I read this article Optimize Parallel Downloads to Minimize Object Overhead and write a test demo But the result is not I expected，look at the waterfall figure multiple domain's images indeed parallel download but the total time no less.
Who can tell me why,thanks
multiple domain image download
single domain image download
What I think the problem with your test is that the network latency is so low (assuming its a local server), that your network performance isn't even playing a huge role here. If you look at the time difference between those images it doesn't' even register in HTTPWatch. So the browser may be spending more time parsing, processing and rendering the downloads than it does actually downloading (just a guess).
I would hit this test site with something that will show off latency more. If these sites are reachable on the internet, you can just use http://www.webpagetest.org/ and hit them from around the world...
~Sniff
P.S. Check out Amdahl's law, it may have a little bearing here here ;-).