Signaling protocol channel unit

Abstract

Disclosed is a channel unit for directly interconnecting a toll office multiplex carrier channel line and a terminal unit line such as that of a private branch exchange (PBX) or a telephone station set, thereby eliminating the normal local end office interconnection. In particular, the channel unit interfaces the different signaling protocols of the two lines and generates call progress controls signals such as dial tone and audible ringing which are normally generated by the local end office. The channel unit comprises a converter for each line for converting the electrical interface signals representative of the busy and idle conditions of the line to logic level signals also representative of the busy and idle conditions of the line. A predetermined series of these logic level signals form a control signal that indicates the state in one signaling protocol of a call on the line. Since the control signal indicative of the state in one signaling protocol of the call on one line is typically not useable by the other line, a microprocessor included in the unit generates a second control signal to advance the state in another signaling protocol of the call on the other line to an equivalent call state. An additional converter then converts the logic level signals of this second control signal to the electrical interface signals of the other line to advance the state in the other signaling protocol of the call to the equivalent call state. The unit further comprises a receiver and transmitter for exchanging dial pulse and dual tone multifrequency address signals between the lines. Also, included are circuits for applying call progress control signals such as dial-tone, audible ringing, and power ringing to the lines.