I have a D-Link wifi router on my cable network. It works great for my computers and smart phone with good speed and reliability.
I had my Xbox hard wired to my network and again good speed and a reliable connection with no lag.
I moved my box to the other side of the room where I don’t have a Cat-5 outlet, so I just picked up the Xbox wifi adapter. I can connect to the network and Xbox Live. But, MW3 in multiplayer is super laggy. The ping is fast because it always drops me into the first set of available games. I’m also typically reading four bars and only occasionally drop to three.
I know the Xbox wifi adapter is working because I connected it through my 4G smart phone hot spot. The ping is slower and I only get three bars, but I don’t experience much lag in game.