TL;DR
Quick Answer
TL;DR
Key Facts
- STIR/SHAKEN framework: Attestation is a core component of the STIR/SHAKEN caller ID authentication framework.
- Caller confidence level: Attestation reflects a service provider's confidence in a caller's identity and authorization to use a telephone number.
- Digital call signing: Attestation levels are included when an originating provider signs a call using STIR/SHAKEN.
- A-Level Attestation: Indicates the provider knows the caller and has verified the caller's right to use the phone number.
- B-Level Attestation: Indicates the provider knows the caller but cannot verify the caller's right to use the specific phone number.
- C-Level Attestation: Indicates the provider is acting as a gateway and has limited information about the original caller.
- Authentication, not reputation: Attestation helps verify caller identity information but does not evaluate call intent, legitimacy, or reputation.
- Spam labels: Calls with A-Level Attestation can still receive spam labels based on separate reputation and analytics systems.
What Is Attestation?
In the context of STIR/SHAKEN, attestation refers to the level of confidence an originating service provider has that a caller is authorized to use the telephone number displayed on a call.
Attestation is assigned when a call is digitally signed and enters the voice network. The attestation level becomes part of the call authentication process and helps downstream providers understand the relationship between the caller, the phone number, and the provider that originated the call.
Attestation Levels
STIR/SHAKEN defines three attestation levels:
A-Level Attestation (Full Attestation)
A-Level Attestation indicates that the originating provider:
- Knows the identity of the customer placing the call.
- Has authenticated that customer.
- Has verified the customer's right to use the calling number.
B-Level Attestation (Partial Attestation)
B-Level Attestation indicates that the provider knows the customer placing the call but cannot verify the customer's right to use the specific telephone number being displayed.
C-Level Attestation (Gateway Attestation)
C-Level Attestation indicates that the provider is acting primarily as a gateway and cannot authenticate the identity of the original calling party.
What Does Attestation Establish?
Attestation helps establish accountability within the voice ecosystem by identifying how much confidence a provider has in the caller and the phone number being used. It can help downstream providers validate caller ID information and support traceback investigations when unlawful activity occurs.
However, attestation does not determine whether a call is legitimate, wanted, or trustworthy from the recipient's perspective. It verifies authorization and caller ID integrity, not caller intent.
How It Works
How Is Attestation Assigned?
When a call originates on a provider's network, the provider evaluates its relationship with the caller and the telephone number being used.
Based on the information available, the provider assigns an attestation level before digitally signing the call through the STIR/SHAKEN framework. The signed call is then transmitted through the network along with information that can be validated by downstream providers.
How Do Terminating Providers Use Attestation?
When a call reaches a terminating provider, the STIR/SHAKEN signature and attestation information can be verified.
This helps the terminating provider determine whether:
- The caller ID information was authenticated.
- The call was signed by a trusted provider.
- The attestation level supports confidence in the caller's authorization to use the number.
Attestation becomes one trust signal among many that providers may use when processing calls.
Does Attestation Determine Whether a Call Is Spam?
No. Attestation addresses caller ID authentication, while spam labels typically rely on separate reputation and analytics systems. These analytics systems may consider factors such as complaint activity, number reputation, calling patterns, and historical behavior. As a result, even calls with A-Level Attestation can still receive Spam or Scam labels.
Why This Matters
Why Attestation Is Important
Attestation helps strengthen trust in caller ID information by reducing opportunities for illegal caller ID spoofing. It gives providers a standardized way to communicate confidence in the relationship between a caller and a telephone number.
By establishing accountability at the point a call enters the network, attestation can support traceback efforts, enforcement actions, and broader robocall mitigation initiatives.
A-Level Attestation Isn't Enough by Itself
A common misconception is that A-Level Attestation guarantees successful call delivery or prevents spam labeling. In reality, attestation verifies authorization, not reputation. A caller may be fully authorized to use a number and still experience spam labeling if analytics providers identify risk signals associated with the number or calling behavior. This is why authentication and reputation management are often viewed as complementary parts of communications trust.
Enterprises Should Care About Attestation
For enterprises, attestation is an important component of outbound calling because it helps verify ownership and authorized use of calling numbers. Higher attestation levels can support caller identity authentication and accountability within the voice ecosystem.
However, attestation should be considered one part of a broader strategy that may also include:
- Responsible dialing practices
- Number reputation management
- Caller identity management
- Branded calling solutions
- Ongoing monitoring of call performance
Organizations often achieve the best outcomes when authentication, identity, and reputation are managed together rather than independently.
Common Questions
What is the highest attestation level?
A-Level Attestation is the highest attestation level in the STIR/SHAKEN framework and indicates that the provider knows the customer and has verified the customer's authorization to use the telephone number.
Does A-Level Attestation mean a call is trustworthy?
No. A-Level Attestation does not automatically mean a call is trustworthy. Within the STIR/SHAKEN framework, A-Level Attestation indicates that the originating service provider knows the caller and has verified the caller's right to use the phone number being displayed. It is an authorization signal, not a determination of trustworthiness.
Attestation answers a specific question: Is the caller authorized to use this phone number? It does not evaluate whether the call is wanted, whether the caller's behavior is appropriate, or whether the recipient should trust or answer the call.
Trust is often influenced by additional factors outside the STIR/SHAKEN framework, including call reputation, calling patterns, complaint activity, and historical behavior associated with the number. Because these factors are evaluated separately, even calls with A-Level Attestation may still be labeled as Spam or Scam.
For enterprises, A-Level Attestation is an important foundation for caller authentication and accountability, but it is not a guarantee of positive call treatment. Strong call performance typically requires both authenticated calling and active management of caller identity, dialing practices, and number reputation.
Can a legitimate business receive B-Level Attestation?
Yes. B-Level Attestation may occur when a provider knows the customer but cannot verify the customer's right to use the specific number being displayed.
Can calls with A-Level Attestation still be labeled as spam?
Yes. Spam labels are generally based on separate reputation and analytics systems rather than attestation alone.
Does attestation prevent caller ID spoofing?
Attestation helps reduce and identify caller ID spoofing by authenticating caller ID information within the STIR/SHAKEN framework. However, it is one component of a broader anti-spoofing and robocall mitigation strategy.
Our platform empowers organizations to manage branded calling, improve caller id reputation, and stay compliant with evolving regulatory and industry standards. FAQs and Glossary terms like this are designed to provide clear, actionable guidance backed by our expertise in verified identity, call labeling mitigation, and spam prevention.
To explore how Numeracle supports trusted and effective outbound communications, visit www.numeracle.com.
