The surge in Internet traffic from video data has drawn the attention of industry groups, analysts and researchers who are concerned about service delays.
The threat is mostly from the increasing visual richness of online communications and entertainment: video clips and movies, social networks and multiplayer games.
It is estimated that YouTube consumed as much bandwidth in 2007 as the entire Internet did in 2000.
Nemertes Research projected in a November 2007 report that user demand for the Internet could outpace network capacity by 2011.
The title of a debate scheduled for an April technology conference in Boston sums up the concerns: "The End of the Internet?"
While a lights-out Internet crash is not expected, analysts say users would experience sluggish download speeds and frustration with data-heavy services.
"The Internet doesn't collapse, but there would be a growing class of stuff you just can't do online," said Johna Till Johnson, president of Nemertes Research, which predicted the bandwidth squeeze by 2011 and projected that demand will grow by 100 percent or more each year.
Andrew M. Odlyzko, a professor at the University of Minnesota, is among those who are worried about the short term. He estimated that digital traffic on the global network is growing about 50 percent each year, in line with a recent analysis by Cisco Systems.
However, the technology for handling Internet traffic also is advancing at an impressive pace, Odlyzko said, noting that router computers for relaying data are getting faster, fiber-optic transmission is getting better, and software for juggling data packets is getting smarter.
"The 50 percent growth is high - it's huge. But it basically corresponds to the improvements that technology is giving us," said Odlyzko, a former AT&T Labs researcher.
Demand is not likely to overwhelm the Internet, he said.
It is more than a technical problem, since it will affect the shape and cost of the nation's policy on broadband infrastructure, a matter that is expected to attract political attention after a new presidential administration takes over in 2009.
While experts debate the urgency of addressing the challenge, they agree that it points to a larger issue. High-speed networks sometimes spawn new businesses, markets and jobs. American investment must not lag behind, they warn, or the nation risks losing competitiveness with countries that are making it a priority to move to higher-speed Internet access.
"The long-term issue is where innovation happens," Odlyzko said. "Where will the next Google, YouTube, eBay or Amazon come from?"
The worries about digital traffic congestion also hit close to home, since analysts estimate that it can cost $1,000 or more to string high-speed optical fiber to a home.
This leads to access speeds that vary in different countries. It depends on local patterns of corporate investment and government subsidy.
Frederick J. Baker, a research fellow at Cisco, attended a professional conference last month in Taiwan, where Internet access is more than twice as fast and costs far less than his premium high-speed service in California.
Baker said that when he described his service to people in Taiwan, they would "shake their heads in disbelief."
In the United States, the investment required to cope with rising Internet traffic will have to be established at several levels, not just cable and telecommunications carriers.
Tim Pozar, an engineer and a co-owner of the Internet service company UnitedLayer in San Francisco, said a number of forces were combining, including the surge in bandwidth-hungry video applications on websites, the need to handle traffic from more Internet-enabled devices like cellphones, and shortages of electrical power for data centers in places like San Francisco.
"We're running out of horsepower to accommodate the demand," he said. "And upgrades needed in data centers are going to be a lot more expensive than in the past, now that all the excess capacity left over after the dot-com bubble burst has been gobbled up."
Demand is catching up with supply. In its prediction of more than 100 percent annual growth, telecommunications research company Nemertes assumed brisk use of new innovations like high-end videoconferencing, known as telepresence, which corporations are beginning to embrace as an alternative to costly, time-consuming travel.
If this technology becomes a consumer product in the next few years, as some analysts predict, Internet traffic could spike even more sharply.
