Technology behind speed test

Question

I was wondering what is the technology behind Internet Speed test, which some websites use to check your speed e.g; http://www.speedtest.net/

The reason behind this question is, i wanted to write my own with one more feature and that is to keep checking speed after some interval so that i can have better idea of what i am getting for what i am paying for.

I am not sure if this question belongs to stackoverflow, so please forgive me if it is not.

Thanks.

Answer 1

Download a reasonably large amount of data from the server (N bytes). Record how long it takes. (M seconds) Download rate is N / M bytes per second.

Repeat for upload.

Answer 2

You download file of known size and time is measured. then speed is file size / time.

Answer 3

Its not that simple. For example how do you know that the protocol you will use to download the file will exploit the whole network capacity and so you will be able to find your network speed? You will only find the speed that you downloaded the file. If this is what you are interested in then ok. Speed test does not just download a large file. It uses more advanced techniques.