Patent GB-957226-A (GB)
Title: Improvements in or relating to automatic telephone systems
Inventor: CORNER ARTHUR CHARLES
IPC: H04Q3/00
Filed: 1961-12-23
Abstract: 957,226. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Nov. 30, 1962 [Dec. 23, 1961], No. 46156/61. Drawings to Specification. Heading H4K. In a PABX employing cross-bar switches of the kind described in Specifications 890,235 and 909,237 for establishing local calls and incoming and outgoing public exchange calls, means are provided whereby an extension engaged in an exchange call may make an enquiry call to another extension or to the exchange whilst holding the original connection. The PABX described has 60 extensions and 8 exchange lines with provision for 6 local or inter-extension calls, and primary and secondary cross-bar switches are used to connect extensions to originating and terminating trunks, the former being connected to local relay sets and the latter to terminals in two sections of a crossconnecting field concerned respectively with local and exchange calls. Local calls. When an originating call is extended to a local relay set, registering equipment determines the destination of the call, and if it is a local one the relay set is connected over a local route cross-bar switch and the appropriate section of the cross-connecting field to a terminating trunk and thence to the wanted line. If the line is busy, a line classifier indicates whether the caller is entitled to cut in, and if he is he may do so by dialling 1. Before the completion of a connection the continuity of the speech path is tested, and if necessary a second attempt is made to set up the call. Outgoing calls. When the first dialled digits indicate an exchange call the line classifier is at once taken into use. If the caller is denied such calls he is routed to a manual board or is given NU tone. Otherwise an exchange line circuit is seized and the calling extension is connected thereto over an exchange route cross-bar switch and the other section of the connecting field mentioned above. Two exchange route switches are provided, and their outlets are wired to the terminating trunks in graded fashion. The connection to the local relay set is released and the caller dials directly into the public exchange. But if the line classifier indicates that trunk calls are barred to the caller, a restriction circuit receives one, two or three digits of the number dialled and determines whether the call can proceed, NU being returned if not. Incoming calls. If in-dialling is not catered for, on the seizure of an exchange line circuit from the public exchange the call is routed to a manual board. The operator may set up the connection required by keying into a register, but the line classifier sends a signal to the operator and prevents the completion of the call if the extension is not entitled to receive incoming calls. Enquiry calls. By actuating a push-button an extension engaged in an exchange call may cause the exchange line circuit to be connected to an enquiry circuit whilst holding the original connection. The extension may then set up an enquiry connection by dialling, the called extension being connected to an enquiry path of the exchange line circuit. The caller may revert to the original connection by again actuating his push-button, or the connection may be transferred to the second extension either by the original caller clearing or by the second party actuating his push-button. The line classifier comes into use to check that the second extension is entitled to exchange calls. An enquiry call may also be made to another public exchange subscriber, the connection being set up from the enquiry path of the exchange line circuit already in use to a second exchange line circuit. Tie lines. These are terminated on extension line circuits, and outgoing calls may be made thereto in response to a single digit. Incoming calls are handled like those from a normal extension line circuit. Specification 739,905 also is referred to.