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

Hana Gazoli   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.

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.

• 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 specifies the application protocol of the A1 interface.

• 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.

• 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.

• Non-RT RIC – Functional Architecture: This technical report provides the overall functional architecture of the Non-RT RIC.

• Non-RT RIC – Architecture: This is a new document that was released for the first time in July 2021 that 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.

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.

WG3 is responsible for the following deliverables:

• WG3 Use Case and Requirements: This technical specification describes the initial use cases that have been approved within O-RAN WG3.

• 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.

• Near-RT RIC E2 Application Protocol (E2AP): This TS specifies the Near-RT RIC layer signaling protocol for the E2 interface.

• 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.

  • E2SM RAN Function Network Interface (NI): 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.
  • E2SM RAN Control (RC): This TS specifies the E2 Service Model for the Near RT RIC RAN Control interaction.

• Near-RT RIC Architecture: This TS specifies the overall architecture of the Near-RT-RIC and function descriptions.

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.