Apparently RFC 3229 has existed since 2002, but I wasn't even aware of it until the IE7 team mentioned the new Windows RSS Platform will support it. What RFC 3229 describes is a method for doing HTTP GETs for only the differences between a cached version of a response and the latest version. In English, a browser or RSS reader can download only what's changed on a page or RSS feed rather than downloading the whole thing every time.

RSS is beautiful in its simplicity, but until now, aggregators had to download the entire RSS file every time the feed changed in any way. Content providers could try to limit bandwidth requirements by reducing the amount of past posts available in an RSS feed, but this makes new subscribers miss out and requires aggregators to check for updates more often. What RFC 3229 will provide is the ability for an aggregator to effectively download only the new posts in an RSS feed.

Bottom line: Downloading a new post in an RSS feed that makes 20 past posts available will be 95 percent more efficient than it is today!

In my opinion, building this support into Windows is a huge deal because it will cause RFC 3229 to gain popularity and get implemented by web server and blog software. And it's not just useful for RSS. The new Windows Calendar coming in Vista can subscribe to iCalendar (RFC 2445) files just like Apple's iCal. iCalendars are much like RSS feeds, but now we're talking about hundreds or thousands of appointment and task entries per file rather than a few dozen blog posts.

RFC 3229 makes the bandwidth requirements of sharing incrementally updated files like RSS feeds and iCalendars a total non-issue. It's a good thing, too, because bringing iCalendar and RSS to the millions of mainstream Windows users could require a lot of bandwidth.

Posted by JoshC at February 3, 2006 6:45 AM

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