In previous blogs in this “Who Disaggregated My RAN? series, we have looked at the benefits of a disaggregated Open RAN, including the growth of an ecosystem to support the deployment of an Open RAN. We have also looked at how these disaggregated solutions compare in terms of performance. Naturally, as we consider the benefits of using commercial off-the-shelf (COTS) hardware for Open RAN solutions, the next logical cost savings option comes in the area of virtualization. Here the term virtualization is used to mean a VNF (Virtualized Network Function) or a CNF (Cloud-native Network Function). What are these VNFs and CNFs anyways? Let’s dig into this topic further.
The many benefits of a virtualized RAN solution
A virtualized implementation means dynamic scaling in and scaling out of functions as per the demand (capacity, throughput and load balancing). This is in contrast to the traditional approach of spending more CapEx on proprietary hardware in order to add capacity. Also, as the software architecture becomes more flexible to support multiple deployment scenarios, operators can avoid buying different hardware and software configurations to support different deployment scenarios. Thus, the overall savings in TCO that can be achieved with virtualized RAN solutions are very attractive for operators.
ETSI NFV architecture
The concept of a virtual machine isn’t new and has been used in both Enterprise and Telecom. However, the telecom industry has many stringent requirements with less tolerance for down-time, so there had been considerable skepticism about telecom solutions working well in virtualized environments. In 2012, an initiative was launched by operators to create virtualized solutions for telecom industry. A whitepaper was released that addressed meeting performance and resiliency requirements, and the European Telecommunications Standards Institute (ETSI) began to develop standards that laid the foundation for networks nodes to be implemented in virtualized environments. ETSI continues to work on this topic, with many releases of specifications to ensure standardization and interoperability in virtualization.
Most of the initial implementations of virtualized machines for telco products adopted the strategy of creating multiple virtual machines within the same host hardware. The telco world capitalized on this strategy and much of the cloud implementation, mostly on the core network, was moved to virtualized implementations called Virtualized Network Functions (VNF). Some of the LTE network core network implementations started adopting control and user plane separation and virtualization, and many of these implementations were compliant to ETSI NFV architecture.
RAN-specific challenges in virtualization
While the virtualization principles can be applied to RAN nodes as well, there are some specific challenges especially in processing related to Layer 1 and Layer 2 functionalities. Meeting the tight timing and latency constraints in the RAN data path can be a challenge. It is also harder to separate out tightly intertwined functions and call processing across Layer 1 and Layer 2 modules.
With the advent of many fast data path options and hardware accelerators, some of these challenges were solved. Intel’s FlexRAN solution was one of the earliest reference designs made available for RAN vendors to start the journey to virtualized RAN implementations. Radisys and Intel have been partnering since the initial release of FlexRAN reference design to provide 4G and 5G virtualized RAN solutions.
Going cloud-native
Another important trend in cloud computing has been the widespread use of containers to implement cloud-based solutions. This allows a lightweight and efficient way of spinning many instances of network functions rather than creating many virtual machine instances. This approach, called Cloud-native Network Function (CNF) is now being adopted by many vendors to virtualize the RAN. There are many design paradigms like microservices-based architecture and stateless processing in network functions that can be applied to create high performance and highly scalable RAN solutions. The goal is to design highly granular software modules and make them scale dynamically as per demand.
O-RAN cloud architecture for RAN
As operators are moving forward with their O-RAN deployments, the question remains of which virtualization approach to take: VNF or CNF?
The answer to that question is in many ways subjective. Open RAN allows for either option in some of the nodes. The O-RAN Alliance uses a neutral term – “cloudified” – to represent both VNF and CNF.
The O-RAN Alliance has a working group that is focused on cloudification and orchestration for RAN nodes. The O-RAN Cloud (called O-Cloud) platform is illustrated in the diagram below.
The unique aspect about this cloud platform definition is the inclusion of hardware acceleration abstraction APIs. These APIs (called AAL APIs) cover commonly required functions like encryption, integrity, channel encoding/decoding, and fronthaul acceleration.
An edge cloud
As 4G and 5G technologies are enabling higher bandwidths and multiple use cases, there has also been a strong trend of co-locating edge computing infrastructure and RAN functions in a cloud environment at the edge. This trend is creating a demand in the market for appropriate hardware and cloud platforms to cater to both RAN and edge requirements. Projects in the LFEdge open source community, especially Akraino, are providing deployment options for these requirements.
Virtualized RAN is here to stay
With COTS hardware and cloud platforms becoming a reality for RAN deployments, operators are now prepared to deal with the nuances of fully cloudified radio access networks. This requires more “IT like” skills in the operations teams and this journey has already begun. Recently there has been a slew of announcements from many RAN vendors about their virtualized RAN products. vRAN deployments are here to stay. The industry forums, open source community and cloud infrastructure vendors are all working to solve the vRAN deployment challenges.
One such challenge is the need for deploying and managing vRAN solutions in an automated fashion. Service Management and Orchestration (SMO) platforms solve these problems. How do these SMOs deploy and manage cloudified RAN solutions? We’ll take a look at that in detail in our next blog.
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