Survivor is a levelpack created by Blurredd. It's not a gametype. The gametype is called Ground Force.

In Ground Force, all the players get dumped into an arena which mostly consists of destroyable blocks and some other stuff, like TNT crates.

The one who is the last one to fall into the warp at the bottom of the level wins.

Assault is a more complicated gametype, as far as I know every team has to guard a number of trigger crates and destroy the ones of the other team.