Connections in cellular telephone system:

The three subsystems of the cellular system are connected using high speed data links.

The mobile unit and cell site are connected through radio link that conveys the voice and signaling information between them.

The channel used by each mobile unit for communication is not fixed, the channel can be any one in the complete bandwidth allocated by the serving area .But only a single channel is used at a time to convey information between two entities.

                A standard Common Air Interface (CAI)carries out the communication between the mobile and  base-station or cell unit with the help of four different channels. They are :

1. Forward Voice Channels:

This channel is used to transmit the voice signal to mobile from cell unit.

2. Reverse Voice Channels:

This channel transmits the voice channels from mobile unit to base station.

3. Forward Control Channels:

This channel initiates the cells at base station. As this channel continuously broadcasts all of the traffic requests of all the mobiles in the system, it can also be used as beacons.

4. Reverse Control Channel  :

This channel initiates the calls at mobile unit.

The control channels only deal with the setting up of a call and transferring it to the vacant channel. Hence , these are also called as setup channels.

These channels transmit and receive the  data that uphold call setup and service requests. When there is no call in progress, mobile unit handles the channels.