O-RAN ALLIANCE Introduces Minimum Viable Plan Towards Commercial O-RAN Solutions and 28 New O-RAN Specifications Released Since November 2020

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

O-RAN specification effort, open software development, as well as testing and integration, will focus on priorities set by its operator members. This approach will allow 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.

The first release of the MVP includes already published specifications and additional work items in the following areas:

  • Open fronthaul specifications provide fully specified control, user and synchronization interface, management plane interface between O-RU and O-DU, and relevant conformance and interoperability tests, enabling multi-vendor interoperability.
  • Open transport defines the requirements of xhaul transport, proposes the best practices of deploying WDM and IP technologies in xhaul.
  • Open hardware offers hardware reference designs for different modes of indoor picocell, outdoor microcell, outdoor Macro cell and open fronthaul gateway to accelerate the use of whitebox and facilitate RAN ecosystem diversity.
  • Open stack provides a software reference design for O-CU/O-DU architecture, interfaces, internal modules, and APIs, to promote and guide the open source software development.
  • Open cloud presents O-Cloud reference design with the fundamental synchronization requirements and real life deployment recommendations.
  • Testing and integration sets the criteria and guidelines for the formation of Open Testing and Integration Centers (OTICs), ensuring consistency and quality of the testing of O-RAN products and solutions.

Subsequent O-RAN releases will extend the MVP with additional features and functionalities based on continuing surveys and updates of the operators’ deployment priorities.

28 New or Updated O-RAN Specifications Released since November 2020

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 November 2020 introduce the initial version of 10 new technical specifications or reports, comprising:

  • Information Model and Data Models
  • Non-Real-Time Radio Intelligent Controller (Non-RT RIC) Functional Architecture
  • Cooperative Transport Interface Transport Management Plane (CTI-TMP)
  • O1 Interface specification for O-DU
  • Acceleration Abstraction Layer (AAL) General Aspects and Principles
  • White Box Hardware Reference Design Specification for Indoor Pico Cell with Split Option 6
  • Stack IOT Test
  • WDM-based Fronthaul Networks
  • Xhaul Transport Requirements
  • Xhaul Packet Switched Architectures and Solutions

Another 18 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 the newly published documents.

WG1: Use Cases and Overall Architecture Workgroup

O-RAN Architecture Description v3.0

The O-RAN Architecture Description document specifies the overall architecture of O-RAN. It describes all of the O-RAN functions and relevant interfaces that connect these functions. This version introduces the functional architecture of Non-Real-Time Radio Intelligent Controller (Non-RT RIC) with a brief description of rApps, R1 interface, and Non-RT RIC Framework. Other enhancements include implementation options of Fronthaul Multiplexer (FHM) function and Fronthaul Gateway (FHGW) function; definition of Managed Application (MA); and addition of ‘legends’ in the architecture figures.

O-RAN O1 Interface v4.0

This specification defines O-RAN OAM interface functions and protocols for the O-RAN O1 interface, which is the management interface between Service Management and Orchestration (SMO) and O-RAN Managed Elements. Version 4 of this document introduces Trace Management for both file based and streaming trace and provides an informative annex on the use of stndDefined VES events.  More detail is provided on the supported format for restful notifications with updates in applicable existing services.  Additional updates in this version include Heartbeat Management Service, CM services in the area of Subscription Control, Provisioning and CM notifications, fault supervision to identify required notifications, and Performance Assurance with streaming Performance Measurement.

O-RAN OAM Architecture v4.0

The O-RAN OAM Architecture identifies management services, managed elements, functions and applications supported in O-RAN, including the interworking between SMO and O-RAN O-Cloud management components. Requirements are derived from end-to-end OAM use cases, including the initial provisioning of O-RAN service across VNFs and PNFs and the collection of measurement data. This version identifies the interfaces between SMO and Managed Elements for different models and deployment options. It also provides a framework for lifecycle management of applications delivered from a Solution Provider to a Service Provider/Network Operator.

O-RAN Use Cases Analysis Report v4.0

This document describes potential O-RAN use cases at a very high level, emphasizing how the use case is enabled by the O-RAN architecture along with basic input data and actions required. This version includes 4 new use cases: SU-MU MIMO TM Optimization, Signaling Storm Protection, Cell Congestion Prediction, and L2 IIoT Optimization.

O-RAN Use Cases Detailed Specification v4.0

This document describes selected O-RAN use cases in further details to facilitate relevant O-RAN Work Groups to define requirements for associated O-RAN functions and interfaces. This version includes 2 new use cases: DSS, Long Term NSSI Optimization.

O-RAN Slicing Architecture Specification v3.0

This document describes at a high level the O-RAN slicing related use cases, requirements and a reference slicing architecture, and slicing related impact to O-RAN functions and interfaces. This version includes requirements update to capture use case impacts, additional requirements for Multi-vendor slices use case, and addition of ONAP deployment options in the Annex section.

O-RAN Information Model and Data Models v1.0

The O-RAN Information Model and Data Models document specifies the Information Model and the Data Models that are foundational for O-RAN’s model-driven architecture and for the functions carried out over O-RAN interfaces.  This document includes information about existing standards and industry work referenced in O-RAN, e.g., a prosumer relationship between O-RAN and 3GPP.  It also describes the evolving methods and procedures with respect to a modeling continuum that aims to establish one common and coherent Information Model for 5G/LTE RAN from which Data Models may be generated either manually or automated with a set of tools.

O-RAN ALLIANCE Logical Architecture

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

O-RAN Use Case and Requirements Specification v2.1

The purpose of the use cases is to help identify requirements for Non-RT RIC and A1 interface, eventually leading to formal drafting of interface specifications. For each use case, the document describes the motivation, resources, steps involved and data requirements, followed by the Non-RT RIC and A1 requirements section detailing the functional and non-functional requirements derived from these use cases. This version p updates to Traffic Steering use case with multi-access network scenario enhancements.

O-RAN Non-RT RIC Functional Architecture Technical Report v1.0

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.

O-RAN A1 interface General Aspects & Principles Specification v2.1

The A1 General Aspects and Principles have been enhanced with the definition of the lifecycle management of A1 Enrichment Information (A1-EI). It includes details on the lifecycle of EI Types, EI jobs, and EI Results. These principles are further defined in the A1 Application Protocol.

O-RAN A1 interface Application Protocol specification v3.0

The A1 Application Protocol has been enhanced to introduce the service descriptions and data models to support the Non-RT RIC delivering Enrichment Information to the Near-RT RIC over the A1 interface.  Several enhancements to the A1 Policy (A1-P) aspects have been added, and the versioning and compatibility aspects of the A1 interface and services have been defined.

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

O-RAN Near-RT RIC Architecture Specification v1.1

This document describes the internal architecture of O-RAN Near-RT RIC from a functional perspective,including the general principles, requirements, basic functions and Near-RT RIC API. This version introduces updated requirements, a new platform function "API management services", and minor enhancements on xApp life-cycle management and O1 termination.

WG4: The Open Fronthaul Interfaces Workgroup

O-RAN Control, User and Synchronization Plane Specification v5.0

Version 5.0 of the specificaitons delivers enhanced C-Plane/U-Plane to increase fronthaul efficiency:

  • Includes enhancements for non-contiguous frequency allocations and frequency hopping
  • Enhancements to support CoMP CB
  • Support of ueID-based beamforming in mixed-numerology systems
  • Enhancements for Channel information based uplink beamforming
  • Support for generating advanced beamforming weights based on UE channel at O-RU.
  • PRACH support using section Type 1 (when PARCH is using same SCS as PUSCH)

Clarification on PRACH C/U-plane window timing reference and Section Type 3 usage.
Added selective transmission/reception using beam ID for a shared cell in O-RAN.
Added Cascade-FHM mode for shared cell scenario.
Multiple updates to clarify existing material, including:

  • Meaning of numPrbc = 0,
  • Clarification of freqOffset for mixed numerology and PRACH channels
  • Clarification of FFT sampling offset affects on UL U-plane timing.
  • Clarification on modulation compression with mixed MCS and correction of u-law com/decomp description
  • PRACH RB Indexing clarification for Section Type 3.
  • S-plane: Applicability of Category A+ TE/TAE metrics to LLS-C1/C2/C3/C4 topologies; O-DU behavior when sync is lost in shared cell scenario
  • Message type 6 U-plane clarification
  • Other miscellaneous corrections of typographical and formatting error

Renamed NMS to SMO.

O-RAN Management Plane Specification v5.0

In this specification and associated YANG models, following features are added on top of the previous version:

  • Updating mandatory cipher to AES128-CTR
  • Bandwidth management to avoid over-subscription of O-RU resources
  • Shared cell updates - selective Tx/Rx using Beam ID and cascaded FHM Operation
  • New capability to support coordinated (self) antenna calibration
  • New NACM permissions for SMO and hybrid O-DU
  • New optional feature for performing pnfRegistration
  • New optional feature for configured YANG subscriptions sent over JSON/REST

Version 5.0 also provides multiple updates to clarify existing material, including:

  • Clarification of operation of default account for certificate access, operation of supervision in lock state and PRACH patterns
  • Fixing copy/paste errors in the S-plane PTP status definitions
  • Corrected omissions from optional feature table
  • Clarification of the center bandwidth parameter
  • Replacement of previous NMS terms with SMO
  • Corrections to C/U plane monitoring for FHM

O-RAN Fronthaul Interoperability Test Specification (IOT) v3.0

Version 3.0 of the document delivers several enhancements over the previous versions, such as:

  • Updated mandatory cipher in M-Plane profiles to align with M-Plane
  • Updated M-Plane profile names to reflect profile content following CUS plane approach
  • Mandate that both IOT profile and Spec version are nominated to ensure appropriate parameters are referenced
  • Altered Synchronization description to more closely align to Conformance Spec/ITU-T
  • Replaced “slave” with “subordinate”
  • Miscellaneous editorial to text and figures

O-RAN Conformance Test Specification v2.0

Version 2.0 of the document delivers several enhancements over the previous versions, such as:

  • Align to the Fronthaul version CUS.0-v03.00
  • Add TDD FR1 Conducted Mode Scenario test cases for O-RU
  • Add FDD FR1 Non-conducted mode scenario test cases for O-RU
  • Add TDD FR1/FR2 Non-conducted mode scenario test cases for O-RU
  • Revamp / Clarify / Correct S-Plane O-RU test cases
  • Add S-Plane O-DU test cases

O-RAN Cooperative Transport Interface Transport Management Plane (CTI-TMP) Specification v1.0

This document describes the Transport Management Plane for the Cooperative Transport Interface (CTI), which specifically provides cooperation between the O-DU and the resource allocation based transport network to reduce the upstream transport latency due to the allocation process. CTI consists of a Transport Control plane (TC) and a Transport Management Plane (TM). This document specifies the TM-plane. Its goals are to define the CTI-related configurable parameters at Transport Node (TN) and at O-DU, to define a suitable set of YANG modules to capture these parameters, to describe necessary steps in the configuration of the parameters, and to define an auto-discovery method to automate the correlation between TN specific parameters and CTI parameters.

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

O-RAN O1 Interface specification for O-DU v1.0

The scope of this document is to specify the interface that links O-DU to the SMO. It includes:

  • O-DU management operations inline with Work Group 1 O1 interface specification
  • Performance counters, Fault supervision, and Software management
  • Configuration parameters for O-DU (NSA mode), complementary to 3GPP SA5-defined parameters
  • Synchronization aspects and Fronthaul delay management support

Future versions will include adding support for SA deployments, updating YANG models and configuration parameters accordingly, and adding Trace support and Antenna Line Device (ALD) support.

WG6: The Cloudification and Orchestration Workgroup

O-RAN Acceleration Abstraction Layer (AAL) General Aspects and Principles v1.0

This first version of the Acceleration Abstraction Layer (AAL) General Aspects and Principles introduces the hardware accelerator interface functions and protocols for the O-RAN AAL interface. The document studies the functions conveyed over the interface, including configuration and management functions, and identifies the requirements as well as general procedures and operations. It also introduces the initial set of the O-DU/O-CU AAL profiles.

O-RAN O-Cloud Reference Designs v2.0

This is an update of the O-Cloud Reference Designs document to encompass both deployment scenario B and scenario C. Another update concerns the Time Sync for LLS-C3 configuration with detailed requirements and an example design for the cloud platform to support the LLS-C3 configuration.

O-RAN Orchestration Use-Cases v2.0

This is an update of the Orchestration Use-Cases document to include more use-cases, specifically adding the Scale Out/In of Network Function, the Software Upgrade, and the xApp Deployment use-cases.

WG7: The White-box Hardware Workgroup

O-RAN White Box Hardware Reference Design Specification for Indoor Pico Cell with Split Option 6 v1.0

The document specifies a high-level architecture and hardware design for an Indoor Pico Cell using the Split Option 6 deployment scenario as specified in the Deployment Scenarios and Base Station Classes document.

WG8: Stack Reference Design Workgroup

O-RAN AAD Specification v3.0

The O-RAN Base Station O-CU and O-DU Architecture and APIs specification provides the reference architecture, design and APIs for O-CU and O-DU implementation. The specification details the functional block of O-CU and O-DU, including messages across L1, L2 and L3 layers and call flows. This version includes the timing sync aspects of L1, additions and corrections to L2 and L3 APIs, description of O1 and E2 interfaces, and new call flows.

O-RAN Stack IOT Test Specification v1.0

The O-RAN WG8 Stack Interoperability Test Specification provides interoperability test cases of O-CU and O-DU for end to end call flows. It includes the details of test setup, test profiles, and basic interoperability test cases.

WG9: Open X-haul Transport Work Group

O-RAN WDM-based Fronthaul Networks v1.0

This document is intended to describe best practices for O-RAN fronthaul transport based on the Wavelength Division Multiplexing (WDM) technology. It is recognized that other solutions, not based on WDM technology, could be employed or mixed with a WDM solution. Beyond the technologies in this document, other WDM solutions may be adequate for fronthaul transport network and can be considered for future versions of this document.

O-RAN Xhaul Transport Requirement document v1.0

This document defines the requirements for an Open Xhaul transport infrastructure. As far as possible it tries to make no assumptions about the underlying transport technology, rather define a set of requirements about the overall capabilities of an Open Xhaul transport infrastructure that can support different 5G services, different radio architectures and is multi-service in nature. This document refers to 5G services, but the transport requirements also apply to O-RAN networks deploying 4G services.

O-RAN Xhaul Packet Switched Architectures and Solutions v1.0

The document is intended to describe best practices for O-RAN transport based on end-to-end packet switching technology. It is recognized that other solutions, not based on packet switching, could be employed or mixed with a packet switching solution. Beyond the solutions described in this document, other packet switching solutions may be adequate for Xhaul transport networks and can be considered in future versions of this document.

TIFG: Test and Integration Focus Workgroup

O-RAN Criteria and Guidelines of Open Testing and Integration Centre v2.0

The present document describes the essential criteria and guidelines (guiding principles) from process, organization, space and technical perspective on the qualified Open Testing and Integration Centre (OTIC). Comparing to version 1.0, the details of OTIC qualification process have been added to Chapter 4, and OTIC application form has been added to Annex A.

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.