Even though most ISPs nowadays offer an unlimited bandwidth program, they do not always hold true to their word. If you use an abnormally large amount of data each month, your ISP might impose some restrictions under the radar like throttling your connection to use less bandwidth. There are some ways to check if this is happening to you and in what way. Note that before you perform any of the following tests you should stop any downloads and uploads as they are very likely to affect the results. Moreover, if you are in a network with multiple users, you cannot really control what they do. If that is the case, try to test when no one is on the network.
Traffic or packet shaping is the process of limiting an aspect of a network in order to boost others. However, this can also be used by ISPs to completely limit a network aspect without boosting anything else. For example, they might impose limits on your P2P network connections if you are using too much bandwidth on them. A perfect way to check it out is through Glasnost Tests. Simply select a test from the list and run it. The tests take quite a bit of time but they are very accurate. Note that the website uses the Java plugin so use at your own risk.
2. Bandwidth limiting
One of the best ways to test your current connection is SpeedTest. The website is extremely popular amongst internet users for its tests and the ability to compare results. Moreover, you can see the results of people around your areas so that you know what the average is right away. Note that tests in this website are not always going to be accurate. If you are currently running an application that is heavy on network resources, the results will be inaccurate. Run it a couple of times each day for a few days for more accurate results.
3. Diagnostics tools
The Measurement Lab is an internet paradise for those that want to test every aspect of their connection. The site offers a ton of tools in three different categories: Performance, Transparency and State. IT will give you details about each tool before you use it as well as what every category entails. You will be hard pressed to find a better site for such tools than M-Lab so be sure to give it a go.