The device required for the internet connection is a MODEM.
A modem (modulator–demodulator) is a network hardware device that modulates one or more carrier wave signals to encode digital information for transmission.
Explanation : In each group of 3 boxes, calculate the difference in numerical values between the top two letters, and add 1 to give the value of the letter in the lower box
This is one type of Letter Equations which are well known phrases or facts where the key words have been replaced with the first letter of that word. These are often in the form of an equation, which contain a number, an = sign and the rest of the obscured phrase or fact.