Apparatus for transmitting information via telephone lines

Details Apparatus for transmitting information via telephone lines Apparatus for transmitting information via telephone lines

1983-02-18

1985-06-04

George, Keith E.

179 5R, G06B 2600, H04M 1104, H04M 1106

Patent

active

045216436

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.

REFERENCES:
patent: 3845247 (1974-10-01), Jurschak et al.
patent: 3930246 (1975-12-01), Campbell
patent: 3937889 (1976-02-01), Bell et al.
patent: 4044351 (1977-08-01), Everson
patent: 4068096 (1978-01-01), Rattenborg et al.
patent: 4262283 (1981-04-01), Chamberlain et al.
patent: 4442320 (1984-04-01), James et al.

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