Q:

How speedtest.net or any other online speed test site works, if they cannot use the client's device to download or upload a file from it?

I have read many questions, answers and blogs regarding saving a file to a temp location of client's device they all says its not possible. But if its not posible then how online speed test sites determines the exam speed of our internet connections.??
There must be some way!!
Can anyone share his/her experiences on this?
And if someone willing to tell the ways how can it be done using php, will be really appreciated.

A:

Speedtest.net operates entirely over HTTP.  It tests pings. This test sends HTTP requests to the selected server, and measures the time it takes to get a response.
For Download speed test:
User computer downloads small binary files from the web server to the client, and they measure that download to estimate the connection speed. 
You can read more here : https://support.speedtest.net/hc/en-us/articles/203845400-How-does-the-test-itself-work-How-is-the-result-calculated

