Patent GB-754653-A (GB)
Title: Improvements in or relating to telecommunication exchange systems
IPC: H04Q3/00
Filed: 1950-01-16
Abstract: 754,653. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Hertog, M. den). Jan. 12, 1951 [Jan. 16, 1950], No. 1097/50. Class 40 (4). In final selector equipment operating generally in the manner disclosed in Specification 754,652 the scanning equipment in the common control circuit reverts two impulses in a cycle of 1100 time units for each outlet scanned, instead of one impulse per outlet. One of these impulses characterizes part of the identity of the outlet and its busy or idle condition, whereas the other characterizes part of the identity and the class. All this information is sent to the register - controller without requiring the individual selector to be operated. Final selectors and line finders occur in the same multiswitch and share the same common control sircuit. The type of switch used and its method of operation are described in Specification 700,089. Operation of final selector and common control circuit, Figs. 1 and 2. Whenever a register-controller has to control the operation of a switch it is connected to the relevant common control circuit over wires 1 to 10 via a common control circuit connector as described in Specification 700,089. Such connection is here assumed to have taken place. The outlets are scanned by the explorer in the common control circuit which is controlled by pulse sources Na1-Na5, Nb1-Nb5, and Nc1-Nc4 to produce a 100-impulse cycle (one impulse per outlet) as in Specification 700,089. Eleven further impulse sources Nd1-Nd11 (not shown) are provided each having an impulse length equal to that of the Na sources and are used to indicate the condition and class of the outlets. One Nd source is connected to each of the terminals A and B, Fig. 2, individual to each outlet. The source Nd8 is not connected to these terminals except in the case of dead lines but is employed to indicate the busy condition. Thus whenever a line is engaged by a line finder or final selector, Nd8 is connected over contact H3, Figs. 3 or 1, to the d lead which is extended to the explorer so that the Nd8 impulses suppress those of the source connected to terminal A. Suppression of those of the source connected to terminal B is prevented by the rectifier between lead d and terminal B. Thus when an outlet is free the Nd sources connected to A and B are effective and when it is busy Nd8 and the source connected to B are effective. During each 1100 time unit cycle there are 11 time units for each outlet in which its Na, Nb, and Nc sources are all positive simultaneously but in only two of these will the effective Nd sources be positive. Two impulses will therefore be reverted for each outlet which together characterize the identity, class, and condition of the outlet. Signals from free outlets. Sources Nd6 and Nd7 characterize unrestricted and restricted lines respectively and are combined with Nd1 ... Nd5 to characterize lines of non- consecutively numbered PBX groups 1 . . . 5 respectively, with Nd11 for single lines and lines of consecutively numbered PBX groups, or with Nd9 for long period absentee lines. Signals from busy outlets. In all cases Nd8 is effective in lieu of the source connected to terminal A which results in combinations of Nd8 with the following: Nd1 ... Nd5 for 1st lines of non-consecutively numbered PBX groups 1 ... 5; Nd6 or Nd7 for other lines of these groups, single lines, last lines of consecutively numbered PBX groups, and long period absentee lines; and Nd11 for other lines of consecutively numbered PBX groups. Arrangements are also provided for 4-party lines using Nd10 on terminal B. Call to a free single line. The register in all cases connects up a combination of Na, Nb and Nc secures characteristic of the tens and units combination of the line to be selected so that the register-controller will accept impulses only in time units corresponding to this line and the comparator in the register-controller includes means for registering the Nd impulse sources corresponding to the two received impulses (see Specification 754,654). Two tubes corresponding to these Nd sources (Nd6 or Nd7 and Nd11) are fired and their anode relays indicate a free line and initiate operation of the registercontroller to control the selector. A double test of the common control circuit is made over wire 9, Fig. 2 (as in Specification 700,089) which if successful results in the operation of a combination of code bar magnets AM to EM in the control circuit, Fig. 2. Relay Cr operates whereafter Sra or Srb is operated and Er or Dr released as in the last mentioned Specification. A test is then made over the c lead of the wanted line to ensure that it is free and if this is successful the selector is switched through. The c lead has - 48 V. connected thereto from a preceding selector to prevent operation of the call detector equipment when the called line is looped on the reply of the wanted party. Call to a busy single line. The reception of impulses corresponding to sources Nd8 and Nd6 or Nd7 indicates that no PBX hunting is to take place, busy tone is reverted from the link circuit (not shown) under control of the register-controller, and the partial connection is immediately released back to the first group selector. Call to free 1st line of non-consecutive PBX group. Impulses are received corresponding to Nd6 or Nd7 and one of Nd1-Nd5, and since Nd6 or Nd7 indicates a free line the line is selected as for a free single line. 1st line busy. Impulses are received corresponding to one of sources Nd1-5 and Nd8 and this combination initiates hunting. The register-controller connects the corresponding source Nd1-5 to the comparator in place of the Na, Nb, and Nc sources and thus responds to the first free line of the relevant PBX group. Lines of the group other than the first cannot be selected if busy since the Nd1-5 source (in this case connected to terminal A) is suppressed by Nd8. The register-controller records the identity of the selected line and controls switching through thereto. All lines of group busy. After hunting is initiated all the outlets of the selector are scanned without success and then a second set of impulses will be received from the 1st line of the group. Hunting is stopped and the c lead is tested. The line proving to be busy procedure is then as for a busy single line. Direct selection of a line other than the first of a PBX group with non-consecutive numbers. If free the line gives signals as for the first line of a group, and if busy as for a busy single line. Procedure is then as for a single line in each case. Call to " directory number " of non-numerical PBX group. This number corresponds to an outlet which is not allocated to a line but which has Nd6 and Nd7 connected to its terminal A and B. The register-controller operates as for a single line and since no line equipment is connected to the c lead the test results in the reversion of an impulse from a combination of sources Na, Nb, Nc and Nd, Fig. 2, characteristic of the PBX group over wire 5 or 6 to the register-controller. The connection is then released and a new connection set up as described in Specification 678,319 to the first line of the relevant PBX group. Call to PBX group with consecutive numbers. Free lines of such groups are characterized by Nd6 or Nd7 in combination with Nd11 and are selected as is a free single line. However, any line but the last of a group reverts impulses associated with Nd8 and Nd11 when busy thus informing the register-controller that the line is a busy PBX line of this type of group. The impulse sources connected to the comparator are then changed to those characterizing the next consecutive number as in Specification 678,319, and the selecting operation is repeated. This continues until either a free line, or the last line of the group, is reached. In the latter case the impulses reverted are as for a single line so that if it is busy, busy tone is reverted and hunting ceases. Arrangements are also provided for signalling the stations on a 4-party line associated with a called number, and for causing calls to long period absentee lines dead numbers or changed numbers to be re-routed to an operator all under control of the Nd sources connected to the outlet terminals A and B. Operation of line finder. The line finders, Fig. 3, and final selectors for a group of 100 lines constitute one multi-switch and are served by the same common control circuit. The identity of a calling line is signalled to the registercontroller by equipment as described in Specification 737,865. All calls are handled as calls to single free lines via final selectors, busying being performed by the connection of - 48 V. to the c lead from the link circuit (not shown). The d lead is used during the call for metering and for identification. The metering signal which is + 24 V. connected to the d lead in the link circuit passes via make contact HB1, Fig. 3, of the horizontal bar and a rectifier to the E contact of the line finder and thus to the meter SM, Fig. 4. Identification, which takes place as in Specification 698,802, is initiated by the connection to the d lead via the link circuit of a negative potential (-44 V.). This lead is extended via gate GIG at the 1st line finder, Fig. 3, and via the D contact of the 1st line finder to the d lead of the subscriber's line circuit, Fig. 4. The gate in the 1st line finder is connected to one source in each of the groups Na, Nb, and Nc together characteristic of the thousands and hundreds digits of the line finder and to source Nd1 and thus an impulse is sent forward over the d lead, when all four sources are simultaneously relatively positive. The d lead at the subscriber's line circuit extends to the d1 lead of the final selector and thence to the explorer, Fig. 2. The explorer sources Na, Nb, Nc connected to the d1 lead in combination with Nd8 in the line finder produce an impulse on