O-RAN Architecture & the SMO

Updated: Apr 15, 2021

Bhanu Chandra K.

In this three part blog series, I am going to talk about O-RAN architecture with a little extra emphasis on the Service Management & Orchestration component, the NONRTRIC, and finally some NONRTRIC use cases. Today we'll cover the first topic.

The O-RAN specification allows service providers to speed up 5G network development through its standardized architecture. It minimizes proprietary hardware dependency and makes the network more accessible to a broader range of designers.

The O-RAN alliance architecture principles are:

● Radio area network (RAN) virtualization, open interfaces, and AI-capable RAN

● Disaggregation of RAN element deployment and leveraging multi vendor solutions

● Minimization of proprietary hardware and a push toward merchant silicon and off-the-shelf hardware

● Interfaces and APIs to drive "standards to adopt them as appropriate" and explore "open source where appropriate"

O-RAN Architecture

O-RAN Components

  • Service Management & Orchestrator (SMO): The component that oversees all the orchestration aspects, management and automation of RAN elements. It supports O1, A1 and O2 interfaces.

  • Non-RT RIC (non-real-time RAN Intelligent Controller): A logical function that enables non-real-time control and optimization of RAN elements and resources, AI/ML workflow including model training and updates, and policy-based guidance of applications/features in near-RT RIC.

  • Near-RT RIC (near-real-time RAN Intelligent Controller): A logical function that enables near-real-time control and optimization of O-RAN elements and resources via fine-grained data collection and actions over the E2 interface. It includes interpretation and enforcement of policies from Non-RT RIC. and supports enrichment information to optimize control function.

  • O-CU (O-RAN Central Unit): A logical node hosting RRC, SDAP and PDCP protocols. O-CU includes two sub-components O-CU-CP (O-RAN Central Unit – Control Plane) and O-CU-UP (O-RAN Central Unit – User Plane).

  • O-DU (O-RAN Distributed Unit): A logical node hosting RLC/MAC/High-PHY layers based on a lower layer functional split.

  • O-RU (O-RAN Radio Unit): A logical node hosting Low-PHY layer and RF processing based on a lower layer functional split.

O-RAN SMO Interfaces

The key O-RAN SMO interfaces are:

  • O1: Interface between management entities in Service Management and Orchestration Framework and O-RAN managed elements, for operation and management, by which FCAPS management, software management, and file management shall be achieved.

  • O2 (previously O1*): Interface between Service Management and Orchestration Framework and Infrastructure Management Framework supporting O-RAN virtual network functions.

  • A1: Interface between non-RT RIC and near-RT RIC. Over this interface non-RT RIC performs policy management, enrichment information and AI/ML model updates on the near-RT RIC.

In the next post we will see the various requirements and current limitations, and how the O-RAN architecture — especially the non-RT RIC — optimizes the 5G network.

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