105

4.3.1. Requests 105

4.3.2. Responses 109

4.3.3. Headers 112

4.4. Description of the media 116

4.5. Procedures 118

4.5.1. Registration 118

4.5.2. The session 120

Chapter 5. The IMS Network  137

5.1. Architecture of IMS 137

5.1.1. Session control 139

5.1.2. Application servers 141

5.1.3. Databases 142

5.1.4. Interconnection 142

5.1.5. Media processing 143

5.1.6. Charging 144

5.2. Registration 146

5.2.1. First phase of registration 146

5.2.2. Second phase of registration 150

5.2.3. Subscription 153

5.2.4. Notification 155

5.3. The session between IMSs 158

5.3.1. Establishment of the session 158

5.3.2. Termination of the session 164

5.4. DIAMETER messages 165

5.4.1. The messages related to registration and routing 166

5.4.2. Messages relating to control of the media 166

5.5. Interoperation with the CS network 167

5.5.1. Call initiated by the IMS network 167

5.5.2. Call generated by the CS network 169

5.5.3. Release of the communication 170

Chapter 6. Telephone Services 173

6.1. Service profile 173

6.2. Communication Diversion 175

6.2.1. CFU 175

6.2.2. CFB 176

6.2.3. CFNR 177

6.2.4. CD 179

6.2.5. CFNL 180

6.3. Identification presentation 180

6.3.1. OIP and OIR 180

6.3.2. TIP and TIR  181

6.4. Message Waiting Indication 181

6.5. Call parking 184

6.6. Conferencing 185

6.7. Communication transfer 187

6.8. Communication Waiting 189

6.9. Malicious Communication Identification 192

6.10. Automatic callback 193

6.10.1. CCBS 193

6.10.2. CCNR 196

6.10.3. CCNL 197

6.11. Communication rejection 198

6.11.1. ACR 198

6.11.2. ICB 198

6.11.3. OCB 198

6.12. Announcements 198

Chapter 7. The SRVCC Function  203

7.1. Impact on architectures 203

7.1.1. Impact on mobile networks 203

7.1.2. Impact on the IMS network 205

7.2. Procedures 207

7.2.1. Registration 207

7.2.2. Session establishment 211

7.2.3. PS-CS handover 214

7.2.4. Transfer of the communication 216

Bibliography 221

Index 225

André Perez is a consultant and a trainer in networks and telecommunications, who defines the implementation of operator networks. He also teaches network technologies in engineering and technical schools.