What's a SIN?
The Supplier Information Notes - Essentially a guideline for manufacturers and/or suppliers involved in provision of BT services and products, giving a specification of the service's intended use and/or operation, and any specific technical requirements or recommendations for use.

It's NOT a certification!

A product or service may be proven to conform to the guidelines laid out in a SIN though, and while it's by no means a requirement, it's certainly a very good indication of suitability and/or compatibility as applicable.


In the case of ADSL filtering equipment, the relevant paper is SIN 346, published for viewing here;

BT SIN 346 v2.4
You'll need Adobe Acrobat Reader to view PDF files, which if you haven't already got by now then it's time you did. The icon on the right links to free Reader versions for Mac, Windows and Unix systems.

The complete listing of all SIN documents is also available to view should you want to;
BT Supplier Information Notes Page