Patent GB-777112-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: PEARCE JAMES GORDON
IPC: H04Q3/00
Filed: 1953-12-19
Abstract: 777,112. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Dec. 14, 1954 [Dec. 19, 1953], No. 35404/53. Class 40 (4). In a register-controller system in which each switching stage consists of primary and secondary cross-bar switches connected by links, the group selector stage includes a plurality of group selectors each of which has associated therewith equipment which is taken into use only during the setting up of a connection and which includes a number of connecting circuits each corresponding to one of the primary switches and a common control circuit, a connecting circuit when taken into use completing a path over which digits are sent from a register temporarily associated with the connection to a storage circuit, common to the connecting circuits, which determines from these digits whether the connection is to be set up by the connecting circuit in conjunction with the common control circuit or if a marker is required in addition, information being then transferred to the connecting circuit or to the marker and the connecting circuit, whereupon the storage circuit is released for use on another connection. General description (Figs. 1, 2). The exchange employs two selection stages, a combined line finder/final selector stage (LF/FS) and a group selector stage (GS), each stage using 12 X 10 cross-bar switches arranged for doublegroup working. A 10,000-line exchange comprises twenty-five 400-line groups, each associated with a LF/FS embodying a plurality of switching units each consisting of two primary switches PSAA, PSBA and one secondary switch SSA. Each subscriber's line circuit SLC has an appearance at a corresponding position in each pair of primary switches of the LF/FS and is directly connected to the control equipment CE(LF/FS). Each originating trunk (ORIG) includes a local transmission equipment (e.g. LTE1) which incorporates speaking battery feed, call-metering and supervision arrangements, means for testing the condition of a called local subscriber's line, and means for causing a register connector RC serving ten transmission equipments to take an idle register REG of the forty common registers into use. Dial tone is reverted from the register, the dialled digits are stored and a voice frequency sender 7VFS is then seized. The stored digits are transferred en bloc to the sender in a 4-unit code and if they correspond to a local call, they are extended to a number indicator NI which determines (a) if the dialled number corresponds with the point of termination of the required line, or (b) if it does not, or (c) if the number is that of the first line of a P.B.X. group, or (d) if the number is unequipped, or (e) if the number has recently been changed. If (a) be the case, the number indicator NI signals the sender to start transmission of V.F. signals indicative of the dialled digits together with a prefix signal indicative of the straightforward nature of the call. In case (b) NI returns to the sender a digital signal denoting the thousands group location of the wanted line circuit in the LF/FS stage, and causes the sender to transmit a "changed position" prefix followed by this "new thousands" digit and the dialled hundreds, tens, units, and thousands digits. In case (c) NI translates the dialled four-digit number into an arbitrary two-digit number assigned to the wanted P.B.X. group, and causes the sender to transmit a distinctive prefix followed by this two-digit number. If the number is unequipped the number indicator causes the sender to transmit a two-digit code (91) to set the group selector to a relay set which returns N.U. tone. If the number has recently been changed, the sender is caused to transmit a two-digit code (90) appropriate to a group of group selector outlets giving access to a special service manual position. The group selector stage consists of ten primary and twenty secondary switches, each switch having ten inlets and twenty outlets. The ten inlets of each primary switch are associated with a group of ten local transmission equipments served by a register connector individual to the group. The twenty outlets of each primary switch are distributed by links LKS, one to each of the secondary switches SS1 to SS20, terminating on corresponding bridges in each. The four hundred secondary switch outlets are divided into twenty " levels " LEV1 to LEV20. For control purposes the group selector incorporates ten connecting relay sets CRS1 to CRS10, a storage relay set SRS including a voice frequency receiver 7VFR, and a control equipment CE. A connecting relay set, which is seized by its associated register connector when the register taken into use has accepted all the digits necessary for the setting up of the call, establishes a path to SRS and 7VFR, and signals the sender to commence high-speed transmission of the prefix digit and one or more routing digits in a code in which each signal consists of two of the seven available frequencies in succession. The digits received are converted to 4-unit code and stored by groups of storage relays. Call to a local subscriber in which the directory number agrees with the line circuit position. The storage relay set determines from the thousands digit which of the 2000-line markers MKR is required and also causes the thousands digit to be stored by the CRS involved. The SRS extends to the marker a signal indicating that the equipment position corresponds to the dialled number, together with the hundreds tens and units digits and a signal indicative of odd or even thousands digit. The marker is connected to the CRS, and the CRS to the control equipment CE; SRS and 7VFR being released. The marker extends a marking appropriate to the required line to the control equipment CE(LF/FS) of the relevant one of the five LF/FS serving the 2000-line group and signals to the CRS which LF/FS is to be used. The latter signal is extended to CE(GS) and, in combination with the thousands digit relays of CRS, defines the required LF/FS, and a particular route relay is operated to initiate testing of the terminating trunks extending to secondary switches of the marked LF/FS. The route relay, in conjunction with the testing relay corresponding to the outlet seized, controls the operation of the magnets in the group selector switches (other than the primary switch bridge magnet) necessary for the setting up of a connection to the seized outlet. The operation of the primary bridge magnet is determined by the LTE employed. The register controller, marker and CE(LF/FS) are released, the LF/FS bridge magnets are operated and the required line is tested by the LTE with the usual results. Local call in which dialled number and line equipment position number do not correspond. The prefix digit ensures that a marker shall not be seized until the full complement of six digits has been received by 7VFR. The storage of the second (" new thousands ") digit determines the appropriate 2000-line marker for seizure and causes the second digit to be stored in the CRS also. A marker is taken into use and the dialled digits are transferred to it together with a signal indicating whether the "new thousands" digit is odd or even, and a signal indicating that the directory and position numbers do not correspond. The marker seizes a 2000-line number translating device NTD (associated with the I.D.F.) appropriate to the dialled thousands digit and refers to it the remaining dialled digits, together with an odd or even thousands digit signal which chooses one of two groups of cross-bar switches in the NTD for operation. Setting of these switches in accordance with the hundreds, tens and units digits causes a terminal to be marked in each of three terminal fields, strappings from which cause the hundreds, tens and units digits of the corresponding line equipment position to be transferred to the marker, which uses them in conjunction with the "new thousands" digit to control the setting up of the connection as for a straightforward call. Call to a private branch exchange. The relevant prefix digit and the two-digit P.B.X. group number are stored in SRS, a P.B.X. hunter PH is seized and the two-digit number is transferred to it. The hunter thereupon connects itself to the relevant CRS, the SRS is released, and the control equipment CE is taken into use. A group relay distinctive of the wanted P.B.X. group is operated, whereupon the hunter tests all the lines except the last of that group by testing the private wires directly, and temporarily busies the first idle one found. A cross-bar switch in the hunter, which is set jointly by the group relay and the test relay, marks a distinctive terminal in each of four terminal fields, thus causing a four-digit number indicative of the position of the chosen line to be set up in the hunter. The thousands digit brings about seizure of a relevant 2000-line marker, whereafter the call is set up in the usual manner. If all the tested lines of the group are busy, the hunter causes a path to be completed over the switching stages to the last line of the group which is tested as for a call to an ordinary subscriber. Calls other than those to local subscribers. The prefix digit received in SRS indicates that the call is not for a local subscriber and also the class (ordinary or coin-box) of the calling subscriber. This digit together with the digit (S) dialled enables the SRS to assess the nature of the call and to transfer the digits to the CRS. The SRS is released, the CRS connected to the CE, and the appropriate route relay is operated; no marker being required. Detailed description. A register taken into use. by a calling subscriber seizes the voice frequency sender (Figs. 4, 5, 6) by the applica. tion of battery to the seize lead SZ (Fig. 4) individual to the register. Identification relay IR pulls up followed by common relay DR which ensures that only cne relay IR can remain operated. Ground t