Packet Data Convergence Protocol


Packet Data Convergence Protocol is specified by 3GPP in TS 25.323 for UMTS, TS 36.323 for LTE and TS 38.323 for 5G New Radio. 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. The following services are provided by PDCP to upper layers:
The header compression technique can be based on either IP header compression or Robust Header Compression. If PDCP is configured for No Compression it will send the IP Packets without compression; otherwise it will compress the packets according to its configuration by upper layer and attach a PDCP header and send the packet.
Different header formats are defined, dependent on the type of data to be transported. In LTE, there are e.g. header formats for Control Plane PDCP Data PDU with long PDCP SN, for User plane PDCP Data PDU with short PDCP SN and others.