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Open RAN

Architecture

Overall structure of the whole network would look like follows (at least to me -:)). I know it is too much simplified at CoreNetwork part... but I think this is good enough for OpenRAN since it is mostly about RAN, not about Core Network. The only important part of Core Network in this context would be the interface to RAN part which is shown in this illustration.

Now let's look into RAN part which is labeled as Segment 1. Probably the ideal (maximum) level of modularization and separation of RAN can be something as shown below (Segment 1) which is described in 3GPP 38.801. If we can provide industry standard interface at all the split level labeled as Option 1 ~ 8, we may implement RAN with the components from all over the provides and put them together as lego block. But in practice, it may be a little overkill to define too many interfaces like this at this point. In most of OpenRAN standization and implementation, we focus mostly on Option 7 and 2 (In some SDR based implementation especially for LTE, Option 8 is also a common interface). Actually in recent Open RAN activities, Option 7 has been evolved into a few different flavours and the most popular one is 7.2x.

NOTE : There can many different implementation of open RAN and the overall architecture would vary depending on the specific implementation. But in this note, I would write on this based on ORAN and 3GPP since they are sharing the specification in public and I think they will be main stream of Open RAN implementation.

O-RAN Architecture

The architecture of a RAN defined by O-RAN specification looks as below. The blue part shown below indicates the components that are commonly defined in 3GPP as well.

The Open FH interface (the interface between O-DU and O-RU) corresponds to Option 7 and F1 interface corresponds to Option 2. As you see here, the interface between DU and CU and the interfaces among other RANs (e.g, X2, Ng, Xn etc) are also commonly defined by 3GPP.

< Figure 4.1 2: Logical Architecture of O-RAN >

Source : O-RAN.WG1.O-RAN-Architecture-Description

O-RAN Specifications

Followings are the list of OpenRAN specification from O-RAN allience. This is just a list for you to do quick check on what kind of subjects are specified. You can download each of the specification from O-RAN allience specification site.

WG1: Use Cases and Overall Architecture Workgroup
	O-RAN Architecture Description
	O-RAN Operations and Maintenance Architecture
	O-RAN Operations and Maintenance Interface
	O-RAN Use Cases Detailed Specification
	O-RAN Use Cases Analysis Report
	O-RAN Slicing Architecture
	O-RAN Study on O-RAN Slicing
	O-RAN Information Model and Data Models Specification
WG2: The Non-Real-Time RAN Intelligent Controller and A1 Interface Workgroup
	O-RAN Non-RT RIC Architecture
	O-RAN A1 interface: Type Definition
	O-RAN AI/ML Workflow Description and Requirements
	O-RAN A1 interface: General Aspects and Principles
	O-RAN A1 interface: Application Protocol
	O-RAN A1 interface: Transport Protocol
	O-RAN Non-RT RIC & A1 Interface: Use Cases and Requirements
	O-RAN Non-RT RIC: Functional Architecture
WG3: The Near-Real-Time RIC and E2 Interface Workgroup
	O-RAN Near-RT RAN Intelligent Controller Near-RT RIC Architecture
	O-RAN Near-Real-time RAN Intelligent Controller Architecture & E2 General Aspects and Principles
	O-RAN Near-Real-time RAN Intelligent Controller, E2 Application Protocol
	O-RAN Near-Real-time RAN Intelligent Controller E2 Service Model
	O-RAN Near-Real-time RAN Intelligent Controller E2 Service Model (E2SM), RAN Function Network Interface (NI)
	O-RAN Near-Real-time RAN Intelligent Controller E2 Service Model (E2SM) KPM
WG4: The Open Fronthaul Interfaces Workgroup
	O-RAN Open Fronthaul Conformance Test Specification
	O-RAN Fronthaul Cooperative Transport Interface Transport Control Plane Specification
	O-RAN Fronthaul Interoperability Test Specification (IOT)
	O-RAN Fronthaul Control, User and Synchronization Plane Specification
	O-RAN Management Plane Specification
	O-RAN Cooperative Transport Interface Transport Management Plane Specification
WG5: The Open F1/W1/E1/X2/Xn Interface Workgroup
	O-RAN O1 Interface specification for O-CU-UP and O-CU-CP
	O-RAN Interoperability Test Specification (IOT)
	O-RAN Transport Specification
	O-RAN NR C-plane profile
	O-RAN NR U-plane profile
WG6: The Cloudification and Orchestration Workgroup
	O-RAN O-Cloud Notification API Specification for Event Consumers
	O-RAN O2ims Interface Specification
	O-RAN Acceleration Abstraction Layer FEC Profiles
	O-RAN Acceleration Abstraction Layer General Aspects an Principles
	O-RAN Orchestration Use Cases and Requirements for O-RAN Virtualized RAN
	O-RAN O2 General Aspects and Principles Specification
	O-RAN Cloud Platform Reference Design
	O-RAN Cloud Architecture and Deployment Scenarios for O-RAN Virtualized RAN
WG7: The White-box Hardware Workgroup
	O-RAN Hardware Reference Design Specification for Indoor Pico Cell with Fronthaul Split Option 6
	O-RAN Hardware Reference Design Specification for Indoor Picocell FR1 with Split Architecture Option 7-2
	O-RAN Hardware Reference Design Specification for Indoor Picocell FR1 with Split Architecture Option 8
	O-RAN Indoor Picocell Hardware Architecture and Requirement (FR1 Only) Specification
	O-RAN Deployment Scenarios and Base Station Classes
	O-RAN Hardware Reference Design Specification for Outdoor Micro Cell with Split Architecture Option 7-2
	O-RAN Outdoor Micro Cell Hardware Architecture and Requirements (FR1) Specification
	O-RAN Hardware Reference Design Specification for Fronthaul Gateway
	O-RAN Outdoor Macrocell Hardware Architecture and Requirements (FR1) Specification
WG8: Stack Reference Design Workgroup
	O-RAN Stack Interoperability Test Specification
	O-RAN Base Station O-DU and O-CU Software Architecture and APIs
WG9: Open X-haul Transport Workgroup
	O-RAN Xhaul Transport Testing
	O-RAN Synchronization Architecture and Solution Specification
	O-RAN Management interfaces for Transport Network Elements
	O-RAN WDM-based Fronthaul Transport
	O-RAN Xhaul Packet Switched Architectures and Solutions
WG10: OAM Workgroup
	O-RAN Operations and Maintenance Interface Specification
	O-RAN Operations and Maintenance Architecture

Video

Reference : Specification

[1] O-RAN Fronthaul Spilt Option 7-2x