Skip to main content

Documentation Index

Fetch the complete documentation index at: https://developers.telnyx.com/llms.txt

Use this file to discover all available pages before exploring further.

STUN (Session Traversal Utilities for NAT) and TURN (Traversal Using Relays around NAT) servers enable NAT traversal for SIP clients behind firewalls and private networks.

​
When to use STUN/TURN

Use STUN/TURN servers when the SIP client is:
  • Behind a firewall or NAT gateway
  • On a private network without public IP addresses
  • Unable to receive inbound connections directly
  • Experiencing one-way audio issues

​
Telnyx STUN/TURN endpoints

Telnyx provides the following public endpoints for NAT traversal:
TypeEndpointPortProtocol
STUNstun.telnyx.com3478UDP
TURNturn.telnyx.com3478UDP/TCP

​
Configuration

​
Standard STUN configuration

Configure the SIP client to use Telnyx STUN servers for NAT traversal: 
STUN Server: stun.telnyx.com:3478

​
TURN with authentication

TURN requires credentials. Contact Telnyx support to obtain TURN server credentials for the account. 
TURN Server: turn.telnyx.com:3478
Username: [provided by Telnyx]
Password: [provided by Telnyx]

​
Alternative STUN servers

While Telnyx provides its own STUN infrastructure, third-party STUN servers may also be used: 
stun.l.google.com:19302
stun1.l.google.com:19302
stun2.l.google.com:19302

​
Network requirements

Ensure the firewall allows outbound traffic:
ServicePortProtocolDirection
STUN3478UDPOutbound
TURN3478UDP/TCPOutbound
RTP media16384-32768UDPBidirectional

​
ICE candidate types

When using STUN/TURN, the client will gather different types of ICE candidates:
  • host: Local network addresses (cannot traverse NAT)
  • srflx: Server reflexive addresses (via STUN)
  • relay: Relayed addresses (via TURN)
  • prflx: Peer reflexive addresses (discovered during connectivity checks)
For successful call establishment across NAT, at least one of the following candidate types must be available:
  • srflx (server reflexive via STUN)
  • relay (relayed via TURN)
  • prflx (peer reflexive)

​
Troubleshooting

​
One-way audio

If one-way audio occurs:
  1. Verify STUN server is reachable: stun.telnyx.com:3478
  2. Check that UDP port 3478 is allowed outbound
  3. Ensure RTP media ports (16384-32768) are open bidirectionally

​
Connection failures

If calls fail to connect:
  1. Verify firewall rules allow outbound UDP to port 3478
  2. Check that the SIP client supports STUN/TURN
  3. Confirm TURN credentials are correct (if using TURN)
  4. Review ICE candidate gathering logs in the client

​
Restrictive networks

In highly restrictive networks that block UDP traffic:
  • Use TURN over TCP: turn.telnyx.com:3478 (TCP)
  • Consider using TLS for SIP signaling: port 5061
  • Contact support for additional configuration options

​
See also