Dr. Nishith D. Tripathi is a Research Associate Professor at Virginia Tech. Dr. Tripathi has 24 years of industry experience at Nortel Networks, Huawei Technologies, Award Solutions, and Samsung Research America. He is a co-author of five books related to cellular communications, AI, 5G, and NTN.

Dr. Vijay K. Shah is an Assistant Professor at North Carolina State University. Prior to joining NC State, he was an Assistant Professor at George Mason University (GMU) and a Research Assistant Professor at Virginia Tech.

About the Authors xiii

Preface xv

Acknowledgments xix

Acronyms xxi

About the Companion Website xxxi

1 Introduction to O-RAN 1

1.1 Evolution of Cellular Technologies 1

1.2 Components of Cellular Systems 3

1.3 Evolution of the RAN 4

1.3.1 Horizontal Disaggregation of RAN: A Protocol Perspective 5

1.4 Introduction to the O-RAN ALLIANCE and the O-RAN Architecture 7

1.4.1 O-RAN ALLIANCE: A Brief Overview 7

1.4.2 The O-RAN Architecture in a Nutshell 8

1.4.3 Groups in the O-RAN ALLIANCE 10

1.5 Driving Forces Behind O-RAN 10

1.6 O-RAN Ecosystem 12

1.7 O-RAN Use Cases 14

1.7.1 Context-Based Dynamic HO Management for V2X 14

1.7.2 Flight Path-Based Dynamic UAV Radio Resource Allocation 15

1.7.3 Radio Resource Allocation for UAV Application Scenario 15

1.7.4 QoE Optimization 16

1.7.5 Traffic Steering 16

1.7.6 Massive MIMO Beamforming Optimization 16

1.7.7 RAN Sharing 17

1.7.8 QoS-Based Resource Optimization 17

1.7.9 RAN Slice SLA Assurance 17

1.7.10 Multivendor Slices 18

1.7.11 3GPP 4G/5G Dynamic Spectrum Sharing (DSS) 18

1.7.12 NSSI Resource Allocation Optimization 18

1.7.13 Local Indoor Positioning in RAN 19

1.7.14 Massive MIMO SU/MU-MIMO Grouping Optimization 19

1.7.15 O-RAN Signaling Storm Protection 19

1.7.16 Congestion Prediction and Management 20

1.7.17 Industrial IoT Optimization 20

1.7.18 BBU Pooling to Achieve RAN Elasticity 21

1.7.19 Integrated SON Function 22

1.7.20 Shared O-RU 22

1.7.21 Energy Saving 23

1.7.22 MU-MIMO Optimization 23

1.7.23 Sharing Non-RT RIC Data with the Core 23

1.7.24 Industrial Vision SLA Assurance 25

1.7.25 Non-Public Network (NPN) RAN-Sharing via Midhaul for Multioperator Coverage 25

1.7.26 Interference Detection and Optimization 25

1.8 O-RAN: Accomplishments, Technical Priorities, and Potential Future Work 26

1.8.1 O-RAN Accomplishments 26

1.8.2 O-RAN Technical Priorities 26

1.8.3 Role of O-RAN Beyond 5G 27

1.9 Major Takeaways of the Chapter 27

References 28

2 O-RAN Architecture 31

2.1 O-RAN Logical Architecture 31

2.2 O-RAN Components: A Closer Look 34

2.2.1 SMO and Non-RT RIC: A Closer Look 34

2.2.1.1 SMO Support for FCAPS to O-RAN Network Functions 34

2.2.1.2 SMO: O-Cloud Management, Orchestration, and Workflow Management 35

2.2.1.3 Non-RT RIC 35

2.2.1.4 Logical Functions in the Non-RT RIC Framework or the SMO Framework 38

2.2.2 Near-RT RIC 39

2.2.3 O-CU-CP 42

2.2.4 O-CU-UP 43

2.2.5 O-DU 44

2.2.6 O-RU 45

2.2.7 O-eNB 46

2.2.8 O-Cloud 47

2.3 O-RAN Interfaces: A Closer Look 49

2.3.1 O1 Interface 49

2.3.2 O2 Interface 52

2.3.3 A1 Interface 53

2.3.3.1 A1 Policies and A1 Policy Management 53

2.3.3.2 A1 Enrichment Information (EI) and A1 EI Service 54

2.3.3.3 ml Model Management Service 54

2.3.3.4 A1 Interface Protocol Stack 54

2.3.4 E2 Interface 55

2.3.5 Open FH Interface 58

2.3.5.1 M-Plane: A Closer Look 58

2.3.5.2 CUS-Plane: A Closer Look 60

2.3.6 O-Cloud Notification Interface 63

2.3.7 CTI (Cooperative Transport Interface) 63

2.3.8 3GPP Interfaces Relevant to O-RAN 65

2.4 Functional Split 7.2x 66

2.5 Inside O-RAN Domain: Functional Distribution Between O-RAN and Other SDOs 68

2.6 O-RAN Deployment Scenarios 68

2.6.1 Hierarchical Cloud Architecture 68

2.6.2 O-RAN Cloud Deployment Scenarios 69

2.6.3 Example Mapping of O-RU Functions to Hierarchical O-RAN Cloud Architecture 70

2.7 Major Takeaways of the Chapter 71

References 72

3 O-RAN Applications: xApps and rApps 75

3.1 O-RAN Control Loops 75

3.2 Near-RT Control Loop: Near-RT RIC and xApps 76

3.2.1 Near-RT Internal Components of the Near-RT RIC 76

3.2.2 Open-Source Near-RT RIC Implementations 78

3.3 Near-RT RIC xApps: Enabling RAN Customization 79

3.3.1 Defining xApps 79

3.3.2 Embracing Evolving Standards 80

3.4 E2 Interface: Empowering RAN Control and Data Exchange 81

3.4.1 E2 Application Protocol (E2AP) 82

3.4.2 E2 Service Models 84

3.5 xApp Use Cases 86

3.5.1 KPIMON xApp 86

3.5.2 RAN Slicing xApp 88

3.5.2.1 RAN Slicing Configuration and Resource Allocation 89

3.5.2.2 Throughput Performance 89

3.6 Machine Learning (ML)-Based xApps 90

3.6.1 AI/ML Workflow 90

3.6.1.1 Data Collection and Processing 91

3.6.1.2 Training 91

3.6.1.3 Validation and Publishing 91

3.6.1.4 Deployment 91

3.6.1.5 AI/ML Execution and Inference 91

3.6.1.6 Continuous Operations 91

3.6.2 Example ML-Based xApp Use Cases 92

3.7 xApp Workflow 93

3.8 xApp Development: A Closer Look 94

3.8.1 Undeployment/Removal of xApps 101

3.9 Non-RT Closed Loop: Non-RT RIC and rApps 102

3.9.1 Requirements for the Non-RT RIC Framework 102

3.9.2 Non-RT RIC Architecture 103

3.9.2.1 A1 Interface: General Principles 104

3.9.2.2 Role of the A1 Interface 105

3.9.2.3 A1-P Management Service (A1-P) 106

3.9.2.4 A1 Enrichment Information Service (A1-EI) 106

3.9.2.5 A1 ML Model Management Service (A1-ML) 107

3.9.3 R1 Interface 108

3.9.3.1 R1 Service Definitions 109

3.9.4 Service Management and Orchestration 112

3.9.5 rApp Use Cases 113

3.9.5.1 Traffic Steering Use Case 113

3.9.5.2 QoE Use Case 114

3.9.5.3 Operational Flow 114

3.10 Real-Time RIC Closed Loop: RT RIC and Apps/dApps 115

3.10.1 Resource Block (RB) Scheduling App 117

3.10.1.1 Workflow for a RB Scheduling App 117

3.10.1.2 Other Features and Future Directions 117

3.10.2 Beam Management dApp Use Case 118

3.10.2.1 Key Elements and Their Functions 118

3.10.2.2 Operational Flow for Beam Management 118

3.11 Multi-time-scale RIC Framework 119

3.11.1 Use Case: SPARC for Multi-Site Spectrum Management 120

3.11.2 Key Elements and Operational Flow for SPARC Framework 120

3.12 Major Takeaways of the Chapter 121

References 122

4 O-RAN Security 125

4.1 Motivation for O-RAN Security 125

4.1.1 Vulnerabilities of O-RAN Compared to Non-O-RAN Implementations 126

4.1.2 Scope of O-RAN Security Specifications 127

4.1.2.1 Within O-RAN Security Scope 127

4.1.2.2 Outside O-RAN Security Scope 128

4.1.3 Critical Assets 128

4.1.3.1 Critical Data Assets 129

4.1.3.2 Critical Component Assets 129

4.1.4 Protection Levels 130

4.2 Methodology of O-RAN Security Analysis 130

4.2.1 Stage 1: Risk Identification 130

4.2.2 Stage 2: Risk Assessment 133

4.2.3 Stage 3: Risk Treatment 133

4.3 Threat Model 134

4.3.1 Building Blocks of the Threat Model 134

4.3.2 An Overview of O-RAN Security Threats 135

4.3.2.1 Threats Against O-RAN System 135

4.3.2.2 Threats Against O-Cloud 138

4.3.2.3 Threats to Open-Source Code 141

4.3.2.4 Physical Threats 141

4.3.2.5 Threats Against 5G Radio Networks 142

4.3.2.6 Threats Against ML System 142

4.3.2.7 Protocol Stack Threats 143

4.3.3 O-RAN Threat Agents 143

4.3.4 Potential Security Vulnerabilities of O-RAN 145

4.4 Risk Assessment 145

4.4.1 Key Elements of Risk Assessment 146

4.4.2 O-RAN Risk Assessment Analysis: A Brief Overview 148

4.5 Security Principles, Security Requirements, and Security Controls in O-RAN 152

4.5.1 O-RAN Security Principles 152

4.5.2 Security Requirements for O-RAN 157

4.5.3 Security Controls for O-RAN 159

4.6 O-RAN Security Protocols 161

4.6.1 Security Protocols in a Nutshell 161

4.6.2 SSH 161

4.6.3 TLS 162

4.6.4 DTLS 162

4.6.5 NETCONF over Secure Transport 163

4.6.6 IPsec 163

4.6.7 CMPv 2 164

4.6.8 OAuth 2.0 165

4.7 O-RAN Security Testing 165

4.7.1 Tools for O-RAN Security Testing 166

4.7.2 Test Report Template 166

4.7.3 Security Testing Framework 168

4.7.3.1 Security Protocol Validation 168

4.7.3.2 Common Network Security Tests and System Security Tests for O-RAN Components 171

4.7.3.3 Software Security Evaluation 174

4.7.3.4 Open Fronthaul Security Validation 175

4.7.3.5 Validation of O-RAN-Component-Specific Security Protection Mechanisms 175

4.7.3.6 Security Testing of xApps and rApps 177

4.7.3.7 Validation of Miscellaneous Components 178

4.8 Major Takeaways of the Chapter 178

References 179

5 O-RAN Ecosystem 181

5.1 Internal and External O-RAN Ecosystems 181

5.2 Internal O-RAN Ecosystem 182

5.2.1 Work Groups of O-RAN Specification Efforts 182

5.2.1.1 WG1 Work Products 183

5.2.1.2 WG2 Work Products 183

5.2.1.3 WG3 Work Products 184

5.2.1.4 WG4 Work Products 184

5.2.1.5 WG5 Work Products 184

5.2.1.6 WG6 Work Products 184

5.2.1.7 WG7 Work Products 184

5.2.1.8 WG8 Work Products 185

5.2.1.9 WG9 Work Products 185

5.2.1.10 WG10 Work Products 185

5.2.1.11 WG11 Work Products 186

5.2.2 Focus and Research Groups of O-RAN 186

5.2.3 Testing and Integration Entities 191

5.2.4 O-RAN Demonstrators and O-RAN Field Trials and Development Entities 194

5.2.5 O-RAN Software Community 195

5.3 External Ecosystem 196

5.3.1 Standards Developing Organizations (SDOs) 197

5.3.2 Commercial Developers of xApps...