Call concentrator with automatic line supervisor

Abstract

An automatic line supervisor is disclosed for a telephone system having a line concentrator which converges a plurality of subscriber lines into a single output line to a telephone answering service (TAS) which is coupled to the concentrator by a telephone line with automatic ring down (ringing tie line). In order for the line to properly operate after the TAS has answered a subscriber call, and gone back on hook, the telephone concentrator must be disconnected from the ringing tie line and from the caller. In a first embodiment, the automatic line supervisor is an integral part of the concentrator and operates to make the requisite disconnection of the concentrator from the ringing tie line and the caller on a subscriber line by monitoring the tie line for appropriate audio tones, generating a control signal either in response to the presence of a dial tone for a particular time interval or in response to the absence of DTMF tones (dual tone multifrequency) for a particular time interval. The control signal is used to open appropriate relays to disconnect the line concentrator from the caller and the ringing tie line to prepare the ringing tie line for ringing the TAS that another call is present. In the second embodiment, the automatic line supervisor is a separate device which is located at the TAS. The second embodiment monitors the current flow in the ringing tie line coupling the telephone concentrator with the TAS to sense the discontinuance of current flow which is indicative of the operator going on hook. When the discontinuance of current flow is sensed, a control signal is produced which is coupled to the telephone concentrator via the tie line. The control signal is sensed at the concentrator and initiates the opening of the requisite switches to disconnect the concentrator from the ringing tie line and the subscriber line.