LTE & LTE Advanced

4Data Link Layer

4.1. PDCP protocol

The Packet Data Convergence Protocol (PDCP) is used for Radio Resource Control (RRC), relating to dedicated control data, and for traffic data relating to Internet Protocol (IP) packet.

The PDCP protocol performs the following functions:

• – compression of traffic data headers using the Robust Header Compression (ROHC) mechanism;
• – security of traffic data (confidentiality) and of RRC (integrity and confidentiality);
• – delivery in sequence of RRC messages and IP packets;
• – recovery of PDCP frames lost during the handover.

Several PDCP instances can be activated simultaneously:

• – two instances for Signaling Radio Bearers SRB1 and SRB2;
• – SRB1 bearer is used for the transmission of an RRC message that can support a Non-Access Stratum (NAS) message;
• – SRB2 bearer is used for the transmission of a NAS message only;
• – one instance, for each Data Radio Bearer (DRB) relating to traffic data.

4.1.1. Procedures

4.1.1.1. Security architecture

Figure 4.1 describes the implementation of security keys used for traffic data and RRC signaling.

Figure 4.1. Key generation

During the procedure of attachment and development of the Authentication and Key Agreement (AKA) mechanism, the Home Subscriber Server (HSS) entity retrieves the Ki key of the mobile, draws a Random Number (RAND) and calculates the Integrity Key (IK) and Cipher Key (CK).

The Ki Key ...