The USB-IF offers a Qualification by Similarity program to member companies that allows certain products to be granted USB certification and be placed on the USB-IF Integrators List with little or no testing. The QbS program enables a new USB peripheral, host or hub that is substantially similar to a fully tested and certified USB product to be granted certification based on its similarity to the originally certified product. The purpose of the QbS program is to speed time-to-market and to minimize certification costs. It is not intended to eliminate the requirement that a product actually pass USB-IF compliance tests.
The only authority to grant Qualification by Similarity to a product is the USB-IF compliance committee and the certification review board. No test facility or any other entity is authorized to grant or pursue Qualification by Similarity requests on behalf of the USB-IF. The qualifying product must be similar to a USB certified product that has undergone full and complete compliance testing. The qualifying product cannot be compared to another product that itself has been granted Qualification by Similarity. If the original certified product on which the Qualification by Similarity is based is older than 3 years, then a complete and full retest is required of the new product.
NOTE: Connectors and Cable Assemblies, due to their simplicity, may base the similarity on a product that itself has been granted QbS. Also, the age of the certification of the base connector or cable assembly is not limited to 3 years.
Modifications to the qualifying product are not allowed after submitting a Qualification by Similarity Request to the USB-IF.
Below is a general description of the Qualification By Similarity process:
NOTE: Should the qualifying product fail any required compliance test, the authorized test lab must immediately notify the USB-IF of the failure where the product is automatically denied certification and becomes ineligible for the Qualification by Similarity program. In order to obtain certification, the qualifying product will have to satisfactorily complete the entire compliance test program for its category. In addition, the USB-IF may require the base (certified) product undergo a certification audit at the vendor’s expense.
Requirements for Retest
The qualifying product must be derived directly from the certified product with only minor changes. If any changes are made that would create "significant differences" between the certified product and the qualifying product then retesting is required. The definition of "significant differences" is sometimes debatable and the final judgment is the responsibility of the compliance review board which reports to the USB-IF Board of Directors.
Notable decisions on what is considered a "significant difference" will be listed here. The following guidelines posted below are not comprehensive. The ultimate responsibility for making sure that production product matches the product samples submitted for compliance testing lies with each vendor. Audits by USB-IF that reveal discrepancies between shipping product and samples tested may be cause for required re-test, revocation of certification, and/or legal action.
It is recommended that the most full featured and power demanding version of a product be tested for USB certification. Removing features, functions and depopulating components are more likely to be granted QbS than otherwise.
Signficant Difference Guidelines
Chipsets are modular in nature and changes in one module are unlikely to affect the IP in a different module. Changes to chipsets that are unrelated to USB still require testing, but the tests are limited to validating signal quality of USB. There is no need to validate protocol timings related to packets.