Voice XML

SignalWire Compatibility XML is a set of actions defined in an XML document you can use to tell SignalWire what to do when you receive an incoming call or instructions for outbound calls.

When a call is made to one of your SignalWire phone numbers, SignalWire looks up the SignalWire Compatibility XML document from the URL you configured and reads the instructions you provided to determine what to do.

SignalWire Compatibility XML allows you to dynamically control what happens, responding with specific instructions based on the caller, time of day, incoming call, and much more.

info

Not making a call? Check out Messaging XML for more details.

Request for XML

SignalWire makes an HTTP request to your configured endpoint just like a regular web form submission (POST) or page load (GET). The request includes contextual information about the call, allowing you to respond dynamically and fluidly to the call to meet the needs of your application.

You can configure the endpoint URL and HTTP Method in your phone number settings panel on your SignalWire dashboard, or via the REST API.

Request Parameters

SignalWire sends the following parameters, as either URL query parameters or POST parameters, to your endpoint when it receives a call:

Parameter	Type
CallSid	string	A unique identifier for the call.
AccountSid	string	The unique ID of the Account this call is associated with.
From	string	The phone number that sent this call, in E.164 format.
To	string	The phone number of the call recipient, in E.164 format.
CallStatus	string	The status of the call. Can be one of the following values: ringing, in-progress, queued, failed, busy, no-answer, or completed.
ApiVersion	string	The version of the SignalWire API. Incoming calls use the API version placed on the number called. Outgoing calls use the version of the REST API request.
Direction	string	An identifier to describe the direction of the call: outbound-dial: calls launched through the <Dial> verb outbound-api: calls launched through the REST API inbound: for inbound calls
ParentCallSid	string	A unique identifier for the call that created this call.

CallStatus Values

The following are the possible CallStatus parameter values. These are also used in <Dial>'s DialCallStatus:

Value
ringing	The call is ringing.
in-progress	The call was answered and is in progress.
queued	The call is ready and in line to initiate.
failed	The call could not be completed. Usually occurs when phone number does not exist.
busy	The caller encountered a busy signal.
no-answer	The call ended without an answer.
completed	The call was answered and ended normally.
canceled	The REST API canceled the call while it was ringing or queued.

Responding to SignalWire

An example of a SignalWire Compatibility XML document that reads a message to the caller before playing an audio file:

XML

<?xml version="1.0" encoding="UTF-8"?>
<Response>
    <Say>Hello, World!</Say>
    <Play>https://your-application.com/audio.mp3</Play>
</Response>

JavaScript

const { RestClient } = require("@signalwire/compatibility-api");
const response = new RestClient.LaML.VoiceResponse();

response.say("Hello, World!");
response.play("https://your-application.com/audio.mp3");
console.log(response.toString());

PHP

<?php
  use SignalWire\LaML;
  $response = new LaML;

  $response->say('Hello, World!');
  $response->play('https://your-application.com/audio.mp3');
  echo $response;
?>

C#

using Twilio.TwiML;
using System;


class Example
{
    static void Main()
    {
        var response = new VoiceResponse();
        response.Say("Hello, World!");
        response.Play(new Uri("https://your-application.com/audio.mp3"));

        Console.WriteLine(response.ToString());;
    }
}

Python

from signalwire.voice_response import VoiceResponse, Say, Play

response = VoiceResponse()
response.say('Hello, World!')
response.play('https://your-application.com/audio.mp3')

print(response)

Ruby

require 'signalwire/sdk'

response = Signalwire::Sdk::VoiceResponse.new do |response|
  response.say(message: 'Hello World!')
  response.play(url: 'https://your-application.com/audio.mp3')
end

puts response.to_s

When a message comes into one of your SignalWire phone numbers, SignalWire makes an HTTP request to the URL endpoint you configured for that number. Your response to that request instructs SignalWire on what to do next.

Responses to the HTTP request are in SignalWire Compatibility XML. SignalWire starts at the top of your Compatibility XML document and executes your XML commands in order, from top to bottom.

tip

SignalWire Compatibility XML verbs and their attributes are case-sensitive, so using <play>instead of <Play> will result in an error.

Status Callbacks

SignalWire can send your application callbacks at various lifecycle stages of your call. Status callbacks do not allow you to change the application execution directly, so callbacks do not have to respond with SignalWire Compatibility XML, but they allow your application to get updates as a call is happening.

You should respond to any callbacks with a 200 OK or 204 No Content, otherwise you will see failures in your application log on SignalWire.

The StatusCallback request contains the Standard Request Parameters plus the following optional parameters:

Parameter	Type
ForwardedFrom	string	The number this call was forwarded from.
CallerName	string	The name of the caller. Only available if Caller ID lookup is enabled.
CallDuration	integer	The duration, in seconds, of the finished call. Only present on the completed event.
RecordingUrl	string	The URL of the recorded audio call.
RecordingSid	string	The unique identifier for the audio recording.
RecordingDuration	integer	The duration, in seconds, of the recording.
CallbackSource	string	The source of the status callback.
Timestamp	string	The timestamp, in RFC 2822 format, of when the event occurred.
SequenceNumber	integer	The order in which events occur. Starts at 0. Although events are fired in order, they each take time and may not appear in the order you expect.
AudioInMos	string	The mean opinion score that helps to determine audio quality. The scale is from 1-5 with 1 being worst and 5 being best.
HangupBy	string	A indicator of which number ended the call
HangupDirection	string	A indicator of which direction ended the call