Patent GB-863854-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: DAVISON ALAN
IPC: H04Q3/52
Filed: 1956-10-27
Abstract: 863,854. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Sept. 30, 1957 [Oct. 27, 1956], No. 32828/56. Class 40 (4). Subscribers' line circuits have trunking connections A and B to both sides of a number of centre link circuits CLC. Either connection may be used for a terminating or an originating call, but if one type is used by a calling subscriber then the other type is used to make connection to the called subscriber. Speech trunking circuits, Fig. 1. The subscribers' line circuits are divided into groups of 400 having access in multiple to primary switches PRI of co-ordinate type. The outlets from the various columns in half of the switches are connected to primary speech bridges PB1A-PB20A and in the other half of the switches to primary speech bridges PB1BPB20B. Secondary switches A and B are also associated only with the 400 line groups and connect to secondary bridges such as SB1A1- SB1A10, SB25A1-SB25A10, SB1B1- SB1B10, SB25B1-SB25B10, which are connected by tertiary switches to centre link circuits CLC 1-250. Connecting to register, Fig. 2. The subscribers' line circuits are connected over an independent set of primary switches to register bridges RB1-RB400 which are connected by secondary switches to groups of registers. The outlets of the primary switches make three appearances on the register bridges. By this means any subscriber can have access to any register. Operation, Figs. 3 and 4. In setting up a call, the register multiple is used first and the speech multiple is not used until all the digits have been dialled. A control circuit SGCC for each group of 400 subscribers scans the lines until it finds a calling line when a circuit LIC identifies the line. A register selecting circuit RSC seizes the first free register accessible to the group and the register marks the appropriate columns in the register selecting switches from which it is accessible, the appropriate rows being marked by the line identification circuit LIC so that the calling line is connected to the register. The register returns dial tone to the calling subscriber and control circuit SGCC releases. Dialled impulses are accompanied by an A.C. signal. Meanwhile, the 2000-line control circuit LGCC has been seized and its scanning circuit SCR hunts for and seizes the register when dialling is complete. The digits are transferred to storage circuits DS1-DS7 and a translation field CC determines whether the call is local or distant. In the former case CC marks the appropriate 400 group, hundreds, tens and units leads through FM, HM, TM, UM. The 2000- line control circuit then reseizes the originating 400-line control circuit SGCC and through the exchange control circuit ECC seizes the wanted 400-line control circuit as soon as it is free. Normal line scanning is suspended and the hundreds, tens and units markings of the wanted line are displayed to all 400-line control circuits, only that line in the wanted 400 group responding. If the wanted line is free the line identification circuit LIC stores the called subscriber's identity and tests all free paths through the A and B appearances in the speech multiples to the appropriate centre line control circuits CCC. This information is stored in the comparison circuit LDC in each CCC affected. The 2000- line control circuit next tests the speech paths from the calling line circuit to the centre link control circuits CCC. Provided calling and called connections exist on opposite sides of a centre link circuit CLC then a full connection can be made and sequence circuit CSC of a CCC able to fulfil these conditions marks a corresponding position in a high-speed hunt HSH. When HSH receives a signal from a timing control it hunts for and seizes the first centre link control circuit CCC able to complete the connection. The selected centre link control circuit CCC then allots its first free centre link circuit CLC which marks outlets in the A and B tertiary switches associated with the CCC. The selected centre link control circuit CCC also signals back over the testing circuit to the calling and called subscribers' line circuits and so to the 400-line control circuits to initiate setting up of the speech path. The switches are operated by coincident markings from the bridge circuits and line identification circuits or allotter as the case may be. If the called subscriber were busy or if no free path were available then HSH would complete one cycle and then cause release of the 2000-line control circuit. Fig. 5 shows a circuit suitable for use as a multiple switching element and bridge circuit. Pulse and bias applied to leads P, B, respectively fires VK1 which then fires VK2, provided the necessary anode and cathode potentials are supplied from the bridge circuit BC and line circuit LC.