smitted [17]. 2.2.3 Packet Data Convergence Protocol Sublayer 2.2.3.1 PDCP Services and Functions The services and functions of the PDCP sublayer on the user-plane include sequence num- bering; header compression and decompression; transfer of user data; reordering and dupli- cate detection; in-sequence delivery; PDCP PDU routing in multi-connectivity; retransmission of PDCP SDUs; ciphering, deciphering, and integrity protection; PDCP SDU discard; PDCP re-establishment and data recovery for RLC-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. 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 [8]. In some services and applications such as VoIP, interactive gaming, and multimedia messaging, the data payload of the IP packet is almost the same size or even smaller than the header itself. Over the end-to-end connection comprising multiple hops, these protocol headers are extremely important, but over a single point-to-point link, these headers serve no useful purpose. It is possi- ble to compress these headers, and thus save the bandwidth and use the expensive radio resources more efficiently. The header compression also provides other important benefits, such as reduction in packet loss and improved interactive response time. The payload header New Radio Access Layer 2/3 Aspects and System Operation 223 compression is the process of suppressing the repetitive portion of payload headers at the sender side and restoring th