What is the difference between stats, global ranks, and experience?
There is a persistent stats and ranking system, which means that you will accumulate stats and ranks for the aggregate time you play on a certified server, regardless of how many game sessions this takes. You will, presumably, also be able to view your stats off line. This is completely separate from the XP system which awards you additional weapons and abilities, based on your in-game performance, but only for the duration of that map campaign.