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134 From GSM to LTE-Advanced Pro and 5G

CCCH DTCH DCCH Figure 3.12 Logical, transport and physical channels in
uplink direction (without HSPA).

RACH DCH

PRACH DPDCH DPCCH

Logical Channels
The topmost channel layer is formed by the logical channels. Logical channels are used
to separate different kinds of data flows that have to be transferred over the air interface.
The channels contain no information on how the data is later transmitted over the air.
The UMTS standards define the following logical channels:
The Broadcast Control Channel (BCCH): This channel is monitored by all mobile
devices in idle state to receive general system information from the network.
Information distributed via this channel, for example, includes how the network can
be accessed, which codes are used by the neighboring cells, the LAC, the cell ID and
many other parameters. The parameters are further grouped into System Information
Block (SIB) messages to help the mobile device to decode the information and to save
air interface bandwidth. A detailed description of the messages and parameters can
be found in 3GPP 25.331, chapter 10.2.48.8 [2].
The Paging Control Channel (PCCH): This channel is used to inform users of incom-
ing calls or SMS messages. Paging messages are also used for packet‐switched calls if
new data arrives from the network once all physical resources (channels) for a sub-
scriber have been released owing to a long period of inactivity. If the mobile device
receives a Paging message it has to first report its current serving cell to the network.
The network will then reestablish a logical RRC connection with the mobile device
and the data waiting in the network is then delivered to the mobile device.
The Common Control Channel (CCCH): This channel is used for all messages from
and to individual mobile devices (bidirectional) that want to establish a new connec-
tion with the network. This is necessary, for example, if a user wants to make a phone
call, send an SMS or establish a channel for packet‐switched data transmission.
– The Dedicated Control Channel (DCCH). While the three channels described
above are common channels observed by many mobile devices in the cell, a DCCH
only transports data for a single subscriber. A DCCH is used, for example, to trans-
port messages for the MM and CC protocols for circuit‐switched services, Packet
Mobility Management (PMM) and SM messages for packet‐switched services
from and to the MSC and SGSN. These protocols are described in more detail in
Sections 3.6 and 3.7.
– The Dedicated Traffic Channel (DTCH). This channel is used for user data
transfer between the network and a single user. User data can, for example, be a
digitized voice signal or IP packets of a packet‐switched connection. If a dedicated
logical channel carries a traditional voice call, the channel is mapped to a dedicated