METHOD AND APPARATUS FOR CONTROL SIGNALING IN FDM SYSTEM

• US 3,869,577 A
• Filed: 04/24/1972
• Issued: 03/04/1975
• Est. Priority Date: 04/24/1972
• Status: Expired due to Term

• Current Assignee: Bank of New York Commercial Corporation As Agent
• Original Assignee: Robbins G. Howard, Robert A. Couturier, Steven J. Davis
• Inventors: Couturier, Robert A., Davis, Steven J., Robbins, G. Howard
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): D'Amico, Thomas
• Application Number:
  US05/246,589
• Time in Patent Office: 1,044 Days
• Field of Search: 325/163,30,320 179/2DP,15BY 178/66R,58 343/175 340/147R,152R
• US Class Current: 370/496
• CPC Class Codes: H04B 3/46 Monitoring; Testing
• CPC Class Codes: H04J 1/14 Arrangements providing for calling or supervisory signals
• CPC Class Codes: H04M 11/06 Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors

Abstract

A data communication system is described in which dial access control signals such as RING, DATA SET READY, DATA TERMINAL READY, CARRIER DETECT, and OUT OF SERVICE are transmitted between a central processing unit (CPU) and remote terminals in the form of special frequency or tone signals. A special frequency signal is transmitted from a remote terminal whenever a RING or DATA SET READY control signal is present and a CARRIER DETECT signal is not. Preferably, this special frequency is midway between the center frequency used for data communication and the frequency of either the MARK or the SPACE signal. Upon reception, this special frequency signal is processed in a particular fashion to generate signals comparable to the RING or DATA SET READY signals of the prior art. DATA TERMINAL READY and CARRIER DETECT control signals are transmitted as carrier signals and the OUT OF SERVICE signal is transmitted as a center frequency signal. Suitable processing at the receiver forms these signals into signals comparable to those of the prior art. Advantageously, the OUT OF SERVICE signal is used with appropriate apparatus to initiate testing of the remote terminal. Circuitry in this apparatus permits one to switch repeatedly from testing of just an FDM transmitter/receiver in the remote terminal to testing of both the FDM transmitter/receiver and a modem.

Claims

1. In a data communication system comprising at least first and second FDM transmitter/receivers in which dial access control signals received at the first FDM transmitter/receiver from a first data communication means are transmitted to the second FDM transmitter/receiver for application to a second data communication means and dial access control signals received at the second FDM transmitter/receiver from the second data communication means are transmitted to the first FDM transmitter/receiver for application to the first data communication means, first apparatus at the first FDM transmitter/receiver for transmitting to the second FDM transmitter/receiver at a special frequency other than that used for transmitting MARK or SPACE signals or their center frequency dial access control signals received from the first data communication means, said first apparatus further comprising means for transmitting the special frequency signal only when at least one of a RING signal and a DATA SET READY signal is received from the first data communication means and no CARRIER DETECT signal is received from the first data communication means;

and second apparatus at the second FDM transmitter/receiver for forming a CARRIER DETECT signal for application to the second data communication means by producing said CARRIER DETECT signal only when signal energy is received from the first FDM transmitter/receiver that is not the special frequency signal.

2. The apparatus of claim 1 wherein said special frequency is a frequency between those used for transmitting MARK and SPACE signals.

3. The data communication system of claim 1 wherein the apparatus for forming the CARRIER DETECT signal at the second FDM transmitter/receiver comprises:

an energy detector to which is applied signals received from the first FDM transmitter/receiver;

a first delay device connected to an output of said energy detector;

a slicer for detecting the special frequency signal received from the first FDM transmitter/receiver;

a second delay device connected to an output of said slicer, said second delay device having a rising signal time constant that is less than that of said first delay device and a falling signal time constant that is greater than that of said first delay device; and

means for inhibiting an output signal from the first delay device in response to an output signal from the second delay device.

4. The data communication system of claim 3 wherein a DATA SET READY signal is derived from the output of the first delay device for application to the second data communication means.

5. The data communication system of claim 3 wherein both a RING signal is derived from the output of the second delay device and a DATA SET READY signal is derived from the output of the inhibiting means for application to the second data communication means.

6. The data communication system of claim 1 further comprising apparatus for transmitting from the second FDM transmitter/receiver a DATA TERMINAL READY signal received from the second data communication means as a carrier frequency and apparatus for receiving the transmitted DATA TERMINAL READY signal at the first FDM transmitter/receiver for application to the first data communication means.

7. The data communication system of claim 1 further comprising apparatus for transmitting from the second FDM transmitter/receiver an OUT OF SERVICE signal received from the second data communication means as a center frequency and apparatus for receiving the transmitted OUT OF SERVICE signal at the first FDM transmitter/receiver for application to the first data communication means.

8. The data communication system of claim 1 wherein the special frequency is midway between the frequency used to indicate one of the two states of a digital signal and its center frequency.

9. In a data communication system comprising at least first and second FDM transmitter/receivers in which dial access control signals received at the first FDM transmitter/receiver from a first data communication means are transmitted to the second FDM transmitter/receiver for application to a second data communication means and dial access control signals received at the second FDM transmitter/receiver from the second data communication means are transmitted to the first FDM tramsmitter/receiver for application to the first data communication means, a method of transmitting and receiving dial access control signals comprising the steps of:

transmitting from the first FDM transmitter/receiver to the second FDM transmitter/receiver a special frequency signal only when at least one of a RING signal and a DATA SET READY signal is received from the first data communication means and no CARRIER DETECT signal is received from the first data communication means, said special frequency being a frequency other than that used for transmitting MARK or SPACE signals or their center frequency; and

forming at the second FDM transmitter/receiver a CARRIER DETECT signal for application to the second data communication means by producIng said CARRIER DETECT signal only when signal energy is received from the first FDM transmitter/receiver that is not the special frequency signal.

10. The method of claim 9 for operating a data communication system wherein the step of forming a CARRIER DETECT signal at the second FDM transmitter/receiver comprises the steps of:

forming a first signal in response to reception of signal energy at the second FDM transmitter/receiver;

forming a second signal in response to reception of the special frequency signal at the second FDM transmitter/receiver; and

inhibiting the first signal whenever the second signal is formed.

11. The method of claim 10 for operating a data communication system further comprising the step of deriving from said first signal a DATA SET READY signal for application to the second data communication means.

12. The method of claim 9 for operating a data communication system wherein the first data communication means is a modem and the second data communication means is a central processing unit further comprising the steps of:

applying a DATA TERMINAL READY signal from the central processing unit to the second FDM transmitter/receiver;

transmitting said signal from the second FDM transmitter/receiver as a carrier signal;

receiving the carrier signal at the first FDM transmitter/receiver and forming a DATA TERMINAL READY signal similar to that from the central processing unit; and

applying said signal to the modem.

13. The method of claim 9 wherein a RING signal is received at the first FDM transmitter/receiver from the first data communication means and a RING signal is formed at the second FDM transmitter/receiver from said special frequency signal for application to the second data communication means.

14. The method of claim 9 wherein said special frequency is a frequency between those used for transmitting MARK and SPACE signals.

15. The method of claim 13 for operating a data communication system wherein the first data communication means is a modem and the second data communication means is a central processing unit further comprising the steps of:

applying a DATA TERMINAL READY signal from the central processing unit to the second FDM transmitter/receiver;

transmitting said signal from the second FDM transmitter/receiver as a carrier signal;

receiving the carrier signal at the first FDM transmitter/receiver and forming a DATA TERMINAL READY signal similar to that from the central processing unit; and

applying said DATA TERMINAL READY signal to the modem to cause it to answer a call indicated by the RING signal.