riority handling between logical channels of one UE; Priority handling between UEs through dynamic scheduling; Transport format selection. The E-UTRA defines MAC entities in the UE and in the E-UTRAN. These MAC entities control the following transport channels: Broadcast Channel (BCH); Downlink Shared Channel (DL-SCH); Paging Channel (PCH); Uplink Shared Channel (UL-SCH); and Random Access Channel (RACH). The exact functions performed by the MAC entities are different in the UE and the E-UTRAN. Figure 7-18 illustrates a sample structure for the UE MAC entity. 7.4 3GPP LTE radio link control and medium access control sub-layers Radio Bearers Security Security Security Security Segmentation Segmentation Segmentation Segmentation CCCH BCCH PCCH Logical Channels Scheduling / Priority Handling Multiplexing UE1 Multiplexing UEn Transport Channels FIGURE 7-16 LTE Layer 2 structure in the downlink [9] This MAC sub-layer provides services such as data transfer and radio resource allocation to upper layers. The physical layer provides the MAC sub-layer with data transfer services, signaling of HARQ feedback, signaling of scheduling request, and measurements. The access to the data transfer services is through the use of transport channels. The characteristics of a transport channel are defined by its transport format, which specifies the physical layer processing to be applied to the transport channel, such as channel coding and interleaving, and any other service-specific rate matching. 7.4.2 Logical and Transport Channels The different logical and transport channels in LTE are illustrated in Figures 7-19 and 7-20, respec- tively. Each logical channel type is defined by what type of information is transferred. The logical channels are generally classified into two groups: (1) Control Channels (for the transfer of control- plane information) and (2) Traffic Channels (for the transfer of user-plane information), as shown in Figure 7-19 [9]. The control channels are exclusively used for transfer of control-plane information.