US 4,001,512 AGranted

Automatic telephone number identification circuit

AssigneeProctor & Associates Company

InventorsDarryl F. Proctor, Peter T. Skelly

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Abstract

An identification circuit, which is useful in a communication system comprising a plurality of remote stations and one central station, for automatically distinguishing between two remote stations in the system which are common to a single communication line pair connection to the central station. A two-party telephone line in a telephone network is an example of such a system. The identification circuit includes a ground mark circuit which in turn includes sufficient dc resistance to provide an electrical imbalance on the communication line pair when the ground mark circuit is connected between the communication line pair and ground. A sensing circuit and a control circuit are also provided, with the sensing circuit being responsive to a dc current in a portion of the communication line pair connected to a selected one of the two remote stations to energize the control circuit, which is in turn operable to connect the ground mark circuit between the communication line pair and ground. The electrical imbalance thereby appearing on the communication line pair is detectable by the central station.

Claims24

Dependent claims

An identification circuit for use with automatic number identification apparatus in a communication system which includes a central office and a plurality of remote stations, each of said remote stations being connected to said central office by a communication line pair, at least one communication line pair in said communication system being common to first and second remote stations, said one communication line pair being split at a point along the length thereof into first and second branches, said first branch being connected to said first remote station, said first branch, said first remote station and said one communication line pair forming a first communication line loop, said second branch being connected to said second remote station, said second branch, said second remote station and said one communication line pair forming a second communication line loop, said identification circuit comprising:

signal sensing means for detecting the presence of a dc loop current in said second communication line loop, and providing an output in response thereto;
circuit means operative to cause a signal imbalance on said one communication line pair when said circuit means is connected to said second communication line loop;
and,
means responsive to said output from said signal sensing means for connecting said circuit means to said second communication line loop.

1 more element

Dependencies are inferred from the claim text.