The internet connection is preferably cable, but this is relative since both cable and wireless connections are dependent on the distance between the location of the server(s) and your computer. Zombie Escape maps are among the poorest performers in the Source Engine, even with near-perfectly optimized maps.
Ensure that you have at least the recommended settings for Counter-Strike: Source or Counter-Strike: Global Offensive.You need to own a legal copy of Counter-Strike: Source or Counter-Strike: Global Offensive to play Zombie Escape.