EXFO FTB-800 Series for FTB-1 - Manual (Page 567)

Glossary
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G.709 Optical Transport Network (OTN)
The FEC uses a Reed-Solomon RS (255/239) coding technique. This means
that 239 bytes are required to compute a 16-byte parity check. The FEC can
correct up to eight (bytes) errors per sub-row (codeword) or detect up to
16 byte errors without correcting any. Combined with the byte interleave
capability included in ITU G.709 implementation, the FEC is more resilient
in regards to error burst, where up to 128 consecutive bytes can be
corrected per OTU frame row.
Forward Error Correction