GB1212572A - Time-division multiplex telephone system - Google Patents

Abstract

1,212,572. Automatic exchange systems. TELEFONBAU UND NORMALZEIT G.m.b.H. 17 July, 1968 [9 Aug., 1967; 26 Sept., 1967], No 34090/68. Heading H4K. An exchange employing T.D.M. speech transmission employs a connecting circuit (of the conference type) comprising demodulators, mixing amplifiers and modulators to allow a third subscriber to join in (in break in fashion) an existing connection between two subscribers, the period of actuation of the modulators of the stations involved in the existing connection being reduced when the third party joins in. As shown, each substation TA, TB or TC is connected to the multiplex highway by a separate modulator and demodulator. Each substation may have a four wire connection as shown for substation TC or may be a two-wire substation connected to its modulator and demodulator by a two to four-wire network as shown at TSA or TSB. During a normal call between, say, substations TA and TB, the modulator of one substation and the demodulator of the other substation are simultaneously actuated during one time slot and the demodulator of the one substation and the modulator of the other substation are simultaneously activated during a second time slot to provide a full duplex connection. If a subscriber at a third substation TC wishes to join in he presses a special key requesting the use of a connecting circuit KN. He is allotted two time slots X and Y in which his modulator " Mod C " and his demodulator " Dem C " are activated. The connecting circuit demodulates at Dem 3 the signals from his modulator and applies them to mixing amplifiers M1 and M2 associated with the other two substations TA and TB. The time slots U and V already in use for the connection between TA and TB are each divided into two i.e. into U<SP>1</SP> and U<SP>11</SP> and V<SP>1</SP> and V<SP>11</SP> and while the demodulators of the substations TA and TB are allowed to continue operating during their full time slots V and U respectively, operation of the modulators " Mod A " and " Mod B " is restricted to a first half U<SP>1</SP> and V<SP>1</SP> respectively of each of their time slots. In the connecting circuits modulators " Mod 1 " and " Mod 2 " associated with these two substations are enabled during the other halves U<SP>11</SP> and V<SP>11</SP> respectively of the time slots, and demodulators " Dem 1 " and "Dem 2 " operate during the first halves of the time slots. Each mixing amplifier receives speech signals from both the demodulators in the connecting circuit and associated with the other two stations, thus a full conference connection is established. The whole system is controlled by a central circulating store.