Load diagram is created based on the website analysis results. If the website hasnt been downloaded by the analyzing tool, it's impossible to simulate its load. The load time of every file required to display the whole page is taken as a basis of the diagram. The load time consists of the network delays (also redirects) and files' download time. Also the fact that browsers can download files in several concurrent flows is taken into consideration.
Load diagram allows you to simulate the behavior of several browsers (Internet Explorer, Firefox, Opera, and Safari) when they open websites using different connection types and with empty of full cache. The main characteristic that distinguishes among these browsers is the different limitation on the concurrent flows number for different file types (HTML, CSS, JS). Normally all resource files are downloaded in 4 flows (by HTTP specification) from 1 host (but not more than 8 concurrent flows). Firefox (
about:config) and Opera (
opera:config) have different default limitations, so for these browsers the numbers are 8/16.
If cache is enabled, files with
Cache-Control: max-age headers won't be displayed on the diagram (because they shouldn't be loaded by the browser).
Connection speed differences include 30% packet loss for dial-up. Also there is some randomness for the same resources load time (because the same files can be loaded by browsers at different times when users visit the web page).
By now the application has been tested and works properly with the following browsers: IE6+, Firefox 2+, Opera 9+, Safari 3+.
window.onload handler. It's also possible to emulate browser behavior after introducing additional resource hosts (for static files), their number is calculated depending on the total files number. Images optimization is also available.
When files are merged, their size is summed up but network delay doesn't increase (total network delay is reduced by this action). After files minimization and gzipping their initial size is replaced by the reduced one. Additional resource hosts have names like
i0...i3.website.address, this step can speed up the load process by increasing the number of concurrent flows.
The resulting speeding-up is very close to the real value (actually doesn't differ more than by 20%). You should register, if you want to use visual optimization for your websites.