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.