Logical Channel Types of LTE
Logical channels are in a one-to-one fashion associated with radio bearers. Logical channel types are used to distinguish the type of information transmitted within the attached radio bearer. The two major groups of logical channel types are therefore control channels for signaling and traffic channels for IP user data. Currently the following logical channel types are defined for EUTRAN signaling:
BCCH (Broadcast Control Channel): The BCCH is used to transmit system
information regarding access and non-access stratum. It allows the UE to retrieve cell and network configuration parameters (e.g. PLMN code, cell identity, cell reselection parameters, etc.) required for normal operation within EUTRAN.
PCCH (Paging Control Channel): The PCCH is used to transmit the paging
messages from RRC. Hence it is a downlink point-to-multipoint channel a UE is
using when it is in LTE_IDLE mode.
CCCH (Common Control Channel): The CCCH is an uplink (NOTE: DL is under investigation.) RRC signaling channel used by UEs to do the initial access
signaling when it is in RRC_IDLE state and wants to enter RRC_CONNECTED
state. The UE will send only one message (RRC CONNECTION REQUEST) and
the rest of the communication takes place on DCCH.
DCCH (Dedicated Control Channel): The DCCH is a bidirectional RRC signaling channel used for point-to-point (dedicated) RRC and NAS signaling procedures. It is the main signaling channel to be used by RRC_CONNECTED UEs.
MCCH (Multicast Control Channel): The MCCH is associated with MBMS. It allows the eNB to inform UEs that want to listen to broadcast or multicast service traffic about availability of such services and about the associated MBMS radio bearer (point-to-multipoint) radio bearers.
On the traffic channel side we have currently only two types defined:
DTCH (Dedicated Traffic Channel): The DTCH is used for user radio bearers carrying IP traffic. The eNB connects DTCHs with their associated S1-U tunnel to the SAE GW. DTCH can be bidirectional, uplink only or downlink only. DTCH are of course point-to-point.
MTCH (Multicast Traffic Channel): The MTCH is a point-to-multipoint traffic channel for MBMS. It carries IP traffic for broadcast or multicast services driven by the MBMS feature.