automatic protection switching (APS)

Automatic Protection Switching (APS) is a safety architecture in Synchronous Digital Hierarchy ( SDH) and Synchronous Optical Network ( SONET) that automatically switches to a substitute path or from the primary circuit to the secondary circuit in the event of an error frequency. In this safety architecture, a distinction is made between the linear protection mechanism for point-to-point links and the ring protection mechanism for SDH ring topologies.