a tdma network for reader - transponder communications including a receiver having an antenna for receiving and transforming radiated energy to a first rf signal and a detector for demodulating and converting the first rf signal to a digital signal . a protocol logic device is provided for decoding the digital signal and for executing a protocol . the protocol comprises a plurality of randomly selected time slots to gain admission to the tdma network and a plurality of assigned time slots to transmit messages during the reader - transponder communications . in a transponder implementation , an oscillator is provided for converting protocol formatted digital signals from the logic device to a second rf signal . thereafter , the antenna transforms the second rf signal to radiated energy and transmits the radiated energy . in a preferred embodiment , the tdma network includes a transmit / receive switch for directing the first and second rf signals along the receive and transmit paths , respectively . a digital memory which communicates with the protocol logic device is provided for storing data unique to a transponder . the protocol also includes a reader control message time slot for interrogating the transponder and an acknowledgment time slot for indicating the reception of a message .