TURN                                TURN           Peer          Peer
client                              server          A             B
  |--- ChannelData ------------------>|             |             |
  |    Channel-number=0x4000          |--- UDP datagram --------->|
  |    Data=...                       |    Data=...               |
  |                                   |             |             |
  |                                   |<-- UDP datagram ----------|
  |                                   |    Data=... |             |
  |<-- ChannelData -------------------|             |             |
  |    Channel-number=0x4000          |             |             |
  |    Data=...                       |             |             |