Patent GB-904164-A (GB)
Title: Telephone switching system
IPC: H04Q3/545
Filed: 1958-10-06
Abstract: 904,164. Automatic-exchange systems. WESTON ELECTRIC CO. Inc. Oct. 6, 1958 [Oct. 7, 1957], No. 31800/58. Class 40 (4). In an automatic exchange in which the talking connections are set up over a gas-tube matrix, sequences of plural bit programme order words derived from a permanent store determine the control actions to be performed by the common control circuit. These control actions may be of the non-decision type to establish initial conditions within the exchange, or they may be actions requiring a binary decision. In each decision action a choice is made between advancing in the current programme sequence or transferring to a new sequence, in dependence upon the conditions obtaining at the time in question. The programme sequences are all calculated to minimize the interruption of sequences by taking into account the probability of a given event occurring. In the drawings, the hundreds digit, or the thousands and hundreds digits, of a reference number correspond to the number of the figure in which the corresponding item is to be found. A gate or amplifier symbol represents a number of gates or amplifiers having a number of channels equal to the number of individual signals to be transmitted therethrough. For example, output amplifier 1065 has eighteen channels to handle the eighteen-bit signal from the permanent store (see below). Setting up a call-general (Fig. 1).-It is assumed that an interrogation of the permanent store 111 has resulted in the receipt by common control 110 of an order commanding the scanning of the lines (e.g. 105, 106) and trunks (e.g. 113, 114). The open and closed loop states of these are represented by a binary " 0 " or " 1," respectively, the state of each line and trunk being recorded in the temporary store 112 in spots specifically assigned to each. Each time that a line or trunk is scanned its present state is compared with its recorded state in order to recognize requests for service. Normally each line and trunk is scanned once every 100 mins., but when a change from " 0 " to " 1 " is detected the common control 110 causes the line or trunk concerned to be scanned once every 10 ms. to ensure detection of all dial pulses. In the case of a calling line, common control also commands the concentrator control 109 to establish a connection between the line and an idle trunk to the distribution network 101, and commands the network control 102 to establish a connection between that trunk and a dial tone trunk terminating on the opposite side of the network 101. Originating registers, each consisting of a column of spots in the temporary store 112, are scanned to find an idle register, the address of the line requesting service being written in the idle one found, and the line spots in the temporary store 112 being changed to indicate that that line is being served by common control. The dial pulses are detected and the called line number is stored in binary decimal code in the originating register assigned to the call. On the first dial pulse, common control orders the distribution network control 102 to release the connection to the dial tone trunk. Assuming the call to be one to another subscriber of the exchange, common control orders the recently changed directory number-to-line equipment number translations in the temporary store 112 to be scanned and if the called line does not correspond to one of those, determines from the permanent store 111 the line equipment number of the called line. The line spots assigned to the called line in the temporary store 112 are then interrogated to determine whether it is busy or idle. If the line is busy, a connection is set up to a busy tone trunk and the caller hangs up. If the line is idle, its line spots in the temporary store 112 are changed to indicate that it is being served by common control. Common control then orders the concentrator control 109 to establish a connection between the called line and an idle trunk to the distribution network 101, and to establish two paths through the ringing concentrator 104, one to connect to one ringing trunk the relevant one of the six ringing tone frequencies provided, and the other to connect to a second ringing trunk the ringing induction signal. Common control then orders the distribution network control 102 to extend these two ringing trunks to the called and calling lines, respectively. Common control also causes a free-ringing register to be found in the temporary store 112 and the line equipment numbers of the calling and called lines to be entered therein; and orders the line scanner 108 to scan the called line at the high (10 ms.) rate to detect the reply of the called party. Upon this reply, common control orders the distribution network control 102 to release the connections to the ringing trunks and to establish a direct connection between the line concentrator trunks of the two parties. Common control also causes the calling and called line spots in the temporary store 112 to be changed to the " talking " state. When either party hangs up, the change from the " 1 " to the " 0 " state is detected and initiates first party release. Permanent store (Fig. 10).-This is a flying- spot store of the type described in Specifications 789,660 and 836,236. Information is stored in binary code on high resolution photographic plates, each having a rectangular array of storage areas, referred to as spots, an opaque spot representing " 0 " and a transparent one " 1." A cathode-ray tube 1000 provides an extremely small and intense spot of light which is focused by eighteen separate objective lenses 1021 to 1038 on to eighteen spots, one on each of eighteen plates 1001 to 1018, photo-sensitive elements 1041 to 1058 receiving the eighteen light channels. The output signals from these elements comprise in parallel an eighteen-bit word, which is either an order word, including the address of a scene of action in the exchange and commands to be undertaken, or translation information regarding the line equipment number of a line or trunk. The spots are addressed by positioning the cathode-ray beam under control of horizontal and vertical deflection amplifiers 1059, 1060. The desired X and Y addresses are passed to the respective input registers 1039, 1040 in binary code over conductor groups 1070, 1071, and are processed separately in the servo mechanisms 1072, 1073 to develop the required beam deflecting potentials. As the beam is positioned, the two ribbon-shaped light channels obtained through the cylindrical lenses 1019, 1020 fall upon the code plates 1061, 1062 and, through their transparent areas, upon groups of photosensitive elements 1063, 1064 the output conductors of which should, if the beam is correctly positioned, carry the same coded signal as is supplied to 1039, 1040. The signal on these output conductors is applied as feed-back information to 1072, 1073. The eighteen-bit word from 1041 to 1058 is applied via amplifier 1065 to AND gate 1066, and when this gate is enabled by the flying spotstore programmecontrol circuit 1067, the word passes to the output register 1068. As <SP>1</SP>/ 10  ms. pulses are employed in the flying-spot store, whereas the common control requires to receive ¢ ms. pulses, the output of register 1068 passes to common control via the pulse stretcher 1080. The programme control circuit 1067 is responsive to two orders from common control, viz. " Transfer to the new address now being transmitted to 1039 and 1040," and " Advance to the horizontal address adjacent that last registered in 1039 without changing the vertical address." The latter is accomplished by an " add 1 " circuit in the programme control circuit 1067 which increments the X address by 1. and is employed wherever possible as it requires less time to perform than does the former. A signal is given to common control over conductor 1074 when the last command given has been completed. The assignment of spots in the plates 1001 to 1018 is indicated in Fig. 18 (not shown), part of each plate carrying directory number-to-line equipment number translations and another part order information. Temporary store (Fig. 6).-This is a barrier grid store, which, as in the case of the flying- spot store, is set by a fourteen-bit binary word. This word is passed to the horizontal (seven bits) and vertical (seven bits) address registers 601, 602, whence the horizontal and vertical addresses pass to the digital-to-analogue converters 605, 606 and amplifiers 607, 608 to set the beam. To read a storage area the beam is set to that area and the grid 609 is pulsed from grid drive source 610. If " 0 " was stored, a small amplitude negative pulse will be present at collector 611 and output cable 612; if " 1 " was stored, the pulse will be of larger amplitude. The output is amplified by video amplifier 613, and gated to pulse stretcher 616. The process of reading an area also writes " 0 " in that area; but to write " 1 " the grid 609 is first pulsed (as in reading), whereafter the backplate 618 is pulsed during the grid pulse period, the grid and back-plate pulse drives being terminated simultaneously. The output from amplifier 613 also passes to the barrier grid tube control circuit 619 which is able to carry out the orders " Read and regenerate," " Read and change," " Read and write ' 1 '," " Read and write 0 '." The arrangement of barrier grid storage areas is illustrated in Fig. 17. The two upper quadrants of the tube are assigned to the L1 and L2, and T1, T2 and T3 spots used to denote the state of line and trunk circuits. L1 and L2 are both " 0 " when the line is idle; L1 '1' and L2 ' 0 ' indicate that the line is engaged in a call; L1 0 ' and L2 1 ' that it is being served by common control; and L1 ' 1 ' and L2 ' 1 ' that it is denied service. The T1 and T2 spots serve a similar purpose for a trunk. As trunks in traffic groups do not occupy adjacent equipment locations,