Overview

Caller ID Number (CID) is a service that displays your phone number to the phone of the individual you are calling on an outbound call. Telnyx upholds a strict policy around the handling of Caller ID Numbers for outbound calls. 

All outbound calls with Caller ID Numbers that are not valid will be rejected with a SIP response code of “403 Caller Origination Number is Invalid D35”.


Supported Number Formats:

If the Connection’s Localization Country is set then the following formats will be accepted:

  1. National format of the country selected (i.e. Localization Country: USA, Number: 3129457420)
  2. +E.164 format (i.e. +13129457420)

If the Connection’s Localization Country is not set then the following formats will be accepted:

  1. +E.164 format (i.e. U.K. number: +441234567890)
  2. E.164 format (i.e. U.K. number: 441234567890)
  3. National format will only work if it is a U.S or U.K nationally formatted number

If the Connection’s Caller ID Override is set and used for an outbound call

  1. Send any format if you setup override in your Connection's Outbound settings.

How Telnyx handles the Caller ID Number:

  • The Localization Country can be set through the Telnyx Mission Control Portal under the Connection's Outbound Settings.
  • If a Connection does not have a Localization Country and the number dialed appears to be invalid, Telnyx will attempt to validate the number using USA as the Localization Country.
  • If the previous check failed, Telnyx will return a 404 invalid destination response.

Which headers from the SIP INVITE can carry the Caller ID Number?

Below listed is the following SIP headers that are accepted for Caller ID, ordered by priority (1 highest and 4 lowest priority)

1. P-Preferred-Identity User
2. P-Asserted-Identity User
3. Remote-Party-Id User
4. FROM User

In the case that more than one header is provided the highest priority header is followed.

How to Anonymize Caller ID Number 

The following SIP header needs to be provided along with a caller ID that obeys the specifications described in the two points above.

Privacy: id

As well as the above, you need to ensure that the user@domain parts of the URI's in any of the above SIP headers contain "anonymous". If any caller ID header exists with the user or domain part of the SIP URI without "anonymous", calls will be rejected with 403 Caller Origination Number is Invalid D35

Good Examples:

The display name including user/domain of the SIP URI are all anonymized

From: "Anonymous" <sip:anonymous@anonymous.invalid>;tag=12345-6789
P-Asserted-Identity: "Anonymous" <sip:anonymous@anonymous.invalid>
P-Preferred-Identity: "Anonymous" <sip:anonymous@anonymous.invalid>

Bad Examples:

Where the users name or IP/domain is exposed and not anonymized

From: "Anonymous" <sip:john@12.13.14.15>;tag=12345-6789
P-Asserted-Identity: "Anonymous" <sip:anonymous@12.13.14.15>
P-Preferred-Identity: "Anonymous" <sip:john@anonymous.invalid>

Where the display name is exposed and not anonymized

From: "John" <sip:anonymous@anonymous.invalid>;tag=12345-6789
P-Asserted-Identity: "John" <sip:anonymous@anonymous.invalid>
P-Preferred-Identity: "John" <sip:anonymous@anonymous.invalid>


Note: The Caller ID of an outbound call will be anonymized downstream as the "Privacy: id" SIP Header is present. 

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