Attestation Levels of Stir/Shaken calls

Full Attestation (A) — The service provider has authenticated the calling party and they are authorized to use the calling number. An example of this case is a subscriber registered with the originating telephone service provider’s softswitch.

Partial Attestation (B) — The service provider has authenticated the call origination, but cannot verify the call source is authorized to use the calling number. An example of this use case is a telephone number behind an enterprise PBX.

Gateway Attestation (C) — The service provider has authenticated from where it received the call, but cannot authenticate the call source. An example of this case would be a call received from an international gateway.