O-RAN ALLIANCE Summit - Accelerating Open RAN Adoption
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O-RAN ALLIANCE Introduces 33 New Specifications Released Since March 2021

By Chih-Lin I and Sachin Katti.

O-RAN ALLIANCE’s Minimum Viable Plan (MVP) Towards Commercial O-RAN Solutions

O-RAN ALLIANCE’s specification effort, open software development, as well as testing and integration, focus on priorities set by its operator members needs. This approach allows the O-RAN ecosystem players to prioritize the delivery of a minimum viable set of end-to-end O-RAN solutions applicable in commercial networks.

33 New or Updated O-RAN Specifications Released since March 2021

O-RAN technical specification effort grows with healthy momentum. We keep expanding Radio Access Networks (RAN) standards with open interfaces and intelligent RAN functions. All published specifications are available to the general public upon agreement to the O-RAN ALLIANCE Adopter License.

O-RAN specifications published since March 2021 introduce the initial version of 11 new technical specifications or reports, comprising:

  • A1 interface: Type Definition Specification
  • Hardware Reference Design Specification for Fronthaul Gateway
  • Hardware Reference Design Specification for Outdoor Micro Cell with Split Architecture Option 7.2
  • Outdoor Micro Cell Hardware Architecture and Requirements (FR1) Specification
  • Outdoor Macrocell Hardware Architecture and Requirements (FR1) Specification
  • Synchronization Architecture and Solution Specification
  • Management interfaces for Transport Network Elements
  • Security Threat Modeling and Remediation Analysis
  • Security Protocols Specifications
  • End-to-end Test Specification
  • Certification and Badging Processes and Procedures

Another 22 newly released specifications bring updates to existing O-RAN standards, enriching them with new functions or updated features according to the O-RAN Architecture.

Below is a brief overview of all recently published specifications:


WG1: Use Cases and Overall Architecture Workgroup

O-RAN Architecture Description v4.0

The O-RAN Architecture Description document specifies the overall architecture of O-RAN. It describes all the O-RAN functions and relevant interfaces that connect these functions. This version enhances the O-RAN control loops by making their execution times and interactions dependent on the use cases. It further elucidates that the execution times of the Non-Real-Time (Non-RT) and Near-Real-Time (Near-RT) control loops may overlap as dictated by the use cases. Designating the O1 interface between the Service Management and Orchestration (SMO) and the O-RU as an For Future Study (FFS) topic is another notable modification of this version. Other improvements include designating color coding to all logical interfaces shown in the architecture figures.

O-RAN Use Cases Analysis Report v5.0

This document describes potential O-RAN use cases at a very high level, emphasizing how each use case is enabled by the O-RAN Architecture along with basic input data expectations and resulting actions. This version includes 1 new use case (BBU Pooling to achieve RAN Elasticity) and updated use cases (Massive MIMO Optimization).

O-RAN Use Cases Detailed Specification v5.0

This document describes selected O-RAN use cases in further detail to facilitate relevant O-RAN Work Groups to define requirements for associated O-RAN functions and interfaces. This version includes 1 new use case (Signaling Storm Protection) and updated use cases (Massive MIMO Optimization).

O-RAN Slicing Architecture Specification v4.0

This document describes O-RAN slicing related use cases, requirements and architecture. Along with requirements and a reference slicing architecture, slicing related impact to O-RAN functions and interfaces is also captured. This version includes addition of transport network slicing sub-section and two detailed procedures: O-RAN Network Slice Subnet Instance (O-NSSI) Allocation and O-NSSI Deallocation.

O-RAN ALLIANCE Logical Architecture

WG2: The Non-Real-Time RAN Intelligent Controller (Non-RT RIC) and A1 Interface Workgroup

O-RAN Non-RT RIC & A1 Interface: Use Cases and Requirements v3.0

This document describes the set of use cases that have been approved within O-RAN Work Group 2. It helps identify requirements for Non-Real-Time Radio Intelligent Controller (Non-RT RIC) and A1 interface and will lead to formal drafting of interface specifications. The motivation, resources, steps involved and data requirements for each use case are described, followed by the respective functional and non-functional requirements derived therein.

O-RAN Non-RT RIC Functional Architecture Technical Report v1.01

Non-RT RIC functional architecture technical report offers the rApp definition, the Non-Real Time (RT) Radio Intelligent controller (RIC) Framework functions and the R1 interface. The external interfaces are also described. The requirements on the Non-RT RIC framework and rApp are collected for the future specification of the Non-RT RIC functional architecture. Version 1.01 adds service-based view of non-RT RIC architecture and functionalities and enhances the AI/ML functionalities.

O-RAN AI/ML workflow description and requirements v1.02

This document provides details on AI/ML lifecycle management including model design, composition, and model runtime access to data and the model deployment solutions. Criteria for determining various ML training host and ML inference host deployment options is highlighted. It also elaborates on AI/ML models used in O-RAN use cases aligned with the WG1-Use Case Task Group work effort.

O-RAN A1 interface Application Protocol specification (A1 AP) v03.01

Version 03.01 separates the OpenAPI aspects of the A1 interface from the Policy and Enrichment Information data models. The OpenAPI specification remains in the A1AP, and the data models are moved to a new specification, A1 interface Type Definitions.

O-RAN A1 interface: Transport Protocol specification (A1 TP) v01.01

This document specifies the transport protocol of the A1 interface. Version 01.01 clarifies the default port number to be used for the A1 interface and adds some editorial improvements.

O-RAN A1 interface General Aspects & Principles Specification (A1 GA&P) v02.02

Version 02.02 adds a lot of editorial improvements and a definition of the life cycle of A1 policies.

O-RAN A1 interface: Type Definitions specification (A1 TD) V01.00

This new specification defines the data types for A1 Policies and A1 Enrichment Information in a reusable and extensible way. It allows new policy types to be created independently of the generic application protocol parts. The policy types that were previously defined in A1 interface Application Protocol specification are now included in this specification.


WG3: The Near-Real-Time RAN Intelligent Controller (Near-RT RIC) and E2 Interface Workgroup

O-RAN Near-RT RIC Architecture Specification v2.0

The document describes the internal architecture of O-RAN Near-Real-Time RAN Intelligent Controller (Near-RT RIC) from a functional perspective, including the general principles, requirements, basic functions and Near-RT RIC API. This version introduces API procedures stage-2 definition, including A1 related API, E2 related API, management API, SDL API and enablement API.


WG4: The Open Fronthaul Interfaces Workgroup

O-RAN Open Fronthaul M-Plane Specification v06.00

This document describes O-RAN Open Fronthaul M-Plane Specification, which defines the Management Plane of the Open Fronthaul Interface as well as the associated YANG models. This specific version is v06.00 in which there are several clarifications and a few new capabilities, most significantly support for Netconf/TLS and IPv6-only O-RUs.

O-RAN Open Fronthaul CTI TC-Plane Specification v02.00

This document describes O-RAN Open Fronthaul CTI TC-Plane Specification, which defines an interface between the O-DU and a PON or DOCSIS Transport Node (TN) to enable fronthaul traffic to transit what would otherwise be a too-high-latency network. This version adds several clarifications and a few new capabilities, including the handling of UL C-Plane traffic (used for LAA) and support for pattern normalization.

O-RAN Open Fronthaul Conformance Test Specification v03.00

This document describes O-RAN Open Fronthaul Conformance Test Specification, which defines conformance tests of the Open Fronthaul Interface. This version adds a few new test capabilities including O-DU Synchronization tests.

O-RAN Open Fronthaul CUS-Plane Specification v06.00

This document describes O-RAN Open Fronthaul CUS-Plane Specification, which defines the Control Plane, User Plane and Synchronization Plane of the Open Fronthaul Interface. This version adds several clarifications and a few new capabilities, most significantly special provisions for sending SRS from O-RU to O-DU in an efficient manner.

O-RAN Open Fronthaul CTI TM-Plane Specification v02.00

This document describes O-RAN Open Fronthaul CTI TM-Plane Specification, which defines an interface between the O-DU and a PON or DOCSIS Transport Node (TN) to enable fronthaul traffic to transit what would otherwise be a too-high-latency network. This version adds several clarifications and a few new capabilities, including enhancements for the handling of C-Plane traffic and support for pattern normalization.

O-RAN Open Fronthaul IOT Specification v04.00

This document describes O-RAN Open Fronthaul IOT Specification, which defines tests to validate the ability for O-DU and O-RU equipment to operate together using the the Open Fronthaul Interface. This version adds several clarifications and a few new capabilities, most significantly a new set of IOT Profiles covering the mMIMO use case.


WG5: The Open F1/W1/E1/X2/Xn Interface Workgroup

O-RAN Interoperability Test Specification (IOT) v2.0

This document specifies Inter-operability tests for RAN Node from different vendors implemented in accordance to the WG5 C-plane and U-plane profiles. This version focuses on:

  • X2 interoperability testing (Devices under Tests (DUTs) are eNB and en-gNB)
  • F1 interoperability testing (DUTs are en-gNB consisting of the gNB-CU and gNB-DU)
  • Xn interoperability testing (DUTs are gNBs)

This version further introduces:

  • 15 new test cases for use cases specified in WG5 profiles
  • Maintenance of the existing test cases

O-RAN NR U-plane profile v4.0

The scope of U-Plane profile specification is to further clarify (i.e. profile) the expected behavior for each RAN node (still within the scope of the 3GPP specifications), e.g. usage of IEs for each use case, general behavior of each node, etc. The document contains profiles of X2/F1/Xn U-Plane procedure for EN-DC use cases, NR-SA use cases and NR-DC use cases. This version mainly introduces updates of the existing use cases to follow the latest 3GPP specs.

O-RAN NR C-plane profile 4.0

The scope of C-Plane profile specification is to further clarify (i.e. profile) the expected behavior for each RAN node (still within the scope of the 3GPP specifications), e.g. usage of IEs for each use case, general behavior of each node, etc. The document contains profiles of X2/F1/Xn C-Plane procedure for EN-DC use cases, NR-SA use cases and NR-DC use cases. This version of the C-Plane profile spec mainly introduces:

  • Additional use cases, mainly NR-DC use cases are newly introduced in this version
  • Updates of the existing use cases to follow the latest 3GPP specs.
  • Fault corrections

WG7: The White-box Hardware Workgroup

O-RAN Hardware Reference Design Specification for Indoor Picocell (FR1) with Split Architecture Option 7-2 v2.0

This specification describes one white box hardware reference design example for indoor deployments. This version covers:

  • The reference designs for O-CU, O-DU7-2, O-RU7-2 and FHGW7-2/FHGW7-2 → 8.  FHGW7-2 → 8 will be used for Base stations having requirements to change their fronthaul interfaces from a split option from 7-2 to a split option 8.
  • Major revision of the O-RU architecture figures and added text for explaining the figures.

This version of the specification is compliant to Indoor Picocell Hardware Architecture and Requirement (FR1 Only) v01.00.

O-RAN Hardware Reference Design Specification for Outdoor Micro Cell with Split Architecture Option 7.2 v1.0

This document specifies system requirements and high-level architecture for the Outdoor Micro Cell for FR1 deployment scenario as specified in the Deployment Scenarios and Base Station Classes document and Microcell Hardware Architecture and Requirement (FR1 Only).

O-RAN Hardware Reference Design Specification for Indoor Picocell (FR1) with Split Architecture Option 8 v2.0

This specification describes one white box hardware reference design example for indoor deployments. In this version you will find:

  • The reference designs for O-CU, O-DU8, O-RU8 and FHGW8.  FHGW8 is only used for interfacing O-DU8 with an O-RU8 stations.
  • A vendor specific CPRI Interface (in Annex 2), which includes User Plane data and Control and Management Plane transport mechanisms. This specification supports the Option 8 split fronthaul connection between O-DU8 and O-RU8(s). For indoor Picocell deployment case, it also supports FHGW8 between O-DU8 and O-RU8.
  • Major revisions including the O-RU architecture figures and added text for explaining the figures.

This version of the specification is compliant to  Indoor Picocell Hardware Architecture and Requirement (FR1 Only) v01.00.

O-RAN Outdoor Micro Cell Hardware Architecture and Requirements (FR1) Specification v1.0

This document specifies system requirements and high-level architecture for the Outdoor Micro Cell deployment scenario case as specified in the Deployment Scenarios and Base Station Classes document.

O-RAN Hardware Reference Design Specification for Fronthaul Gateway v1.0

This document specifies a hardware reference design for the fronthaul gateway. The fronthaul gateway can be used to terminate O-RAN fronthaul user, control, synchronization, and management planes for option 7-2x and to translate the signals to and from a number of CPRI interfaces (option 8). It can further multiplex or demultiplex option 7-2x fronthaul signals to or from a number of O-RUs. This version of the specification only supports option 7-2x to option 8 conversion and vice versa in addition to the transport of other traffic streams.

O-RAN Outdoor Macrocell Hardware Architecture and Requirements (FR1) Specification v1.0

This document specifies system requirements and high-level architecture for the Outdoor Macrocell deployment scenario case as specified in the Deployment Scenarios and Base Station Classes document (V2).


WG9: Open X-haul Transport WorkGroup

O-RAN Synchronization Architecture and Solution Specification 1.0

This document is intended to describe best practices for O-RAN Architecture and Solution for X-haul timing & synchronization. Beyond the solutions described in this document, other Architectures and Solutions may be adequate for X-haul timing & synchronization and can be considered in future versions of this document.

O-RAN Management interfaces for Transport Network Elements v1.0

This specification describes best practices for O-RAN transport Network Element (TNE) management interfaces. Beyond the solutions described in this document, other management solutions may be adequate for transport network element management and can be considered in future versions of this document. In this version, first generic requirements are given for these interfaces with more specific technology-related recommendations.


SFG: Security Focus Group

O-RAN Security Threat Modeling and Remediation Analysis v1.0

This document specifies the O-RAN Security Threat Modeling and Remediation Analysis. It identifies assets to be protected, analyzes the O-RAN components for vulnerabilities, examines potential threats associated with those vulnerabilities and provides security principles, which stakeholders should address when building a secure end-to-end O-RAN system.

O-RAN Security Protocols Specifications v1.0

This document specifies Secure Shell (SSH) and Transport Layer Security (TLS) to be used for O-RAN implementations.


TIFG: Test and Integration Focus Group

O-RAN End-to-end Test Specification v1.0

This test specification is focused on validating the end-to-end system functionality, performance, and key features of the O-RAN system as a black box.

O-RAN Certification and Badging Processes and Procedures v1.0

This document describes the certification and badging processes and associated detail technical procedures for the Open Testing and Integration Centres (OTIC) and various other testing entities.

Chih-Lin I
(China Mobile Research Institute)

Co-chair of the O-RAN ALLIANCE’s Technical Steering Committee,
Member of O-RAN Executive Committee,
Chief Scientist of China Mobile.

Chih-Lin I has been a distinguished expert with nearly 40 years of rich experience in wireless communications. She is a key proponent of ICDT convergence for future wireless networks. She proposed 5G being “Green and Soft” from the first day of 5G design. The philosophy continuously evolved and embraced “Open and Smart” later on, which laid out the foundation for O-RAN.


Sachin Katti
(Stanford University)

Co-chair of the O-RAN ALLIANCE’s Technical Steering Committee,
Professor of EE & CS at Stanford University.

Sachin Katti is also Co-Founder and ex-CEO of Uhana (now part of VMware), as well as previously co-founder of Kumu Networks, which is commercializing breakthrough research from his lab on full duplex radios. He received his PhD in EECS from MIT in 2009. His research has won numerous awards, including the 2008 ACM Doctoral Dissertation Award - Honorable Mention, the George Sprowls Award for Best Doctoral Dissertation in EECS at MIT, the IEEE William Bennett Prize, and the Best Student Paper Award at ACM SIGCOMM 2012.