STIR/SHAKEN Compliance Guide

A-Level (Full Attestation): The originating carrier fully vouches for the caller — knows the customer and their right to use the calling number. This is the gold standard and typically results in the highest deliverability. B-Level (Partial Attestation): The carrier knows the customer but cannot verify the specific number being used (common with SIP trunking and multi-number operations). C-Level (Gateway Attestation): The call entered the US network from abroad and cannot be fully verified. C-level calls face the highest block/flag risk.

Call centres dialing at high volumes are disproportionately impacted by STIR/SHAKEN. When a call centre dials many numbers in a short period from the same caller ID, carriers may downgrade attestation or flag numbers even if they're technically compliant. This is why CLI rotation and number reputation management are now inseparable from STIR/SHAKEN strategy — maintaining A-level attestation on a pool of rotated numbers is the optimal approach.

Carriers are required to file Robocall Mitigation Database (RMD) certifications with the FCC. If your upstream carrier is not compliant or has a poor RMD standing, calls may be blocked even when your own operations are clean. Always verify that your voice carrier holds a valid RMD certification and has implemented full STIR/SHAKEN. Klozer.io works exclusively with STIR/SHAKEN-compliant carriers.

Analytics providers (companies that power 'Spam Likely' labels) operate separately from STIR/SHAKEN. Even with A-level attestation, a number can still be labeled spam by analytics providers if it generates excessive complaint signals (rapid call velocity, low talk time, high hang-up rates). Call centres must manage call behavior alongside technical compliance — spacing calls, maintaining healthy answer-to-hangup ratios, and using local presence numbers.