Voice app components

Your Voice app interacts with the Voice API to securely create, receive and control Voice communication with your users.

The components in a Voice app are:

VAPI Architecture

  • Outbound - this component:
    • Generates JSON Web Tokens (JWTs) using the private_key allocated to your Voice app
    • Makes requests to Voice API to create calls to one or more users
    • From webhook endpoints, provides the Nexmo Call Control Objects (NCCO) to control the calls
    • Customizes live calls following user interaction using the Voice API and NCCOs
  • Inbound - From webhook endpoints, provides the NCCOs that handle inbound calls to and conferences hosted on the virtual number associated with this app
  • Status - a webhook endpoint that handles the progression of a live call and downloads recordings when the call status is complete

Your Voice app components communicate with one or more users in either a:

  • Conversation - a collection of one or more Calls. From an inbound text-to-speech message to a company conference call. The audio is a mix of all legs connected to the Conversation.
  • Call - a single leg connected to a Conversation. The audio in a Call consists of transmitted audio (Tx) and received audio (Rx). You use a Call to communicate between two end points.

A Conversation and the legs connected to it are identified by separate UUIDs (Universally Unique IDentifiers). This means you can manipulate Conversations and legs independently. For example, you can move a leg from one Conversation to another.

The following figure shows the components for a private voice communication system:

Voice API Call

Using the Voice API or NCCOs you can:

Action NCCO API
Connect to a phone number. connect POST https://api.nexmo.com/v1/calls
Record your Call. record  
Create a standard or moderated conference. conversation  
Send synthesized speech to a Call or Conversation. talk PUT https://api.nexmo.com/v1/calls/{uuid}/talk
Send an audio stream to a Call or Conversation. stream  
Collect digits input by the person you are calling. input  
Send dual-tone multi-frequency signalling (DTMF) tones to an active call   PUT https://api.nexmo.com/v1/calls/{uuid}/dtmf