Patent GB-864985-A (GB)
Title: Improvements in or relating to remote line concentrators in telephone systems
IPC: H04Q3/52
Filed: 1959-01-02
Abstract: 864,985. Automatic exchange systems. LUCAS, P. M., and SAUTEL, A. Jan. 2, 1959 [Jan. 4, 1958], No. 222/59. Class 40 (4). An automatic satellite (non-exchange) serving m subscribers and having n trunks to a main exchange, m being greater than n, includes an m x n switching matrix, at least two controllines between the satellite and the main exchange, the first carrying synchronizing pulses, and the second called line switching pulses, a subscriber's identification pulse distributer controlled by the synchronizing pulses and having m outputs, one per subscriber, means responsive to the closure of each subscriber's loop, and gating circuits, one per subscriber, each having an output leading to the matrix and at least three inputs, one from the pulse distributer, one from the second control line, and one from the loop-closure responsive means, whereby a subscriber's gating circuit controls the connection of that subscriber to a trunk at the time of his identification pulse under control of the loopclosure-responsive means when he is calling, and under control of the called line switching pulse when he is called. General arrangement.-As in the concentrator described in Specification 832,727, fifty subscribers have access to the main exchange over ten trunks. Four two-wire control lines (Fig. 2) carry synchronizing pulses from the subscriberidentification pulse generator (line 22), the loop frequency f (line 20), the connection control frequency fcc (line 132), and the called subscriber switching pulses (line 120). The phantom on lines 20 and 22 conveys direct current supply from the main exchange. The operating cycle of 100 ms. is divided into fifty " major cycles " of 2 ms. which characterize the subscribers of a concentrator, each major cycle being divided into one hundred " minor cycles " of 20 Ás. characteristic of the one hundred concentrators. A 20 Ás. pulse thus identifies a particular subscriber of one concentrator. Fig. 4 shows the gate circuitry at the concentrator in more detail than does Fig. 2, and both Figures will be referred to. Originating call at concentrator.-When the subscriber takes down his handset the potential rise at point 414 (Fig. 4) blocks the transistor 403 of gate 125 and is also applied to the base of transistor 406 of gate 122, so that when a negative subscriber-identification pulse next appears on lead 19 from the distributor 18 (Fig. 2) transistor 409 (Fig. 4) of gate 121 conducts and the rise in its collector potential causes 406 to conduct, thus passing a negative pulse via diode 411 and capacitor 413 to the pulse amplifier 126, which applies a positive pulse to wire 11 leading to the 50 X 10 switching matrix 10. If there is no free trunk, the caller does not receive dial tone and must wait, but when a trunk is free the gas diode 13 (Fig. 2) at the relevant cross-point fires. The resulting fall in potential at point 401 is applied to the emitter of 409 which is thus blocked, and to the base of 403. The positive-going pulse produced at point 402 is applied via the circuit comprising resistor 16 and capacitor 47 to the gate 127. Diodes 420 and 422 are normally blocked as is transistor 418, but on the occurrence of the pulse, capacitor 47 charges and both diodes conduct followed by the transistor 418, thus allowing the connection control frequency (fcc) from line 132 to pass to the trunk 15. When the charging current of 47 falls to a limiting value, diode 420 is again blocked and cuts off 418. A sharp pulse of fcc is thus transmitted over the trunk 15. At the main exchange this pulse is rectified by the tuned detector 49 (Fig. 3) and sets the trigger circuit 50. The common pulse generator 88 produces on lead 53 the minor cycle pulse 104 (Fig. 1) of the concentrator to which the trunk 15 leads, the phase difference between this pulse and the pulses produced by the distributer 18 being such that, taking into account the propagation time from the concentrator to the main exchange and the firing time of the diodes 13, trigger circuit 50 is set just before the minor cycle of the concentrator forming part of the major cycle of the subscriber concerned, but after the same minor cycle of the preceding major cycle. The pulse 104 passes through gates 51 and 52, sets the trigger circuit 57 which opens gate 59 to revert dial tone FN to the caller, records the trunk identity in the number indicator 54, and restores trigger circuit 50, thus closing gates 51 and 52. Caller dials wanted number.-At each break of the line loop transistor 403 (Fig. 4) of gate 125 passes the loop frequency f from line 20 via transformer 4, the fired tube 13, diodes 431 and 430, and transformer 128 to the trunk 15. These pulses are rectified by the tuned detector 55 (Fig. 3), the first pulse resulting in the resetting of trigger circuit 57 and the cessation of dial tone through gate 59. With gate 70 open (trigger circuit 58 normal), the pulses pass to the register 74 which stores the wanted number. The main exchange reverts busy tone, or completes the connection, according as the wanted party is not, or is, available. The generator 39 transmits called subscriber pulses, in the minor cycle concerned, over line 120 to the called concentrator and over lead 41 to set the trigger circuit 42 of the exchange equipment of that concentrator, which opens gate 64 of the trunk circuits to that concentrator. At the called concentrator, the called subscriber pulse is applied to the base of transistor 415 (Fig. 4) of gate 123. If the called line is busy, gate 121 is is inhibited, and the main exchange eventually reverts busy tone to the caller. If it is free, the subscriber-identification pulse present on lead 19 causes 409 of gate 121 to pass a positive pulse to the base of 415 of gate 123, which pulse, in combination with the called subscriber pulse, unblocks 415 which passes a negative pulse via the OR gate 124 to the pulse amplifier 126. The resulting positive pulse on lead 11 causes the cross-point 13 relating to a free trunk to fire. With the called loop open the potential of 414 unblocks 403 of gate 125 which passes the loop frequency f from line 20 to the trunk concerned. At the same time the connection control frequency fcc passes via gate 127 to the trunk as in the case of an originating call. The main exchange connects the called and calling trunks together. Trigger circuit 50 of the called trunk line equipment is set, but the pulse transmitted by gate 51 cannot set trigger circuit 57 which is held in the reset condition by the rectified loop frequency on lead 56. It passes instead via gate 64, setting the trigger circuit 58, which opens gate 60, and resetting the trigger circuit 42, which closes the gate 64. The ringing signal F and ringing supervisory signal F<SP>1</SP>, thus pass to transformer 30 of the called trunk. The audio frequency F rings the called party's bell and is also heard by the caller. In the caller's trunk line equipment the detector 65 rectifies the supervisory signal F<SP>1</SP> and applies it to the device 68 via the open gate 67. Called party answers.-Closure of the called loop raises the potential of 414 (Fig. 4) whereupon 403 ceases to pass the loop frequency f. The resulting removal of the steady voltage from lead 56 (Fig. 3) causes the device 63 to deliver a pulse to the trigger circuit 58 which is thus reset, closing the gate 60 and cutting off the supply of signals F and F<SP>1</SP>. In the calling party's trunk line equipment the cessation of F<SP>1</SP> causes the device 68 to apply a pulse to lead 69 which may be used for metering the call. Release.-When a subscriber hangs up, the loop frequency f is transmitted over the trunk concerned and results in a signal on lead 90. If this persists for more than 200 ms. it is recognized as a clearance signal. The pulse distributer 33 then opens the gate 32 to pass a pulse of disconnection frequency from generator 134 over the trunk concerned. This energizes the tuned circuit 129 (Fig. 4), is rectified by detector 130 and applied to amplifier 131 which delivers to point 402 a positive pulse of sufficient amplitude to extinguish the fired tube 13.