STIR/SHAKEN: the operator's guide —
from a carrier that signs its own calls.
Most STIR/SHAKEN content online is written by consultants, resellers, or CPaaS platforms that don't hold their own certificate. SIPNEX is the actual licensed carrier signing your calls with its own SP-KI keys. Every section below is implementation, not theory.
What STIR/SHAKEN actually is.
STIR — Secure Telephony Identity Revisited — is the IETF framework for cryptographically signing caller ID information, specified in RFC 8224, RFC 8225, and RFC 8226.
SHAKEN — Signature-based Handling of Asserted information using toKENs — is the ATIS/SIP Forum implementation that actually delivers STIR over SIP trunks. When people say "STIR/SHAKEN" they usually mean the SHAKEN profile running on production carrier networks, which is what the FCC has mandated for US carriers since June 2021.
The goal is narrow: verify that the phone number shown on an outbound call belongs to a caller who has the right to use it. The originating carrier signs the call with a private key tied to its FCC-issued Service Provider certificate. The terminating carrier validates the signature and reads the attestation level the originator claimed. The phone then displays — or blocks — accordingly.
What STIR/SHAKEN is not: it's not a consent mechanism, not a do-not-call replacement, not TCPA compliance, not a magic box that makes answer rates go up regardless of who you're calling. It's one layer of a multi-layer trust system. Treating it as anything more is a mistake.
A, B, C: the three levels nobody explains clearly.
Every signed call carries an attestation level. Your answer rate depends on it. Here's what each level actually means — and which one SIPNEX delivers.
Full attestation
WHAT SIPNEX DELIVERSOriginating carrier has direct customer relationship AND verified the caller has authority to use the phone number.
Terminating carriers display 'Verified Caller' with a checkmark. Highest answer rates.
Partial attestation
Originating carrier has direct customer relationship but cannot verify phone number authority.
Neutral or unverified display. Measurable answer-rate drop vs A.
Gateway attestation
Originating carrier received the call from another network. Cannot attest to origin at all.
Frequently displayed as 'Scam Likely' or 'Potential Spam.' Significant answer-rate penalty.
The reseller ceiling is B-level, and nobody tells you.
Most "VoIP providers" you can buy a SIP trunk from are not carriers. They're resellers or CPaaS platforms sitting on top of an actual carrier. The call path looks like this:
The problem is that the upstream carrier signing the call has a relationship with the reseller — not with you. It doesn't know your business, doesn't know which numbers you're authorized to use, can't verify number authority on your behalf. So it signs at B-level — "I know my reseller customer, but I can't attest to their customer's phone number authority."
B-level is the ceiling for calls originated through a reseller. You can have perfect TCPA compliance, clean DNC scrubbing, legitimate consent — it doesn't matter. The signature will still say B because the carrier holding the pen doesn't have the information needed to sign A.
This is why most dialer operators report a mysterious answer-rate drift as their volume scales. It's not mysterious. It's the attestation ceiling catching up with their call patterns.
We hold the certificate. We sign your calls ourselves.
SIPNEX is the licensed carrier in the call path. Not a reseller wrapper. Not a CPaaS abstraction over someone else's trunk. Our name is on the FCC filing. Our private key is on the signature.
That means three things your current provider probably can't offer:
- Direct A-level attestation — Because the direct customer relationship is with you (not with a middleman), we can attest to your authority over the phone numbers you dial from.
- Direct RMD filing — We're in the Robocall Mitigation Database as a primary filer, not under an umbrella.
- Signature reputation we own — Our SP-KI reputation is ours to protect. We actively manage it. Bad actors don't last on our network because the reputational cost is on our company, not some distant upstream.
FCC Robocall Mitigation Database.
Every US carrier is required to be listed in the FCC's Robocall Mitigation Database with a filed robocall mitigation plan. SIPNEX is a direct filer. Our plan covers number authority verification, suspicious traffic detection, customer vetting, and incident response.
Read our mitigation approach →STIR/SHAKEN is not TCPA.
A-level attestation doesn't make your campaign TCPA-compliant, and TCPA compliance doesn't give you A-level attestation. They operate at different layers. You need both: the right carrier signing your calls, and your own policy for consent, DNC, and calling hours.
TCPA compliance guide →About STIR/SHAKEN implementation.
What is STIR/SHAKEN?
What does 'attestation level' mean?
What's the difference between A, B, and C level attestation?
Why does attestation level matter for my answer rate?
Does SIPNEX provide A-level attestation?
Do I need to file anything with the FCC as a SIPNEX customer?
How does STIR/SHAKEN interact with TCPA compliance?
What happens if I try to spoof caller ID on your network?
Stop accepting B-level as the ceiling.
If your current answer rate feels capped and you can't figure out why, the answer is usually in the attestation your carrier can give you. Move to a carrier that holds its own certificate. Move to SIPNEX.