A TURN server (Traversal Using Relays around NAT) is a media relay that WebRTC falls back to when ICE (Interactive Connectivity Establishment) cannot find a direct peer-to-peer path or a STUN-assisted path between two endpoints. STUN (Session Traversal Utilities for NAT) allows an endpoint to discover its public IP address and port; for many NAT types this is sufficient to establish a direct connection. However, symmetric NAT — common in enterprise and hotel networks — blocks direct connections entirely, making a relay mandatory. When TURN is used, both peers connect to the TURN server over UDP or TCP, and the server forwards media packets between them; from a media-routing perspective the TURN server is transparent, but it does introduce additional latency equal to the sum of each peer's RTT to the relay, plus server processing overhead. For live learning this matters because corporate training environments and school networks frequently use symmetric NAT or strict firewall policies; a platform that lacks TURN infrastructure will fail for a significant fraction of users in these environments. TURN servers consume substantial bandwidth since they relay all media, so they are typically deployed in multiple regions to keep relay distance short. The TURN credential is time-limited and per-session to prevent unauthorized relay use. Configuring TURN correctly — with failover, geographic distribution, and capacity planning for peak class sizes — is one of the less glamorous but critical infrastructure tasks for any live-learning platform.
The handbook · 7 volumes
Fora Soft Video Engineering Handbook
A TURN server is what keeps corporate learners connected when their firewall blocks direct WebRTC traffic, and it also carries real bandwidth cost. We wrote seven volumes on the video stack; for TURN start with Volume 2 on NAT, TCP versus UDP, and congestion control, then Volume 3 on WebRTC and delivery economics. Written by Nikolay Sapunov, CEO at Fora Soft.
Learners behind corporate firewalls dropping out of live classes? Is your TURN server set up right?
We will review your TURN and ICE configuration and send fixes plus a bandwidth cost estimate for relayed traffic. 250+ video products shipped since 2005.
