O-RAN Alliance Workgroup 2 and Workgroup 3: Specifications and Other Deliverables

Zahid Ghadialy, Senior Director, Technology & Innovation Strategy   September 29, 2021

In our last blog post we looked at O-RAN Alliance workgroup 1 task groups and other deliverables. Let us continue the momentum and now look at workgroup 2 and 3 deliverables. Let’s start with workgroup 2.

Work-Groups

Workgroup 2 (WG2) deals with Non-Real-Time (Non-RT) RIC and the A1 interface. Its activities fall within three main streams:

  • use cases and requirements,
  • A1 interface specifications, and
  • AI/ML technical report.

The primary goal of Non-RT RIC is to support:

  • Non-Real-Time intelligent radio resource management,
  • higher layer procedure optimization,
  • policy optimization in RAN, and
  • providing AI/ML models to support Near-RT RIC and other RAN functions.

The A1 interface supports communication and information exchange between Non-RT RIC and Near-RT RIC. The key objective is:

  • to support policy-based guidance of near-RT RIC functions and use-cases,
  • transmission of enrichment information in support of AI/ML models into Near-RT RIC, and
  • basic feedback mechanisms from Near-RT RIC.

WG2 is responsible for the following deliverables:

  • Non-RT RIC and A1 Interface – Use Cases and Requirements technical specification: This document describes the RAN optimization and control related initial use cases that have been approved within WG2. The purpose of these use cases is to help identify requirements for O-RAN defined interfaces and functions, specifically, Non-RT RIC function and the A1 interface, eventually leading to formal drafting of interface specifications. For each use case identified, this document describes the motivation, resources, steps involved, and data requirements. Finally, the requirements section details the functional and non-functional requirements derived from these use cases.
  • A1 Interface – General Aspects and Principles (A1GAP): This document specifies the general aspects and principles of the A1 interface.
  • A1 Interface – Application Protocol (A1AP): This document, as the name says, specifies the application protocol of the A1 interface. It is important to note with this particular specification that if the version numbers are different for the Near-RT and Non-RT RIC, there may be implications for compatibility. This document handles the service compatibility aspects while A1 Interface – Type Definitions, handles the compatibility for data types used by the A1 services.
  • A1 Interface – Transport Protocol (A1TP): This document specifies the transport protocol of the A1 interface.
  • A1 Interface – Type Definitions (A1TD): This document specifies the data model and the data types that are used in the body of the procedures in the A1 interface. Chapter 5 of this document describes policy type compatibility while chapter 7 describes EI type compatibility. For compatibility of A1 implementations in Non-RT and Near-RT RICs, it must be ensured that all implemented policy and EI types are compatible with each other.
  • AI/ML Workflow Description and Requirements: This technical report addresses the overall architecture and solution for AI/ML related requirements for the use-cases described in the WG2 use cases and requirements document. The document provides the terminology, workflow, and requirements, related to AI/ML model training, and its
  • distribution and deployment in the Radio Access Network (RAN).
  • Non-RT RIC – Functional Architecture: This technical report provides the overall functional architecture of the Non-RT RIC. It is a collection of concepts and requirements that are intended to be used in the subsequent specification of the Non-RT RIC architecture. It is not intended to define normative requirements for the conformance of implementations.
  • Non-RT RIC – Architecture: This is a new document that was released for the first time in July 2021. This technical specification for the Non-RT RIC architecture consists of a collection of requirements on the Non-RT RIC framework, hosted applications, and services of the R1 interface. This document specifies the Non-RT RIC framework functionalities and services exposed to the applications.

As O-RAN enables “mix-n-match” modules from different vendors, it is important to highlight the fact that compatible versions of A1AP and A1TD should be used between Near-RT and Non-RT RICs.

An incremented first digit of this specification could indicate that a new major feature, for example, new A1 service, has been added or that an incompatible change has been made to an A1 service. An incremented second digit could indicate that an optional feature has been added, or that clarifications or corrections have been made.

Turning our attention to workgroup 3 (WG3) now. WG3 deals with Near-Real-Time RIC and the E2 Interface. Its main activities are to specify:

  • the Near-RT RIC open architecture and its functionalities,
  • the Radio-Network Information Base and Network Topology, and
  • modular on-boarding of new Control Applications.

In addition, WG3 is responsible for specifying the E2 interface between the near-RT RIC and the CU/DU stack.

Finally, WG3 oversees the interaction with WG2, WG5 and WG6 to drive aspects related to near-RT RIC.

WG3 is responsible for the following deliverables:

  • WG3 Use Case and Requirements: This technical specification (TS) describes the initial use cases that have been approved within O-RAN WG3. The purpose of the use cases is to help identify requirements for O-RAN defined interfaces and functions, specifically Near-RT RIC functions and the E2 interface, eventually leading to the formal drafting of interface specifications. For each use case, this document describes the motivation, resources, steps involved, and data requirements. Finally, the requirements section within the document details the functional and non-functional requirements derived from these use cases.
  • Near-RT RIC Architecture and E2 General Aspects and Principles (E2GAP): This TS describes the overall architecture of the Near-RT-RIC and the general aspects and principles of the E2 interface, including the interaction with applications hosted in the Near-RT RIC.
  • Near-RT RIC E2 Application Protocol (E2AP): This TS specifies the Near-RT RIC layer signaling protocol for the E2 interface. The E2 interface provides the means for interconnecting a Near-RT RIC and an E2 Node. The E2AP supports the functions of the E2 interface by signaling procedures defined in this document. E2AP is developed in accordance with the general principles stated in the E2GAP TS.
  • E2 Service Model (E2SM): There are four documents for the E2 Service Model:
    • E2SM Common: The E2 Services Model technical specification describes the O-RAN specified RAN Function-specific Service Models supported over E2 and presents a recommended layout for additional E2SM specifications.
    • E2SM RAN Function Network Interface (NI): The RAN function “Network Interface” is used to provide RIC Service exposure of the network interface logical function of the E2 Node. This TS specifies the E2 Service Model “Network Interface” for the RAN function handling the Network Interfaces in an E2 Node.
    • E2SM Key Performance Measurement (KPM): This TS specifies the E2 Service Model “Key Performance Measurement” for the RAN function handling reporting of the cell-level performance measurements for the 5G networks as well as for the EPC networks, and their possible adaptation of UE-level or QoS flow-level measurements.
    • E2SM RAN Control (RC): This TS specifies the E2 Service Model for the Near RT RIC RAN Control interaction. Each E2 Node terminating the E2 Interface is assumed to host one or more instances of the RAN Function “RAN Control”.
  • Near-RT RIC Architecture: This TS specifies the overall architecture of the Near-RT-RIC and function descriptions, including the interaction between hosted applications and common functions in the Near-RT RIC.

So, these were O-RAN Alliance workgroups 2 and 3 in brief. I plan to discuss workgroup 4 and workgroup 5 in the next blog post.

Further Reading:

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