Chapter 5: Radio Interface: RLCMAC Layer

Overview

This chapter provides a detailed description of the RLC/MAC layer procedures. The RLC/MAC layer is dedicated to the management of radio resources. As described in Chapter 3, in GPRS, temporary radio resources are allocated to the mobile in the downlink or uplink direction for the duration of the data transfer. MAC manages all the signaling necessary for their allocation (i.e., TBF establishment) and their release. It is also responsible for the mapping and multiplexing of signaling and data onto the different logical subchannels . The RLC protocol is in charge of the data transfer management during the TBF. It provides an acknowledged mode allowing selective retransmission of radio blocks as well as an unacknowledged mode of transmission.

For GPRS, the movement of the mobile through the network is entirely managed by a procedure of cell reselection. The mobile can perform autonomous cell reselection or reselection can be controlled by the network. In any case, the RLC/MAC layer manages this process.

The first section of this chapter introduces the RLC/MAC block structure. The RLC/MAC block is the most frequently used transport element on the air interface for signaling and data transfer between the mobile and the BSS. In order to be able to access the network, the mobile must acquire cell and network configuration parameters on the broadcast channel. The second section of the chapter describes how the network schedules these parameters and how the mobile monitors them. The cell reselection process, which partly relies on these broadcast parameters, is then explained. The three next sections deal with the management of the TBF. The way the mobile monitors its PCH in order to detect a downlink transfer is described. Then the different procedures for uplink and downlink resource allocation, release, and data transfer (RLC protocol) are introduced.

The last section provides case studies dealing with RLC/MAC implementation aspects.