16 October 2020
Open RAN explained
The introduction of Open RAN, is the final piece of the unbundling puzzle that enables mobile network operators to use equipment from multiple vendors and still ensure interoperability.
How networks work
To understand Open RAN, it is useful to first have a high level understanding of how networks work and how they have evolved through the various generations.
The mobile, or cellular/wireless network comprises two domains: the Radio Access Network (RAN) and the Core Network (Core).
The RAN is the final link between the network and the phone. It is the visible piece and includes the antennae we see on towers, on top of buildings or in stadia, plus the base stations. When we make a call or connect to a remote server e.g. to watch a YouTube video, the antenna transmits and receives signals to and from our phones or other hand-held devices. The signal is then digitalized in the RAN base station and connected into the network.
The Core has many functions. It provides access controls ensuring users are authenticated for the services they are using, it routes telephone calls over the public-switched telephone network, it enables operators to charge for calls and data use, and it connects users to the rest of the world via the Internet. It also controls the network by making handovers happen as a user moves from coverage provided by one RAN tower to the next.
Evolution of the networks
Cellular networks have evolved rapidly since they were first digitized to create 2G and each new generation has seen a step change in technical complexity.
Whilst it was always possible for operators to have one vendor for their core network and a separate vendor for the RAN, interoperability between RAN equipment from different vendors was deprioritised at the expense of adding overall functional capability. As a result, with current solutions it is difficult to mix vendors for the radio and base band unit, and in most cases they come from the same supplier.
Open RAN looks to change this and enable operators to mix and match components.
Opening the RAN
As the equipment-makers enhanced the capabilities, so the industry consolidated around those with the strongest offer and often proprietry functionality. But operators today want a more diverse ecosystem of vendors and are re-defining their requirements for the network architecture, especially in the RAN.
In an Open RAN environment, the RAN is disaggregated into three main building blocks:
the Radio Unit (RU)
the Distributed Unit (DU)
the Centralised Unit (CU)
The RU is where the radio frequency signals are transmitted, received, amplified and digitized. The RU is located near, or integrated into, the antenna. The DU and CU are the computation parts of the base station, sending the digitialized radio signal into the network. The DU is physically located at or near the RU whereas the CU can be located nearer the Core.
The key concept of Open RAN is “opening” the protocols and interfaces between these various building blocks (radios, hardware and software) in the RAN. The O-RAN ALLIANCE has defined 11 different interfaces within the RAN including those for:
Fronthaul between the Radio Unit and the Distributed Unit
Midhaul between the Distributed Unit and the Centralised Unit
Backhaul connecting the RAN to the 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 vendors providing the building blocks, there is more innovation and more options for the Operators. They can also add new services. For example, Artificial Intelligence can be introduced via the RIC to optimize the network in the vicinity of a football stadium on a match day.
Daryl Schoolar, Practice Leader at Omdia shares his perspective on why operators are interested in Open RAN:
Best of breed features and a faster update cycle
Capex (but not leading driver)
User benefits – new features can be added more quickly for end users, operators can provide enterprise level services to support industry 4.0
vRAN (Virtualized Radio Access Network) and Cloud RAN
Whilst Virtualization of the RAN is not the same as Open RAN, it can be deployed in conjunction and makes the RAN much more flexible. What was done in hardware can now be done in software which reduces entry barriers into the market. The DU and CU are effectively computers running software. Instead of using custom hardware, they can now be virtualized and run on any Cloud Server, as long as it is near the base station to reduce latency. Nokia calls this Cloud RAN and its software is the same as which is runs on bespoke hardware to ensure feature parity and facilitate maintenance of the releases.
Nokia and Open RAN
Nokia is a firm supporter of Open RAN and was the first major telco equipment vendor to join both the O-RAN ALLIANCE and the Open RAN Policy Coalition.
Brian Hendricks, Vice President of Government Relations Americas, Nokia said: “Nokia believes that policymakers, operators and equipment providers should work together to support research and development of emerging network technologies that include open systems, advanced 5G technologies and foundational 6G research, with policies that support a robust ecosystem of trusted suppliers that will create a strong U.S. position in secure wireless technology. We believe this coalition strongly supports this approach and we are pleased to join and help the industry move forward on this important effort.”
Interview with Sandro Tavares, Head of Marketing for Nokia Mobile Networks on Nokia Today
Nokia RAN products include:
Radio Access Network (RAN). The final link between the network and the phone. Contains Radio Unit (RU), Distributed Unit (DU) and Centralised Unit (CU).
Core Network (Core). Controls the network.
Open RAN is about disaggregated RAN functionality built using open interface specifications between elements. It can be implemented in vendor-neutral hardware and software-defined technology based on open interfaces and community-developed standards. Open interfaces include (open) Fronthaul and (open) Midhaul connecting the different parts of the RAN and (open) Backhaul between the RAN and the Core.
O-RAN. O-RAN refers to the O-RAN ALLIANCE or its designated specifications. O-RAN Alliance is a specification group defining next generation RAN infrastructures, empowered by principles of intelligence and openness. It is a world-wide community of around 200 mobile operators, vendors, and research & academic institutions operating in the Radio Access Network (RAN) industry. Its mission is to re-shape the industry towards more intelligent, virtualized network elements, white-box hardware and standardized and open interfaces. The term O-RAN refers to interfaces and architecture elements as specified by the O-RAN alliance.
Open RAN Policy Coalition represents a group of companies formed to promote policies that will advance the adoption of open and interoperable solutions in the Radio Access Network (RAN).
RAN Intelligence Controller (RIC) is a new network element enables new services to be introduced into the Radio Network for e.g. software which optimizes the performance the network. The RIC works by exposing an API (application programming interface) which lets software talk to each other.
Cloud RAN or vRAN means an implementation of the RAN in a more open and flexible architecture which virtualizes network functions in software platforms based on general purpose processors. vRAN utilizing open interfaces is one component of Open RAN.
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