Subscriber line interface and power circuit

Apparatus comprising

• means for generating in sequence first, second and third control signals, and
• means, responsive to receipt in turn of a current one of said first, second and third control signals, for independently generating as a function of said one of said first, second and third control signals a corresponding signal selected from a group of signals including an off-hook, ringing and on-hook signals, in which the level of said one of said first, second and third control signals is indicative of the level of the independently generated signal.

A subscriber line circuit for interfacing a telephone station set with a transmission facility extending to a switch comprising

• a signal generator, and
• a detector that supplies to the signal generator a control signal when the switch indicates receipt of an incoming call, in which the level of the control signal varies over time in accordance with a predetermined rate,
• the signal generator, responsive to receipt of the control signal generates and outputs to the station set a ringing signal having a level that varies with said rate.

A subscriber line interface circuit disposed between a telephone station set and a telephone switch network comprising

• means for generating and outputting in turn first, second and third control signals, said first and second control signals being respectively indicative of when (a) said station set is on-hook, (b) said station set is off-hook and (c) said telephone switch network has an incoming call for said station set, and
• means for independently generating in turn first, second and third signals as a function of said first, second and third control signals, respectively, in which said third signal is generated as though it originated from a telephone central office ringing generator.

A subscriber line interface circuit for interfacing a telephone station set with a telephone system comprising

• means, responsive to receipt of an indicator indicating that said telephone system has received a telephone call for said telephone station set, for outputting a control signal, and
• means, responsive to receipt of said control signal, for generating internally a ringing signal having a level and frequency as though it were generated by a telephone central office ringing generator and supplying said ringing signal to said station set, said ringing signal being generated independent of any external source of ringing signal.