resegmentation, reassembly, and duplicate detection of SDUs. An RLC entity in any mode can be config- ured either as a transmitting or a receiving entity. The transmitting RLC entity receives RLC SDUs from the upper layer and sends RLC PDUs to its peer receiving RLC entity via lower layers. The receiving RLC entity delivers RLC SDUs to the upper layer and receives RLC PDUs from its peer transmitting RLC entity via lower layers. Fig. 2.10 illustrates the Upper layer RLC channel Transmitting Receiving Transmitting Receiving AM RLC entity TM RLC entity TM RLC entity UM RLC entity UM RLC entity Logical channel Lower layers Radio interface Lower layers Logical channel Receiving Transmitting Receiving Transmitting AM RLC entity TM RLC entity TM RLC entity UM RLC entity UM RLC entity RL€ channel Upper layer Figure 2.10 High-level architecture of RLC sublayer [10]. 216 Chapter 2 high-level architecture of the RLC sublayer. The [octet-aligned] RLC SDUs of variable sizes are supported for RLC entities. Each RLC SDU is used to construct an RLC PDU without waiting for notification from the MAC sublayer for a transmission opportunity. In the case of RLC-UM and RLC-AM entities, an RLC SDU may be segmented and trans- ported using two or more RLC PDUs based on the notification(s) from the lower layer [10]. In RLC-TM, no RLC headers are added. The RLC-UM supports segmentation and duplicate detection, while the RLC-AM supports retransmission of erroneous packets. A key differ- ence with LTE is that the NR RLC sublayer does not handle in-sequence delivery of SDUs to the upper layers. Eliminating the in-sequence delivery function from the RLC sublayer reduces the overall latency since the correctly received packets do not have to wait for retransmission of an earlier (missing) packet before being delivered to the higher layers. Another difference is the removal of concatenation function from the RLC protocol to allow RLC PDUs to be assembled prior to receiving the uplink scheduling grant. By eliminating the concatenation from RLC fu