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A SONET Overview
Issue 1 December 1997 A-9
VT Path Overhead 1
There is one byte of VT path overhead called V5. It occurs on every fourth frame;
that is, 2000 times a second.
This byte provides for VT paths the same functions that B3, C2, and G1 provide
for STS paths, namely:
■ Error checking
■ Signal label
■ Path status.
The bit assignments of the VT path overhead are specified in the following list and
are illustrated in Figure A-4:
— Bits 1 and 2 are used for error performance monitoring (BIP-2).
— Bit 3 is a VT path far-end-block-error (FEBE) indication that is sent back
toward an originating VT PTE when errors are detected by the BIP-2.
— Bit 4 and Bit 8 are used for remote defect indication (RDI)
— Bits 5 through 7 provide a VT signal label.
Figure A-4. VT Path Overhead Byte
BIP-2 FEBE
Signal Label
12345678
VT Path Signal Label Coding:
0 0 0
0 0 1
Unequipped
Equipped-Nonspecific
RDI
RDI
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