GB1462653A - Telecommunications exchange systems - Google Patents

Abstract

1462653 Automatic exchange systems SIEMENS AG 28 Feb 1974 [9 March 1973] 9141/74 Heading H4K A subscriber line circuit comprises a first gate which is enabled in response to the application of a code representing the directory number of the subscriber associated with the line circuit and a second gate which is enabled in response to the application of a code representing the equipment number of the line circuit, the output of the second gate being coupled to an output of the line circuit such that an output is only produced in response to the application of said equipment number code if the subscriber circuit is free. The arrangement is used in a PBX having a single ended switching network K, and in which a calling subscriber is connected through to a register WE, in known manner. Dialled digits are transferred from the register WE to a store P associated with a central control Z which determines whether the digits relate to an internal or external call. An external call is set up in an undisclosed manner. For an internal call, the central control causes three groups of ten wires R1, R2, R3 to be marked in accordance with a three figure directory number of the called subscriber and these markings are extended to all line circuits such as TAI. In the line circuit of which ten position switches D1- D3 are set to the directory number marked on the wires R and a gate G1 is enabled in conjunction with a mark supplied from the central control to all such gates G1. A hunting impulse is thus supplied to a scanner S via OR gate G3 and the marked line circuit is identified according to a three figure equipment number by the scanner S which transmits this number to central control. Central control then marks the code wires R according to this equipment number and enables gates G2 provided in each line circuit, and coupled to the code wires in accordance with the equipment number of the respective line circuit. In the identified line circuit, gate G2 provides an output via a contact b and OR gate G3 to the scanner S if the line circuit is idle. The scanner is thus caused to hunt for the marked line circuit so as to indicate to central control that the line circuit is free, i.e. a "line state" scan is performed. Had the line circuit been in use, i.e. the associated subscriber engaged, the contact b would have been open and the mark would not have been supplied to the scanner. If the scanner is of the type which establishes the identity of an equipment number in a series of stages, only the first stage may be used for the "line state" scan, e.g. the scanner'may only establish that a line circuit in the hundred's group has been marked. The switches D1-D3 permit the directory number associated with a particular line circuit to be easily changed.