• The O-RAN architecture introduces a new management interface - “A1 interface” - between the network management system and the radio access network (RAN)

  • A1-AP (Application Protocol) specified by O-RAN Alliance WG2

• A1 interface enables vendor-agnostic policy-based guidance (“A1 Policies”) to be sent to underlying RAN elements from the management system.

  • “A1-EI” will also support transmission of enrichment information from the management platform to the RAN elements (Still being defined – currently out of scope)

  • “A1-ML/AI” may also assist with ML Model management in the RAN (Still being defined – currently out of scope)

• The A1 interface connects Non-RealTime-RIC logical function in OAM/SMO layer with the Near-RealTime-RIC logical function in the RAN.

A1 in O-RAN Architecture for Disaggregated RAN

Open

A1 in O-RAN Architecture

• From ORAN-WG1 Architecture Description - v01.00.00 - https://www.o-ran.org/specifications

A1 Adapter in Frankfurt

• Implemented as an SDNC/CCSDK extension to terminate & expose A1 interface

• https://lf-onap.atlassian.net/wiki/display/DW/A1+Adapter+in+ONAP

• Developed for Release Requirement (REQ-38): 5G / ORAN & 3GPP Standards Harmonization

• Can be used by other ONAP functions to perform A1 Policy Operations over A1 Interface

• Provides DMaaP northbound interface, and REST (A1) southbound interface

Enhancements for Guilin Release

• Add additional support for standardized A1 protocol (O-RAN A1-AP v1.1)

  • Current (Frankfurt) supports only O-RAN-SC’s (draft) non-spec version of A1 Application Protocol

  • Will add support for upcoming A1 standard spec evolution

  • Will add support for multiple versions for different A1 connections

• Managing A1 Policies

  • Operations:

    • Query A1 Policy Types in near-RT-RICs

    • Create/Query/Update/Delete A1 Policy Instances in near-RT-RICs

    • Query Status for A1 Policy Instances

  • Maintain transient cache of RAN’s A1 Policy information

    • Support RAN-wide view of A1 Policy information

    • Streamline A1 traffic

    • Enable (optional) re-synchronization after inconsistencies / near-RT-RIC restarts

• Add support for multiple near-RT-RICs (with multi-version support)

• Unified REST & DMaaP NBI

• Add support for TLS/HTTPS REST for southbound A1 interfaces (and NBIs)

  • Leverage existing ONAP cert management approaches

• Converge ONAP & O-RAN-SC A1 Adapter/Controller functions in ONAP SDNC/CCSDK

  • Proposed functionality is currently available as 2 functions in O-RAN-SC

  • Basic A1 Adapter is an ODL extension & Policy Management is a separate microservice

A1 Policies - Northbound Interface (REST & DMaaP) Proposed

• See CCSDK-2489: Unified REST & DMaaP NBI for A1 Policy Management - A1 GuilinClosed  and Open API (yaml)

Policy Types / Policy Instances / Policy Status Operations  (REST)

/policies?ric=yy&service=zz&type=xx (GET)

/policy?id=ww (GET, PUT, DELETE)

/policy_types?ric=zz (GET)

/policy_schema?id=xx (GET)

/policy_schemas?ric=yy (GET)

/policy_status?id=ww (GET)

DMaaP

{

  "type": "string",

  "correlationId": "string",

  "target": "string",

  "timestamp": "timestamp",

  "apiVersion": "string",

  "originatorId": "string",

  "requestId": "string",

  "operation": "string",

  "url": "string",

  "body": "string"

}

Example

To get all policy types for a specific Near‑RT RIC:

{

  "type":"request",

  "correlationId":“xyz123",

  "target":"policy-agent",

  "timestamp":"<timestamp>",

  "apiVersion":"1.0",

  "originatorId":“12345",

  "requestId":“6789",

  "operation":"GET",

  "url":"/policy_schemas?ric=ric_1"

}

{

  "requestId": "string",

  "correlationId": "string",

  "originatorId": "string",

  "type": "string",

  "message": "string",

  "type":  "string",

  "timestamp": "string",

  "status": "string"

}

Example

The response containing all policy types for a specific Near‑RT :

{

  "requestId":"6789",

  "correlationId":“xyz123",

  "originatorId":" 12345",

  "type":"response",

  "message":" <response – in this case an array

  of Policy type schemas> ",

  "timestamp":"<timestamp>",

  "status":"200 OK"

}

Propose to deprecate / phase out existing A1 Adapter DMaaP Interface

A1 Policies – Southbound (A1-P Application Protocol)

O-RAN Alliance (spec) v1.1.3 (Proposed)

/A1-P/v1/policies (GET)

/A1-P/v1/policies​/{policyId}  (GET,  PUT, DELETE)

/A1-P/v1/policies​/{policyId}​/status (GET)

O-RAN-SC A1 (non-spec) v2.1.0 (Existing)

​/a1-p​/healthcheck (GET)

​/a1-p​/policytypes (GET)

​/a1-p​/policytypes​/{policy_type_id} (GET, DELETE, PUT)

​/a1-p​/policytypes​/{policy_type_id}​/policies (GET)

​/a1-p​/policytypes​/{policy_type_id}​/policies​/{policy_instance_id} (GET, DELETE, PUT)

​/a1-p​/policytypes​/{policy_type_id}​/policies​/{policy_instance_id}​/status (GET)

Use Case Functional Definitions

Synchronize A1 Policy Information in RAN

Open

Synchronize A1 Policy Information in RAN

A1 Policy Type / Instance Operations

A1 Policy Instance Status Operations

Affected ONAP Functions:

• SDNC / CCSDK only

Integration of bordering ONAP components:

• Guilin: None required – Studies only

  • Stretch Goal: “Hello world” demonstrations with other ONAP components

• Honolulu: A&AI, Configuration & Persistency Service, DCAE, CLAMP, Policy. (TBC)

  • Will form part of cross-project 5G integration use cases envisioned for Honolulu (TBC)

Interfaces:

• Northbound Interface – See earlier section

  • Add/Change SDNC NBI for A1 Policy Management (REST & DMaaP)

    • REST (New)

    • DMaaP (New – Deprecate Existing – goes beyond existing A1 interface message mediation)

• Southbound Interfaces – See earlier section
  
  

  • OSC A1 v2.1 (Existing)

  • O-RAN A1 v1.1 (New)

Usage outside ONAP:

• Used in O-RAN-SC NONRTRIC Project (Downstream)

• Southbound Interface: O-RAN A1 Interface + Information Model is specified and maintained by O-RAN Alliance

Modelling Impacts:

• TBC

Other:

• Update Documentation with A1 interface aspects

• Update Integration & Existing Test requirements

Test use-cases:

• Synchronize A1 Policy Information in RAN

• A1 Policy Type / Instance Operations

• A1 Policy Instance Status Operations

• See REQ-447 and linked resources for more information on TEST Release Requirements

Test variations:

• A1 Adapter with/without A1 Policy Management Service

• A1 versions:

  • O-RAN Alliance (spec) v1.1.3

  • O-RAN-SC A1 (non-spec) v2.1.0

OSC A1 Simulator: 

• https://docs.o-ran-sc.org/projects/o-ran-sc-sim-a1-interface/en/latest/

• https://gerrit.o-ran-sc.org/r/gitweb?p=sim/a1-interface.git

• https://wiki.o-ran-sc.org/display/RICNR/Release+B

• https://wiki.o-ran-sc.org/pages/viewpage.action?pageId=20873402#ReleaseBBuild/Run-RunNear-RTRICA1SimulatorDockerContainers

Integration Story:

• INT-1654: Test A1 Adapter connection to OSC A1 SimulatorClosed

Use Case Functional Definitions

News & Updates:

• May 26, 2020 - GO decision from Architecture Sub-Committee: Presentation:
    

• Jun 24, 2020 - Presentation to LFN vDTF (June 2020): "A1 Adapter in OSC and ONAP -Converging A1 Control in ONAP (Guilin)"