d duplicate detection; in-sequence delivery; PDCP PDU routing (in case of split bearers); retransmission of PDCP SDUs; ciphering, deciphering, and integrity protection; PDCP SDU discard; PDCP re- establishment and data recovery for RLC acknowledged mode (AM); PDCP status reporting for RLC-AM; duplication of PDCP PDUs and duplicate discard indication to lower layers. The main services and functions of the PDCP sublayer on the control-plane consist of sequence numbering; ciphering, deciphering, and integrity protection; transfer of control- plane data; reordering and duplicate detection; in-sequence delivery; duplication of PDCP PDUs and duplicate discard indication to lower layers [8]. The PDCP protocol performs (optional) IP-header compression, followed by ciphering, for each radio bearer. A PDCP header is added, carrying information required for deciphering in the other end, as well as a sequence number used for retransmission and in-sequence delivery. The RLC sublayer supports three transmission modes, which include transparent mode (TM), unacknowledged mode (UM), and the acknowledged mode. The main difference between these 198 Chapter 2 modes is the presence or absence of ARQ function to provide higher reliability required for RRC and NAS messages. The RLC configuration is per logical channel with no dependency on numerologies and/or transmission duration, and ARQ can operate on any of the numerologies and/or transmission durations that the logical channel is configured to support. The radio bearers in NR are classified into two groups of DRBs for user-plane data and signaling radio bearers (SRBs) for control-plane data. The RLC-TM mode is used for transport of SRBO, paging, and broadcast system information (SI), whereas for other SRBs, RLC-AM mode is used. For trans- port of DRBs, either RLC-UM or RLC-AM mode is used. Some of the services and functions of the RLC sublayer depend on the transmission mode. Those services include transfer of upper layer PDUs; sequence numbering independent of the one in PDCP (RL