mbol #N-1 **for a multi-symbol C-Plane message, the message must be received by the RU *t2a_min_cp_ ul* before the receipt by the RU's antenna of the lowest-numbered symbol in the C-Plane message Figure 4.5.12 Fronthaul transmission procedure. (Source: Reproduced by permission of © O-RAN). 4.5 Lower-Layer Split 4.5.4.3 Beamforming Methods Beamforming is an optional feature in 5G, which is supported by the O-RAN fronthaul via the control-plane procedures described below. All three types of beamforming - digital, analog, or hyper beamforming are supported. When selecting a beamforming method, one needs to consider both fronthaul transport network impact and O-RU complexity. Some methods described below require significant amounts of beamforming-related information to be transferred over the fronthaul inter- face. Furthermore, the frequency of beamforming information update is also different for different methods. Finally, some methods require more processing capabilities in an O-RU, which may increase the hardware complexity and cost. 4.5.4.3.1 Beamforming Indexing Method To use this method, the O-RU must be preconfigured with a table of beamforming weights and their assigned indexes. The beam index can then be used in either digital or analog beamforming, and one additional method described below. The management-plan specification defines the file download method that can be used to provision the beamforming table. Alternatively, the OAM can be used or the beamforming table could be preconfigured in the persistent memory of the O-RU by the vendor. 4.5.4.3.2 Real-Time Weights Method In this method, the O-DU sends the beamforming weights generated in real time to the O-RU to be associated with a specific user's data. A beam index can be assigned (and used in subsequent messages) if the beamforming weights are stable for a period of time. 4.5.4.3.3 Beam Attributes Method In contrast to the previous method in which the O-DU provides the weights, this method relies on the O-RU to generate the beamforming weights using 