, after describing the logical channels, the MAC functions and services are explained, with emphasis laid on the main differences compared to LTE. 7.6.2 Logical Channels The MAC sublayer provides services to the upper layers through logical channels. Log- ical channels can be categorized into two different groups: Control Channels (CCHs), used exclusively for the transport of CP signaling, and Traffic Channels (TCHs), used for carrying UP data. Different logical channels are defined for different data transfer services: Broadcast Control Channel (BCCH), used for broadcasting system information in the downlink (see Section 7.7.2). Paging Control Channel (PCCH), used in the downlink to transfer paging informa- tion and notify UEs of system information changes and public warning system (PWS) transmissions (see Section 7.7.3). Common Control Channel (CCCH), used by SRBO to transfer control information between the UE and the network (see Section 7.7.1), in both the downlink and uplink. Dedicated Control Channel (DCCH) used by SRB1, SRB2, and SRB3 as a point-to-point channel for dedicated control information between the UE and the network (see Section 7.7.1), in both the downlink and uplink. Dedicated Traffic Channel (DTCH,) used as a point-to-point channel for transferring UP data, in both the downlink and uplink. Mapping of the logical channels to the transport channels and further to the physical channels is shown in Figure 7.11, where: 7.6 MAC Layer Logical Channels CCCH DCCH DTCH BCCH PCCH CCCH DCCH DTCH Transport Channels UL-SCH DL-SCH PDSCH Physical Channels PRACH PUSCH Figure 7.11 Mapping of the uplink and downlink logical and transport channels. In the uplink, all the logical channels are mapped to the Uplink Shared Channel (UL-SCH), and there is no logical channel mapped on the Random Access Channel (RACH), as it does not carry any information above the MAC layer. In the downlink, BCCH uses the Broadcast Channel (BCH) as the transport channel for the Master Information Block (MIB), while the actual System Inf