Microsoft Knowledge Base Article 319824 contains the following summary:
This step-by-step article describes how to configure vendor specific attributes for Network Address Server (NAS) clients
in an Internet Authentication Service (IAS) remote access policy.
You can use a server that is running IAS to provide Remote Authentication Dial-In User Service (RADIUS) authentication and accounting for remote access to the domain. However, many vendors include features that are specific to their NAS. To turn on the functionality of these features, customize the remote access policy on the IAS server.