Well, in POTBS you also get the RvR. (Realm Vs. Realm) What happens is that you also flip ports, and then 46 hours after the port is flipped, you get a port battle of 24 people vs 24 people max and then whoever wins that battle gets to keep/get the port.
You have to keep port flipping to win a map, and a map check is every week. See screenies:
