Abstract: An off-hook management telecommunication system comprising a DTMF detector, an encoder and a microprocessor located within a channel unit. The system allows the user to depress a selected sequence of keys during a line connection which indicate to the microprocessor to hold the line off-hook, via signaling to a central office, despite the fact that the telephone is being returned to an on-hook position. The line is held off-hook for a predetermined amount of time to allow the user to switch telephones.

Abstract: An off-hook management telecommunication system comprising a DTMF detector, an encoder and a microprocessor located within a channel unit. The system allows the user to depress a selected sequence of keys during a line connection which indicate to the microprocessor to hold the line off-hook, via signaling to a central office, despite the fact that the telephone is being returned to an on-hook position. The line is held off-hook for a predetermined amount of time to allow the user to switch telephones.

Abstract: A two-wire channel unit or line card for use in a digital loop carrier (DLC) telephone system is disclosed. The channel unit is provided with a loopback test capability by using relays to open-circuit or short-circuit the input terminals of the hybrid circuit that couples the two-wire subscriber line to the separate two-wire transmit and receive paths within the channel unit. When open-circuited or short-circuited in this manner, the hybrid circuit couples voice frequency test signals between the receive and transmit paths of the channel unit, thereby allowing loopback testing to be carried out without providing a dedicated loss/gain circuit in the channel unit. An additional relay may be provided to vary the gain of an amplifier stage in the transmit or receive path of the channel unit during operation in the loopback test mode, in order to control the overall gain of the channel unit during loopback testing.

Abstract: A telephone system uses above voice-band ASK control and supervisory signals which are appended to digitally encoded voice by forcing the least significant bits to a selected level for transmission to the receiving end. At the receiving end, the ASK is regenerated by a circuit including special filter and a pulse generator. To eliminate audible noise resulting from the filter action, the ASK signal or the pulses from the pulse generator is shifted in phase by about 90.degree. before application to a filter. The result is significantly reduced noise.