SDH Optical Terminal refers to the optical fiber transmission equipment based on Synchronous Digital Hierarchy (SDH) technology. At low transmission rates, data can also be. Future-proof your network with our full-stack offer. Buy more and save up to 25% on eligible Cisco switching, routing, wireless, and software products. Get started with the right security solution for you. See more, move faster, go farther. Higher-level signals are integer multiples of STS-1, creating the family of STS-N. Synchronous digital hierarchy (SDH) and synchronous optical network (SONET) refer to a group of fiber-optic transmission rates that can transport digital signals with different capacities.