From Technologic Systems Manuals

The TS-8551 offers two Ethernet ports labeled on the silkscreen as T1 and T2. The T1 connector is a jack with built-in gigabit magnetics, it supports 1000Base-T operation. The T2 connector is a jack with built-in 10/100 magnetics, it supports 100Base-TX operation. Each connector includes LEDs indicating link and activity. The T1 connector supports both link and activity, while T2 uses a single LED to indicate both link and activity. The link LED will be illuminated when the TS-8551 is powered on and connected to a network.

Not all SoM devices will be able to support 1000Base-T operation on T1, however our SoM devices with 100Bast-TX support are able to correctly utilize the T1 port for 10/100 operation.