Air Interface Layer 2

This chapter discusses the long‐term evolution (LTE) air interface by describing the three protocols in the data link layer, layer 2 of the OSI model. The medium access control (MAC) protocol schedules the transmissions that are carried out on the air interface and controls the low‐level operation of the physical layer. In the transmitter, the logical channel prioritization function determines how much data the mobile should transmit from each incoming logical channel in every transmission time interval. The mobile transmits Buffer status report (BSR) MAC control elements to tell the base station about how much data it has available for transmission. The radio link control (RLC) protocol maintains the layer 2 data link between the mobile and the base station. The packet data convergence protocol (PDCP) supports data streams that are using RLC acknowledged mode, by ensuring that none of their packets are lost during a handover.