03943305 is referenced by 23 patents and cites 6 patents.

Telephone line testing equipment in which a series of alternating current tone pulses are transmitted from the central office along the lines to a sensing means placed at a remote point in the circuit. The sensing means receives the coded tone pulse sequence, decodes it to determine if the address is correct, and if so, what information is present, and then either connects or disconnects the remote equipment from the line or, in the alternative, connects suitable loopback testing circuits to the line.

Title
Telephone line control system
Application Number
5/522417
Publication Number
3943305
Application Date
November 11, 1974
Publication Date
March 9, 1976
Inventor
Guenter E W Hagedorn
Minneapolis
MN, US
Agent
Neil B Schulte
Assignee
Magnetic Controls Company
MN, US
IPC
H04B 3/46
View Original Source