O-RAN A1 Interface

The O-RAN Alliance defines a new management interface “A1” for Radio Access Network (RAN) Management. This interface interconnects a new logical “Non-RealTime RAN Intelligent Controller (Non-RT-RIC)” function in the Service Management & Orchestration (SMO) layer with a new logical “Near-RealTime RAN Intelligent Controller (near-RT-RIC)” function in the RAN. This new A1 interface allows the Non-RT-RIC to provide Policy Guidance to the RAN (near-RT-RIC) to steer its operation. These policies are defined by the O-RAN Alliance as “A1 Policies”. The specifications for the A1 Interface, including A1 Policy support, can be found on the O-RAN Alliance Specifications website.

The A1 Policy functions are Orchestration and Automation functions for non-real-time intelligent management of RAN functions. The primary goal of the A1 Policy functions is to support non-real-time radio resource management, higher layer procedure optimization, policy optimization in RAN, and providing guidance, parameters, policies and AI/ML models to support the operation of Near-RealTime RIC (RAN Intelligent Controller) functions in the RAN to achieve higher-level non-real-time objectives.

A1 Policy functions form part of a Non-Realtime RIC as defined by O-RAN Alliance. Non-Realtime RIC functions include service and policy management, RAN analytics, and model-training for the Near-RealTime RICs. The ONAP & O-RAN-SC A1 Policy work provides concepts, specifications, architecture and reference implementations for A1 Policy support as defined and described in the O-RAN architecture.

A1 Policy Management Service (from ONAP CCSDK)

The A1 Policy Management Service is a microservice which maintains a transient repository of:

  • All A1 policies instances in the network. Each policy is targeted to a near-RT-RIC instance and is owned by a ‘service’ (e.g., rApps or the NONRTRIC Dashboard).

  • All near-RT-RICs in the network.

  • All Policy types supported by each near-RT-RIC.

The service provides :

  • Unified REST API for managing A1 Policies in all near-RT-RICs.

  • Compliant with O-RAN R1 specification for A1-Policy Management (R1-AP v5.0, with additional features & fixes)

  • Synchronized view of A1 Policy instances for each rAPP

  • Synchronized view of A1 Policy instances in each near-RT-RIC

  • Synchronized view of A1 Policy types supported by each near-RT-RIC

  • Lookup service to find the near-RT-RIC to control resources in the RAN as defined in O1 (e.g. which near-RT-RIC should be accessed to control a certain CU or DU, which in turn controls a certain cell).

  • Monitors all near-RT-RICs and maintains data consistency, e.g. recovery from near-RT-RIC restarts

  • Support for different Southbound APIs to the near-RT-RICs (different versions of the A1-P and other similar APIs).

  • HTTPS can be configured to use a supplied certificate/private key and to validate peers towards a list of trusted CAs/certs.

  • HTTP proxy support for tunneling HTTP/HTTPS connections.

  • Fine-grained access-control - with new optional callouts to an external auth function

  • Fine-grained monitoring metrics, logging & call tracing can be configured

See also A1 Policy Management Service in ONAP: Wiki, Documentation.

Implementation:

  • Implemented as a Java Spring Boot application.

This product is a part of NONRTRIC.