n and Maintenance (OAM) There are two architecture options for the fronthaul OAM: hierarchical and hybrid, as shown in Figure 4.5.14. In the hierarchical model (ORAN-WG4.MP.0), the network management system (NMS) communicates with the O-RU via the O-DU. All the messages from the NMS are passed to the O-RU by the O-DU. On the other hand, in the hybrid architecture (ORAN-WG4.MP.0) the NMS directly connects both the O-DU and the O-RU. The config- uration information, the radio operation status, and error conditions can be directly sent and received between the network management and the O-RU. The OAM can share the transport network with the control and user data traffic. Alter- natively, a dedicated transport network can be used. In the case of shared transport net- work, the OAM traffic shall be labeled as lower priority to minimize impact on the regular fronthaul traffic (control, user, and synchronization [CUS] plane messages) latency. The OAM protocol stack is shown in Figure 4.5.15. 4.5 Lower-Layer Split Network Network Management Management System System OAM DU/RU Msg OAM DU Msg OAM RU Msg M-plane M-plane OAM RU Msg M-plane M-plane Hierarchical Model Hybrid Model Figure 4.5.14 Management plane architecture options. Figure 4.5.15 Management plane protocol stack. M-plane over NetConf Ethernet The management plane protocol, which is based on NETCONF/Yang data models, supports the following features: Initial installation Fronthaul interface management O-RU and O-DU software management Configuration management Performance management Fault management Timing synchronization. For further details refer to the O-RAN OAM specification (ORAN-WG4.MP.0). 4.5.7 Further Reading This section outlines the basic principles of the O-RAN functional split and the fronthaul interface defined to support it, covering control, data, and management protocols between O-DU and O-RU. 4 NG-RAN Architecture For further details, refer to the O-RAN Fronthaul CUS Plane specification and manage- ment plane specification provided below. Reference