I would like to implement the download estimator using the JavaScript and the Ajax.

I have gone trough Google to find the existing implementations for the download estimator and i found most of the time asking user bandwidth and then calculating the number is strategy. It good approach and there is hardly anything on reliable to get the estimated time right.

What i would like to try is use Ajax to request file size 100KB - 200 KB and do the maths get the number and update the display. Now this is surrounded with so many questions like network, number of packets formed, proxies etc ? These all factors are sufficient to turn down the approach. But THIS IS HOW I HAVE TO DO THIS ?

Now i would like here inputs from you all to make it better (as good discussion)? what all can be added to this ? Can we get to know bandwidth user using without asking ?