http://i3xi5qxvbrngh3g6o7czwjfxwjzigook7zxzjmgwg5b7xnjcn5hzciad.onion/proposals/348-udp-app-support.html
Proposal 339 chooses a different UDP subset to support, but otherwise the main technical distinction vs. TURN's per-local-port stream comes down to the framing layer.
TURN defines an additional header to be used within a TCP-like stream, whereas proposal 339 avoids the two redundant length bytes by defining new Tor message types: CONNECT_UDP , CONNECTED_UDP , and DATAGRAM .