SDH and optical modules
Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs). At low transmission rates, data can also be transferred via an electrical interface. Difference from PDHSDH differs from (PDH) in that the exact rates that are used to transport the data on SONET/SDH are tightly across the entire network, using. The basic unit of framing in SDH is a (Synchronous Transport Module, level 1), which operates at 155.
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