The "Privacy" header is originally defined in RFC 3323, and was later extended in RFC 3325 and RFC 4244. An explanatory memo is available at RFC 5379. I highly recommend reviewing the explanatory memo if you're unclear on the purpose of the Privacy header. The purpose of this article is to document VoicePulse's treatment of the Privacy header on the FIVE platform.
The privacy value "id" is defined in RFC 3325, and is used to indicate that the "P-Asserted-Id" header should be deleted as requests cross trust boundaries. Whenever you send us a request (i.e. INVITE) and we complete the request by creating a PSTN phone call or forwarding it to an off-net SIP domain, we consider that to be "crossing a trust boundary." Consequently, in those situations, we remove the P-Asserted-Id header.
For PSTN calls, this means the information in the From: header of your request will be used as the caller-id number. By default, the username portion of the From: header is used:
The part highlighted in green is the username portion of the From header. For outbound calls to the PSTN, it must be a valid 10-digit phone number (or 10 zeros if you wish the caller-ID to be blocked) in order to be displayed properly.