Apparatus for transmitting information via telephone lines
First Claim
1. Apparatus comprising a telephone subscriber line connected at a first end to a telephone and at a second end to a central office, means for transmitting information via the line when the telephone is on-hook, means for applying a pilot tone to the line at the first end when the telephone is off-hook, means coupled to the line at the first end for detecting the presence of ringing signals on the line, means for selecting one of two frequencies of the pilot tone applied to the line when the telephone goes off-hook in dependence upon the detection of the presence of ringing signals, and means for monitoring the pilot tone at the second end of the line.
5 Assignments
0 Petitions
Accused Products
Abstract
Voice-band modems are used to transmit information via a loaded telephone line when a telephone connected to the line is on-hook. When the telephone is off-hook, the integrity of the line is checked by transmitting a pilot tone from the subscriber end to the central office end of the line, where the pilot tone is monitored. Filtering of pilot tones in the central office is avoided by using two different pilot tones for originating and answered calls. An alarm condition at the subscriber produces a shifted pilot tone frequency. Loss or a change in frequency of the monitored pilot tone causes a telephone call on the line to be temporarily interrupted for checking the line and alarm condition. The central office and equipment can be switched to poll consecutively a plurality of telephone lines.
-
Citations
42 Claims
- 1. Apparatus comprising a telephone subscriber line connected at a first end to a telephone and at a second end to a central office, means for transmitting information via the line when the telephone is on-hook, means for applying a pilot tone to the line at the first end when the telephone is off-hook, means coupled to the line at the first end for detecting the presence of ringing signals on the line, means for selecting one of two frequencies of the pilot tone applied to the line when the telephone goes off-hook in dependence upon the detection of the presence of ringing signals, and means for monitoring the pilot tone at the second end of the line.
-
9. Apparatus comprising:
-
a telephone subscriber line connected at a first end to a telephone and at a second end to a central office; first and second hook state detection means coupled to the line at respectively the first and second ends for determining whether the telephone is on-hook or off-hook; means, responsive to the hook state detection means determining that the telephone is on-hook, for transmitting information via the line; means, responsive to the first hook state detection means determining that the telephone is off-hook, for applying a pilot tone to the line at the first end; first ringing signal detection means coupled to the line at the first end for detecting the presence of ringing signals on the line; control means for selecting one of two frequencies of the pilot tone, applied to the line when the telephone goes off-hook, in dependence upon the detection of the presence of ringing signals; and means, responsive to the second hook state detection means determining that the telephone is off-hook, for monitoring the pilot tone at the second end of the line. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
-
-
35. Apparatus for connection to a telephone subscriber line comprising:
-
a high input impedance buffer having an input for connection to the line; a hook state detector, having an input coupled to an output of the buffer, for determining whether a telephone connected to the line is on-hook or off-hook; means for transmitting and receiving information via the line when the hook state detector determines that the telephone is on-hook; means for generating a pilot tone when the hook state detector determines that the telephone is off-hook; coupling means for coupling the pilot tone generating means and the information transmitting and receiving means to the line; a ringing signal detector, having an input coupled to the output of the buffer, for detecting the presence of ringing signals on the line; and control means for selecting one of two frequencies of the pilot tone, to be generated by the pilot tone generating means when the telephone goes off-hook, in dependence upon the detection of the presence of ringing signals by the ringing signal detector. - View Dependent Claims (36, 37, 38, 39, 40)
-
-
41. Apparatus for connection to a telephone subscriber line comprising:
-
a high input impedance buffer having an input for connection to the line; a hook state detector, having an input coupled to an output of the buffer, for determining whether a telephone connected to the line is on-hook or off-hook; means for transmitting and receiving information via the line when the hook state detector determines that the telephone is on-hook; means for generating a pilot tone when the hook state detector determines that the telephone is off-hook; coupling means for coupling the pilot tone generating means and the information transmitting and receiving means to the line; and control means for causing the pilot tone generating means to generate the pilot tone with a shifted frequency in response to a predetermined condition occurring while the hook state detector determines that the telephone is off-hook.
-
-
42. Apparatus comprising:
-
a telephone subscriber line connected at a first end to a telephone and at a second end to a central office; first and second hook state detection means coupled to the line at respectively the first and second ends for determining whether the telephone is on-hook or off-hook; means, responsive to the hook state detection means determining that the telephone is on-hook, for transmitting information via the line; means, responsive to the first hook state detection means determining that the telephone is off-hook, for applying a pilot tone to the line at the first end; means, responsive to the second hook state detection means determining that the telephone is off-hook, for monitoring the pilot tone at the second end of the line; first control means for causing the pilot tone to be applied to the line at the first end with a shifted frequency in response to a predetermined condition occurring while the first hook state detection means determines that the telephone is off-hook; and second control means responsive to the second hook state detection means and to the monitoring means for causing the transmitting means to transmit information via the line in response to detection of the shifted frequency or loss of the monitored pilot signal while the second hook state detection means determines that the telephone is off-hook.
-
Specification