The game is constantly uploading and downloading data to and from everyone. So if one of your friends is lagging or not uploading/downloading data fast enough, it would cause the game to slow down so that person could catch up. (This is what I came up with, since my friend's internet is spontaneousl...

You can try using a virtual VPN network such as Hamachi or Tunngle. My friend and I have tried using Tunngle and it works, but I haven't tested Hamachi.