Identification forwarding circuit for use with tone-to-pulse converters

Abstract

A circuit for making existing automatic number identification (ANI) equipment in a telephone central office compatible with multifrequency tone telephone using tone-to-pulse converters. In a typical ANI system, the telephone of one party on a two-party line includes an identification circuit, such as a connection to ground, while the other telephone does not include such a connection. When one party initiates a call, the tone-to-pulse converter interrupts the direct line pair connection between the telephone and the central office, in order to convert the multifrequency tones generated by the telephone into corresponding pulses recognizable by the central office. During this period, a voltage comparator in the preferred embodiment of the identification forwarding circuit serves to detect the voltage condition of the line pair portion connected to the one telephone, which condition varies depending on the presence or absence of the connection to ground in the telephone. A controlled gate, responsive to the voltage comparator, in turn connects a similar identification circuit as in the telephone to the line pair portion connected to the central office in the event that the voltage comparator recognizes a first voltage condition, and isolates the similar identification circuit from the line pair portion connected to the central office when the voltage comparator recognizes a second voltage condition.