A Flexible and Programmable Platform for Software-Defined Radio Access Networks
Although SDN is considered as one of the key technologies behind the impending evolution of mobile networks towards 5G, the opportunity of reaping its benefits is largely still untapped for the Radio Access Network (RAN) part due to the lack of a software-defined RAN (SD-RAN) platform. FlexRAN is the first concrete implementation of an SD-RAN platform specifically developed to fill this void.
The FlexRAN platform is made up of two main components: the FlexRAN Control Plane and FlexRAN Agent API. The FlexRAN control plane follows a hierarchical design and is in turn composed of a Master Controller that is connected to a number of FlexRAN Agents, one for each base station (eNodeB in 4G LTE). The control and data plane separation is provided by the FlexRAN Agent API which acts as the southbound API with FlexRAN control plane on one side and eNodeB data plane on the other side. The FlexRAN protocol facilitates the communication between the master controller and the agents.
FlexRAN decouples the RAN control and data plane with several benefits, including: reducing the complexity of developing new control solutions; promoting openness and innovation by allowing operators to open their RAN service environment to authorized third-parties to rapidly deploy innovative applications and services for mobile subscribers, enterprises and vertical segments.
FlexRAN consolidates the control plane into a single logically centralized controller, enabling easier coordination among base stations, effectively simplifying the development of more sophisticated control applications. Moreover, FlexRAN has been designed in a way that enables support for the deployment of real-time control applications, like MAC schedulers, with very stringent time constraints.
FlexRAN allows the flexible and programmable control of the underlying RAN infrastructure through the introduction of a number of virtualized control functions that have a modular structure and well-defined interfaces and are responsible for performing the various control operations of the base station. This allows part of the system’s logic, like the mobility manager or the MAC scheduler, to be easily upgraded by replacing or extending the corresponding function without affecting the rest of the system.
The virtualized control functions of FlexRAN are exploited through a set of mechanisms designed to allow the delegation of control functions, like schedulers and mobility managers, from the master controller to the base stations at runtime and the reconfiguration of their behavior and parameters on-the-fly in a simple and seamless manner. This feature makes the system very flexible and adaptable to the underlying networking conditions and to the specific requirements of the network operator.