D-Link 16-Port 10/100/1000Mbps Gigabit Ethernet Switch + 2-Port Mini GBIC Web-Smart Switch DGS-1216T - Manual (Page 23)

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Option Ports mini-GBIC 15 & mini-GBIC 16 mini-GBIC
Status LEDs
Link/ACT: Link/Activity
On : When the mini-GBIC module is installed and connected to a
network, the Link/ACT LED lights on.
Blinking : When the LED is blinking, the mini-GBIC module is
receiving data on a network.
Off : No link.
1000Mbps
On : When the 1000Mbps LED lights on, the respective port is
connected to a 1000Mbps Gigabit Ethernet network.
Off : When the respective port is disconnected to the network