XTurn is a STUN/TURN relay server for real-time media (WebRTC, VoIP, and similar).

What problem this solves

Many devices sit behind NAT or firewalls and cannot receive inbound UDP/TCP directly. Interactive Connectivity Establishment (ICE) lets two peers find working paths; when direct paths fail, a TURN relay forwards media through a server the client can reach. STUN discovers reflexive addresses and tests NAT behavior; TURN allocates relay ports, permissions, and channels so peers can exchange packets via the server.

XTurn implements the server side: it listens for STUN/TURN, authenticates clients, opens relay sockets, and forwards media on a fast path separate from control requests. STUN message encoding and decoding use xmedialib (XMediaLib.Stun).

Main modules

• Xirsys.XTurn -- OTP application entry; starts stores and RootSupervisor
• Xirsys.XTurn.RootSupervisor / Supervisor -- listener and worker tree
• Xirsys.XTurn.Pipeline -- control-plane STUN/TURN request dispatch
• Xirsys.XTurn.DataPlane -- relay media fast path (ChannelData, Send)
• Xirsys.XTurn.Conn / Response -- per-request context for action chains
• Xirsys.XTurn.Binding -- STUN Binding (address discovery)
• Xirsys.XTurn.Allocate.Client / Store -- per-allocation GenServer and index
• Xirsys.XTurn.ClientWorker.Pool -- sharded control workers
• Xirsys.XTurn.ListenConfig / ListenRegistry -- bind ports and RFC 5780 sockets
• Xirsys.XTurn.DualIp -- dual-homed NAT behavior discovery helpers

RFCs

• RFC 8489 / RFC 5389 (STUN)
• RFC 5766 (TURN)
• RFC 8656 (TURN extensions: address families, even-port)
• RFC 5780 (NAT behavior discovery: CHANGE-REQUEST, OTHER-ADDRESS)
• RFC 6062 (TURN over TCP / TCP relay)
• RFC 7635 (TURN REST API; optional access tokens)
• RFC 3489 (classic STUN interop when :rfc3489_compat is enabled)