Telephone system in which communication between stations is controlled by computers at each individual station

• US 4,262,171 A
• Filed: 01/08/1979
• Issued: 04/14/1981
• Est. Priority Date: 01/08/1979
• Status: Expired due to Term

• Current Assignee: Mine Safety Appliances Company (MSA Safety, Inc.)
• Original Assignee: Catalyst Research Corporation
• Inventors: Schneider, Alan A., Gadwal, Govind R.
• Primary Examiner(s): Brown, Thomas W.
• Application Number:
  US06/002,067
• Time in Patent Office: 827 Days
• Field of Search: 179/37, 179/1 H, 179/18 BF, 179/84 T, 340/147 P, 340/147 F, 370/71, 370/69, 370/76, 370/57, 370/30, 370/32
• US Class Current: 370/295
• CPC Class Codes: H04M 9/027 Frequency division multiplex systems

Abstract

A telephone system is provided which requires no central office. All the stations on the system are interconnected by a single line or cable and each station includes a computer which carries out the necessary switching. Each station is then able to call any other station, or to respond to a call, without requiring any central office. Frequency division multiplexing is used to permit a number of conversations to be carried on simultaneously and two frequencies are assigned to each conversation to permit duplex operation. A page capability is also provided.

Claims

1. A telephone system comprising a plurality of stations, a single line cable interconnecting all stations in the system, each station including transmitting means, receiving means and switching means, the switching means in each station comprising a self-contained computer adapted to control said transmitting and receiving means at each station to provide frequency multiplexed communication between selected pairs of stations in the system without the use of any auxiliary switching or control means connected to said cable other than the self-contained computers in the respective stations, means at each of said stations for imposing a page signal on said single line cable, and means at each of said stations for receiving said page signal.

2. The system of claim 1 in which the computer of each station controls the frequency transmitted by its transmitting means and the frequency received by its receiving means.

3. A telephone system comprising a plurality of stations, a single line cable exclusive of any central station circuitry interconnecting all stations in the system, transmitting and receiving means at each station, multiplexing means at the respective stations for establishing communication via carrier signals between any two selected stations in the system, and a computer in each station of the system, said computers acting to establish communication between any two stations in the system exclusive of all other stations and independently of any other instrumentality in the system other than the computers of the stations between which communication is established, each station in the system being assigned a telephone number and each digit of a telephone number being assigned a specific frequency, the computer at each station being adapted to cause its transmitting means to transmit on a frequency corresponding to a digit in its telephone number.

4. A telephone system comprising a plurality of stations, means at each of said stations for transmitting and receiving carrier signals, a computer at each of said stations, a modem at each of said stations, the computers and modems at any two selected stations in the system acting to establish communication between those stations exclusive of all other stations in the system, a conductor exclusive of any central circuit component common to all stations for interconnecting said stations, whereby communication can be established between any two stations in the system without the use of any central circuit components, means at each of said stations for imposing a page signal on said conductor, and means at each of said stations for receiving said page signal.

5. The system of claim 4 including loud-speaker means connected to the page signal receiving means at each station.

6. A telephone system comprising a plurality of stations and a common conductor interconnecting the stations, each of said stations having transmitter means including a first local oscillator and adapted to generate a modulated carrier signal for transmission on said common conductor at a frequency determined by said first oscillator, receiving means including a second oscillator adapted to receive and demodulate signals present on said conductor of frequency determined by said second oscillator, and computer means for controlling the frequencies of said oscillators to cause said transmitter means to transmit on a first preselected frequency and to cause said receiving means to receive signals of a second preselected frequency, each station being assigned a telephone number and each digit of a telephone number being assigned a specific transmitting frequency, the computer means at each station being adapted to cause its transmitter means to transmit on a frequency corresponding to a digit in its telephone number.

7. The system of claim 6 including means for causing transmission by a first station and reception by a second station of signals of said first preselected frequency, and means for causing transmission by the second station and reception by the first station of signals of said second preselected frequency.

8. The system of claim 6 in which each station includes means for transmitting individual call signals for each other station, and in which reception by a second station of its call signal on said first preselected frequency initiates transmission by said second station on said second preselected frequency.

9. The system of claim 8 in which each station includes a loud-speaker, means for producing a ring signal, and means controlled by said computer means for supplying said ring signals to the loud-speaker upon reception of that station'"'"'s call signal.

10. The system of claim 8 in which each station includes a loud-speaker, means in each station for generating a low-frequency carrier signal and for transmitting page messages on said carrier signal, and means in each station for receiving said low-frequency carrier signal and for supplying said page messages to its loud-speaker.

11. The system of claim 10 including means by which transmission of a page message by one station after calling another station results in reception of the page message by the called station only.

12. The system of claim 6 wherein said computer means causes said transmitter means to transmit on one of a set of preselected frequencies and causes said receiving means to receive signals of a corresponding one of another set of frequencies, each frequency of one set corresponding to a single frequency of the other set.

13. The system of claim 6 including means in the computer means of each station for sampling carrier frequencies on said conductor interconnecting the stations, means at each station for causing that station to initially transmit on a carrier frequency corresponding to the lowest digit in its telephone number, and means responsive to the sampling means for causing said station to transmit on a carrier frequency corresponding to the next highest digit in its telephone number when the sampling means determines that the frequency corresponding to said lowest digit is already present on said conductor interconnecting the stations.

14. The system of claim 6 wherein each of said stations is provided with a modem and wherein code signals are transmitted by said modem on a carrier frequency corresponding to a digit in the telephone number of a calling station to a called station which responds to said code signals on a carrier frequency corresponding to a digit in the telephone number of the called station.