04475193 is referenced by 122 patents and cites 4 patents.

In a power line carrier telephone extension system for transmitting electrical signals between the telephone line and an extension telephone over the AC electric power line available at a telephone subscriber's premises, that includes a main station for processing signals between the subscriber's telephone line and power lines and an extension telephone of the system that plugs into the power line, means that provides for a plurality of such extension telephones all of which can place calls to the telephone line, answer calls from the telephone line and conference together in full duplex communication.

Title
Power line carrier multi telephone extension system for full duplex conferencing between telephones
Application Number
6/431400
Publication Number
4475193
Application Date
September 30, 1982
Publication Date
October 2, 1984
Inventor
William M Brown
Acton
MA, US
Agent
Hamilton Brook Smith & Reynolds
Assignee
Astech
MA, US
IPC
H04M 11/00
View Original Source