GSM provides a number of different types of channels for user traffic and signalling.
These channels are divided into two classes:
- traffic channel
- signalling channels
Traffic Channels:TCH falls into two categories namely TCH Half(TCH/H) and TCH Full(TCH/F).A GSM traffic channel (TCH) carries speech and data traffic. Of each 26-frame multiframe, 24 frames are used for traffic channels, one is used for the slow associated control channel (SACCH) and one is unused.
TCH/H: A GSM half-rate traffic channel (TCH/H) has a raw rate of 11.4 Kbps, with a useable rate of 4.8 Kbps for data.
TCH/F: A GSM full-rate traffic channel (TCH/F) has a raw rate of 22.8 Kbps, with a useable rate of 9.6 Kbps for data.
Signalling Channels: There are three types of GSM signaling channels namely broadcast channels, common control channels and dedicated control channels.GSM signalling channels are used for the control of the GSM network.
Broadcast Channel:The GSM broadcast channels are used to provide information to a mobile station about the network and timing information required for synchronization.
Common Control Channel:The GSM common control channels are used to inform mobile stations of incoming calls and to request and grant channels.
Dedicated Control Channel:GSM dedicated control channels carry data used during connection establishment and for handover decisions.