Subscriber loop verification device and method

A subscriber loop test system for verifying the serviceability of subscriber loops associated with a switching facility in a telephone system, the system comprising in combination:

• a test device connected in series between the subscriber loop and a subscriber equipment associated with the subscriber loop;
• the test device including at least two oscillators having different operating frequencies for generating predetermined inband AC signals in response to a predetermined DC signal, to modulate current in the subscriber loop, and means for connecting the two oscillators each between one of said leads and earth in response to the predetermined DC signal;
• a circuit, associated with the switching facility, for controlling and monitoring test devices, the circuit including two receivers each for detecting the operation of one of the oscillators, switch contacts for selectively connecting a source of said predetermined DC signal and the tone receivers between one and the other leads and earth, and a resistance means connected in series with said source, whereby in operation of the system detection by the appropriate receiver indicates that a selected lead in the subscriber loop being tested is in a serviceable condition.

A method of verifying the serviceability of a subscriber loop circuit at an associated switching facility, comprising the steps of:

• a. providing a test device at the end of the subscriber loop circuit remote the switching office for drawing an energizing current and generating two distinct predetermined inband frequency signals, one signal in response to a predetermined DC signal being applied to one lead of the subscriber loop at the switching facility and the other signal in response to the predetermined DC signal being applied to the other lead of the subscriber loop at the switching facility;
• b. applying said predetermined DC signal at the switching facility to one and then the other of the leads of the subscriber loop for a time longer than that required to cause the test device to operate;
• c. at the switching facility, detecting one and then the other of said two distinct predetermined frequencies on one and then the other of said leads in the subscriber loop, whereby the serviceability of one and the other of the leads is verified independently one from the other.