According to 3GPP, several types of data transfer services are offered by MAC. Each logical channel type is defined by the type of information to be transferred.
A general classification of logical channels is into two groups:
- Control Channels (for the transfer of control plane information)
- Traffic Channels (for the transfer of user plane information).
Control channels are used for transfer of control plane information only. 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.
- Dedicated Control Channel (DCCH)
A point-to-point bi-directional channel that transmits dedicated control information between a UE and the network. Used by UEs having an RRC connection.
Traffic channels are used for the transfer of user plane information only. The traffic channels offered by MAC are:
- Dedicated Traffic Channel (DTCH)
A Dedicated Traffic Channel (DTCH) is a point-to-point channel, dedicated to one UE, for the transfer of user information. A DTCH can exist in both uplink and downlink.
- Multicast Traffic Channel (MTCH) (from Release 9)
A point-to-multipoint downlink channel for transmitting traffic data from the network to the UE. This channel is only used by UEs that receive MBMS.
The figure below depicts the mapping between logical channels, transport channels and physical channels for downlink and uplink:
Figure 18: Downlink Channel Mapping
Figure 19: Uplink Channel Mapping