5.3.3 PDCP Services and Function

25.3013GPPRadio interface protocol architectureTS

This subclause provides an overview on services and functions provided by the Packet Data Convergence Protocol (PDCP). A detailed description of the PDCP is given in [9].

5.3.3.1 PDCP Services provided to upper layers

– PDCP SDU delivery.

– CS counter delivery to JBM.

5.3.3.2 PDCP Functions

– Header compression and decompression. Header compression and decompression of IP data streams (e.g., TCP/IP and RTP/UDP/IP headers) at the transmitting and receiving entity, respectively. The header compression method is specific to the particular network layer, transport layer or upper layer protocol combinations e.g. TCP/IP and RTP/UDP/IP.

– Transfer of user data. Transmission of user data means that PDCP receives PDCP SDU from the NAS and forwards it to the RLC layer and vice versa.

– Support for lossless SRNS relocation or lossless DL RLC PDU size change. Maintenance of PDCP sequence numbers for radio bearers that are configured to support lossless SRNS relocation or lossless DL RLC PDU size change.

– CS counter. A CS counter provides the PDCP PDU with a timestamp value called the ‘CS counter’. The value of the ‘CS counter’ is set to the first to fifth LSBs of the CFN at which the packet is received from higher layers.