What is STIR/SHAKEN?
STIR/SHAKEN is a set of standards used by US voice carriers to authenticate caller ID and reduce spoofed calls. STIR defines how to create a digital signature for a call. SHAKEN defines how that signature is used and verified in IP networks. When a call is placed over SIP, the originating provider signs the call with an Identity header that includes the caller ID, timestamp, and an attestation level. Downstream carriers validate the signature against trusted certificates before deciding how to present or treat the call.
In practice, STIR/SHAKEN creates a chain of trust in the caller ID. If a carrier can verify that the caller ID was not altered in transit and that the originating provider has vetted the caller, the call is more likely to pass through without labeling or blocking.
Attestation levels explained
Every signed call includes an attestation that reflects the originating provider’s confidence in the caller’s right to use the number:
- A Attestation: The provider has verified the caller’s identity and that the caller is authorized to use the specific calling number.
- B Attestation: The provider knows the caller but cannot verify that they are authorized to use the specific calling number.
- C Attestation: The provider is simply passing through the call as a gateway and has not verified the caller or the number.
Calls with A attestation generally see better completion and fewer labels than B or C. However, attestation alone does not guarantee delivery. Analytics engines still assess calling patterns, reputation, and consumer feedback.
Why do US calls get blocked or labeled?
Carriers and analytics services use multiple signals to protect subscribers. The combination of STIR/SHAKEN verification and reputation scoring drives most stir shaken call blocking outcomes. Common reasons include:
- No or invalid STIR/SHAKEN signature: Unsigned or failed-verification calls are more likely to be flagged, especially on mobile networks.
- Low attestation: B or C attestation can trigger labeling or stricter scrutiny.
- Poor number reputation: High consumer complaints, negative feedback, or repeated ignored calls degrade a number’s score over time.
- Calling pattern anomalies: Very high call volumes, short call duration outliers, rapid redialing, or concentrated bursts to the same rate centers can look like unwanted traffic.
- Mismatched or unassigned caller ID: Using numbers not assigned to your business, wrong format, or invalid CNAM can cause policies to kick in.
- Neighbor spoofing behavior: Rotating local-looking numbers or area code matching patterns increases suspicion.
- Regulatory flags: DNC violations, illegal prerecorded campaigns without consent, and certain lead-generation practices draw enforcement and network-level mitigation.
- Cross-border ingress: Internationally originated calls may lose identity headers or fail verification if the chain of trust breaks before reaching the US network.
What STIR/SHAKEN does not do
It is important to set expectations. STIR/SHAKEN authenticates caller ID. It does not make a campaign compliant, guarantee delivery, or override spam analytics. A fully verified call with A attestation can still be labeled if call behavior or consumer feedback suggests it is unwanted.
How to improve call completion under stir shaken call blocking
For BPOs, call centers, and VoIP resellers, consistent process and clean signaling matter. The steps below reduce friction across the major US networks:
- Use numbers you control: Obtain DIDs from a reputable carrier and assign them directly to your business. Keep clear records of number ownership and use cases.
- Seek A attestation: Work with a provider that can sign your traffic and attest A when you originate calls using numbers assigned to you and your identity has been verified.
- Register caller IDs with analytics registries: Many mobile carriers and analytics firms offer free business number registries. Register your brands, use cases, and phone numbers to improve labeling outcomes.
- Maintain correct caller ID formatting: Present E.164 where required. Do not present blocked or anonymous caller ID for routine outreach.
- Stabilize call patterns: Avoid aggressive redials, extreme short calls, or sudden spikes. Pace campaigns, align call windows with local time, and throttle new lists.
- Keep CNAM and business data accurate: Update listings and business names associated with your numbers so consumers see consistent identity when supported.
- Separate use cases: Use distinct numbers for sales, service, and billing to build appropriate reputation by line of business. Do not rotate numbers excessively.
- Honor consent and opt-outs: Maintain clear records of consent for automated or prerecorded content, scrub against DNC where applicable, and offer easy opt-outs.
- Monitor reputation: Track answer rates, complaint signals, and labeling feedback. Replace numbers that accumulate negative reputation and investigate root causes.
- Test and measure: Place control calls to major destinations, verify display, and check verification status in SIP headers. Adjust routing if signatures are being stripped.
How TalkTelX helps
TalkTelX is a US-registered VoIP carrier, FCC RMD-listed and STI-PA authorized. We provide US and Canada termination, inbound origination, and US DIDs with prepaid, per-second billing. For outbound traffic, we support STIR/SHAKEN signing and attestation aligned with industry requirements. When you originate calls using DIDs assigned by TalkTelX and complete standard vetting, we can apply the appropriate attestation level for your traffic. We also help ensure your SIP signaling is clean so identity headers survive downstream and verification succeeds where supported.
Our team works with call centers and VoIP resellers to implement practical measures that improve call completion without overpromising. That includes guidance on number assignment hygiene, caller ID presentation, and campaign pacing. We can review sample SIP traces, suggest routing options, and recommend steps to register your brands and numbers with recognized analytics registries.
Key takeaways
- STIR/SHAKEN verifies caller ID using signed SIP Identity headers and certificates.
- Attestation levels A, B, and C reflect how well your provider can verify your identity and number authorization.
- Stir shaken call blocking is driven by a mix of signature validation, attestation, reputation, patterns, and consumer feedback.
- To improve outcomes, secure A attestation where possible, use assigned numbers, register your caller IDs, stabilize campaign behavior, and maintain compliance.
If you need a carrier partner who understands STIR/SHAKEN and call reputation, contact TalkTelX. We will review your use case and help you set up outbound and inbound voice with the right foundation for consistent call delivery.