Cisco has just issued a report that backs up claims by many Internet service providers that video viewing over the Web is gobbling up huge quantities of network capacity and the problem is only going to get worse. The Cisco Visual Networking Index (PDF) predicts that IP traffic will nearly double every two years to 2012.

Released Monday, the 2007-2012 forecast projects that IP traffic will grow at a combined annual rate of 46%.

The growth is creating a new vocabulary of IP metrics of exabytes and zettabytes. One exabyte equals 1 billion GB, or 250 million DVDs. A zettabyte equals 1 trillion GB, or 1,000 exabytes or 250 billion DVDs.

"The broad and increasing adoption of visual networking is having a significant impact on IP traffic growth for both consumer and business services markets worldwide," said Suraj Shetty, Cisco's VP of service provider marketing, in a statement. "Until just a few years ago, 'exabyte' was an unheard-of term. However, because of the massive growth we're seeing, by 2012 we will have to reorient our vocabulary once again, as the metric that we need then will be the zettabyte."

Cisco didn't say so in its discussion of the report, but the explosive growth is likely to cause Internet service providers to push for Internet metering in an attempt to limit use of the Web by businesses and consumers who tend to be heavy video users. ISPs like Comcast and AOL Time Warner are experimenting with attempts to limit usage or to charge higher prices for some users who download large quantities of video.

Noting that its Visual Networking Index is part of its ongoing effort to forecast the growth of Web traffic, Cisco said the growth surge will be a result of video communications, entertainment, and social networking. The networking company said it expects Internet video traffic to grow to 400 times the amount of video traffic that was carried on the U.S. Internet backbone in 2000.

Cisco said nearly 90% of all consumer IP traffic is expected to consist of video on demand, IP peer-to-peer video, and Internet video in 2012.

While most business IP traffic through 2012 will be concentrated in North America, the fastest growing Internet traffic region will be in Latin America, which is expected to have the highest growth rate through 2012, according to the report.