Systems for transmitting data via telephone lines

Details Systems for transmitting data via telephone lines Systems for transmitting data via telephone lines

1989-09-05

1991-08-06

Ng, Jin F.

Telephonic communications

Telephone line or system combined with diverse electrical...

Having transmission of a digital message signal over a...

379377, H04M 1100

Patent

active

050383728

ABSTRACT:
A system for transmitting data via a telephone line by means of a data communications device (4) connected to the telephone line, at least one other communications device being connected to the telephone line and each device being switchable between an inactive state, in which the device is not in use and presents a high impedance to the telephone line, and an active state, in which the device reduces the telephone line voltage and signals can be transferred between the device and the telephone line, the system including a telephone line state detection unit (10) associated with the data communications device (4) and connected to the telephone line for electrically monitoring the telephone line to provide an indication of the state of another communications device connected to the telephone line.

REFERENCES:
patent: 3564143 (1971-02-01), Stewart, Jr.
patent: 4002837 (1977-01-01), Ebner et al.
patent: 4059727 (1977-11-01), Kingswell et al.
patent: 4394540 (1983-07-01), Willis et al.
patent: 4469917 (1984-09-01), Shelley
patent: 4540849 (1985-09-01), Oliver
patent: 4811389 (1989-03-01), Balch
patent: 4833618 (1989-05-01), Verma et al.
patent: 4958371 (1990-09-01), Damoci et al.

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