A data link control device which is implemented in a Layer 2 Protocol of a subscriber unit in order to establish and maintain data link between the subscriber unit and a radio port. In which, the Layer 2 Protocol is located between a physical layer and a Layer 3 Protocol. The data link control device comprises a media access control module, a state control module and a data processing module. The media access control module transmits and receives data between the subscriber unit and the radio port. The state control module controls and manages the flow of states of the subscriber unit. States in the state control module can be classified as Off State, Acquiring State, Standby State, and Active State. According to system information channel (SIC) message and alerting channel (AC) message received, or requests from the state control module, the data processing module carries out corresponding actions to the state control module. Also, the data processing module uses acknowledged mode transfer (AMT) communication protocol and through the media access control module, uplinks and downlinks information to and from a radio port control unit, in order to transmit information of Layer 3 Protocol between the subscriber unit and the radio port control unit. In which, the AMT communication protocol instructs the information receiver to feed back the correctness of the information transmitted.