API Call Markup Language

The API Call Markup Language (ACML) represents a set of instructions you can use to tell the Call API what to do when you receive an incoming call.
When someone makes a call to one of your Call API numbers, the service will look up the URL associated with that phone number and make a request to that URL. The Call API will read the markup instructions at that URL to determine what to do: record the call, play a message for the caller, prompt the caller to press digits on their keypad, etc.
An an example, the following will say a short message, and then record the caller’s voice:
<?xml version="1.0" encoding="UTF-8"?>
<Say voice="woman">Please leave a message after the tone.</Say>
<Record maxLength="20" />
ACML is similar to HTML. Only one ACML document is rendered to the caller at once, but many documents can be linked together to build complex interactive voice applications.
Calls from a Call API number to an outside number are controlled using ACML in the same manner as incoming calls. The initial URL for the call is provided as a parameter to the Call API request you make to initiate the call.

How the Call APIs Interacts with Your Application

Call API Request

The way the Call API passes data to your application depends on the request method for the given URI. If the request method is GET then the data is passed in the query string (the part after the question mark). If the request method is POST then the data is sent as multi-part form data just like when a browser submits a form.
When the Call API makes a request to your application it will include the following data as request parameters.

Request Parameters

The unique identifier for the call.
Your account id.
The phone number of the originator of the call.
The phone number of the call recipient.
The status of the call. Possible values are queued, ringing, in-progress, completed, busy, failed, and no-answer.
The version of the Call API used to handle this call.
The direction of the call. The possible values are inbound and outbound-dial.
The caller ID for the caller in the case of an inbound call.

Call API Response

In the response to the request from the Call API, you should provide ACML that will instruct our service on how to handle the current call.
MIME Types. Call API supports the MIME types described in the table below.

Supported MIME Types

text/xml, application/xml
Call API interprets the returned document as an XML instruction set.
When your application returns the ACML document the root element of the document must always be specified or the parser will complain.

The Markup Verbs

Using combinations of the verbs below allow you to create all kinds of interactive voice and messaging applications.
  • Say Say some words with text to speech
  • Dial Call someone else, a phone number or other
  • Play Play a wav or mp3 file to the caller
  • Gather Gather digits or words and send them back to your server
  • Record Record the current call
  • Message Send a text message
  • Hangup Hangup on the call
  • Pause Pause the call for a moment (maybe to wait for digits)
  • Reject Reject this call
  • Redirect Redirect this call to another URL
  • Email Send an email with data
References to ACML, RCML or CML are all the same.