How come when i play Call of Duty WaW zombies, I lag?

I ALWAYS have 4 bars of connection, but it drops all the way to one bar, then back to 4 bars. It always does that everytime i play it. In Modern Warfare to, i ALWAYS have good connection. I always get 4 bars if connection. but on WaW zombies, I get horrible connection. It goes to 4, drops to 1, and it keeps on going. Please Help, Thanks