I keep getting randomly disconnected from xbox live why is that i have a bt home hub?

for some reason every so often my xbox disconnects me from live i don't know why and its been doing it quite allot and im trying to download some thing big and i can't please help its really annoying my router is just at the bottom of my stairs and my xbox is one room away i don't know if its the download what it is is avp (aliens v predetors)