GB1264704A - - Google Patents

Abstract

1,264,704. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. 21 May, 1969 [22 May, 1968], No. 25874/69. Heading H4K. A programme controlled exchange system, in which a complete record of each established connection is held in store, uses one of a group of three-port access circuits in a new path set up in substitution for an existing connection when access to that connection is required for any reason. The invention is described primarily in respect of supervising pay stations and is set out as an algorithm showing the programme sequences in association with call store access. From the point of identification of a pay station originating a call an access circuit is seized and associated with a supervisory circuit while providing a path to a register. As soon as routing digits have been dialled and the charging rate has been determined the supervisory circuit is released. When the wanted party is known the connection is established and, on reply, a transmission relay set is seized and is used to set up a speech path, the original connection using the access circuit being discarded. A timing function written into the programme counts out the period of prepayment which when expired precipitates re-seizure of an access circuit associated with a supervisory circuit and the substitution of a speech path using this access circuit in place of the existing path employing the transmission relay set. Warning tone is sent to the pay station and, failing a suitable determination of prepayment, the connection is released. The invention may also be employed to provide an operator's break-in facility; to provide a facility whereby a busy subscriber is sent a tone indicating that he is wanted by a further party to whom he may transfer by dialling a digit; to provide a call transfer facility; to provide access to a recording machine; and with multi-port access circuits to provide conference facilities. A three-port access circuit is described and involves the use of three relays. The facilities to be connected over the access circuits may be connected to the access circuits over switching stages. The access circuits may be reached over the line and group switching stages and may be available over a separate switching stage.