SHAKEN/STIR has a three-level system to categorize the essential information about the caller into levels of “attestation” for the call. The different levels describe the level of trust a provider has in the caller’s right to use that number, with attestation levels ranging from 'A' to 'C'.
Full Attestation (A) — The calling party is authorized to use the calling number. An example of this case is a subscriber registered with the Cloudli services directly.
Partial Attestation (B) — The call originator is authenticated but unable to verify if 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 call is received from an authorized party, but the call source is not authenticated. An example of this case would be a call received from other carriers.