EXFO FTB-800 Series for FTB-1 - Manual (Page 441)

Test Functions
NetBlazer 431
OH - SONET/SDH
REI:
RDI/ERDI:

F2: User Channel. The User Channel provides a 64 Kbit/s channel for
communication between two PTEs. This byte is only defined for the
first STS-1/STM-1 frame of a composite signal.

H4: Multiframe Indicator. The H4 byte provides a multiframe phase
indication of a VT/TU payload. This byte is not programmable with
VT/TU or VCAT.

Z3 and Z4:
SONET only: Growth.
Bits 1 to 4 of G1 Description
0000 No error
0001 1 error
0010 2 errors
: :
1000 8 errors
1001 to 1111 No error
Bits 5, 6, 7 of G1 Description
000, 001, 011 No defect
100, 111 RDI
010 ERDI-PD
101 ERDI-SD
110 ERDI-CD