SDCCH in GSM

Full form of SDCCH is Stand Alone Dedicated Control Channel GSM. 

The Standalone dedicated control channel is allocated for every mobile station.

It contains the signaling data that follows the connection of the mobile with the base station, prior to the allocation of TCH by the base station ( BS ) to the MS.

It guarantees that mobile station, as well as base station, will remain connected. The base station and mobile switching center will verify subscriber unit and assign the needed resources to the mobile.

This channel that accepts the newly completed call from the BCH. It holds the traffic while waiting for the base station to assign a TCH channel.

The SDCCH is also used to transmit authentication and alert messages as the mobile synchronize itself with the frame structure and wait for TCH.

SDCCH can be assigned their own physical channel. Also, they can occupy the TS0 slot of the BCH if there is low demand for BCH or CCCH traffic.