L_TTI.request message. Transmission of the Downlink Shared Channel (DL-SCH) transport channel. The DL- SCH transport channel is used to send data from the NB to a single UE. HARQ is applied on the DL-SCH transport channel and it's up to the L2/L3 stack to schedule enough uplink bandwidth for HARQ (Physical Uplink Shared Channel (PUSCH) or Physical Uplink Control Channel (PUCCH) based) for acknowledgment (ACK)/ negative acknowledgment (NACK) feedback to be returned. Transmission of the DL- SCH transport channel includes the TX_Data.request messages that defines the MAC PDU data-this message is special in that it contains large (bulk) payload whereas all other (DL) messages or message components are small. For that reason, TX_Data. Chapter 5 System software request is often implemented in a hardware-optimized manner (using DMA engine rather than a memory copy) that reduces CPU loading. Transmission of Downlink Control Information (DCI). Transmission of the Channel State Information (CSI) reference signal. Per-Channel Reception APIs Reception of the Random Access Channel (RACH) transport channel. The RACH procedure begins when the L1 receives an UL_TTI.request message indicating the presence of a RACH. If no RACH preamble is detected by the PHY then no RACH. indication message is sent. Reception of the UL-SCH transport channel. The UL-SCH transport channel is used to send data from the UE to the gNB. HARQ is always applied on the UL-SCH transport channel and the ACK/NACK value is indicated when the next transmission for the HARQ process is scheduled via DCI including in the next iteration of this procedure. Reception of Uplink Control Information. Reception of the sounding reference signal. Defined to be flexible and support varying levels of sophistication, beamforming APIs are defined in tables loaded into the L1 at configuration time. In slot messages, a precoding index and/or beamforming index is included in each PDU. nFAPI Designed to support operation for an Option-6 split with MAC and Physical layers connecte