It's a bit misleading to say no gateways are required. As far as I can tell it uses STUN/TURN for NAT busting. When NAT busting does not work (in case of corporate firewall for example), communication falls back to the TURN server as a relay.

IIRC according to google a few years ago, something like 10-20% of STUN/TURN traffic needs to be routed over the TURN relay server.

This is a gateway.