SIP reference
A focused reference to the SIP headers that decide whether a call is trusted, signed, downgraded or blocked at the edge of your network.
INVITEThe Request-URI names the called party, and the body usually carries SDP for negotiating media. Every fraud and compliance decision VoIP Radar makes is anchored to an INVITE.
INVITE sip:+12025550148@carrier.example SIP/2.0FromThe logical originator of the call as stated by the sender. On IP networks it is trivially set to anything, so it should never be trusted on its own.
From: <sip:+13055550199@pbx.example>;tag=8a7c1P-Asserted-IdentityThe caller identity asserted by a trusted network element. Used inside and between carriers for billing, routing and as the basis for STIR/SHAKEN signing.
P-Asserted-Identity: <sip:+13055550199@carrier.example>IdentityCarries the signed PASSporT (RFC 8224/8225/8588) that binds the calling number, called number and attestation level to the originating provider's certificate.
Identity: eyJhbGciOiJFUzI1NiIs...;info=<https://cert.example/sp.pem>;alg=ES256;ppt=shakenDiversion / History-InfoRecord how a call has been forwarded or redirected. Useful for reconstructing call paths, handling forwarded calls' attestation and spotting loops or laundering.
ContactThe direct SIP URI for reaching the device or server. Fraud tooling checks it for suspicious IP ranges, unexpected hosts and unregistered endpoints.
User-AgentIdentifies the device or software sending the request. It can be faked, but known scanner and auto-dialer signatures are still a useful signal.
Reason / Call-InfoExplain rejections and provide extra information — for example a redress contact returned with SIP 608 so a legitimate caller can dispute a block.
VoIP Radar reads every INVITE as it arrives and cross-checks From, P-Asserted-Identity and Identity against the customer's KYC record, number inventory, STIR/SHAKEN verification result and behavioral history. The result decides whether a call is signed (and at what level), downgraded, tagged or rejected — with the reasoning stored for audit.
Get in touch
Tell us about your switch and traffic. A VoIP Radar engineer will map your STIR/SHAKEN, RMD and fraud exposure and send a written assessment — free, within one business day.