(
Synchronous
Optical
NETwork/
Synchronous
Digital
Hierarchy) A high-speed optical network technology used worldwide. SONET is employed in the U.S. and Canada, and SDH is everywhere else. SONET and SDH have relatively small differences; for example, the frame sizes are not identical, and some of the terminology is different. Otherwise, SONET and SDH are very similar technologies. See
SONET.