How to get Nat type Open on PS3?

While playing Modern Warfare 2, my matchmaking takes longer then other people and i often can't communicate through the mic. This is happening on Nat type 3, while i am okay with these problems, what really irrates me is that how i cant host a private game and if i join a private game, i start lagging too much. this isn't the game, i have had the same problem with black ops too. My router is TL-WR741N.