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Julia Biro for Vonage

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Build a Conference Call with Node-RED

In previous tutorials you’ve had a chance to get your feet wet in the world of Nexmo APIs, making and receiving phone calls using the Voice API, and hopefully also customizing these experiences.

In today’s tutorial, we’ll take it a step further and build a voice-based conferencing service.

The user calls a predefined virtual number and inputs a meeting ID using the dial pad, then they get placed in the same conference call with everyone else who has provided the same ID.


  1. Prerequisites
  2. Expose Your Local Server to the Internet
  3. Define the Webhook Endpoint for Inbound Calls
  4. Define the Webhook Endpoint for the Input Event
  5. Create a Nexmo Voice Application
  6. Set Up a Number to Call
  7. Handle Your Call Events
  8. Try it out!


Before getting started, you’ll need a few things:

Getting Your Credentials

To interact with the Voice API, you’ll need to make note of a couple of things. Once you’ve created a Nexmo account, go to the dashboard to find your API key and secret.

Next, you’ll need a Voice-enabled virtual number. Go to Numbers > Buy numbers to get one.

Setting Up Your Node-RED Editor

First, you’ll need to install the runtime and editor. This could be done either on your local machine, on a Single Board Computer (eg. Raspberry Pi), or through several cloud-hosted options. This example will be using your local machine, so once you’ve installed Node-RED globally, type the command below in your terminal to get started.

$ node-red
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You can then access the Node-RED editor by pointing your browser at http://localhost:1880.

Once you have your editor open, you’ll need to install the Nexmo nodes. You can do so under the Manage palette menu, by searching for the node-red-contrib-nexmo package and clicking install.

Now you should see all of the Nexmo nodes appear on the left side of your screen—in your node palette, among other default nodes.

Expose Your Local Server to the Internet

The Nexmo API will need access to this webhook to make calls against it, so let’s make the URL accessible over the public internet. If you’re running Node-RED on a public web server instead of your local machine, you’re all set and ready to move on to the Create a Nexmo Voice Application step.

Otherwise, a convenient way to do this is by using a tunneling service like ngrok.

First, you’ll need to install the ngrok node. To do so, open up Manage palette from the hamburger menu in your Node-RED editor, search for the node-red-contrib-ngrok package, and click install. After restarting your editor, the ngrok node should appear in the node palette.

The ngrok node takes the strings on or off as input to start/stop the tunnel, and outputs the ngrok host address as the msg.payload.

The easiest way to set this up is to wire two inject nodes as the ngrok node’s input, one with the payload of the string on and the other with off. For easier use, you could also set the Name of these nodes accordingly in the node properties, so that it’s clear what functionality they have. Next, to display the host address in the debug sidebar, connect a debug node after ngrok.

As the last step before hitting Deploy, open up the ngrok node properties and specify the port number. In case of Node-RED, the default value is 1880. The default ngrok Region is US but you can also set it to Europe or Asia. You can also add your authtoken for your ngrok account if you have one. Don’t worry if you don’t, just skip this step for now. The node will warn that it is not fully configured but this is not an issue.

And you’re all set! Once you hit Deploy and click on the on inject node’s button, navigate to the URL displayed in the debug area (YOUR_URL for future reference) to find your Node-RED editor at a public address.

Define the Webhook Endpoint for Inbound Calls

Nexmo calls are controlled using Nexmo Call Control Objects, also known as NCCOs. An NCCO defines a list of actions to be followed when a call is handled. There are lots of different actions available; find the corresponding nodes under the Nexmo palette in your Node-RED editor or check out the NCCO Reference to find out more about them.

When handling inbound calls, you need your NCCO hosted at an Answer URL. In this case, we’ll be using a talk action to ask tor the meeting ID, then an input action to collect it.

Add a voice webhook input node to your canvas, followed by a talk node, an input node and a return NCCO output node.

Next, in the voice webhook node, select GET as a Method and type /answer in the answer URL field.

In the talk node properties set the Text{} field to the message you’d like to be read out when the call is answered. E.g. “Please enter the meeting ID”. You can also select a Voice Name, see the Text to Speech Guide for the full list of options.

Finally open the input node editor, set YOUR_URL/input as the URL {} and POST as a Method.

At this time you could also set a couple of other parameters to further customize the experience:

Name Description
Submit On Hash: Set to true so the caller’s activity is sent to your webhook endpoint at YOUR_URL/input after they press #. If # is not pressed the result is submitted after Time Out seconds. The default value is false.
Time Out: The result of the caller’s activity is sent to the YOUR_URL/input webhook endpoint Time Out seconds after the last action. The default value is 3. Max is 10.
Max Digits: The number of digits the user can press. The maximum value is 20, the default is 4 digits.

Find out more about these in the NCCO Reference.

Define the Webhook Endpoint for the Input Event

You’ll also need a second endpoint to capture the DTMF input from the user, and based on the code they have submitted, place them into a conversation.

Add another voice webhook input node to your canvas, followed by a talk node, a conversation node and a return NCCO output node.

voice webhook

In the voice webhook node properties, select POST as a method and type /input in the answer URL field.

If you were to connect a debug node after it, after finishing and running the flow, you would see the parameters returned to the /input URL:

Name Description
uuid The unique ID of the Call leg for the user initiating the input.
conversation_uuid The unique ID for this conversation.
timed_out Returns true if this input timed out based on the value of Time Out.
dtmf The numbers input by your caller, in order.

In our use case, we are trying to get the dtmf value, as this is the meeting ID provided by the caller.

Having a closer look at the debug sidebar on completions, we can see that it’s going to be in the dtmf property of the call object nested inside the msg object, so we can reference it as {{}} in the other nodes of this path.


Next, open up the talk node editor and set the Text{} field to the message you’d like to be read out once the caller inputs the meeting ID.

Note the {} sign next to the Text label, showing that this value can be set dynamically, using Mustache templating, so you could go with something like Joining meeting {{}}.

Feel free to further personalize the experience by selecting a Voice Name or by making use of SSML tags


We’re using the conversation action to create a standard conference, so the only parameter we have to set is Name {}. Using the conversation action with the same name reuses the same persisted Conversation, so it’s handy to name it after the meeting ID, referencing {{}} The first person to call the virtual number assigned to the conversation creates it.

In the future, you might want to take this a step further and create a moderated Conversation with selective audio controls. Check out the NCCO reference to find out more.

Once you’re done with this path, it should look similar to this:

Create a Nexmo Voice Application

Some of Nexmo’s APIs, including the Voice API, use Nexmo Applications to hold security and config information needed to connect to Nexmo endpoints.

In the Nexmo Node-RED palette, several nodes have the capability to create these applications: getrecording, earmuff, mute, hangup, transfer, createcall, playaudio, playtts and playdtmf.

Drag any of these nodes into your workspace, then double-click on it to open up the node properties.

Next to the Nexmo Credentials, select “Add new nexmovoiceapp…” from the drop-down menu and click the edit button. Fill in the details below and click Create New Application.

Name Choose a name for your Voice Application, for example Conference Call.
API Key Your Nexmo API key, shown in your account overview.
API Secret Your Nexmo API secret, shown in your account overview.
Answer URL YOUR_URL/answer, you’ll be hosting a Nexmo Call Control Object (NCCO) here. – more about this later on.
Event URL YOUR_URL/event, you’ll need to reference this when setting up the event handler.

Node-RED will then create a new Nexmo Application on your account and fill in the App ID and Private Key fields for you to save. After this step, feel free to delete the Nexmo node you used, as a nexmovoiceapp config node has been created, and that contains all the Nexmo credentials this flow needs.

Set Up a Number to Call

Next, you’ll have to link your virtual number to this application.

Find the Voice Application you’ve just created in your Nexmo Dashboard by navigating to Voice > Your Applications.

Click on the name of this application, then under the Numbers tab click on the Link button next to the virtual number you’ve rented earlier.

In case the number you’d like to use is already linked to another app, click on Manage number and configure it to forward incoming calls to your app.

Bonus tip: Use a comment node to take note of the Nexmo number linked to your application, this way you always have it handy.

Handle Your Call Events

If you’d like to receive events about the progress of your call, you can also set up an event webhook.

Connect an http input node to an http response node, as well as to a debug node, so that you can view your call events in the debug area.

In the http input node, select POST as a Method and fill in the URL field with /event.

The http response node should have 200 set as Status code, but don’t worry about it; this is the default value as well.

Try it Out!

And that’s a wrap! Get a friend or more and take it for a spin! Don’t forget to take a peek in the debug area to follow your call events. Enjoy!

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