Hi @orville,
In the centralized network architecture, the central AP proxy AC shares the centralized management and coordination functions of the RU, such as STA online, configuration delivery, and STA roaming between RUs. The remote unit(RU) serves as the remote radio frequency module of the central AP and is responsible for sending and receiving air interface 802.11 packets.
Simplely, central AP likes a management device, while RU looks like a data transferring device.