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radisys.com 37 Radisys Series — Who Disaggregated My RAN? eBook RAN Slicing In the radio access network, a RAN slice (part of the network slice) is created to provide appropriate resources in the RAN for the service requirements. There could be dedicated or shared RAN slices based on the use cases. A slice-aware scheduler in the Distributed Unit (DU) allocates radio resources as per slice requirements. One of the key challenges in serving multiple slices is to develop a sophisticated scheduling algorithm in the DU to meet competing and conflicting needs of different use cases like eMBB and URLLC among others. In the Centralized Unit (CU), slicing might require differentiated handling of data traffic. Often, separate CU User Plane (CU-UP) instances are created to serve the slices in a dedicated fashion. In view of the challenges in realizing the RAN slices, the continuous monitoring of slice performance is often required. Appropriate KPIs of slice performance can be reported back to an orchestrator or a RAN controller (or a slice manager) for needed corrective actions in a closed loop manner. This is an active area of research. Radisys partnered with KDDI Research to collaborate on one such study to demonstrate RAN slicing and its control via a RAN controller for KPI based analytics. Slicing and Orchestration Network slices are created dynamically for serving specific use cases and decommissioned when they are no longer needed. Given the dynamic nature of slice creation, activation and deactivation, there is a need for automating these operations. This is often achieved by using various levels of orchestrators in the mobile network. 3GPP specifications address in great detail, management and orchestration of network slices. Open source projects like ONAP (Open Network Automation Platform) incorporated slice management aspects defined by 3GPP. With the availability of orchestrators with such features, automated and sophisticated network slice management is now possible. There is a significant amount of work being done to provide automation features and user-friendly interfaces to design and deploy network slices. In the radio access network, slice management and orchestration can be realized in different ways. How do we implement network slicing in open and disaggregated networks? Let's look at the O-RAN Alliance's approach. O-RAN Architecture and Network Slicing With its disaggregated CU and DU nodes, the O-RAN architecture naturally fits the network slicing need for scaling, isolation and dedicated processing, etc. The O-RAN Alliance's approach to RAN slicing is to employ SMO (Service Management and Orchestration) and RIC (RAN Intelligent Controller) to create and manage RAN slices. The use of artificial intelligence and machine learning in non-real-time RIC enables slice performance analytics and optimization. The near-real-time RIC can host slice aware xApps and algorithms and collect KPIs over theE2 interface to assure slice Service Level Agreement (SLA) and dynamically control RAN nodes to achieve slice

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