Microsoft’s Bing Search engine is slowly catching up to Google in terms of mobile performance, according to Keynote Systems’ June News & Portal Index.

Google has sat atop the News & Portal Index for months, but Bing has been looking to oust it in mobile speed and performance. In this month’s measurements, Bing’s mobile optimized search site closed the gap and is now 0.3 seconds ahead of Google’s mobile search site. JuneINdex1

Both Google and Bing have maintained their top notch status with the use of a technique known as the Data URI (Uniform Resource Identifier). 

“Using Data URIs is a smart way for mobile websites to avoid slow round-trip HTTP requests for small image files by placing the image content directly into the HTML document itself,” noted Ken Harker, Mobile Evangelist at Keynote Systems. “Top-performing sites make strategic use of this page optimization technique.”

The main benefit from using Data URI’s in mobile site design is avoiding delay and reducing latency with extra HTTP requests, according to Keynote. Including the image directly in the base document for the web page means that no new HTTP request needs to be made, avoiding the delays to receiving content on your mobile device. 

“With the expectations for mobile web performance increasing with consumers, delay is a critical factor in mobile website access and loyalty,” Harker said. “The longer your mobile website takes, the less likely you’ll have return visitors.”

While DATA URIs have their benefits, Harker suggest there are things to consider, as images included with Data URI’s are not cached separately from the HTML file in which they are contained.  JuneIndex2

“That means if your image needs to be used on multiple pages of your site, a Data URI might not be best optimization strategy,” Harker said. “For example, you don’t want to use a Data URI to package your corporate logo that sits on every page of your mobile site, but you do want to use a Data URI for a feature image that’s only on the homepage.”

Harker suggests that Bing has an opportunity to shoot ahead of Google in performance by changing their redirection strategy.  

“By optimizing the homepage for mobile and eliminating the redirection from to Bing’s mobile destination (, it could shave off 0.3 to 0.5 seconds, which would place Bing clearly at the top in terms of page load times in the mobile search engine category,” he says.

Overall average page load time for June was 17.25, up more than two seconds faster than the May average of 19.3 seconds. Average Reliability was 96.26 percent, slightly lower than the May index, while average bytes downloaded is up more than 60 KB to 374.1 KB. Average number of objects downloaded is also up nearly ten items to 50 from 41 last month.

Keynote repeatedly tests the sites in the index hourly and around the clock from four locations over the four largest U.S. wireless networks, emulating the browsers of four different devices, including the iPhone 4 on AT&T, the Android-based HTC EVO on Sprint, the Android-based Motorola Droid X on Verizon Wireless and the BlackBerry Curve on T-Mobile USA. Data is collected from San Francisco, New York, Dallas and Chicago and then aggregated to provide an overall monthly average in terms of both speed and reliability.