Shortcuts: A Simple Mechanism for Reducing the Data Path Delay in 6G/5G RAN

Improved RAN scheduling algorithms and the integration of edge functionality tackle low-latency requirements by reducing end-to-end communication delays. Despite these innovations, key architectural limitations remain, specifically the requirement to route user plane traffic through the core network's User Plane Functions (UPFs). This constraint is relevant in the case of traffic between two User Equipment devices (UEs) served by the same gNodeB (gNB), which is a common scenario in factory floor or campus network deployments where a large amount of the traffic would be between UEs in a small area. To address this limitation, an intra-gNB user plane shortcut mechanism is proposed. This shortcut mechanism involves a gNB directly routing user plane traffic between UEs connected to it, bypassing the UPF and some upper-layer user plane processing on the gNB. Considering the current 5G specifications, the proposed mechanism is investigated, and the necessary extensions are discussed. A proof of concept of this mechanism is also introduced and evaluated, built within the 5G RAN implementation of srsRAN. Our theoretical analysis demonstrates latency reduction, supported by prototype measurements conducted in a simulated environment, illustrating promising results for the shortcut concept in reducing end-to-end latency.