STIR/SHAKEN is a call authentication framework mandated by the FCC and deployed across North American carriers. Its purpose is to reduce caller ID spoofing by cryptographically verifying that the entity making a call has the right to use the number it is calling from.
For most consumers, it surfaces as a small checkmark or "Caller Verified" indicator on a phone screen. For outbound voice operations, it is a compliance requirement, a performance variable, and increasingly a factor in whether calls reach consumers at all.
What the Terms Mean
STIR stands for Secure Telephone Identity Revisited. SHAKEN stands for Signature-based Handling of Asserted information using toKENs. Together they define the protocol by which carriers sign outbound calls with a digital certificate and pass that certificate through the call signaling so downstream carriers can verify it.
When your call leaves your system, the originating carrier attaches a PASSporT — a digitally signed token — to the SIP INVITE. The token contains the calling number, the called number, a timestamp, and an attestation level. Downstream carriers and analytics engines read that token and use it as one factor in evaluating the call.
The attestation level is where most of the practical impact lives.
The Three Attestation Levels
A-level attestation — Full Attestation — means the carrier can verify that the calling party is authorized to use the number, and that the number is a legitimate phone number associated with that customer. This is the strongest signal. It tells the receiving carrier: we know who is calling, we know they own this number, and we have verified both.
B-level attestation — Partial Attestation — means the carrier has verified the call originated from a specific customer, but cannot confirm the customer is authorized to use that specific calling number. This happens commonly when a business is calling from a number that was not directly provisioned through the originating carrier.
C-level attestation — Gateway Attestation — means the call was received from an upstream carrier that did not provide full attestation. The originating carrier cannot verify the source at all. This is the weakest signal and the highest risk profile in the eyes of downstream analytics engines.
The practical difference between A and C attestation is meaningful. Carriers and analytics engines treat low-attestation calls with more scrutiny. On some networks, calls with C-level attestation face elevated termination rates. Number reputation models factor attestation level into their scoring. A number with good call behavior but weak attestation is at higher risk than it should be.
Why Attestation Level Is Not Automatic
Many organizations assume that if their carrier is STIR/SHAKEN compliant, their calls are getting A-level attestation. This is not always true.
Attestation level depends on how your number inventory is provisioned and the relationship between your numbers and your originating carrier. If your numbers were ported from another carrier and the provisioning records have not been fully updated, the originating carrier may not be able to confirm authorization — resulting in B-level attestation even though you legitimately own the numbers.
Calls that route through intermediate carriers — common in complex enterprise voice architectures or hosted contact center environments — may lose attestation level as they traverse the network. What started as an A-level call from the originating carrier may arrive at the destination as B or C if an intermediate carrier does not properly pass the attestation chain.
Multi-carrier environments are particularly susceptible to this. An outbound operation running traffic through multiple carriers simultaneously may have strong attestation on one path and weak attestation on another without knowing it, because the visibility requires carrier-layer instrumentation.
What This Means for Outbound Operations
For collections, financial services, and other high-volume outbound environments, STIR/SHAKEN attestation is a direct performance variable. Every call is being evaluated by Hiya, First Orion, TNS, and the receiving carrier's own systems. Attestation level is one of the inputs to that evaluation.
An operation running at scale with inconsistent attestation is leaving answer rate on the table. The calls are going out. The infrastructure looks healthy from the inside. But at the carrier layer, a portion of the traffic is being treated with elevated suspicion because the authentication signal is weak.
Monitoring STIR/SHAKEN attestation rates in real time — by carrier, by number pool, by campaign — is part of the same carrier-layer visibility that surfaces 487 rates and early media anomalies. These signals are all generated in the same layer of the network. Operations that can see that layer operate with fundamentally better information than those that cannot.
The Bottom Line
STIR/SHAKEN is not a checkbox compliance item. It is an active performance variable in every outbound call you make. A-level attestation is the standard to aim for, and achieving it consistently requires correct number provisioning, clean carrier routing chains, and real-time monitoring to catch degradation before it affects contact rates.
If you do not know your attestation rate by carrier, you do not have full visibility into your outbound voice performance.
