EXFO FTB-8100 Series Transport Blazer for FTB-200 - Manual (Page 485)

Glossary
SONET/SDH Application 473
SDH - Lower-Order Path Overhead
K4: Extended Signal Label
Bit 1 of the K4 byte is allocated for an extended signal label. Bits 12 to 19 of
the 32 bit frame multiframe (see K4 Structure on page 472) contain the
extended signal label.
Bit 2 of the K4 byte is allocated for virtual concatenation. Bits 1 to 5 of the 32
bit frame multiframe (see K4 Structure on page 472) contain the LO virtual
concatenation frame count while bits 6 to 11 contain the LO virtual
concatenation sequence indicator.
Bits 3, and 4 of the K4 byte are unassigned and reserved for APS signaling
for protection at the lower order path level.
Bits 5 through 7 of the K4 byte are allocated for optional use.
Bit 8 of the K4 byte is unassigned and reserved for a lower order path data
link.