Patent GB-991176-A (GB)
Title: An automatic telephone system
IPC: H04Q3/00
Filed: 1961-09-21
Abstract: 991,176. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. Sept. 21, 1961 [Oct. 3, 1960], No. 33787/61. Heading H4K. Alternative, routes over a tandem exchange are established by a translator which in response to the digits of the exchange code sets up a marker to search for a free trunk in a preferred group of outgoing trunks and at the same time primes itself according to a preestablished code output to provide a further translation which directs the marker to a second choice group of trunks should the first group by busy. The actual marking is done by a route register set up in two stages, one stage being set by an initial translation including the priming code which also has the function of providing a secondary translation to set the second stage route register. As shown, an incoming trunk 6 at the top of the drawing seizes a sending circuit 8 by way of a link 7. When the sending circuit 8 has registered the area and exchange codes a connector 10 causes the seizure of a marker 9 comprising a sequence control circuit 17, a magnetic core translating matrix 18 with contact tree relay access selectors CPA, SA, and RA, a buffer output store 23, and the two stages 30 and 33 of the route register. Under instruction from the route register connection is made over crossbar selectors 12 and 13 to an outgoing trunk such as 14. The contact tree relay access selectors, each comprise three relay groups and provide about 600 outlets. The code digits registered in sender 8 mark one relay in each of the groups in access selector CPA and thereby connects earth to a particular one of its 600 outlets of which only three are shown. Each outlet is connected to a particular code wire threading two cores in each row of the 11x9 translating matrix 18 of which only four rows and six cores in each row are shown. When seized by the sending circuit 8 the marker sequence circuit 17 operates relay CK3 which operates relay 1SB over back contacts of relays 1L and TB3. In the drawing normally open, contacts are shown by a cross and normally closed contacts are shown by a single bar. Operation of relay 1SB connects the outputs of translator 18 from rows 1, 2 and 3 to a cable 26a to access selector SA, and the outputs from rows 4 to 9 to a cable 27a to the first stage 30 of the route register. When the access selector CPA connects earth to its chosen code wire a drive pulse generator 21 switches all the cores associated with the code wire and by means of the output generated in the output windings W provided for each core fires two from each of the wire sets of eleven gas tubes provided for each row. Only four of the tranlator output circuits are shown, the gas tubes being numbered TxTy where x identifies the row and y identifies the core in the row. With the firing of the 22 TxTy tubes, corresponding relays RxRy operate and extend marks over contacts of relay 1SB to the cables 26a and 27a. Relays RxRy are connected up by relay UL which operates with 1SB. Rows 4 to 9 of the matrix transmit a code to relays such as RST-10 and RL-0 in the stage 30 of the register which indicates the class of trunk required and the type of impulsing needed. Should . this information indicate that a high-grade trunk is called for, the marker 9 is released to be reseized when the sending circuit 8 has accumulated all incoming digits. This guards the trunk against premature seizure. Supposing the first stage 30 of the register is set up and the marker is retained in service, relay 1L operates to signal the set condition in the sequence circuit where 1SB falls back while 2SB responds. With 1SB back relay UL releases to restore relays RxRy and clear the buffer store 23. Before this and while the register was set up, rows 1, 2 and 3 of the matrix are read out to operate relays in access selector SA which lock up to identify one of the 600 outlets associated with secondary translation wires threading the matrix. With relay 2SB operated the code set up in access selector SA is repeated to the alternative route access selector RA while at the same time a driver unit 32 is connected up and switches all the cores of the matrix associated with the wire selected by SA. All nine rows of the matrix in this instance set up the second stage 33 of the route register which now proceeds to search over the preferred group of outgoing trunks. Relay 2L operates in the route register to release relay 2SB in the sequence circuit 17 and to clear the access selector SA. Relay UL in the sequence circuit which comes up with 2SB to connect the relays RxRy also releases to restore the buffer store 23. If an idle trunk is found in the preferred group the sending circuit releases CK3 in the sequence circuit to release the marker. If all preferred trunks are found busy, however, the busy condition on the last trunk tested is returned over path ATB to the sequence circuit where it operates relay TB3 which releases relays 2SB, 1L, and 2L to clear down the marker and which operates relay 1LA to clear the access selector CPA. Relay TB3 then restores, operates sequence relay 1SB, and leaves intact the code stored in access selector RA which it has been pointed out duplicates the code that in selector SA determined the secondary translation to set up second stage 33 of the route register. A contact of 1SB connects the driving circuit 21 which turns over all the cores threaded by the code wire associated with the marked outlet of selector RA. The translation thus provided corresponds to a second choice of outgoing trunks and the marker responds to this translation as it did to the initial translation produced by the access selector CPA for the first choice. Rows 1 to 3 of the matrix, therefore, provide a code for access selector SA to determine the secondary translation and this code is repeated to access selector RA where it is held in case a third choice of trunks is required.