LTE Radio Protocols
The role of LTE radio interface protocols is to set up, reconfigure and release the Radio Bearer, which provides the means for transferring the EPS bearer (as presented in Chapter 3). The LTE radio interface protocol layers above the physical layer include Layer 2 protocols, Medium Access Control (MAC), Radio Link Control (RLC) and Packet Data Convergence Protocol (PDCP). Layer 3 consists of the Radio Resource Control (RRC) protocol, which is part of the control plane. The protocol layer above (for the control plane) is the Non-Access Stratum (NAS) protocol, which terminates in the core network side and was addressed in Chapter 3. This chapter describes the general radio interface protocol architecture. The main functions of MAC, RLC, PDCP and RRC layers will be introduced, including the principles of ASN.1 used in the RRC protocol. The radio protocol aspects of the control plane of the X2 interface, the interface between eNodeBs, is also covered. From the Release 9 enhancements, the options added for the CS fallback are covered in more detail. This chapter concludes with the introduction of the LTE Inter Operability Testing (IOT) bits intended for early UE handling in LTE.
6.2 Protocol Architecture
The overall LTE radio interface protocol architecture is shown in Figure 6.1. This covers only the protocol part of radio access in LTE. There are also protocols in the core network between ...