ion (U-plane) Header Decompression (U-plane) Packets Associated With PDCP SDU Packets Associated With PDCP SDU Integrity Protection Integrity Verification (C-plane) (C-plane) Ciphering Deciphering PDCP Header Addition PDCP Header Removal Air Interface Transmitting PDCP Entity (UE) Receiving PDCP Entity (UE) FIGURE 5-10 Functional decomposition of PDCP entities [21] the UE, or to the relay at the evolved Node B (eNB). The following services are provided by PDCP to upper layers: Transfer of user-plane and control-plane data; Payload header compression; Ciphering; Integrity protection. The maximum supported size of a PDCP SDU is 8188 octets [21]. The following services are provided by lower layers to PDCP sub-layer: 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. As mentioned earlier, the PDCP sub-layer performs the following functions: Header compression and decompression of IP data flows using the ROHC protocol; Transfer of data (user-plane or control-plane); Maintenance of PDCP Sequence Numbers (SN); 5.5 The 3GPP LTE packet data convergence protocol In-sequence delivery of upper layer PDUs at re-establishment of lower layers; Removal of duplicate SDUs at re-establishment of lower layers for radio bearers mapped on RLC AM; Ciphering and deciphering of user-plane data and control-plane data; Integrity protection and integrity verification of control-plane data; Timer-based discard; Duplicate discarding. The PDCP uses the services provided by the RLC sub-layer. The PDCP is used for SRBs (Signaling Radio Bearer carrying control-plane data) and DRBs (Data Radio Bearer carrying user-plane data) mapped on Dedicated Control Channel (DCCH) and Dedicated Traffic Channel (DTCH) type of logical channels. The PDCP is not used for other types of logical channels. The ROHC protocol is utilized for header compression 