Open RAN Interfaces
🛢High Layer Split (HLS) between Centralized Unit (CU) and Distributed Unit (DU) has been specified by #3GPP.
🛢Each individual functional entities DU, CU-UP, and CU-CP entities may be placed at different physical locations according to operator requirements.
🛢The definition of HLS has introduced two new interfaces. F1/ E1 interface for gNode B (gNB)/gNB-CU functional split, which has been specified in 3GPP for Rel 15, and W1 interface for eNode B (eNB) functional split, which is being specified in 3GPP in Rel 15.
🛢It should be noted that within the central RAN function gNB-CU a split in control and user plane (CU-CP and CU-UP) is specified, which has generated a new interface called E1.
🛢Furthermore, interfaces between RAN nodes are also specified: X2 interface, between central RAN functions in eNB and eNB or en-gNB (for Non-Standalone 5G) and Xn interface, between central RAN functions in ng-eNB (next-generation eNB connected to NGCN) and/or gNB.
Source: O-RAN Alliance