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TwiMLTM Voice: Twilio's Request

How Twilio Passes Data to Your Application

Twilio makes HTTP requests to your application just like a regular web browser. By including parameters and values in its requests, Twilio sends data to your application that you can act upon before responding. You can configure the URLs and HTTP Methods Twilio uses to make its requests via the account portal or using the REST API.

Creating a Twilio Application within your account will allow you to more-easily configure the URLs you want Twilio to request when receiving a voice call to one of your phone numbers. Instead of assigning URLs directly to a phone number, you can assign them to an application and then assign that application to the phone number. This will allow you to pass around configuration between phone numbers without having to memorize or copy and paste URLs.

TwiML Voice Requests

When Twilio receives a call for one of your Twilio numbers it makes a synchronous HTTP request to the Voice URL configured for that number, and expects to receive TwiML in response. Twilio sends the following parameters with its request as POST parameters or URL query parameters, depending on which HTTP method you've configured:

Request Parameters

Parameter Description
CallSid A unique identifier for this call, generated by Twilio.
AccountSid Your Twilio account id. It is 34 characters long, and always starts with the letters AC.
From The phone number or client identifier of the party that initiated the call. Phone numbers are formatted with a '+' and country code, e.g. +16175551212 (E.164 format). Client identifiers begin with the client: URI scheme; for example, for a call from a client named 'tommy', the From parameter will be client:tommy.
To The phone number or client identifier of the called party. Phone numbers are formatted with a '+' and country code, e.g. +16175551212 (E.164 format). Client identifiers begin with the client: URI scheme; for example, for a call to a client named 'jenny', the To parameter will be client:jenny.
CallStatus A descriptive status for the call. The value is one of queued, ringing, in-progress, completed, busy, failed or no-answer. See the CallStatus section below for more details.
ApiVersion The version of the Twilio API used to handle this call. For incoming calls, this is determined by the API version set on the called number. For outgoing calls, this is the API version used by the outgoing call's REST API request.
Direction A string describing the direction of the call. inbound for inbound calls, outbound-api for calls initiated via the REST API or outbound-dial for calls initiated by a <Dial> verb.
ForwardedFrom This parameter is set only when Twilio receives a forwarded call, but its value depends on the caller's carrier including information when forwarding. Not all carriers support passing this information.
CallerName This parameter is set when the IncomingPhoneNumber that received the call has had its VoiceCallerIdLookup value set to true ($0.01 per look up).

Twilio also attempts to look up geographic data based on the 'To' and 'From' phone numbers. The following parameters are sent, if available:

Parameter Description
FromCity The city of the caller.
FromState The state or province of the caller.
FromZip The postal code of the caller.
FromCountry The country of the caller.
ToCity The city of the called party.
ToState The state or province of the called party.
ToZip The postal code of the called party.
ToCountry The country of the called party.

Depending on the what is happening on a call, other variables may also be sent. The individual TwiML verb sections have more details.

CallStatus Values

The following are the possible values for the 'CallStatus' parameter. These values also apply to the 'DialCallStatus' parameter, which is sent with requests to a <Dial> Verb's action URL.

Status Description
queued The call is ready and waiting in line before going out.
ringing The call is currently ringing.
in-progress The call was answered and is currently in progress.
completed The call was answered and has ended normally.
busy The caller received a busy signal.
failed The call could not be completed as dialed, most likely because the phone number was non-existent.
no-answer The call ended without being answered.
canceled The call was canceled via the REST API while queued or ringing.

Call End Callback (StatusCallback) Requests

After receiving a call, requesting TwiML from your app, processing it, and finally ending the call, Twilio will make an asynchronous HTTP request to the StatusCallback URL configured for the called Twilio number (if there is one). By providing a StatusCallback URL for your Twilio number and capturing this request you can determine when a call ends and receive information about the call.

Request Parameters

The parameters Twilio passes to your application in an asynchronous request to the StatusCallback URL include all those passed in a synchronous TwiML request.

The Status Callback request also passes these additional parameters:

Parameter Description
CallDuration The duration in seconds of the just-completed call.
RecordingUrl The URL of the phone call's recorded audio. This parameter is included only if Record=true is set on the REST API request, and does not include recordings from <Dial> or <Record>.
RecordingSid The unique id of the Recording from this call.
RecordingDuration The duration of the recorded audio (in seconds).

Data Formats

Phone Numbers

All phone numbers in requests from Twilio are in E.164 format if possible. For example, (415) 555-4345 would come through as '+14155554345'. However, there are occasionally cases where Twilio cannot normalize an incoming caller ID to E.164. In these situations Twilio will report the raw caller ID string.

Dates & Times

All dates and times in requests from Twilio are GMT in RFC 2822 format. For example, 6:13 PM PDT on August 19th, 2010 would be 'Fri, 20 Aug 2010 01:13:42 +0000'