Patent GB-899761-A (GB)
Title: Improvements in or relating to communication switching networks employing crosspoint devices
IPC: H04M7/06
Filed: 1958-07-18
Abstract: 899,761. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. July 18, 1958 [July 18, 1957], No. 23129/58. Class 40 (4). In a system in which a connection is set up between two terminals by marking the terminals, to break down a series cross-point devices between them, the connection between them being completed by the enablement of one of a plurality of " bisector " circuits arranged between pairs of said cross-points, the marking of said terminals is initiated by a " connect " signal, and the bisector circuits are enabled after the lapse of a predetermined time. This interval is utilized to receive from the bisector circuits indications as to whether one of the marked terminals is busy, such indication being used to prevent the enablement of the bisector circuits. Setting up of connection.-The operator on receiving the identities of the calling and called subscribers by means not shown, registers these addresses respectively in binary form in the address sources 56, 58 and closes the " connect " switch 60. The latter sets the bi-stable circuit 62 which thereupon sets the time-out circuit 64, enables amplifier 140, sets the propagator pulsers 42, 44 and turns on amplifier 71 in the " A " or calling subscriber selector and performs a similar function in the " B " or called subscriber selector. This signal clears any information present on the " core translators " 74, 76, 78, 80 and actuates a pulser 84 whose output circuits 92, 93 control the acceptance by the " core translator " of the caller's number from the address source 56. The output from 84 is fed via a " slow rise " network 85 to clear the core matrices 88, 90. The pulser 96 is then actuated to read out the information of 74 ... 80 on to the core matrices 88, 90. Finally, the read-out pulser 100 is actuated to read out the core matrices 88, 90 to operate corresponding gas tube amplifiers 102, 104 which feed a gas diode matrix 106 which applies a marking on the calling line side of the first switching stage appropriate to the calling line. The operation of this circuit is described in more detail below. This marking is fed via the trunk terminal to an " A identifier (see below for manner of operation) which converts the marking into a binary address which is then compared with the address set up in 56 by the comparator 91, which lights a lamp (not shown) to indicate successful comparison to the operator. Similar operations take place on the called side. The output from bi-stable circuit 62 triggers a flipflop 118 which resets after 250 Ás., during which time busy test is effected. At the end of this period if the line has not tested busy gate 132 opens to set the bisector enabler 46 which causes the bisector circuits to be enabled in sequence. When coincidence between the markings extended from calling and called side (and extended via the propagators) occurs in a bisector circuit which is scanned by the bisector enabler 46, the match and release detector 48 passes an output via amplifier 140 and gate 124 to set the " operation successful " bi-stable circuit 130. The output from amplifier 140 also passes via gate 129 to gate 144 whose output on lead 189 resets the time-out pulser 64, sets the propagator release pulsers 145, 147 and resets the bisector enabler 46. This output also sets bi-stable circuits 149, 151 which set the selector release pulsers 150, 152 which extinguish the gas tubes 102, 104 to remove the calling line marking. The signal on 189 appears on lead 191 after a delay of 250 Ás. to reset 149, 151 and 150, 152 follow. Similar operations occur in the " B " selector 40. The signal on 191 after a further 50 Ás. delay appears on lead 195 to further enable the identifiers. This signal also sets the bi-stable circuit 162 which indicates that the operation is ended and resets bi-stable circuit 62. The operator then momentarily operates key 175 to reset circuits 130 and 162. The control circuit is now normal. Subscriber busy.-The bisector in use in the existing call has a conducting tube which enables the marking potential to be passed through the bisector to the amplifier 140 without the aid of the bisector enabling pulses. Gate 124 is enabled when flip-flop 118 is set so that a pulse is passed to set busy trigger 122 which gives an appropriate indication and also disables gate 132 so that when 118 restores the bisector enabler is not started. Release.-To effect this operation the identity of either the calling or called line is entered in the appropriate address source 56 or 58 and key 172 or 174 operated. Assume address source 56 and key 172 are activated, the latter setting bi-stable circuit 176 to energize the " A " release lead 183. The gas diode in matric 106 is fired to mark the calling line as before. Potential on lead 183 passes to lead 196 where it sets the time-out circuit 186 and activates the bisector release pulser 50 and also the bi-stable circuit 118 which enables the busy output from the bisector to operate the busy trigger 122 and so disable the bisector enabler. The output on 196 also operates the identifier to enable comparison to be made as in the case of a connect operation. The release pulser then deactuates the bisector circuit 18 as described in Specification 850,214, the bisector circuit emitting a release indicating pulse which passes via amplifier 192 and gate 142 to set the " operation successful " bi-stable circuit 130, which operates a corresponding indicator. The release indicating signal from the bisector also passes to lead 189 to deactuate the release order time out pulser 186. Should the release operation be unsuccessful the time-out pulser 186 will itself eventually provide the signal on lead 189. Restoration of the " A " trunk selector then takes place as in the setting up operation. Similarly also, 300 Ás. later, the pulse appears on lead 195 and sets the bi-stable circuit 162 to indicate that the operation is ended and circuit 176 is reset. The breakdown of the through path causes a signal to be emitted by the " B " trunk terminal to the identifier (enabled over lead 195) which may be compared in comparator 37 if 58 has been set up. When the indicators show that the disconnection has been properly effected the operator throws reset key 175 to restore the control circuit to normal. Forced release.-Circuits 64, 186 respectively, set as described above, emit to the lead 189 a pulse after 50 ms. and 2 ms. which releases the control circuit as described above, the longer period being necessary in the first instance to permit complete scan of the bisector circuits. The release pulse is fed to the " operation ended " bi-stable circuit 162 via delay circuits 158, 197 respectively, the delay of the latter being longer to allow sufficient time for ionization of the release tube in the bisector circuit. Operation of " selector."-In Fig. 7A half the address source equipment and the corresponding core translators 74, 76 and core matrix 88 are shown. The initial reset pulse via gate 72, sets all the cores such as 270, 272 in a downwardly magnetized state. The binary address is set up by means of contacts such as 230, 232 which set the bi-stable circuits 220, 222 in one or other of their stable states. When a set pulse is received over amplifier 94 it increases the base current of the transistor 288 which thereupon conducts to pass setting current through the core windings in accordance with the state of the bi-stable circuits 220, 222. The cores are so wound that for any combination, one core only in each of the translators 74, 76 are magnetized in the upward direction. Say these are the cores 270, 272. Meanwhile, a slowly rising pulse has been applied via gate 86 to reset the core matrix 88 in such a manner that no read out signals are produced. Subsequently, a read-out pulse applied to gate 72 sets one of the matrix cores 261 (say) associated uniquely with the pair of cores 270, 272. A subsequent sharp pulse received via gate 86 produces a read out pulse in winding 259. This pulse fires a gas tube 264, Fig. 7B. At the same time a further gas tube 274 is fired in response to the other half of the address. The resulting lowering of potential of the anode of the first tube and the raising of the cathode potential of the second tube causes the firing of a diode 276, ina matrix of such diodes, which diode is associated uniquely with the pair of gas tubes. The resulting rise in potential over resistor 278 is communicated to the trunk terminal to mark that trunk. To terminate the marking the release pulsers 150, 152 are actuated respectively, to depress and raise the anode and cathode potentials of gas valves 274, 264 which together with diode 276 are thereby extinguished. Identification.-This takes place whenever an input is applied to gate 127, Fig. 9. In any of the cases when identification is to take place, a rise of potential occurs at transformer winding 352 and is fed to the mid-point of a resistor 355, 356 of a matrix of such resistors, the pulse being amplified by a row amplifier 112 and a column amplifier 110 to set cores 362, 368. These are read out by the pulser 129 driven by the output from gate 127 to set the translators 135 ... 141 whose output windings are arranged to produce a binary output. This output is obtained when the translators are pulsed by the pulser 134, driven by the pulse from gate 127 as delayed by the device 133. Specifications 686,427, 704,108, 754,338, 770,936, 814,952, 850,211, 850,212 and 850,213 also are referred to.