Short for Synchronous Digital Hierarchy,
an international standard for synchronous
data transmission over fiber optic cables
. The North American equivalent of SDH is SONET
SDH defines a standard rate of transmission at 155.52 Mbps, which is referred to as STS-3 at the electrical level and STM-1 for SDH. STM-1 is equivalent to SONET's Optical Carrier (OC) levels -3.
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