nels. The following services are provided by PDCP to upper layers: Transfer of user plane data. Transfer of control plane data. Next Generation Mobile Communications Ecosystem UE/E-UTRAN E-UTRAN/UE Transmitting Receiving PDCP entity PDCP entity Sequence numbering In order delivery and duplicate detection (u-plane only) Header Compression Header Decompression (u-plane only) (u-plane only) Packets associated Packets associated to a PDCP SDU to a PDCP SDU Integrity Protection Integrity Verification (c-plane only) (c-plane only) Ciphering Deciphering Add PDCP header Remove PDCP Header Radio Interface (Uu) Figure 3.20 Functional view of PDCP sublayer. Reproduced with permission from © 2009 3GPP [18] Robust Header compression [19]. Ciphering. Integrity protection. The following services are expected from lower layers (RLC): Acknowledged data transfer service, including indication of successful delivery of PDCP PDUs. Unacknowledged data transfer service. In-sequence delivery, except at re-establishment of lower layers. Duplicate discarding, except at re-establishment of lower layers. The main functions of PDCP sublayer are shown in Table 3.8. 3.6.3.3 PDCP Structure Figure 3.21 depicts the PDCP PDU structure for user plane data, where PDCP PDU and PDCP header are octet-aligned and PDCP header can be either 1 or 2 bytes long. The structures for control PDCP PDUs and for control plane PDCP data PDUs are specified in [18]. 3GPP Evolved Packet System (EPS) Table 3.8 PDCP functions Functions User Plane Control Plane Header compression and decompression: ROHC only Transfer of user data In-sequence delivery of upper layer PDUs at PDCP re-establishment procedure for RLC AM Duplicate detection of lower layer SDUs at PDCP re-establishment procedure for RLC AM Retransmission of PDCP SDUs at handover for RLC AM Ciphering and deciphering Timer-based SDU discard in uplink Ciphering and Integrity Protection Transfer of control plane data Sources: 2009 3GPP [14] and [16] RRC (sublayer of Layer 3) The RRC sublayer (sublayer of layer 3) a