a communication system is illustrated wherein the communication links include automatically reversible amplifiers with the termination means of two links closing a loop . upon failure of detection of a carrier signal in one of the links at the terminating end due to a break in that link , switches are automatically actuated to connect the momentarily unconnected portion of the broken link to the link that is still intact such that communication is restored in a new link configuration thereby accomplishing &# 34 ; fail - safe &# 34 ; operation without undue redundancy .