EXFO FTB-8100 Series Transport Blazer for FTB-200 - Manual (Page 467)

Glossary
SONET/SDH Application 455
SONET - Line Overhead (LOH)
SONET - Line Overhead (LOH)
This section contains overhead information (LOH) processed by all SONET
equipment along a network path, excluding signal regenerators.
H1 and H2: Pointer
H1 and H2 bytes are combined to form a pointer indicating where the path
overhead begins within each SPE.
H3: Pointer Action
H3 is an extra byte used to compensate for the SPE timing variation. The H1
and H2 pointer tell the receiver when the H3 pointer is used. This byte must
be defined in every STS-1 to STS-n frame of a composite signal.
B2: BIP-8
The BIP-8 (Bit-Interleaved Parity) byte provides line error monitoring. The
byte is calculated by performing a routine even-parity check over all bits of
the LOH and the STS-1 frame capacity of the previous frame of a composite
signal (STS-1 to STS-n). Note that the SOH is not used to calculate the parity
check. This byte must be defined in every STS-1 to STS-n frame of a
composite signal.