The Telephony Control Specification (TCS) provides for the control of voice services, fax and data services in Bluetooth.
The TCS specifications describe the signalling for call handling so that voice connections and data connections can be established between Bluetooth-enabled devices. The TCS protocol can be implemented by TCS binary or by AT commands.
TCS-Binary is a bit-oriented protocol with call control, connection establishment, voice and data transmission. AT commands are used to control mobile phones, modems and also fax machines. AT commands are derived from the standardized AT command set.