What Is STIR/SHAKEN? Why Calls Get Marked 'Spam Likely'

STIR/SHAKEN is a pair of standards (Secure Telephone Identity Revisited and Signature-based Handling of Asserted information using toKENs) that US carriers use to cryptographically sign calls and verify that the caller ID was not spoofed. It was mandated by the FCC under the TRACED Act to fight robocall spoofing. Every call you place now carries a digital signature that receiving carriers check before deciding how to present your call.

A, B, and C attestation

The signature carries an attestation level. A (full): the carrier knows the customer and confirms they own the number. B (partial): the carrier knows the customer but cannot confirm the number. C (gateway): the carrier is just passing the call along. Calls with weak attestation are far more likely to be labeled "Spam Likely" or silently down-ranked, even when the caller is a legitimate business.

Why good businesses still get flagged

Resold or discount routes often deliver B or C attestation, and analytics engines at the big carriers add their own scoring on top. If customers are not answering, this is the first thing to check. Cannon VoIP signs calls at full attestation from our own switching core, and you can hear the proof: our free attestation test line reads back exactly what your current calls carry.

The step beyond clean attestation is Branded Calling, which puts your verified business name and logo on the recipient's screen instead of a bare number. Attestation keeps you off the spam list; branding gets you answered. Our spam protection overview covers both directions.

How the signing actually works

When you place a call, your originating carrier creates a small cryptographic token asserting the caller ID and its confidence in it, signs it with a certificate issued under the industry's certificate authority system, and attaches it to the call. The terminating carrier verifies the signature, confirms the certificate is valid, and feeds the result, along with its own analytics, into the decision of how to display your call. The whole exchange happens in the call setup, invisibly, on every call.

What STIR/SHAKEN does not do

It authenticates the number, not the intent: a scammer calling from a number they legitimately control gets a valid signature. That is why carriers layer analytics engines on top, reputation scoring based on call volume, patterns, and complaint history. It means two things for a business: clean attestation is necessary but not sufficient, and calling behavior (volume spikes, short-duration bursts) can still earn labels even with perfect signing.

A checklist for staying trusted

• Verify your current standing: dial our free test line at (817) 973-1573 and hear your attestation, labeling, and presented caller ID read back.
• Use a provider that signs at full A-level attestation from its own switching core, not a resold route.
• Register your outbound numbers and business name with the major carriers' registries, and keep caller ID name (CNAM) consistent.
• Watch calling patterns: sudden volume spikes from one number look like spam to analytics even when legitimate. Spread predictable campaigns across time.
• For the strongest presentation, add Branded Calling, verified name and logo on the screen instead of a bare number.