EXFO FTB-8510B Guia Del Usuario página 1320

Glossary
Next-Gen - Virtual Concatenation (VCAT)
LO VCAT Multiframe and Sequence Indicator (SQ)
Bit 2 of Z7/K4 is used to convey LO VCAT information. It forms a serial
string of 32 bits (over 32 four-frame multiframes), as defined in ANSI
T1.105 [19] and ITU G.707 (see figure LOP Z7/K4 Bit 2 Multiframe
Structure on page 671). This string is repeated every 16 ms (32 bits x 4 x
125 s/bit) or every 128 frames. This process is repeated until the frame
count reaches 32. This means that the total number of frames for a full
cycle is 128 frames x 32 = 4096 frames.
The following fields define the frame:
The entire cycle is provided by a frame count that is divided into 32
steps of 16 ms, yielding a total of 512 ms for the length of the
multiframe.
The sequence indicator identifies the sequence or the order in which
the individual VTn or VC-n of the VTn-Xv or VC-n-Xv is assembled to
form the contiguous container VTn-Xc or VC-n-Xc, as displayed in
figure SONET VTn-Xv on page 669 and figure SDH VCn-Xv on page 669,
respectively. Each member of the VCG has a fixed unique sequence
indicator in the range of 0 to (X–1). The sequence indicator for the first
VTn or VC-n within the VCG is 0, while the second VTn or VC-n uses
sequence indicator 1, and so on up to the last member (SQ = X-1).
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Frame count is contained in Bits 1 to 5 of the 32-bit string.
Sequence indicator is contained in Bits 6 to 11 of the 32-bit string.
Remaining bits (12 to 32) are reserved for other applications. These
bits must be set to 0 and must be ignored by the receiver when
VCAT is activated without LCAS.
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