Flat UP: Toward RAN-Core Convergence for the 6G User Plane

The industry-wide trends of radio access network (RAN) disaggregation, virtualization, and cloudification have upended the traditional hierarchical structure of cellular networks and paved the way for RAN-core convergence. However, the practical realization of such converged networks poses several challenges relating to architecture and protocol design, quality-of-service (QoS) provisioning, and adaptability to emerging 6G-specific use cases. To that end, this article introduces the flat UP architecture, which brings forth a novel approach to RAN-core convergence with a new 6G-native access user plane function (AUPF) as its centerpiece. Key highlights include a detailed protocol and feature-level description of the flat UP architecture, practical guidelines for real-world deployments, and a concrete systems-level prototype implementation of the AUPF, along with a comprehensive over-the-air evaluation. The results thus obtained showcase that not only does the proposed flat UP architecture lead to better throughput and latency performance, but it also results in a reduction in the overall compute resource utilization compared to the existing hierarchical 5G user plane architecture.