Patent GB-1030710-A (GB)
Title: Automatic telecommunication exchange
IPC: H04Q3/52
Filed: 1963-03-15
Abstract: 1,030,710. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. March 15, 1963 [March 22, 1962], No. 10374/63. Heading H4K. In a system in which connections are set-up between inlets and outlets of a network of cascaded cross-point matrices utilizing PNPN diodes, each inlet is associated with a time position in a repetitive cycle and connection between a marked inlet and a marked outlet is effected by extending during the time position of the inlet a plurality of self-seeking paths through the matrices towards the marked outlet, means being responsive on completion of the path to cause a relatively high value current to flow through the path whereafter the current falls to a lower value which acts as a holding current for the path. A calling subscriber is connected via the network to a free register where the identity of the calling and called parties is stored, the register thereafter allotting idle links in turn to the call until one is found which has access via the network to both parties. The method of connecting a caller to a register is disclosed in Specification 978,370, and a full explanation of the operation of the switching network is given in Specifications 953,895 and 960,960. The following description relates to the completion of a call via a link. Setting up a call.-In response to the looping of a subscriber's line, current flows through a lamp 97 which compensates for differences of line impedance (see Specification 978,368), and thereby switches-on a transistor 99 which in turn switches-off transistor 105. During the time period allotted to the caller, a control circuit (not shown), removes a negative potential from the inputs 39 thereby switching-off transistor 123. Consequently, transistor 110 begins to conduct and capacitor 115 slowly charges-up via capacitor 116. The net effect of these actions is that NPN transistor 66 is switched-on, a slowly " rising " negative pulse is applied to the switching network 22 and capacitor 81 slowly charges. The caller is thereby connected through the network to a register. On completion of the path, transistor 131 turns-on followed by transistor 142 and 105, the latter causing capacitor 115 to discharge. When the register has received the dialled digits it applies a + 24 volt pulse to terminal P3 of the calling line circuit and removes the negative potential from inputs 39 whereby transistors 123, 105 switch-off and capacitor 115 again starts to charge before a slow-rising negative pulse is applied to the network and capacitor 81 slowly charges up. In the link circuit during the same time period, the register removes a positive potential from the Finder control leads 46a whereby transistor 162 slowly turns off and in so doing triggers transistor 165. Transistor 85 then begins to conduct and since it does not saturate at this time it acts as a constant current source. Transistor 74 follows but again as no appreciable current flows therethrough it does not saturate. Due to capacitor 79 however, a slowly-rising positive going pulse is applied to the network. As a result of the positive and negative going pulses a unique path through the network is selected and at the instant the path is completed capacitor 81 discharges to provide the relatively high current flow through the path, whereby transistor 85 and 74 both saturate. The latter transistor in particular together with its associated components then acts as a high impedance to A.C. Transistor 170 turns-on and holds 165, thereby holding the speech path. In an immediately succeeding time period the register causes the removal of a positive potential from Connector control leads 46b of the link and a negative potential from inputs 39 of the called party's line circuit and applies a + 12 volt pulse to its lead P3 whereby a path through the network is selected as before, transistors 178 and 181 saturating when the path is found. With transistors 170 and 181 both on, transistor 191 conducts so as to operate switching transistor 60 and to apply a release pulse on lead P26 to the register. Ringing.-When transistor 131 in the called party's line circuit conducts, it opens gate 92 so that ringing signals can pass therethrough to a transducer 91 at the substation. The gate is closed when the called party lifts his hand-set. Busy conditions.-In a busy line circuit, transistor 105 cannot be switched-off by the application of a +12 volt pulse to terminal 13 when the line is tested by a register and consequently a marking pulse cannot be applied to the network in this case. The apparent busy condition of a calling line connected to a register (i.e. before it is connected to a link) is overcome by applying a +24 volt pulse to terminal P3, as was mentioned above, whereby transistor 105 is switched-off and a path to a link is selected. First party release is provided. When either party hangs up transistor 74 or 178 cuts-off, followed by 170 or 181 so that in either case 191 and 60 are turned-off, thus opening the speech path. Forced release.-A - 24 volt pulse is applied to terminal P5 and negative potential removed from inputs 39 whence transistors 123 and 66 turn off, thereby breaking the holding path. This form of release may be exercized by a subscriber having break-in facilities. Supervisory signals (tones) may be transmitted to either party after gate 60 is closed by the application of ground to terminal P27.