ansport Channels Figure 3.13 Layer 2 structure for DL. Reproduced with permission from C 2009 3GPP [14] Radio Bearers Security Security Segm. Segm. ARQ etc ARQ etc Logical Channels Scheduling / Priority Handling Multiplexing Transport Channels Figure 3.14 Layer 2 structure for UL. Reproduced with permission from 2009 3GPP [14] 3GPP Evolved Packet System (EPS) Table 3.5 MAC function location and link direction association MAC function Downlink Uplink Mapping between logical channels and transport channels Multiplexing Demultiplexing Error correction through HARQ Transport Format Selection Priority handling between UEs Priority handling between logical channels of one UE Logical Channel prioritization Scheduling information reporting Source: C 2009 3GPP [16] The logical channels are used by MAC layer to provide data transfer services. Each logical channel type is defined by what type of information is transferred. The logical channels are divided into two groups namely control and traffic channels. Control Channels are used for the transfer of control plane information. The control channels offered by MAC are: Broadcast Control Channel (BCCH): A downlink channel for broadcasting system control information. Paging Control Channel (PCCH): A downlink channel that transfers paging information and system information change notifications. This channel is used for paging when the network does not know the location cell of the UE. Common Control Channel (CCCH): Channel for transmitting control information between UEs and network. This channel is used for UEs having no RRC connection with the network. Multicast Control Channel (MCCH): A point-to-multipoint downlink channel used for transmitting MBMS control information from the network to the UE, for one or several MTCHs (Multicast Traffic Channel). This channel is only used by UEs that receive MBMS. Traffic Channels are used for the transfer of user plane information. The traffic channels offered by MAC are: Dedicated Traffic Channel (DTCH): DTCH is a point-to-point channe