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

Hana Gazoli    September 29, 2021

In our [last blog post](/content/o-ran-alliance-workgroup-1-task-groups-and-deliverables/index.html) 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.