Chapter 4
User Plane Protocols
4.1 Introduction to the User Plane Protocol Stack
The LTE Layer 2 user-plane protocol stack is composed of three sublayers, as shown in Figure 4.1:
Figure 4.1: Overview of user-plane architecture.
- The Packet Data Convergence Protocol (PDCP) layer [1]: This layer processes Radio Resource Control (RRC) messages in the control plane and Internet Protocol (IP) packets in the user plane. Depending on the radio bearer, the main functions of the PDCP layer are header compression, security (integrity protection and ciphering), and support for reordering and retransmission during handover. For radio bearers which are configured to use the PDCP layer, there is one PDCP entity per radio bearer.
- The Radio Link Control (RLC) layer [2]: The main functions of the RLC layer are segmentation and reassembly of upper layer packets in order to adapt them to the size which can actually be transmitted over the radio interface. For radio bearers which need error-free transmission, the RLC layer also performs retransmission to recover from packet losses. Additionally, the RLC layer performs reordering to compensate for out-of-order reception due to Hybrid Automatic Repeat reQuest (HARQ) operation in the layer below. There is one RLC entity per radio bearer.
- The Medium Access Control (MAC) layer [3]: This layer ...
