Most likely black and connected to a power supply cord.
At t green data cable replacement.
You would need to get this from the device manufacturer.
Your at t equipment package comes with color coded wiring which matches up with color coded ports on your gateway.
Installerparts ethernet cable cat6a cable utp booted 3 ft green professional series 10gigabit sec network high speed internet cable 550mhz.
Wait for the at t gateway to power up.
Connect the other end to the at t broadband jack in your wall.
Plug the green data cable into the green broadband dsl port and your wall jack if you use traditional phone service it will plug into your dual port filter.
The color of the cable is irrelevant.
Connect one end of the green data cable to the green broadband port on your gateway.
If you are speaking of a at t dsl gateway combo dsl modem and router there are two or more cables.
Used to connect to the dsl phone connection.
Smart wi fi extender smart wi fi extender.
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Connect the black power cord to the back of your gateway and plug it into an electrical outlet.
Dsl gateway model 7550 dsl gateway model 7550.
Make good devices great with name brand accessories always free shipping from at t.