the beam attribute, which requires additional processing capability in the O-RU. 4.5.4.3.4 Channel Information Method In this method the RU generates beam weights based on the channel information. 4.5.5 Fronthaul Timing Synchronization IEEE1588 (IEEE1588) is used as the timing synchronization protocol for the O-DU and O-RU local clock synchronization. There are several ways to synchronize O-DU and O-RU, depending on the location of the master clock. Below we explain differences between those various configurations referred to as C1, C2, and SO on. In configurations C1 and C2, the O-DU holds the timing source, which can be either a grandmaster or boundary clock. Alter- natively, in C4, Global Navigation Satellite System (GNSS)-based synchronization is used by the O-RU. These configurations are illustrated by Figure 4.5.13. In configuration C1, the O-DU is directly connected to the O-RU. The O-DU acts as a grandmaster clock or boundary clock, so O-RU synchronizes with O-DU via PTP. With configuration C2, the O-DU is connected with the Primary Reference Time Clock (PRTC). The clock source acts as the master clock and distributes timing to the O-RU. The fronthaul allows more than one Ethernet switch hop. The total allowed network noise limits the number of switches. 4 NG-RAN Architecture Source Source Source Figure 4.5.13 Fronthaul timing synchronization configurations. In configuration C3, the PRTC grandmaster is provided by the network switch within the fronthaul network, the timing synchronization is distributed to the O-DU and the O-RU via the PTP network. The number of hops between switches is limited by frequency and time error in the distribution chain. Configuration C4 is a special case, which does not distribute the timing via fronthaul networks. The O-RU has a local PRTC-traceable time source such as GNSS. The choice of the timing synchronization configuration depends on the deployment use case of the NG-RAN, transport network capability, and availability of the timing source. 4.5.6 Operation, Administratio