Patent GB-1102151-A (GB)
Title: Improvements in or relating to automatic telephone exchanges
Inventor: BROWELL LESLIE JAMES
IPC: H04Q3/00
Filed: 1964-12-15
Abstract: 1,102,151. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. 3 Dec., 1965 [15 Dec., 1964], No. 51113/64. Heading H4K. The cross-bar switch described in Specification 983,507, which has split bridge commons to provide for triple group working, employs one of the outlet groups to accommodate the speech wires and the separate private wires of party lines served by the exchange. The internal wiring of the switch is shown in Fig. 1 for a single inlet distributed over the outlet groups. The three wire outlets associated with the three long bridge commons to the left of the diagram are accessible to the bridge inlet by actuation of any one of the select magnets 1SM to 8SM and by actuation of the particular one of the auxiliary magnets 1AM which directs the inlet to these long commons by way of the short bridge commons b, d and f. The group of three wire outlets associated with the three long commons in the centre of the diagram are sinilarly accessible to the inlet by auxiliary magnet 2AM. Some outlets, numbered 25 to 28 are accessible by operation of auxiliary magnets 1AM or 2AM in conjunction with auxiliary magnet 3AM or select magnet 9SM. Since such connections are made wholly with two sets of short bridge commons they introduce an element of double group working and give the auxiliary magnet 3AM the extra character of a select magnet and for purposes of marker control it is referred to as select magnet 10SM. Party lines are accommodated on the four long bridge commons to the right of the diagram. A select magnet 1SM to 8SM will indicate the speech wires of a shared line in commons a and c and will prepare for the connection of both private wires X and Y in commons e and g. The X party is selected by operation of auxiliary magnet 3AM which over short commons b and d connect the inlet speech wires to long commons a and c, and over short common f connects the inlet private wire to long common e which serves X parties exclusively. The Y party is selected by operation of select magnet 9SM which connects the inlet speech wires to long commons a and c but reverses them, and over short common f connects the inlet private wire to long common g which serves Y parties exclusively. The connection of the Y party subset is reversed relative to the X party so that the X party can call and be rung over the negative speech wire and the Y party has similar service over the positive wire. A single line circuit serves both subscribers and will respond to a call from the X party by operating relay (LR) whereas a call from the Y party operates relay (LY). The exchange connects calling line circuits to idle relay sets (TRG) over cross-bar switching stages (DSA), (DSB) the outlets of DSB being connected to the line circuits and the inlets of the switches in stage DSA being divided into two groups of five, the inlets of one group being connected to one side of relay sets and the inlets of the other group being accessible for call termination to the other side of the relay sets by way of group switching stages. The marker for switches in the (DSB) stage has a set of relays (1LM) to (26LM) which identify the outlet of a calling X party, or non-sharing party, in response to the operation of the corresponding line relay (LR). It is to be noted that only 26 outlets of the switch are utilized. A second group of relays (27LM) to (34LM) identify the outlet of a calling Y party. For party lines, therefore, a call origination results in the marker discriminating between X and Y parties and preparing the appropriate pair of magnets comprising one out of (1SM) to (8SM) and (3AM otherwise referable as 10SM) or (9SM). The appropriate private wire is thereby connected from the line circuit for the operation of the appropriate meter. Since the cut-off relay is brought up over either of these wires they are decoupled beyond the meters by rectifiers. Rectifiers are also placed between the meter windings and earth. When a call is terminated on a party line discrimination takes place in a router control. A mark is put on a terminal of the intermediate distribution frame associated with the wanted line circuit and this terminal is connected to the appropriate one of the relays in the group (1LM) to (26LM) in the marker of switching stage (DSB) so as to prepare the appropriate select and auxiliary magnets. The use of the group (1LM) to (26LM) carries the presumption that an X party is required since such relays normally connect auxiliary magnet (3AM), otherwise known as (10SM). Should a Y party be required, the router control operates a relay (MY) in the marker to disconnect the circuit prepared for (10SM) and connect a circuit for (9SM). Ringing, which is earth with ringing battery return, is connected from the relay set (TRG) and is applied to the negative wire to which an X party bell set is connected. The bell set of a Y party is connected to the positive wire and ringing is guided to a Y party by the reversal of speech wires inherent in the connection over switching stage (DSB). Sharing subscribers may be prevented from intruding on each other as shown in Fig. 5. Here the connection of the X subscriber is reversed and that of the Y party is taken normally to the line. For the potential supplied over the switching stage (DSB) for one or other party, a rectifier MRX or MRY disconnects the idle party by placing a high impedance in the loop. Rectifiers MR1 and MR2 bridging contacts of calling keys KY and KX provide a path for dial tone as these keys are held down to initiate a call and are not released until dial tone has been returned. When initiating calls subscribers of this sort cannot be subjected to battery reversal from the relay set (TRG), such reversal being necessary for supervision over junctions. The register must therefore recognize such substations and operate a relay in the relay set to disconnect the D relay contacts. When terminating calls to such subscribers, as their connection is reversed, the register operates a relay in the relay set to reverse the ringing connections. If, instead of using earth ringing with battery return, battery ringing and earth ringing return is used, the reversed arrangement of Fig. 5 is not necessary to provide security from intrusion between parties. The Y party connection is reversed, as is ordinary in the system described, rectifiers MRX, MRY are provided but are oppositely poled; rectifiers MR51, MR52 are not necessary as the call keys KY, KX normally provide a loop and break it to connect the bell-set side of the station to earth. It is not then necessary to provide a reversal in applying ringing to line but it remains necessary to prevent battery reversal to such stations on reply to a call originated by them.