31009: Transport error
VOICE
ERROR
You might see this error when the Programmable Voice SDK can't establish a transport to send or receive messages during a call.
- Required Voice SDK signaling or media connectivity is blocked by a firewall or not allowed to Twilio destinations and ports, preventing the SDK from establishing a transport.
- The client network's routing or DNS selection leads to suboptimal or incorrect edge selection, which can hinder establishing signaling transport until an explicit edge is chosen.
- A highly restrictive NAT or enterprise network requires TURN relays and none are provided, so media or signaling cannot traverse the network.
- On older Mobile SDK versions that use a non‑standard port, required signaling ports are closed, blocking transport establishment.
- Allow the outbound connectivity the Voice SDKs require. Open TCP port 443 to Twilio signaling gateways and Insights logging, and allow UDP ports 10000–60000 to Twilio media IP ranges for secure media. Coordinate firewall rules with the Voice SDKs Network Connectivity Requirements.
- If you operate in restrictive networks, provide TURN servers through Twilio's Network Traversal Service so calls can relay through firewalls when needed.
- Specify a Twilio edge explicitly when appropriate, especially if upstream DNS or routing selects a distant edge, to improve reliability of the signaling transport.
- For Mobile SDK deployments on legacy versions that require it, ensure port 10194 is open, or upgrade to a current SDK release that uses TCP port 443 for signaling.
- Run a PreflightTest before placing calls to verify end‑to‑end connectivity and capture diagnostics you can use to resolve transport setup failures. Use the JavaScript SDK PreflightTest for web apps and the Mobile SDK PreflightTest for native apps.