LTE and the Evolution to 4G Wireless: Design and Measurement Challenges, 2nd Edition

Chapter 4

Upper Layer Signaling

4.1 Access Stratum

The access stratum (AS) contains the functionality associated with access to the radio network and the control of active connections between a UE and the radio network. The AS consists of a user plane and a control plane. The user plane is mainly concerned with carrying user data—e.g., internet protocol (IP) packets—through the access stratum. The control plane is concerned with controlling the connection between the UE and the network.

An overall description of the evolved universal terrestrial radio access (E-UTRA) and the evolved universal terrestrial radio access network (E-UTRAN) can be found in 36.300 [1]. In contrast to earlier 3GPP protocols, LTE has located the entire access stratum inside one network entity: the base transceiver station or evolved node B (eNB). The aim of this is to simplify the architecture and speed up the control signaling, leading to improved overall performance of LTE. The majority of the physical layer (L1) is explained in Chapter 3; however, there is an important L1/L2 control protocol called the downlink control information (DCI) that resides in the physical layer and is covered in detail in Section 4.1.3. The remainder of the AS covers four protocols: the medium access control (MAC) in 36.321 [2]; the radio link control (RLC) in 36.322 [3]; the packet data convergence protocol (PDCP) in 36.323 [4]; and the radio resource control (RRC) in 36.331 [5].

4.1.1 User Plane

Figure 4.1-1 shows the protocol ...