Arrangement and method for protecting a common highway from false signals

Claim 1

In a common control communication switching system including a plurality of trunks connectable through a switching network to any one of a number of service circuits under the control of a marker, the marker during its cycle time and upon establishing a connection between a trunk and a service circuit coupling an interrogate signal to the latter to interrogate it for its identification number, the identification number being coupled to a common highway for transmission to a call processor within the system, the marker upon failing to properly receive an identification number re-interrogating the service circuit during its next cycle of operation, an arrangement for overcoming a permanent identification signal on said common highway as a result of a permanent fault signal corresponding to said interrogate signal on the connection between said switching network and a service circuit comprising a timer within each of said service circuits having a pre-established time cycle which is less than the cycle time of said marker and activated when said marker couples said interrogate signal to said service circuit to cause the identification number of said service circuit to be provided on said common highway during its time cycle, said permanent fault signal activating a timer within one of said service circuits and thereby causing said identification number of said service circuit to be coupled onto said common highway during said timer''s time cycle until said timer times out, said timer upon timing out being prevented from being reactivated until said permanent fault signal is removed; whereby a permanent fault signal will cause the identification number of a service circuit to appear on the common highway only for a time period less than the cycle time of the marker.