GSM Channels


GSM stands for Global System for Mobile. Developed in the 1980s. GSM technology uses TDMA (Time Division Multiple Access) to support up to eight calls simultaneously.

GSM (Global System for Mobile) channels are divided into two categories: -

  1. Traffic Channels
  2. Signaling Channels


Traffic Channel

This traffic channel is again being classified into two types;

  1. Half-rate traffic channel and
  2. Full-rate traffic channel.


Signaling Channel

Signaling channels are broadly classified into three types;

  1. Broadcast channels
  2. Common control channel and
  3. Dedicated control channel.


Broadcast Channel (BCH)

Broadcast control channels are classified into three channels;

  1. Broadcast control channel (BCCH)
  2. Frequency correction channel (FCCH)
  3. Synchronization channel (SCH)


Common Control Channel (CCCH)

The common control channel is classified into three-channel;

  1. Paging Channel (PCH)

Downlink only, the MS (Mobile Station) is informed by the BTS for incoming calls via the PCII

  1. Access granted channel (AGCH)

Downlink only, BTS allocates a TCII to the MS, thus allowing the MS (Mobile Station) access to the network.

  1. Random access channel (RACH)

Uplink only, allows the MS (Mobile Station) to request an SDCCH in response to a page or due to a call, the MS chooses a random time to send this channel. This creates the possibility of collisions with transmission from other Mobile Stations (MSs).

This is transmitted by the mobile when it wishes to access the system, this occurs when the mobile initiates a call or responds to a page.


Dedicated Control Channel

Dedicated control channel signaling information is carried between the mobile station and base transceiver system using associated and dedicated control channels during or not during a call.

The dedicated control channel is again classified into three categories;

  1. Slow associated control channel (SACCH)
  2. Fast associated control channel (FACCH)

Similar to the SDCCH, but used in parallel to the operation of the TCH, if the data rate of the SACCH is insufficient, ‘borrowing mode’ is used.

  1. Standalone dedicated control channel (SDCCH)

The communications channel between MS (Mobile Station) and the BTS (Base Transceiver Station), signaling during call setup before a traffic channel (TCH) is allocated.



Full-rate channel (TCH/F)

-Carries user data (speech and data)

Halt-rate channel (TCH/F)

-Carries user data (speech and data). Half-rate TCHs double the capacity of a system effectively by making it possible to transmit two calls in a single channel.



Broadcast channel

The broadcast channels (BCH) carry only downlink information and are responsible mainly for synchronization and frequency correction. This is the only channel type enabling point to multipoint communications in which short messages are simultaneously transmitted to several mobiles.



The broadcast control channel (BCCH) is used to broadcast control information to every mobile station within a cell. The broadcast control channel is transmitted on the downlink point to multipoint.

The MS (Mobile Station) receives signals via the BCCH from many BTS within the same network and/or different networks.


The frequency correction channel (FCCH) is used for frequency correction or synchronization of your mobile station the repeated transmission of frequency burst is called the frequency correction channel.


Common control channels (CCCH); A group of uplink and downlink channels between the MS (Mobile Station) card and the BTS. These channels are used to convey information from the network to MS (mobile station) and provide access to the network.

Common control channels (CCCH) are used by a mobile station during the paging and access procedures. Common control channels are of the following types; Paging channel (PCH), Random access channel (RACH) and Access granted channel (AGCH).

Related Posts