Synchronous Optical Network. Proposed by Bellcore in the ‘80s, SONET has become an ANSI (American National Standards Institute) standard as well as an ITU international standard named SDH that defines interface standards at the physical layer 1 level. It allows data streams of differing rates to be multiplexed. It is generally implemented over fiber optic cable and is often configured in a ring allowing it to reroute traffic with no interruption of service, should a cable be cut.