Telecommunications system, particularly a telephone exchange system, having overload protected sequential logic systems

Claim 1

A telecommunication system comprising: a plurality of lines and trunks, arranged in groups, for connection to subscriber stations and for carrying call information including initial switching identifiers and subsequent selection characters to be processed and which are announced by said initial switching identifiers; a central information-processing system having a limited call-handling capability with respect to its information-processing capacity; a switching network connected to said central information processing system; a plurality of partially-centralized switching devices each connected to a respective line/trunk group and to said central information-processing system via said switching network, and each operable to receive, intermediately store and transit call information to said central information-processing system for processing to set up calls between calling and called subscriber stations; traffic load measuring means connected to each of said partially-centralized switching devices and responsive to said initial switching identifiers to produce control signals representing the information-processing traffic load; and a plurality of cyclically-deincremented counting means each connected to a respective partially-centralized switching device and to said traffic load measuring means, each of said counting means incremented by said control signals and operable to produce and transmit an overload signal to the respective partially-centralized switching device upon reaching a predetermined count representing a traffic load limiting value to cause the respective partially-centralized switching device to reject further initial switching identifiers until the respective counting means has been deincremented below said predetermined count so that said central information-processing system does not reach an overload condition.