US 4,302,629 A · Digital data transmission system

Abstract

Simultaneous conventional telephone signaling and audio communication, plus digital data transmission, on nonloaded telephone wires is disclosed. Modems (21) connect a telephone (23) and a digital data terminal (25) to one end of the telephone wires. A data transmitter (59) in each modem (21) converts digital data from binary to FSK form and a receiver (57) converts digital data from FSK to binary form. Each transmitter includes a frequency synthesizer that produces one of two FSK signals (F1, F2) depending upon the binary nature (0 or 1) of a particular data bit; and, the receivers include frequency detectors that detect two other FSK signals (F3, F4) and produce a corresponding binary data bit (0 or 1). Voice filters (51) prevent the FSK data signals from reaching the telephones and spurious telephone high frequency signals from reaching the telephone wires. A CO or PABX subsystem (37) is connected to the other end of the telephone wires and includes modems comprising receivers (97) that convert the F1/F2 FSK signals into binary digital data. The binary digital data from the telephone stations is multiplexed and forwarded to a data processing center (15). The CO and PABX subsystem also de-multiplexes multiplexed binary digital data produced by the data processing center and includes transmitters (99) that convert the de-multiplexed data into F3/F4 FSK signals and forward the F3/F4 FSK signals to the related station. Voice frequency filters (91) prevents the FSK signals from reaching the CO or PABX line switching equipment and prevents high frequency noise signals generated by the CO or PABX from reaching the telephone wires.

In a transmission system for carrying baseband telephone signals, said transmission system including telephone switching equipment connected to telephones via nonloaded loops, the improvement comprising a digital data transmission system for carrying digial data over said nonloaded loops without interfering with the baseband signals carried by said nonloaded loops, said digital data transmission system comprising:

(A) station modems connected between telephones located in the vicinity of associated data terminals and the telephone end of related nonloaded loops running to said telephone switching equipment, said station modems also connected to said associated data terminal, each of said station modems including:
(1) transmitting means for converting digital data produced by said associated data terminal from binary signal form into FSK signal form such that a binary zero (0) causes said FSK signal to have a first frequency, F1, and a binary one (1) causes said FSK signal to have a second frequency, F2, and applying said F1 and F2 FSK signals to said related nonloaded loop;
(2) receiving means for receiving digital data carried by said related nonloaded loop in FSK signal form at third, F3, and fourth, F4, frequencies and converting said F3 and F4 FSK digital data into binary form such that an FSK signal at said third frequency, F3, causes a binary zero (0) and an FSK signal at said fourth frequency, F4, causes a binary one (1) and applying said binary digital data to said associated data terminal;
and,
(3) voice filter means for connecting said related nonloaded loop to said telephone so as to prevent said F1, F2, F3 and F4 FSK signals from reaching said telephone;
and,
(B) a switching equipment subsystem located in the vicinity of said telephone switching equipment and connected to the other ends of said nonloaded loops, said switching equipment subsystem comprising:
(1) modern means connected to the other ends of said nonloaded loops for:
(a) converting said F1 and F2 FSK signals applied to said nonloaded loops by said transmitting means of said station modems from FSK signal form into binary digital data form such that an F1 FSK signal causes a binary zero (0) and an F2 FSK signal causes a binary one (1);
(b) converting binary digital data received from a bidirectional signal forwarding means into FSK signal form such that a binary zero (0) causes said FSK signal to have said third frequency, F3, and a binary one (1) causes said FSK signal to have said fourth frequency, F4, and applying said F3 and F4 FSK signals to said nonloaded loops;
and,
(c) voice filter means for connecting the other ends of said nonloaded loops to line switching equipment forming part of said telephone switching equipment so as to prevent said F1, F2, F3 and F4 FSK signals from reaching said line switching equipment;
and,
(2) bidirectional signal forwarding means connected to said modem means for:
(a) receiving the binary digital data produced by said modem means resulting from the conversion of said F1 and F2 FSK signals from FSK signal form into binary digital data form and forwarding said binary digital data to a data processing center;
and,
(b) receiving binary digital data produced by said data processing center and applying said binary digital data to said modem means for conversion by said modem means from binary digital data form into F3 and F4 FSK signal form.

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Digital data transmission system

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Digital data transmission system

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Abstract

Claims17