RLC layer

The value of the PDCP sequence number ranges from 0 to 65535 . The PDCP SN window size indicates the maximum number of PDCP SDUS, not confirmed to have been successfully transmitted to the peer entity by lower layer, that can be numbered at any given time. The PDCP SN window size is configured by upper layers.

A PDCP layer sets a timer and discards a PDCP SDU upon expiration of the timer . The timer may be set upon receiving the PDCP SDU from an upper layer or upon submitting the PDCP SDU to a lower layer for transmission. The timer and a radio link control (RLC) discard timer may be coordinated.

PDCP is located in the Radio Protocol Stack in the UMTS/LTE/5G air interface on top of the RLC layer. PDCP provides its services to the RRC and user plane upper layers , e.g. IP at the UE or to the relay at the base station.