EXFO FTB-800 Series for FTB-1 - Manual (Page 442)

Test Functions
432 FTB-700G/800 Series
OH - SONET/SDH

F3:
SDH only: User Channel. The Path User Channel provides a channel for
communication purposes between path elements and is payload
dependent.

K3:
SDH only: Automatic Protection Switching (APS). Bits 1 to 4 of the K3
byte are used for APS signaling. K3 bits 5 to 8 are reserved for future
use.

N1:
SONET: The N1 byte (formerly referred to as the Z5 byte) is allocated
for Tandem Connection Maintenance (TCM) and the Path Data
Channel.
SDH: (Network operator byte) The N1 byte is allocated to provide a
Higher-Order Tandem Connection Monitoring (HO-TCM) function.
VT/TU

V5 VT/TU Path Overhead
The V5 byte is allocated to indicate the content of the VT/TU path,
including the status of the mapped payloads. It provides the same
functions for VT/VC paths that the B3, C2, and G1 bytes provide for
STS/STM paths.

BIP-2 is not configurable.

REI, RFI, and RDI: Choices are 0 (disabled), and 1 (enabled).