Tone signalling arrangement for a telecommunications exchange

摘要

A telecommunications exchange having a multiple stage switching network. Calls initiated within the exchange may be local calls to be completed internally, may be trunk calls to a central office or may be enquiry calls completed locally. For calls of the last type, a tone stage in parallel with the first switching stage of the network is used. Resistors each having one half the resistance of the subscriber line input resistance are connected to each inlet wire from the subscriber to the tone stage. The tone stage is used in local calls for providing tone signals and also used for enquiry calls. For providing d.c. bias to the speech wires, a pad stage is provided in parallel with the second switching stage. Resistances in the leads to this stage provide attenuation.