In the GSM (Global System for Mobile communication) system, the SDCCH (Standalone Dedicated Control Channels) are used to provide a reliable connection for signalling and SMS (Short Message Service) messages. The SACCH (Slow Associated Control Channel) is used to support this channel.
SDCCHs are used for signalling exchanges, for example, during call setup or registration and location updates. If SDCCH congestion is outside of threshold limits, the operator loses revenue because of call drops. The dedicated channels are of two main types, signalling and traffic. The signalling channels are used for maintenance of the call and for enabling call setup. The traffic channels handle the actual payload.