D-Link DES-1228P - Manual (Page 25)

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Blinking When the Link/Act LED is blinking, the port is
transmitting or receiving data on the Ethernet network.
Off No link.
1000Mbps
On When the 1000Mbps LED light is on, the respective port
is connected to a 1000Mbps Gigabit Ethernet network.
Off When the respective port is connected to a 10Mbps
Ethernet or 100Mbps Fast Ethernet network, or no link.
100Mbps
On When the 100Mbps LED light is on, the respective port
is connected to a 100Mbps Fast Ethernet network.
Off When the respective port is connected to a 10Mbps
Ethernet or 1000Mbps Gigabit Ethernet network.