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Open RAN

O-RAN is an open architecture that decomposes 5G RAN elements, it allows interoperability standard for RAN elements including non-proprietary white box hardware and software from different vendors

The difference between Open-RAN and O-RAN

Open RAN is the general market trend to virtualize and develop RAN functions in software. It refers to the disaggregated radio access network with open interfaces between network components from multiple vendors. O-RAN is an industry standard pushed by O-RAN ALLIANCE that concretely implements the principles of Open RAN.  


O-RAN ALLIANCE is an international consortium funded by major network operators, namely AT&T, China Mobile, Deutsche Telekom, NTT DOCOMO and Orange in 2018. 

Its 2 main missions are: 

  • Creating O-RAN specifications which extend RAN standards towards openness and intelligence
  • Developing an open software for the RAN

Firecell products are O-RAN/open-RAN compatible and therefore benefit from this architectural approach. 

Open-RAN components

A 5G Open-RAN introduces a new architecture including key components in a 5G NR:

Service Management & Orchestrator (SMO)

The logical node that supervises all the orchestration aspects, management and automation of RAN elements.

Non-Real Time RIC (RAN Intelligent Controller)

This logical node has as its main objectives to optimize the RAN resources and the usage of RAN elements. It supports non-real-Time radio resource management, optimisation of the policy at the RAN level.It includes also functions for TAN analytics or model-training for the near RealTime RICS

Near-RealTime RIC (near-real-time RAN Intelligent Controller)

A logical node that allows near-real-time control and optimization of O-RAN components and resources through granular data collection and actions over the E2 interface, enforcing and interpreting policies from Non-RT RIC., and providing enrichment information to improve control functionality. It supports an open API which allows the integration of services based on XApps (I.e. RRM control functionalities). The management of these services (fault configuration, logging, transfer to an external system for evaluation but also Security Schemes) is also integrated in that node.

The RAN functions are splitted into 3 mains elements. It correspond to Split 7.2 defined by 3GPP

  • O-CU (O-RAN Central Unit): A logical node hosting RRC, SDAP and PDCP protocols. O-CU emcompasses two subcomponents 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.

SPLIT between CU/DU

Eight Functional Splits have been defined by 3GGP in order to allow the logical nodes in the 5G NR stack: 

An interesting survey has been conducted in order to analyze the benefits and the drawbacks of each of them, you can find the survey here.

Currently, 2 main splits are considered for actual deployments:

  • The Small Cell Forum (SCF) advocates for option 6 as the best choice for low-cost, low-capacity deployments
  • The O-RAN Alliance is advocating for Option 7.2. This option is suited to networks with high-capacity and high-reliability requirements. Multiple operators can share a simple RU to help develop the neutral host market that supports network densification and consumes less power and space.

One benefits of this split is the possibility for a specific deployment to centralize the CU and sometimes also the DU.

O-RAN SMO Interfaces

The key O-RAN SMO interfaces are:

  • O1: Interface connecting management nodes in Service Management and Orchestration Framework and O-RAN managed components, for operation and management, in order to achieve  FCAPS management, software management, and file management.
  • O2/O1*: Interface connecting 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 executes policy management, enrichment information and AI/ML model updates on the near-RT RIC.

Features included

  • Policy Management: eases the provisioning of policies for individual UEs or groups of UEs
  • Monitoring: monitor and supply basic feedback on the policy state from near-RT RICs
  • Enrichment Information: provide enhancements of information as required by near-RT RICs
  • AI/Ml updates: facilitate Machine Learning model training, distribution and deduction in collaboration with the near-RT RICs

Benefits of O-RAN architecture

Reducing OPEX

Open Ran distributes the different RAN functions into different modules which allows it to reduce and ease operational aspects. 

Key advantages

  • Open Ran allows multi-vendor ecosystems.
  • Open Ran encourages competition which reduces hardware prices.
  • Open Ran can be easily deployed on a Cloud (reduces infrastructure costs).

Improves the overall efficiency:

By introducing Non-RT RIC and Near-RT RIC concepts, the O-RAN architecture allows for an optimized and fine-tuned control of the Radio resource management which allows to improve *QoS, enhance load balancing or multi-connection control. Open Air Interface is committed to supporting O-RAN Architecture.

This development is supported by 2 different groups within Open Air interface:


The OAI 5G RAN project  is the core group of the OAI RAN development and aims to create and distribute a 5G software stack to support RAN 5G functionalities. In particular, in order to support O-RAN architecture, it has introduced the split of the CU/DU in the gNB and the support of O-RAN interfaces( E2, O1) . You can find out more about this project group by following this link.


This group complements the Activity of the OAI 5G RANProject by developing specific O-RAN functionalities such as the O-RAN E2 protocol named E2 Agent, a flexible RAN intelligent controller named FlexRIC… You can find out more about this project group by following this link.

Firecell and the OpenAirInterface welcome any contributions on all layers of the software stack.

If you’d like to know more about the project, please fill this contact form to join.

As a strong contributor to the OAI roadmap, Firecell supports the O-RAN and Open Air interface pairing. Firecell coordinates the project OAI for Private 5G and commits development resources to develop the open-source software, that supports O-RAN architecture. The project will make use of the OAI software base as well as other open source software to build a complete, cloud-native solution for Private 5G. 

Open Air Interface is committed to supporting O-RAN Architecture