LC SDUs and this function is now part of the MAC multiplexing. This allows the UE to pregenerate uplink RLC PDUs from RLC SDUs before receipt of an uplink grant and therefore speeds up the generation of MAC PDU after the uplink grant is received. This in turn allows low uplink grant to transmission delay and reduction in latency. The last RLC segment of the MAC PDU still need to be generated after reception of an uplink grant as it requires information about the number of bits available. This is considered acceptable as Oct 1 Oct 2 Oct 3 Oct 4 Oct 5 Oct N Figure 3.4.5 RLC AMD PDU with 12 bit Sequence Number with Segment Offset. (Source: Reproduced by permission of © 3GPP). 3.4 NR Protocol Stack Table 3.4.1 Downlink channel mapping. Transport channel DL-SCH (downlink Logical channel (broadcast channel) (paging channel) Shared channel) BCCH (Broadcast Control Channel) PCCH (Paging Control Channel) CCCH (Common Control Channel) DCCH (Dedicated Control Channel) DTCH (Dedicated Traffic Channel) the UE can perform this while it is putting together and possibly already providing to the physical layer the initial bits of the MAC PDU for transmission. The MAC layer (specified in 3GPP TS 38.321) multiplexes the data (RLC PDUs) from different logical channels into a transport block for transmission over the radio interface. Table 3.4.1 shows the mapping between logical channels and transport channels in the downlink. The Common Control Channel (CCCH) is used during the initial access before dedicated channels are established, such as for RRC Connection Request. The Dedicated Control Channel (DCCH) carries UE-dedicated RRC signaling messages, while the Dedicated Traf- fic Channel (DTCH) carries user-plane traffic. As discussed above, this mapping function multiplexes RLC PDUs from different logical channels and also does the concatenation function of including different RLC PDUs from the same logical channel. Each logical channel is assigned a scheduling priority and Prioritized Bit Rate (PBR) by the network. On receipt of a