The new rules cover interstitial and newer interactive ad formats such as floating ads, page take-overs, and tear-backs, as well as standard banners and buttons. They also apply to ads that employ audio, video and Flash animation technologies and programming languages including Java, Javascript and DHTML.

The guidelines are geared to browser-related activity, which no longer links page content changes to ad-serving. "With the emergence of rich media as a more important tool for advertisers in a Web 2.0 environment, the IAB recognizes that it's critical to help the industry define metrics for its continued growth," said David Doty, the IAB's senior vice president for thought leadership and marketing.

In particular, Web 2.0 technologies such as Ajax and JSON have grown increasingly popular by providing updated content without requiring users to refresh an entire Web page. While improving the user experience, however, Ajax and JSON make traditional metrics such as ad impressions and page views more difficult to gauge.

Similar to IAB guidelines for traditional Internet ad impressions, a rich media impression is counted (and charged for) when a user's browser requests an ad from a rich media ad-serving system. Expandable ad formats should be counted the same way, but activities such as mousing over an expandable ad shouldn't be included in the base ad impression count.

The new guidelines also specify that over-the-page and interstitial ads should be tagged so that rich media providers count the ads only when they are played.

Jeff Lanctot, senior vice president for global media at Avenue A | Razorfish, said the guidelines were an important step for the industry. "The more closely aligned publishers and ad servers are on operational standards, the more efficient digital channels will become for advertisers," he said.

In connection with the release of the rich media guidelines, the IAB will host an educational webinar, including participation from the Media Rating Council, on Wednesday, Jan. 23. Doty said the forum would provide a conversational format "where particular questions about the guidelines can be posed and answered."

The IAB is working on a separate set of guidelines for the proper measurement of audience page views in an increasingly AJAX-heavy Web universe. Preliminary audience measurement guidelines are expected during the first quarter of 2008.

This looming problem led Nielsen Online in July to stop issuing rankings based on page views. Instead, Nielsen Online now focuses on other measurements--including total time spent on a site and total visits--to provide a more comprehensive snapshot of Web site usage.