Effects of SD-RAN Control Plane Design on User Quality of Service

Next generation radio access networks (RANs) en-vision softwarization and programmability as the main tools to provide the quality of service (QoS) requirements of emerging applications. Consequently, software-defined radio access networks (SD-RANs) have gained increased traction as a technology to foster network management and alleviate orchestration. While there exist SD-RAN architecture concepts both with single and multiple SD-RAN controllers, currently developed prototypes only include a single controller. Such a design may be sufficient for a low number of managed devices, for instance below 50. When the number of devices increases beyond 300, the controller performance deteriorates. A distributed control plane provides a solution, but renders the management in the control plane complex and incurs additional overhead, for instance control handover. In this way, both single controller and distributed control plane approaches may have a negative impact on a user's QoS. Yet, proper evaluations are missing and therefore the performance remains unclear. In order to investigate the effect of SD-RAN control plane on the user performance, in this work, we provide an extensive evaluation based on a 5G simulator, compliant with 3GPP standardization, as well as measurements with open-source SD-RAN controllers. Based on our simulator, we are able to demystify the user QoS depending on the control plane design choices. Our results demonstrate that having a distributed control plane with control handovers improves the user performance by at least 20% in terms of throughput, 5x regarding the packet loss ratio and 140% in terms of delay compared to a single controller approach. This confirms that the benefits of multiple controllers surpass the overhead caused by more complicated management.