How networks work
To understand Open RAN, it is helpful to first acquire a general level of understanding of how networks work and how they have evolved through several generations.
The mobile, or cellular/wireless, network comprises two domains: the Radio Access Network (RAN) and the Core Network.
The RAN is the final link between the network and the phone. It's the visible component and includes the antennas we see on towers, buildings, or stadiums, as well as the base stations. When we make a call or connect to a remote server, for example, to watch a YouTube video, the antenna transmits and receives signals to and from our phones or other handheld devices. The signal is then digitized at the RAN base station and connected to the network.
The core network has many functions. It provides access controls to ensure users are authenticated for the services they are using, routes calls to the public fixed telephone network, allows operators to charge for calls and data usage, and connects users to the rest of the world via the internet. It also controls the network by enabling handovers as a user moves from the coverage provided by one RAN tower to the next.
Evolution of networks
Cellular networks have evolved rapidly since they were first digitized to create 2G, and each new generation has witnessed a qualitative change in technical complexity.
While it has always been possible for operators to have one vendor for their core network and a different vendor for the RAN, interoperability between equipment from different RAN vendors was prioritized over general functional capabilities. As a result, with current solutions, it is difficult to mix vendors for the radio and baseband units, and in most cases, they are supplied by the same vendor.
Open RAN intends to change this situation and enable operators to mix and match components.
Opening of the RAN
As equipment manufacturers improved their capabilities, the industry consolidated around those offering the strongest solutions, often with proprietary features. But now, operators want a more diverse vendor ecosystem and are redefining their network architecture requirements, especially for the RAN.
In an Open RAN environment, the RAN is broken down into three main blocks:
• the Radio Unit (RU)
• the Distributed Unit (DU)
• the Centralized Unit (CU)
The RU is where radio frequency signals are transmitted, received, amplified, and digitized. The RU is located near or integrated with the antenna. The DU and CU are the parts of the base station where computing takes place, and they send the digitized radio signal to the network. The DU is physically located in or near the RU, while the CU may be located closer to the network core.
The key concept of Open RAN is the "opening" of protocols and interfaces between the various components (radios, hardware, and software) of the RAN. The O-RAN Alliance has defined 11 different interfaces within the RAN, including those responsible for:
• 'Fronthaul' between the Radio Unit and the Distributed Unit
• 'Midhaul' between the Distributed Unit and the Centralized Unit
• 'Backhaul' that connects the RAN to the network core
Another feature of Open RAN is the RAN Intelligent Controller (RIC) which adds programmability to the RAN.
Advantages of Open RAN
An open environment expands the ecosystem, and with more providers offering the various blocks, there is more innovation and more options for operators. They can also add new services. For example, Artificial Intelligence can be introduced through the RIC to optimize the network near a football stadium on match day.
vRAN (Virtualized Radio Access Network) and Cloud RAN
While RAN virtualization is not the same as Open RAN, it can be implemented alongside it and makes the RAN much more flexible. What was previously done with hardware can now be done with software, lowering barriers to market. The DU and CU are, in effect, computers running software. Instead of using custom hardware, they can now be virtualized and run on any cloud server, as long as it's close to the base station to reduce latency. Nokia calls this Cloud RAN, and its software is the same as that running on the custom hardware to ensure feature parity and facilitate version maintenance.
Nokia and Open RAN
Nokia is a strong supporter of Open RAN and was the largest telecommunications equipment provider to join the O-RAN ALLIANCE and the Open RAN Policy Coalition.
Nokia believes that openness is the only way forward. Open communities are what facilitate innovation and co-creation. Open source allows us to share and reuse innovation and focus our efforts on what matters most. We need open interfaces and collaboration to simplify network operation, enable analytics, and allow us to introduce new services more quickly.
Resources:
Nokia's RAN products include:
Key terms
• Radio Access Network (RAN) The final link between the network and the telephone. It contains the Radio Unit (RU), the Distributed Unit (DU), and the Centralized Unit (CU).
• Central network or network core. Controls the network.
• Open RAN is a disaggregated RAN functionality built using open interface specifications between its components. It can be implemented on hardware from any vendor and with software-defined technology using open interfaces and standards developed by the community. These open interfaces include Fronthaul and Midhaul, which connect the different parts of the RAN, and Backhaul, which connects the RAN to the network core.
• O-RAN. O-RAN refers to the O-RAN Alliance or its designated specifications. The O-RAN Alliance is a set of specifications that defines next-generation RAN infrastructures, empowered by principles of intelligence and openness. It is a global community of approximately 200 mobile operators, vendors, and research and academic institutions operating in the Radio Access Network (RAN) sector. Its mission is to reshape the sector by providing smarter, virtualized network elements, white-label hardware, and open, standardized interfaces. The term O-RAN refers to the interfaces and architectural elements as defined by the O-RAN Alliance specifications.
• The Open RAN Policy Coalition represents a group of companies formed to promote policies that advance the adoption of open and interoperable solutions in the Radio Access Network (RAN).
• The RAN Intelligence Controller (RIC) is a new network element that enables the introduction of new services into the Radio Network, such as software that optimizes network performance. The RIC works by exposing an API (Application Programming Interface) that allows different programs to communicate with each other.
• Cloud RAN, or vRAN, refers to a RAN implementation in a more open and flexible architecture that virtualizes network functions on software platforms based on general-purpose processors. vRAN, using open interfaces, is a component of Open RAN.
Technology explanation, by Nokia
This new series of benchmark reports is designed to educate journalists and other commentators on the technology that connects the world. Only Nokia offers a comprehensive portfolio of network equipment, software, services, and licensing options worldwide. Driven by our commitment to innovation, powered by the award-winning Nokia Bell Labs, we are leaders in the development and deployment of 5G networks.
Author: Gloria Touchard, Corporate Technical Director of Nokia
The introduction of Open RAN is the final piece of the disaggregation puzzle that enables mobile network operators to use equipment from multiple vendors while still ensuring interoperability. 
Another feature of Open RAN is the RAN Intelligent Controller (RIC) which adds programmability to the RAN.
