LAN: this green light flashes when data is being sent or received through the ethernet port.
Line TX: this green light flashes when data is being transmitted from your modem over the DSL line.
Line RX: this green light flashes when data is being received by your modem over the DSL line.
Line Sync: this green light flashes when your modem is syncing with the DSL hardware at the other end of the line. When sync has been achieved, this light changes to a steady green.
Power/Alarm: this multi-colored light will start out as flashing red when the modem is first turned on and is performing its power-on-self-test (POST). The light will change to a steady green once it has booted and is ready for use.
There is also a green LED beside the ethernet port on the back of the modem, this light will change to a steady green when a successful connection is made between the modem and whatever ethernet device you have plugged the other end of the cable into.