Open RAN

Ian C. Wong, PhD, is Director of RF and Wireless Architecture at VIAVI Solutions. He is co-chair of the Test and Integration Focus group in the O-RAN Alliance and a Senior Member of the IEEE. Aditya Chopra, PhD, is a communication systems engineer with over 10 years’ experience in wireless standards and transceiver design. Sridhar Rajagopal, PhD, is a SVP and Senior Fellow at Mavenir Systems, where he leads customer engineering and radio integration for Mavenir’s Open RAN products. He has co-invented around 50 issued US patents and is a senior member of IEEE. Rittwik Jana, PhD, is currently a Telco analytics and automation engineer at Google. He is an industry expert with over 25 years of experience in numerous wireless technologies and standards.

List of Contributors xiii

Foreword xv

Preface xvii

About the Authors xix

Definitions / Acronyms xxi

1 The Evolution of RAN 1
Sameh M. Yamany

1.1 Introduction 1

1.2 RAN Architecture Evolution 4

1.2.1 The 2G RAN 5

1.2.2 The 3G RAN 6

1.2.3 The 4G/LTE RAN 6

1.2.4 The 5G RAN 9

1.3 The Case for Open RAN 11

1.4 6G and the Road Ahead 11

1.5 Conclusion 13

Bibliography 13

2 Open RAN Overview 14
Rittwik Jana

2.1 Introduction 14

2.1.1 What is Open RAN and Why is it Important? 17

2.1.2 How Does Open RAN Accelerate Innovation? 17

2.1.3 What are the major challenges that Open RAN can help to address? 18

2.2 Open RAN Architecture 18

2.3 Open RAN Cloudification and Virtualization 19

2.4 RAN Intelligence 20

2.5 Fronthaul Interface and Open Transport 20

2.6 Securing Open RAN 21

2.7 Open Source Software 21

2.8 RAN Automation and Deployment with CI/CD 22

2.9 Open RAN Testing 22

2.10 Industry Organizations 23

2.11 Conclusion 23

Bibliography 23

3 O-RAN Architecture Overview 24
Rajarajan Sivaraj and Sridhar Rajagopal

3.1 Introduction 24

3.1.1 General Description of O-RAN Functions 24

3.1.1.1 Centralized Unit – Control Plane and User Plane Functions (CU-CP and CU-UP) 26

3.1.1.2 Distributed Unit Function (DU) 26

3.1.1.3 Radio Unit Function (RU) 26

3.1.1.4 Evolved Node B (eNB) 27

3.1.2 RAN Intelligent Controller (RIC) and Service Management and Orchestration (SMO) Functions 28

3.1.3 Interfaces 29

3.2 Near-RT RIC Architecture 30

3.2.1 Standard Functional Architecture Principles 30

3.2.2 E2 Interface Design Principles 32

3.2.3 xApp API Design Architecture 34

3.3 Non-RT RIC Architecture 37

3.3.1 Standard Functional Architecture Principles 38

3.3.2 A1 Interface Design Principles 38

3.3.3 R1 API Design Principles for rApps 41

3.4 SMO Architecture 47

3.4.1 Standard Functional Architecture Principles 47

3.4.2 O1 Interface Design Principles 48

3.4.3 Open M-Plane Fronthaul Design Principles 51

3.4.4 O2 Interface Design Principles 52

3.5 Other O-RAN Functions and Open Interfaces 54

3.5.1 O-RAN compliant Centralized Unit Control Plane (O-CU-CP) 54

3.5.1.1 Control Plane Procedures 54

3.5.1.2 Management Plane Procedures 54

3.5.2 O-CU-UP 54

3.5.2.1 Control Plane Procedures 55

3.5.2.2 User Plane Procedures 55

3.5.2.3 Management Plane Procedures 55

3.5.3 O-DU 55

3.5.3.1 Control Plane Procedures 55

3.5.3.2 User Plane Procedures 55

3.5.3.3 Management Plane Procedures 55

3.5.4 O-eNB 56

3.5.5 O-RU 56

3.6 Conclusion 57

Bibliography 57

4 Cloudification and Virtualization 59
Padma Sudarsan and Sridhar Rajagopal

4.1 Virtualization Trends 59

4.2 Openness and Disaggregation with vRAN 59

4.3 Cloud Deployment Scenarios 61

4.3.1 Private, Public, and Hybrid Cloud 61

4.3.2 Telco Features Required for “Any Cloud” Deployment 62

4.3.3 On Premise, Far Edge, Edge, and Central Deployments 63

4.3.4 Classical, Virtual Machines (VMs), Containers, and Hybrid Deployments 64

4.4 Unwinding the RAN Monolith 64

4.4.1 Adapting Cloud-Native Principles 66

4.4.2 Architectural Patterns 67

4.4.3 Software Architecture Portability and Refactoring Considerations 68

4.4.4 Compute Architecture Consideration 69

4.5 Orchestration, Management, and Automation as Key to Success 70

4.5.1 Acceleration Abstraction Layer 73

4.5.2 Cloud Deployment Workflow Automation 75

4.6 Summary 76

Bibliography 76

5 RAN Intelligence 77
Dhruv Gupta, Rajarajan Sivaraj, and Rittwik Jana

5.1 Introduction 77

5.2 Challenges and Opportunities in Building Intelligent Networks 77

5.3 Background on Machine Learning Life Cycle Management 78

5.4 ML-Driven Intelligence and Analytics for Non-RT RIC 80

5.5 ML-Driven Intelligence and Analytics for Near-RT RIC 82

5.6 E2 Service Models for Near-RT RIC 83

5.6.1 E2SM-KPM 84

5.6.2 E2SM-RC 84

5.6.3 Other E2SMs 85

5.7 ml Algorithms for Near-RT RIC 86

5.7.1 Reinforcement Learning Models 87

5.8 Near-RT RIC Platform Functions for AI/ML Training 88

5.9 RIC Use Cases 89

5.10 Conclusion 90

Bibliography 90

6 The Fronthaul Interface 91
Aditya Chopra

6.1 The Lower-Layer Split RAN 91

6.1.1 Lower Layer Fronthaul Split Options 92

6.2 Option 8 Split – CPRI and eCPRI 93

6.3 Option 6 Split – FAPI and nFAPI 94

6.3.1 Subinterfaces 97

6.3.2 Architecture Agnostic Deployment 97

6.4 Option 7 Split – O-RAN Alliance Open Fronthaul 97

6.4.1 Control (C) and User (U) Plane 98

6.4.2 Management (M) Plane 98

6.4.3 Synchronization (S) Plane 100

6.4.4 Key Features 100

6.4.4.1 Fronthaul Compression 100

6.4.4.2 Delay Management 102

6.4.4.3 Beamforming 102

6.4.4.4 Initial Access 103

6.4.4.5 License Assisted Access and Spectrum Sharing 104

6.5 Conclusions 104

Bibliography 104

7 Open Transport 105
Reza Vaez-Ghaemi and Luis Manuel Contreras Murillo

7.1 Introduction 105

7.2 Requirements 105

7.2.1 Fronthaul Requirements 106

7.2.2 Midhaul Requirements 106

7.2.3 Backhaul Requirements 107

7.2.4 Synchronization Requirements 107

7.3 WDM Solutions 108

7.3.1 Passive WDM 109

7.3.2 Active WDM 109

7.3.3 Semiactive WDM 110

7.4 Packet-Switched Solutions 111

7.4.1 Technology Overview 112

7.4.2 Deployment Patterns 112

7.4.3 Connectivity Service and Protocols 113

7.4.4 Quality of Service (QoS) 114

7.5 Management and Control Interface 114

7.5.1 Control and Management Architecture 114

7.5.2 Interaction with O-RAN Management 116

7.6 Synchronization Solutions 117

7.6.1 Synchronization Baseline 117

7.6.2 Synchronization Accuracy and Limits 118

7.7 Testing 118

7.8 Conclusion 119

Bibliography 120

8 O-RAN Security 121
Amy Zwarico

8.1 Introduction 121

8.2 Zero Trust Principles 121

8.3 Threats to O-RAN 122

8.3.1 Stakeholders 122

8.3.2 Threat Surface and Threat Actors 122

8.3.3 Overall Threats 123

8.3.4 Threats Against the Lower Layer Split (LLS) Architecture and Open Fronthaul Interface 123

8.3.5 Threats Against O-RU 124

8.3.6 Threats Against Near- and Non-Real-Time RICs, xApps, and rApps 124

8.3.7 Threats Against Physical Network Functions (PNFs) 124

8.3.8 Threats Against SMO 125

8.3.9 Threats Against O-Cloud 125

8.3.10 Threats to the Supply Chain 125

8.3.11 Physical Threats 126

8.3.12 Threats Against 5G Radio Networks 126

8.3.13 Threats to Standards Development 126

8.4 Protecting O-RAN 126

8.4.1 Securing the O-RAN-Defined Interfaces 126

8.4.1.1 A1 127

8.4.1.2 O1 127

8.4.1.3 O2 128

8.4.1.4 E2 128

8.4.1.5 Open Fronthaul 128

8.4.1.6 R1 130

8.4.1.7 3GPP Interfaces 131

8.4.2 Securing the O-Cloud 131

8.4.3 Container Security 131

8.4.4 O-RAN Software Security 131

8.4.5 Software Bill of Materials (SBOM) 132

8.5 Recommendations for Vendors and MNOs 132

8.6 Conclusion 134

Bibliography 134

9 Open RAN Software 137
David Kinsey, Padma Sudarsan, and Rittwik Jana

9.1 Introduction 137

9.2 O-RAN Software Community (OSC) 138

9.2.1 OSC Projects 138

9.2.2 The Service Management and Orchestration (SMO) Framework 138

9.2.3 Near-RT RIC (RIC) 139

9.2.4 O-CU-CP and O-CU-UP 140

9.2.5 O-DU Project 140

9.2.6 O-RU 140

9.2.7 O-Cloud 140

9.2.8 The AI/ML Framework 141

9.2.9 Support Projects 141

9.3 Open Network Automation Platform (ONAP) 141

9.3.1 Netconf/YANG Support 141

9.3.2 Configuration Persistence 142

9.3.3 VES Support 142

9.3.4 A1 Support 142

9.3.5 Optimization Support 142

9.4 Other Open-Source Communities 143

9.5 Conclusion 144

Bibliography 144

10 Open RAN Deployments 145
Sidd Chenumolu

10.1 Introduction 145

10.2 Network Architecture 146

10.2.1 Network Components 147

10.2.1.1 Antenna 147

10.2.1.2 O-RAN – Radio Unit 148

10.2.1.3 O-RAN-Distributed Unit (O-DU) 150

10.2.1.4 O-RAN-Centralized Unit (O-CU) 150

10.2.1.5 RAN Intelligent Controller (RIC) 150

10.2.2 Traditional vs. O-RAN Deployment 151

10.2.3 Typical O-RAN Deployment 152

10.2.4 Spectrum and Regulatory 153

10.3 Network Planning and Design 153

10.3.1 Cell Site Design 154

10.3.2 Network Function Placement 155

10.3.3 Dimensioning 155

10.3.3.1 Application Dimensioning 155

10.3.3.2 Platform Dimensioning 156

10.3.4 Virtualization Impact 156

10.3.4.1 Non-Uniform Memory Access 157

10.3.4.2 Hyper-Threading 157

10.3.4.3 CPU Pinning 157

10.3.4.4 Huge Page 157

10.3.4.5 Single Root Input/Output Virtualization 158

10.3.4.6 PCI Passthrough 158

10.3.4.7 Data Plane Development Kit 158

10.3.4.8 Resource Director Technology 158

10.3.4.9 Cache Allocation Technology 158

10.3.4.10 Resource Overcommitment 159

10.3.4.11 Operating System 159

10.3.4.12 K8S Impact 159

10.3.5 Networking Hardware 159

10.3.6 Hardware Type 160

10.3.7 Reliability and Availability 160

10.3.8 Impact of Network Slicing 161

10.4 Network Deployment 162

10.4.1 DU Deployment 162

10.4.1.1 DU Deployed at a Centralized Data Center 162

10.4.1.2 Timing Design When DU is at the dc 163

10.4.1.3 DU Deployed at Cell Site 164

10.4.2 CU Deployment 165

10.4.3 Radio Unit Instantiation 165

10.4.4 Radio Unit Management 166

10.4.4.1 Hierarchical Management Architecture Model 166

10.4.4.2 Hybrid Management Architecture Model 166

10.4.5 Network Management 166

10.4.6 Public Cloud Provider Overview 167

10.4.6.1 Native Services 167

10.4.6.2 CD Pipeline 167

10.4.6.3 Cluster Creation and Management 168

10.4.6.4 Transport Design 168

10.4.7 Life Cycle Management of NFs 168

10.4.8 Network Monitoring and Observability 169

10.4.8.1 Prometheus 169

10.4.8.2 Jaeger 169

10.4.8.3 Fluentd and Fluentbit 169

10.4.8.4 Probing 169

10.4.9 Network Inventory 169

10.4.10 Building the Right Team 170

10.5 Conclusion 170

Bibliography 170

11 Open RAN Test and Integration 172
Ian Wong, Ph.D.

11.1 Introduction 172

11.2 Testing Across the Network Life Cycle 174

11.3 O-RAN ALLIANCE Test and Integration Activities 175

11.3.1 Test Specifications 175

11.3.2 Conformance Test Specifications 176

11.3.2.1 A1 Interface Test Specification (O-RAN.WG2.A1TS) 178

11.3.2.2 E2 Interface Test Specification (O-RAN.WG3.E2TS) 179

11.3.2.3 Open Fronthaul Conformance Test Specification (O-RAN.WG4.CONF) 180

11.3.2.4 Xhaul Transport Testing (O-RAN.WG9.XTRP-Test.0) 181

11.3.2.5 Security Test Specifications (O-RAN.SFG.Security-Test-Specifications) 181

11.3.3 Interoperability Test Specifications 181

11.3.3.1 Fronthaul Interoperability Test Specification (O-RAN.WG4.IOT.0-09.00) 182

11.3.3.2 Open F1/W1/E1/X2/Xn Interoperability Test Specification (O-RAN.WG5.IOT.0) 183

11.3.3.3 Stack Interoperability Test Specification (O-RAN.WG8.IOT) 183

11.3.4 End-to-End Test Specifications 185

11.3.5 O-RAN Certification and Badging 186

11.3.6 Open Test and Integration Centers 187

11.3.7 O-RAN Global PlugFests 189

11.4 Conclusion 189

Bibliography 189

12 Other Open RAN Industry Organizations 191
Aditya Chopra, Manish Singh, Prabhakar Chitrapu, Luis Lopes, and Diane Rinaldo

12.1 Telecom Infra Project 191

12.1.1 Organizational Structure 192

12.1.2 Core Activities 194

12.2 Trials and Deployments 194

12.3 Small Cell Forum 195

12.3.1 A History of Openness at SCF 196

12.3.2 Alignment with the 3GPP and O-RAN Alliance Solutions 196

12.4 3rd Generation Partnership Project 197

12.5 Open RAN Policy Coalition 199

12.6 Conclusion 200

Bibliography 200

Index 201