ABSTRACT
Packet Data Convergence Protocol (PDCP) is a thin sublayer that is used for both control- and data-plane. Its main functionality is to provide integrity and security protections to control- and data-plane Protocol Data Units (PDU). Each radio bearer that goes through the PDCP has its own PDCP entity that is mapped to either Radio Link Control (RLC) acknowledged mode (AM) or unacknowledged mode (UM). Each PDCP entity means that each one has its own state, state variables, and operation independent of the other entities. It maintains a reordering Window which is always half of the Sequence Number (SN) space. The purpose of this reordering Window is to receive PDCP PDUs that falls within the window, and then to reorder them according to the COUNT value and deliver them in-order to upper layer. PDCP sublayer receives packets from upper layer, assigns an SN to it, integrity- and cipher-protecting those packets and forward them to RLC sublayer.
