 message, the mes- sage must be decoded by RRC before the integrity protection verification can be performed for the PDU in which the message was received. The parameters that are required by PDCP for integrity protection are defined in reference [11] and are input to the integrity protection algorithm. The PDCP data PDU is used to convey user-plane and control-plane data, as well as MAC-I in addition to the PDU header. The PDCP control PDU is used to transport PDCP status report and/or interspersed ROHC feedback in addition to the PDU header. A PDCP SDUs and PDUs are octet-aligned bit strings. A compressed or uncompressed SDU is included in a PDCP data PDU. Fig. 2.19 shows the format of the PDCP data PDU with 12-bit SN, which is applicable to SRBs. The figure further shows the format of the PDCP data PDU 232 Chapter 2 PDCP SN Octet 1 PDCP SN Octet 1 PDCP SN(cont.) Octet 2 PDCP SN(cont.) Octet 2 Octet 3 Octet 3 MAC-I Octet N-3 MAC-I (optional) Octet N-3 MAC-I (cont.) Octet N-2 MAC-I (cont.) (optional) Octet N-2 MAC-I (cont.) Octet N-1 MAC-I (cont.) (optional) Octet N-1 MAC-I (cont.) Octet N MAC-I (cont.) (optional) Octet N PDCP data PDU format for SRBs PDCP data PDU format with 12 bits PDCP SN PDU type Octet 1 PDU type Octet 1 Octet 2 Interspersed ROHC feedback Octet 2 PDCP control PDU format for interspersed ROHC FMC (cont.) Octet 3 feedback FMC (cont.) Octet 4 FMC (cont.) Octet 5 Bitmap (optional) Octet 6 Bitmap (optional) Octet N+5 PDCP control PDU format for PDCP status report Figure 2.19 PDCP PDU formats [11]. with 12-bit SN for RLC-UM and RLC-AM DRBs. The structure of PDCP control PDU car- rying one PDCP status report, which is applicable to RLC-AM DRBs, as well as the struc- ture of PDCP control PDU transporting one interspersed ROHC feedback, which is applicable to RLC-UM and AM DRBs are shown in Fig. 2.19. In PDCP PDU formats, the sequence number (SN) is a 12- or 18-bit number which is con- figured by RRC. The data field is a variable-size field which includes uncompressed user- plane/control-plane data 