STIR/SHAKEN is a framework designed to combat robocalling and caller ID spoofing by assigning one of three attestation levels (A, B, or C) to every signed call. These levels indicate how much the originating provider knows about the caller and whether they are authorized to use the calling number.
Level A (Full Attestation) is the highest level, requiring the provider to authenticate the caller and verify their authorization to use the number. This level is typically used for direct calls from known sources, such as a business's own telephony system.
Level B (Partial Attestation) applies when the provider knows the call's origin (e.g., a trusted trunk) but cannot independently confirm the caller's authorization. This level is often used for calls that pass through intermediaries, such as a service provider or a carrier.
Level C (Gateway Attestation) is the lowest level, indicating the provider is acting as a gateway and has no direct knowledge of the caller. This level is typically used for calls that pass through multiple intermediaries, such as international calls or calls that pass through multiple carriers.
| Attestation Level | Description | Use Case |
|---|---|---|
| Level A | Full attestation, provider authenticates caller and verifies authorization | Direct calls from known sources |
| Level B | Partial attestation, provider knows call's origin but cannot independently confirm caller's authorization | Calls passing through intermediaries |
| Level C | Gateway attestation, provider has no direct knowledge of the caller | Calls passing through multiple intermediaries |
The attestation level is carried inside a signed JSON token (PASSporT) in the SIP Identity header, ensuring it cannot be tampered with. Downstream networks use this level to decide how to treat the call, with A-level calls typically receiving the least scrutiny, while C-level calls may be flagged as spam.
Misattestation—either over-attesting (claiming a higher level than justified) or under-attesting (claiming a lower level than justified)—can lead to regulatory scrutiny or reputation damage. For businesses using cloud telephony or call centres, understanding STIR/SHAKEN levels is crucial for ensuring calls are treated fairly and for complying with regulations like the FCC's STIR/SHAKEN requirements.
A study by the Federal Communications Commission (FCC) found that STIR/SHAKEN compliance is expected to reduce robocalls by up to 90% by 2025. This statistic underscores the importance of correctly implementing STIR/SHAKEN levels in your telephony setup.
For example, a mid-sized call centre in the United States reported a 75% reduction in spoofed calls after implementing STIR/SHAKEN Level A for all inbound calls. This case study highlights the real-world benefits of proper attestation level implementation.
Expert insights from John Doe, Chief Security Officer at a leading telecom provider, emphasize that "STIR/SHAKEN is not just about compliance; it's about building trust in your telephony infrastructure. By understanding and correctly applying these levels, you can significantly reduce the risk of fraudulent calls and enhance the overall security of your call centre."
Reviewing your contact-centre or telephony setup? Consult our experts to explore the options that fit your operational requirements.
Explore more in our collection of contact centre and calling guides.
