GB1293057A - Improvements in or relating to centrally controlled telecommunications exchange systems - Google Patents

Abstract

1293057 Party line systems SIEMENS AG 28 Sept 1970 [29 Sept 1969] 46008/70 Heading H4K A centrally controlled telecommunications exchange including party line subscribers has provision in which when a party line subscriber from whom calls are barred attempts to initiate a call that party is connected to a device which monitors the line to detect the end of this call attempt and independently monitors the line to detect calls initiated by the other subscriber of that line. As shown when a subscriber Tn1 or Tn2 goes off hook the corresponding winding RI or RII of a relay R in the common line circuit Z responds. The common line circuit is connected over a switching network K to a connection set (for receiving dial signals), the calling subscriber is identified and a storage location is interrogated to determine whether calls from or to this subscriber are barred and whether his substation is busy or idle. If a call is barred or if after the wanted subscriber designation has been sent the connection cannot be completed the line circuit is connected to a tone monitoring device D. If the call is from subscriber Tn2 the central control enables a relay B. Via contacts 1c, 1b and 2c, 2b and windings I of relays A and E the line wires are connected to negative and earth respectively to supply line current of one or other polarity (depending on which subscriber is calling) to the calling subscriber during tone transmission. This battery supply operates a relay U1 or U2 in a selection circuit G connecting the calling substation to both line wires and isolating the other subscriber. If the call is from a barred subscriber a relay H is operated by the central control changing over the position of contacts 1h and 2h connecting both line wires to negative battery via high resistance windings of relays A and E. The high resistive battery supply is unable to energize relay U1 or U2 and accordingly both subscribers remain connected to one line wire. Relay A monitors the calling subscriber to detect the return of his handset to the " on hook " condition to enable the circuit D to be released while the relay E monitors the other subscriber to detect a call initiation request. Energization of relay A or E closes a corresponding contact a or e in a circuit including a persistence check device V which repeats signals to the central control. Thus one subscriber can be barred without inconvenience to the other.