PRBs per data section description) field: 8 bits. reMask - The resource element mask. numSymbol - The number of symbols. ef - The section extension flag. beamId - The beam ID. Figure 4.5.11 shows the I/Q data message. The payload common header fields and section fields are described below. 4.5 Lower-Layer Split Payload common header fields: dataDirection - The data direction indicator (gNB Tx/Rx). payloadVersion - The payload version number. Value = "1" (first version for payload format). filterIndex - The filter index. frameId - The frame ID number. subframeId - The subframe ID number. slotID - The slot ID number. symbolId - The symbol ID number. Payload section header fields: sectionID - The section ID number. rb - Indicates whether every resource block is used or every other resource block is used. symInc - The symbol number increment indicator. startPrbu - The starting PRB ID number of the user-plane section. numPrbu - The number of contiguous PRBs per data section. udCompHdr - The user data compression header containing compression method and IQ bit width information. reserved - The reserved field. udCompParam - The compression method specific parameter. iSample - The in-phase data sample. qSample - The quadrature data sample. The rest of the definitions of O-RAN messages can be found in the O-RAN spec (ORAN-WG4.CUS.0). 4.5.4.2 Scheduling Procedure In this subsection we illustrate the LLS split operation by one typical call flow of the schedul- ing procedure, which is controlled by the O-DU. When the MAC scheduler allocates the UE on a specific subframe, a series of control- and user-plane messages are exchanged between O-DU and RU. It is possible to bundle multiple control messages together in a single message or send each one separately. The O-DU is also able to send the UE schedul- ing Information as well as the PRB usage information to the O-RU. When the system is not fully utilized (some of the PRBs are not used), the I/Q data of unused PRBs are not sent to the O-DU, which may lead to power saving. Figu