The Packet Data Convergence Protocol (PDCP) is located above the RLC layer of the user
plane and PDCP is also used for most of the RRC messages.
The Key features are:
• Ciphering and deciphering both the user plane and most of the control plane data, a functionality
that in WCDMA was located in the MAC and RLC layers.
• Integrity protection and verifi cation, to ensure that control information is coming from the
The PDCP layer receives PDCP SDUs from the NAS and RRC and after ciphering.
Header compression and corresponding decompression of the IP packets. This is based on
the Robust Header Compression (ROHC) protocol, specified in the Internet Engineering Task
Force (IETF) and also part of the WCDMA PDCP layer. Header compression is more
important for smaller IP packets , especially in connection with the VoIP service,
as the large IP header could be a significant source of overhead for small data rates.