When 90% of bandwidth has been used, we will email you every few hours to notify you that you are close to the bandwidth limit. At 100% utilization, your servers MOTD will be overwritten indicating how to resolve the issue. At this point players can still join, but MOTD will show that your resource limit has been reached. At 200% utilization or 5 days after you first reached 100%, your domains will be disabled and players will no longer be able to join through TCPShield.
Bandwidth is calculated via ingress from your server and players to our network. We report the raw bytes we see, so you can keep track on your end as well of your own usage using applications like nload and iftop with 1-1 accuracy.