EXFO FTB-8500 Series for FTB-500 - Manual (Page 45)

Physical Interfaces and LEDs
Ethernet and Fibre Channel Application 31
FTB-8120NGE and FTB-8130NGE Models

LEDs
LASER LED: The red LASER LED is on when the FTB-8500 Series and
FTB-8120NGE/8130NGE is emitting an optical laser signal.
LINK/ACT LED: The LINK/ACT LED is on when the link is up, off when
the link is down, and flashing when frames are transmitted and/or
received.
Clock
Note: Clock Synchronization is only available for Ethernet 10G and Fibre
Channel 10x interfaces or for Dual Test Set in one-way latency
measurement mode.
Connect the signal clock to the AUX port.

Use a DS1 or E1 clock signal for Ethernet 10G and Fibre Channel 10x
tests.

Use an 1PPS signal for Dual Test Set in one-way latency measurement
mode. Only available with FTB-8120NGE and FTB-8130NGE in Dual
Test Set one-way latency measurement mode.