An Automatic Protection System for Digital Lines

An automatic transfer system provides a means of switching both ends of a working digital carrier span line automatically to a protection line when a failure occurs on a working line, without service interruption. Priority schemes enable one or two protection lines to serve any number of working lines. New design concepts expand the flexibility of automatic line transfer. Each digital span line may be protected separately and transferred independently. Interrogation and resetting on a span-by-span basis are also provided. All line transfers are signaled and the location of a failure anywhere in the system may be determined from a central location. Any span feeding lines originating or terminating within the system, or diverging at a remote office, may be protected by one or two protection lines.