METHOD OF AUTOMATIC DUPLEX OR SEMI-DUPLEX COMMUNICATION FOR TWO UNITS VIA A TELEPHONE LINE

Apparatus and methods for establishing half-duplex communication between a first unit and a second unit over a telephone line. The first unit may transmit a first matching signal stream, the first matching signal stream including a first conditioning segment and a first unmodulated carrier signal having a first characteristic carrier frequency, the first characteristic carrier frequency representing a given transmission mode, the given transmission mode being in half-duplex. The second unit may analyze the first characteristic carrier frequency to recognize the given transmission mode.