By building it on top of UDP, which in turn is a thin wrapper around IP. In theory, you could alternately build a new protocol directly on top of IP, just as T

By building it on top of UDP, which in turn is a thin wrapper around IP. In theory, you could alternately build a new protocol directly on top of IP, just as TCP and UDP themselves are built, but middleboxes have a habit of dropping anything that's not TCP or UDP. Plus, unprivileged users on standard OSes can't send arbitrary IP packets, so it would require more setup for users.