SIP Using Custom Headers

Forwarding a PSTN Call Into a Zero Runtime Room

When using Twilio as your SIP/PSTN provider, you may need to forward an incoming phone call into a specific Zero Runtime room.
This is useful when:

You want to route calls dynamically to different room IDs.
You don’t want to configure a fixed room inside Zero Runtime Routing Rules.

Twilio requires a webhook endpoint that returns TwiML, telling Twilio which SIP URI to dial. This SIP URI connects directly to the Zero Runtime SIP Gateway with the room ID appended as a query parameter.

Example: Node.js Express Webhook

Create a simple Express server that Twilio will call whenever someone dials your Twilio number.

const express = require("express");
const VoiceResponse = require("twilio").twiml.VoiceResponse;
const urlencoded = require("body-parser").urlencoded;

const app = express();
app.use(urlencoded({ extended: false }));

// This endpoint is called by Twilio on incoming PSTN call
app.post("/incoming-call-handler", (request, response) => {
  const twiml = new VoiceResponse();

  const dial = twiml.dial();

  // Replace roomId with the Zero Runtime room you want to route the call into
  const roomId = "your-room-id";

  // SIP address provided by Zero Runtime Inbound Gateway
  const sipUri = `sip:your_twilio_number@INBOUND_GATEWAY_ID?x-videosdk-room-id=${roomId}`;

  dial.sip({}, sipUri);

  response.type("text/xml");
  response.send(twiml.toString());
});

// Start server
app.listen(8000, () => {
  console.log("Server running on port 8000");
});

How It Works

Twilio receives an incoming call on your phone number, then it sends a webhook to your server for call instructions.
Your server responds with TwiML containing the SIP URI + room ID.
Twilio dials the Zero Runtime SIP Gateway, which connects the caller into the room.

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SIP Using Custom Headers

Forwarding a PSTN Call Into a Zero Runtime Room

Example: Node.js Express Webhook

How It Works

​Forwarding a PSTN Call Into a Zero Runtime Room

​Example: Node.js Express Webhook

​How It Works

Forwarding a PSTN Call Into a Zero Runtime Room

Example: Node.js Express Webhook

How It Works