EXFO FTB-8500 Series for FTB-500 - Manual (Page 40)

Physical Interfaces and LEDs
26 FTB-8500 Series and FTB-8120NGE/8130NGE
FTB-8120NGE and FTB-8130NGE Models
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LEDs
LED Status Description
LINK/ACT
(Green) On Ethernet link up.
Off Ethernet link down.
Flashing TX/RX activity.
DUPLEX
(Yellow) On Full Duplex mode.
Off Half Duplex mode.
Flashing Collisions are detected.