3GPP Evolved Packet System (EPS) DL-SCH Downlink Transport channels Downlink Physical channels PDSCH PDCCH Figure 3.11 Mapping between downlink transport channels and downlink physical channels. Reproduced with permission from © 2009 3GPP [14] Layer 2 Layer 2 is split into three sublayers, namely: Medium Access Control (MAC), Radio Link Control (RLC) and Packet Data Convergence Protocol (PDCP). Figures 3.13 and 3.14 show the structure of Layer 2 for both uplink and downlink. It shows some services that are performed by these layers and the services that are expected from MAC for RLC and from RLC for PDCP. 3.6.1 MAC Sublayer E-UTRA defines two MAC entities: one in the UE and one in the E-UTRAN. The exact functions performed by the MAC entities are different in the UE from those performed in the E-UTRAN [13, 14]. 3.6.1.1 MAC Services and Functions Table 3.5 shows the functions that are supported by the MAC layer. These functions are mainly supported in UE and eNB. MAC provides data transfer and radio resource allocation to upper layers. It receives data transfer services, signaling of HARQ feedback, signaling of scheduling request and measurements like CQI (Channel Quality Indication), and SO on, from the physical layer. The access to the data transfer services is through the use of transport channels. 3.6.1.2 Channel Structure The MAC sublayer operates on Logical and Transport channels. The transport channels are SAPs between MAC and Layer 1 while logical channels are SAPs between MAC and RLC. The transport channels used by MAC are described in Table 3.6. UL-SCH Uplink Transport channels Uplink Physical channels PUSCH PRACH PUCCH Figure 3.12 Mapping between uplink transport channels and uplink physical channels. Reproduced with permission from C 2009 3GPP [14] Next Generation Mobile Communications Ecosystem Radio Bearers Security Security Security Security Segm. Segm. Segm. Segm. ARQ etc ARQ etc ARQ etc ARQ etc MCCH CCCH BCCH PCCH Logical Channels Scheduling / Priority Handling Multiplexing UE, Multiplexing UE. Tr