Bandwidth throttling almost always comes from your primary internet service provider, not secondary services like Usenet providers.

Bandwidth throttling only comes into play when traffic has reached a level that has a noticeable adverse affect on an ISPs infrastructure. Throttling can be either reactive or proactive. With reactive bandwidth throttling, one's bandwidth would be restricted after the commit an infringing act. A user that downloads several terabytes over the weekend and finds their connection speed reduced to dial-up levels has had their bandwidth reactively throttled. A user that is never able to achieve high speeds on particular networks could be proactively throttled. For example, if a user encounters consistently slow BitTorrent or Usenet speeds, their service might be throttled proactively.

Usenet providers are concerned with providing the highest-quality connectivity to customers as possible. Throttling the bandwidth of users directly conflicts with such goals. Because Usenet servers are specialized for one single task, they can normally offer enough resources for users to receive service at full speeds for as long as they like. This can lead to a user infringing on their ISP's bandwidth restrictions before their Usenet provider has batted an eyelash.

Some Usenet providers offer solutions to defeat bandwidth throttling, such as alternate ports to connect to or utilities that enable encrypted connections. These methods might not be foolproof, so the best means of detecting bandwidth throttling is to consult your ISP.