EXFO FTB-8100 Series Transport Blazer for FTB-500 - Manual (Page 680)

Glossary
666 FTB-8100 Series Transport Blazer
Next-Gen - Virtual Concatenation (VCAT)
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HO VCAT Multiframe Indicator (MFI)
As illustrated in figure below, A two-stage multiframe mechanism is
used to cover differential delays of 0 μs to 256 ms. The two stages can
be functionally represented by a 12-bit counter. In the H4 structure, Bits
5 to 8 of H4 bytes are used to form Multiframe Indicator Stage 1 (MFI1).
MFI1 is incremented for every basic frame and counts from 0 to 15.
Multiframe Indicator Stage 2 (MFI2) is an eight-bit counter based on
Frame 0 (bits 1 to 4) and Frame 1 (bits 5 to 8). MFI2 is incremented
once every time MFI1 completes a cycle from 0 to 15. MFI2 counts from
0 to 255. The result is a two-stage multiframing process that yields a
total of 4096 frames (16 x 256 = 4096) per 512-ms cycle (4096 x 125 μs
= 512 ms).
H4 High-Order Path Multiframe Structure