The RPO is helping New Zealand businesses reach export markets more effectively, and this has generated some great coverage from local media:

• National Business Review: Wellington start-up makes web pages load faster from overseas
• Dominion Post: Aptimize tested by Trade Me
• Computerworld: Wellington developer aims to speed up websites
• CloudAve: It's all about speed

We also presented at the recent Wellington to the World event. Watch the video here

Here is how the RPO performs image combining. Most webpages contain a number of images - PNG, JPG and GIF files.

For example here are some of the images on the "Top 100 WCM sites" page on the SharePoint website www.wssdemo.com

Because PNG, JPG and GIF files have built-in compression, file sizes only marginally increase page load times, however each image adds another HTTP request - another round trip from the browser to the server to retrieve it. This round trip contributes significantly to the page load time, even if the server returns "304 not modified".

What the RPO does

The first time a page is requested, the RPO builds a "spriteset" of the images. A spriteset is a single large image containing the individual images laid out side-by-side. The spriteset generated once and cached on the server to ensure the load on the server is kept to a minimum. Here is what the spriteset looks like for the images above.

When a page is requested, the HTML is modified to use the images inside the spriteset instead of the individual image files. The result is a single HTTP request to display multiple images instead of multiple requests.  The RPO also sets a far-future-expires date for the spriteset so it is cached on the client. When an image in the spriteset changes on the server, the spriteset is re-generated.

Alt-text and layout is preserved. The only difference the user sees is faster page load times.

Making the most of image combining

Image combining is great for site chrome and static images. When a page contains images than dynamically change (eg: news pages), you should exclude these images from combining using an Inclusion rule to avoid the spriteset from being continually recreated. The RPO creates one spriteset for each image type - PNG, JPG and GIF, so if you can limit a page to one image type you'll see one spriteset, less HTTP requests and even faster page load times.

You can see this in action for yourself by opening the "Top 100 WCM sites" SharePoint page with the RPO on or off:

RPO ON:  http://www.wssdemo.com/Pages/topwebsites.aspx

RPO OFF: http://www.wssdemo.com/Pages/topwebsites.aspx?rpo=off

Google's Steve Souders covered the RPO in his blog today. We talked to Steve during the development of the RPO and incorporated some of his ideas like the option to load scripts and stylesheets with dynoding. Before joining Google, Steve was the Chief Performance Yahoo at Yahoo!, invented the YSlow Firefox add-on and wrote the book on performance: High Performance Web Sites.

We've recently authored an introduction to using the RPO with Steve's book, and chapter-by-chapter technical guidance, so you can configure the RPO to instantly implement 9 of the 14 best practices Steve recommends. These best practices are rapidly becoming the standard for high performance sites, providing a better quality experience for users and a greater return on investment for website owners.

Ed Robinson

Find out how fast your pages load from the USA or New Zealand with the AOL page test. Try it from both locations and see the effects of latency on page load times.

This is a free service, and we're really excited to host the New Zealand version. Thanks to  Patrick Meenan from AOL for working with us across timezones to get it set up.

10 second tutorial

	AOL Page test is simple to use. Go to: www.webpagetest.org.nz (NZ), or www.webpagetest.org (USA) Type in the URL of your website Click Submit Page test simulates a real world user by opening the page with IE7 and measuring the performance and several quality metrics.
	After a few minutes you'll see the results. The table at the top shows the page load times for first-time and repeat visitors. Below the table are waterfall diagrams and a more detailed analysis.

For more information, see Patrick Meenan's blog. Email us service@getrpo.com if you'd like to help the community by hosting another location.