How Do the Smaller X-1 Boxes Communicate With the Larger, Main Box

I am curious to how the smaller X-1 tv boxes communicate with the main, larger box.  I have one main box and three different tvs connected to X-1 using the smaller Xfinity boxes.  Do the smaller boxes get the tv signal from the coax cable hooked to the back of them and get all the other things such as recordings, on demand, fast forward, pause, etc from the main box wirelessly? Or is the information exchanged with the larger box via signals sent through the coax cable connected to the smaller boxes?  I hope I explained this correctly.  Thanks for any clarification provided.