Naven
Glossary
STUN and TURN
The two servers that let a direct call find its way through home routers.
Most devices sit behind a router that hides them from the open internet. STUN lets a device discover how it appears from outside, so two of them can meet in the middle. When the network is too restrictive for that — a corporate firewall, some mobile carriers — TURN relays the media instead, which works everywhere and costs the operator bandwidth.
A call that connects instantly at home and fails at work is usually a TURN problem.
Where Naven stands
Naven's calls use both, so a call works on a school or office network that blocks direct connections.