Caller ID Verification In Heterogeneous Telecommunication Networks

This document defines an extension to the INVITE header of the Session Initiation Protocol (SIP) to support a Caller ID Verification (CIV) method. CIV authenticates the caller ID of an incoming call through a challenge-and-response process across both IP and non-IP networks without requiring a trusted third party or a public key infrastructure. When receiving a call with a claimed phone number, the called party holds the call and sends a quickly terminated INVITE request (like a flash call) to that number, carrying a short 4-digit challenge embedded as part of the caller ID. A genuine caller would receive the challenge and respond by echoing the same digits, e.g., through DTMF (Dual-Tone Multi-Frequency). The proposed extension involves two changes to the INVITE header. First, it adds a new option tag, "civ", in the Supported header field of the INVITE request. This tag allows the calling party to indicate support for CIV in the initial call. Second, it adds a special value "civ-veri- call" for the Purpose parameter of the Call-Info header field. This value allows the called party to make a verification call, indicating the purpose of the call is to transmit a challenge rather than establish a phone conversation. CIV uses the standard Session-ID header in the INVITE request to allow the calling party to explicitly match the verification call with the initial call. Whilst this document focuses on IP networks, the same CIV protocol also works with non-IP networks (e.g., SS7) by including the "civ" tag, the "civ-veri-call" value and the session ID in the User-to-User Information (UUI) parameter.