EXFO FTB-8510B Guia Del Usuario página 1319

Glossary
Next-Gen - Virtual Concatenation (VCAT)
SONET VTn-Xv
SDH VCn-Xv
To define its multiframe, LO VCAT uses a similar concept as that
described above for HO VCAT groups. For the LO VCGs, low-order path
overhead bytes Z7 (bit 2) [SONET] and K4 (bit 2) [SDH] are used to
support the multiframe structure and specify the MFI and SQ values.
669
SONET/SDH Application