speedtest.net, or how not to do bandwidth tests

April 9th, 2014 by lucas

While trying to debug a bandwidth problem on a 3G connection, I tried speedtest.net, which ranks fairly high when one searches for “bandwidth test” on various search engines. I was getting very strange results, so I started wondering if my ISP might be bandwidth-throttling all traffic except the one from speedtest.net tests. After all, that’s on a 3G network, and another french 3G ISP (SFR) apparently uses Citrix ByteMobile to optimize the QoE by minifying HTML pages and recompressing images on-the-fly (amongst other things).

So, I fired wireshark, and discovered that no, it’s just speedtest being a bit naive. Speedtest uses its own text-based protocol on port 8080. Here is an excerpt of a download speed test:

> HI
< HELLO 2.1 2013-08-14.01
> DOWNLOAD 1000000

Yeah, right: sequences of “ABCDEFGHIJ”. How course, extremely easy to compress, which apparently happens transparently on 3G (or is it PPP? but I tried to disable PPP compression, and it did not see any change).

It’s funny how digging into problems that look promising at first sight often results in big disappointments :-(

2 Responses to “speedtest.net, or how not to do bandwidth tests”

  1. Josh Triplett wrote on 04/10/14 at 2:01 am :

    I tend to use and recommend testmy.net, which uses large blocks of random data.

  2. Scott "SFITCS" Ferguson wrote on 04/11/14 at 5:47 am :

    Vodaphone also use ByteMobile. I understand that in Europe it can be disabled on request ( or http://accelerator.t-mobile.co.uk/), here in Australia the javascript injection ( can be disabled by:-
    ;in page code

    bmi_SafeAddOnload= function() {};


    if (‘bmi_SafeAddOnload’ in window) {
    var el= document.createElement(‘div’);
    el.style.border= ‘dashed red 2px’;
    ‘Warning. Your wireless ISP is using a crap image recompression system ‘+
    ‘that will make pictures look like mud and which may stop this site ‘+
    ‘from working, and removes metatags. There may be a way for you to ‘+
    ‘disable this feature. Please see your internet provider account ‘+
    ‘settings, or try using the HTTPS version of this site.’
    document.body.insertBefore(el, document.body.firstChild);

    ; at the server
    Header merge Cache-Control no-transform
    ; or in the browser by manipulating headers (using an Iceweasel extension).

    As for speed tests, I’ve tried a lot of them and IMHO the best Open ones are from MLabs:-
    http://www.measurementlab.net/tools/ndt (requires java).

    http://code.google.com/p/ndt/source/ (cli version)

    A HTML5 version is being developed:-

    Kind regards

    Ref:- http://www.programmierer-forum.de/bmi-speedmanager-und-co-deaktivieren-als-webmaster-t292182.htm#3889392