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STS(Synchronous Transport Signal) The electrical equivalent of the SONET optical signal. In SDH, the European counterpart of SONET, STS is known as STM (Synchronous Transport Module). The signal begins in electrical format and is converted to optical for transmission over the SONET fiber facilities. An STS-1 frame is transmitted in 125ms, yielding raw bandwidth of 51.84 Mbps. The STS frame includes five elements: Synchronous Payload Envelope, Section Overhead, Line Overhead, Path Overhead, and Payload.
The STS-1 frame is the basic building block for SONET, much like the DS1 frame in a T-carrier environment. See OC and SONET.