Spotlight on Tech

Open RAN explained: all you need to know and more

May 3, 2023
minute read

When it comes to defining Open RAN, there’s a short explanation and a long one.

The short answer: Open RAN is a revolution in mobile network architecture. One that is providing lower costs, better service provisioning, more flexible network deployment, better network management and more.  

The long answer: Open RAN disaggregates traditional monolithic, single-vendor radio access networks (RAN) into a distributed unit (DU), centralized unit (CU) and radio unit (RU) and connects these elements using open standard interfaces. Disaggregation allows the operator to virtualize the CU and DU components and run them on commercial off the shelf (COTS) servers.

We know all of this from first-hand experience: the Rakuten Mobile network is the first fully virtualized, cloud-native Open RAN network in the world. And Rakuten Symphony has worked with leading mobile network operators (MNOs) across the globe to trial and deploy cloud-native Open RAN solutions.

Open RAN represents a giant step forward in technology for building mobile RAN. According to industry analysts, the Open RAN market size more than doubled in the first three quarters of 2022, leading one analyst to comment: “the Open RAN train continues to move forward and accelerate at a faster pace than expected.”


For the first time, Open RAN puts the mobile network operator (MNO) in control of their network with more transparency, technology choice and competition, resulting in lower costs and more agile networks. Open RAN constitutes a radical transformation of the RAN technology with a new Open RAN architecture and a broad and deep Open RAN ecosystem of companies that provide new Open RAN 4G and 5G networks that are flexible, cost-effective and innovative.  

The O-RAN ALLIANCE is the main standards body for Open RAN. It was started in 2018 by AT&T, China Mobile, Deutsche Telekom, NTT DOCOMO and Orange, and has since become a global community of more than 300 operators, vendors and research and academic institutions jointly developing a sustainable O-RAN ecosystem.

Rakuten Symphony is a leader in this technology having built the world’s first nationwide cloud-native Open RAN-based mobile network. That network took only 18 months to build and now serves millions of 4G and 5G users.  

This blog captures our deep Open RAN experience and market leadership in explaining just how impactful this new technology will be.  

What is Open RAN?

Open RAN is a revolutionary new way to build a 4G or 5G mobile network that reduces total cost of deployment, provides operational simplicity, and increases velocity of new feature rollouts when concepts of cloud are effectively used. An Open RAN solution also increases flexibility and innovation in the network.  

The RAN provides wireless connectivity to mobile users, providing connectivity and converts radio frequency (RF) signals into digital packets and vice versa. Until Open RAN, the RAN was a monolithic system bought from a single vendor and not very flexible.  

The key concept in the Open RAN architecture is to disaggregate the monolithic RAN into its core elements and then create open standards for all the interfaces to connect the different elements of the RAN. The baseband unit (BBU) became the distributed unit (DU) and the centralized unit (CU). The radio unit (RU) is connected to the DU through an open interface. In this way Open RAN networks can be built using interchangeable systems from a competitive Open RAN ecosystem.

What are the current challenges of Open RAN?

Any time there’s a new technology that has such promising potential, customers can wonder if the promises are true.  

Many MNOs are concerned about the maturity of Open RAN technology and whether it can deliver flawless performance in dense user networks. Easing these fears is one reason Rakuten Mobile has been so transparent with its performance data to show how the technology is really working; demonstrating that it’s meeting the needs of 4G and 5G customers in some of the densest cities in the world as well as in sparsely populated areas.

Cyber security is a concern for any equipment that is a part of the mobile network. Open RAN security is mature and yet still evolving and getting better. Because Open RAN uses COTS processors, operating systems and servers, it can benefit from the security functionality built into these components. Find out more about Open RAN security with our Definitive Guide to Open RAN Security.

Another big difference in Open RAN is the shift from working with a single vendor to building an ecosystem. Initially this can be a challenge, but MNOs have responded to this change successfully by training up their own staff or working with system integrators. The point is that there are a number of ways to make an ecosystem work for an MNO while taking advantage of the benefits of a diverse and competitive ecosystem.  

Traditional RAN Deployment Model
Traditional RAN Deployment Model

Does Open RAN only work for greenfield networks?

There are two types of MNOs in the world and each can make Open RAN work in their network differently.  

Greenfield operators are building their network for the first time and for them it makes complete sense to build an Open RAN solution and capture the reduced deployment and operating costs and new service capability. They are among the first MNOs to embrace Open RAN 5G.

Brownfield network operators have already installed working networks that they are not going to replace. Open RAN solutions can work in these networks, but these MNOs must consider how to implement Open RAN alongside these existing networks. These MNOs are taking a prescribed approach to Open RAN that fits within their business, picking exactly what they need from a modular, end-to-end, cloud-based network stack and integrating directly into the brownfield network.

Open RAN 5G

5G is growing in popularity as the next generation of high-speed cellular voice and data service. But 5G will be much more than that, as the technology is engineered for lower latency, better reliability, higher peak data throughput and network “slicing,” which allows a physical network to have multiple slices, each optimized for different data flows (i.e., an IoT stream for low data rates and high connectivity, and a streaming slice for high throughput and low latency).

Open RAN 5G networks offer the flexibility for building nationwide networks, which require many small cell base stations and edge computing infrastructure. Using cloud-native Open RAN architecture brings Open RAN security, flexibility and scalability to networks, while automated management of Open RAN will allow these base stations to be deployed and operated cost effectively.

Open RAN architecture

Open RAN architecture enables use of virtualization to disaggregate a standard RAN into several systems that run on COTS servers and are connected by open networking interfaces.

The O-RAN ALLIANCE is among the standards bodies that have defined the three main systems in the Open RAN architecture. These include:

  • Radio Unit (RU): The RU (also known as remote radio head-RRH) is located at the cell site near the antenna and transmits, receives, amplifies, and digitizes RF signals.  
  • Distributed Unit (DU): This system interacts with the RU providing processing for lower-level networking layers before sending digitalized radio signals into the network.
  • Centralized Unit (CU): This system interacts with multiple DUs and forwards the digitized radio signal into the network or Internet.
  • RAN Intelligent Controller (RIC): The RIC is a software-defined system that helps control and optimize the RAN. It is unique to the Open RAN architecture. The RIC has two parts: the non-real-time RIC and the near-real-time RIC which handle events and resources. The RIC hosts third-party non-RT applications (rApps) and the near-RT applications (xApps).  

Each of these systems are connected by standardized open interfaces that allow MNOs to compose an Open RAN solution that is optimized for their network, for example a high-density urban solution may require different capabilities and capacity than a rural network.

Open vRAN architecture
Open vRAN architecture

Key features of Open RAN

Open RAN solutions are set apart by the following features:

  • Virtualization / containerization: The Open RAN architecture replaces the need for proprietary hardware by virtualizing RAN functions so they can run on x86-based COTS servers – dramatically reducing the cost and increasing the flexibility. Open RAN ecosystem partners are shifting from virtualization to containerization to provide even better scalability.  
  • Disaggregation: The Open RAN architecture breaks the BBU into an RU, DU and CU. This allows innovation, enables virtualization of DU and CU, cost-effective deployment and management, and a proven approach to Open RAN security for cloud-native networks.
  • Open Interfaces: There are 11 different interfaces within the RAN. The Open RAN architecture provides industry-wide standards for RAN interfaces, as defined by O-RAN ALLIANCE, that support interoperation between vendors. It allows for a diverse Open RAN ecosystem.
  • Automation: Zero-touch deployment is a critical requirement for managing a network composed of many thousands of small cell base stations. Open RAN architecture can interoperate with edge cloud platform providers for advanced configuration, deployment and life cycle management.
  • Programmability: The RAN intelligent controller allows the use of applications to program the network bringing innovation in management and services.

The Rakuten Mobile network in Japan has taken advantage of all these features to build its network. It has embraced the full power of open interfaces, installing multiple different radio vendors, both indoor and outdoor base stations and the latest in Open RAN security. The result is a secure, high-performance network that is very cost effective.

How is Open RAN beneficial?

Early proponents of Open RAN focused on the cost reduction benefits of Open RAN that come by replacing proprietary hardware and software with commercial-off-the-shelf (COTS) servers and software that comes from a broad and competitive Open RAN ecosystem rather than the small number of closed RAN providers. As more MNOs have trialed or deployed Open RAN solutions, new benefits have emerged. Industry analyst group STL Partners has identified the following key benefits of Open RAN:

  1. Diversify the supplier ecosystem  
  2. Introduce new innovation models which provide agility  
  3. Lower total cost of ownership (TCO) through increased automation
  4. Unlock new revenue opportunities in private cellular networks and shared/wholesale neutral hosting

Open RAN provides a foundation for services that allow MNOs to be more profitable and competitive. But it also broadens the Open RAN ecosystem allowing more innovative software and services and reducing the risk of relying too much on any one supplier. This innovation is a result of the following:

  • Open interfaces: These standard interfaces connect the different network components (RU, CU, DU) and enable multivendor networks, which in turn invite competition resulting in better products and lower costs.
  • Cloudification: Many Open RAN solutions are cloud-native, allowing them to be run in the telecom cloud. This ensures cloud economics as well as extreme scalability thanks to the compute-on-demand nature of cloud servers and the scalability of microservice cloud-native software.
  • Intelligent automation: Open RAN solutions live at the network edge requiring automated network deployment and lifecycle management to reduce costs and, in many cases, configuration errors.  

With these benefits and features, Open RAN will become the default way that MNOs launch 5G services.

How is Cloudification of Open RAN beneficial?

Cloudification of the CU and DU enables the following benefits:

  • Cloud scale resiliency
  • Elasticity due to automatic scale in and scale out as capacity and throughput demand varies
  • Automatic healing from failures
  • Continuous integration / continuous deployment mode of operating a network allowing features to be continuously upgraded, tested in a sandbox and deployed


Open RAN architecture is a new way to look at building mobile networks. But MNOs have a lot of questions about Open RAN. What is it? How can I fit into my network? Does it offer cybersecurity protection?

In this post, Open RAN was defined as an effort to disaggregate the RAN into a virtualized, software-based CU and DU with the physical aspects of RF confined to RU systems and then to connect them with open standard interfaces. This differs from traditional RAN solutions that are monolithic and come only from a single vendor. The advantages of this approach are many, including lower cost, easier network deployments, network scalability and high performance.  

As a technology first mover, Rakuten is leading this industry revolution by delivering a high-performance Open RAN solution combined with the service assurance platform needed for automated network management.

Growth of the Open RAN market is doubling which is outpacing analyst expectations. With all the benefits of a modern, open architecture, Open RAN solutions will play a major role in how 5G networks – and future 6G networks – are built.

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