Power: This LED will glow as soon as you switch on the modem.
Internet: This internet Activity lamp will blink whenever there is a data flow between internet and the modem.
(*
does not say it should remain lighted ! mine does 110BXi same board )
Ethernet: This LED will glow as soon as you switch on the computer if the computer is connected with modem through LAN/NIC/Ethernet card. Or
USB: This LED will glow as soon as you switch on the computer if the computer is connected with modem through USB port of your computer..
DSL : This LED will start glowing permanently when the connectivity between the Exchange equipment/switch and your modem is proper/established.