If you are getting channels buffering, you can check the speed of your connection using online speed checking websites. These give a rough indication of the upload and download speeds you are currently getting from your provider. These will almost certainly be a little less than what you are paying for. If you are paying for 100mb for example, don't expect to get exactly that!
We recommend using either speedtest.net by Ookla or fast.com - the latter is the Netflix provided speed test. You'll get somewhat different results from each but you need to ensure that you are getting in excess of 6Mb, ideally more for good stream viewing.
One thing to watch for with the Ookla test is that the server shown above where it says 'Change Server' matches your Internet provider - I have found on occasion that Ookla select a different one and then your results will be far from accurate.
http://speedtest.net by Ookla