What is RS-FEC and when is it used on 100G testing?

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What is RS-FEC and when is it used on 100G Testing?
RS-FEC stands for Reed Solomon Forward Error Correction.  It is used on specific 100G interface types to extend the range of the signal by correcting errors in transmission.  It is capable of detecting up to 14 symbol errors and correcting up to 7 symbols per FEC block. Typical 100G interfaces that require RS-FEC are 100GEBASE-SR4 (and KR4 and CR4), CWDM4, PSM4 and possibly to extend distance with ER4-LITE.