Satellite Firms Dealt Blow on Internet Plans

In a significant setback for the satellite industry, NASA scientists have discovered that a key transmission standard that is the foundation of communications over the Internet and corporate computer networks does not work well in space.

The discovery could delay the satellite industry’s ambitious efforts to offer high-speed Internet access to companies with remote plants or offices, as well as to Pacific Islanders and millions of others without high-speed access to the content-rich portions of the Internet such as the World Wide Web.

Over the next decade, the satellite industry has plans to spend more than $20 billion to extend modern communications services such as telephony, video programming and computer networks to remote regions.

If satellites cannot be made to work seamlessly with the Internet, tens of billions of dollars in additional investment in terrestrial transmission systems would be required instead. And many people, particularly those in developing countries, may never get connected at all without satellites.

“Allowing satellites to be a part of the Internet would provide huge benefits to companies and individuals--if we could make it work,” said Daniel R. Glover, a NASA project engineer in Cleveland who has been spearheading the investigation into the problem. “But [the Internet] and satellites really weren’t designed to go together.”

“A satellite system must be designed with the same essential characteristics as fiber networks--broad-band channels, low error rates and low delays--to ensure seamless compatibility with those terrestrial networks,” Teledesic Corp. explains in a white paper discussing the problem.

The Kirkland, Wash., company, which is developing a $9-billion low-Earth-orbiting satellite system, believes it can overcome the problems involved in using the crucial Internet protocol known as TCP. But the firm also noted that widely used geostationary satellites, which are in a much higher orbit than that of the so-called LEO satellites that Teledesic and other new ventures plan to use, pose a much bigger problem.

Officials who oversee the Internet say they will oppose any solutions to the problem that involve modifications of TCP that might adversely affect its performance over land links.

“It would not be an acceptable solution to degrade the current performance of TCP in order to improve it for satellite use,” said Fred Baker, a software executive at Cisco Systems Inc. who is chairman of the Internet Engineer Taskforce, a standards-setting body. “An improvement of TCP is a good thing, but we don’t want to break it just so somebody in New Caledonia can have better Internet access.”

The TCP, or transmission control protocol, problem arises because of the vast distances the data must travel to reach the satellite and the peculiar way the TCP transmission standard works. Electronic data can take as long as half a second to travel up and down to Earth from geostationary satellites, which are positioned 25,700 miles away from the planet. Although a delay of that magnitude causes only a slight echo when placing, say, a telephone call, it can wreak havoc when two computers are trying to communicate.

That’s because the delay causes TCP to believe there is a backup in the network, which in turn disrupts the electronic acknowledgments the receiving computer must relay to the sending computer in order to confirm that messages are being received correctly.

In one NASA experiment, for example, a super-fast technology that normally sends data at 155 megabits per second over fiber-optic land lines was slowed to a crawl of just 10 megabits per second when NASA used a satellite communications network.

Shawn Ostermann, an assistant professor in the electrical engineering and computer science department of Ohio University who is also studying the problem, said satellite networks can degrade even the comparatively slow T-1 computer connections routinely used by corporations and Internet service providers to transmit data at 1.5 megabits per second.

“Throughput is definitely limited with satellites,” Ostermann said.

He said his research found that contrary to the claims of Teledesic and others, satellites orbiting at closer distances to the Earth can also be adversely affected.

Even if the problem does not affect LEOs, most experts agree that something must be done, since most current satellites are geostationary and systems such as Teledesic’s are risky ventures that remain a decade away.

Extending the reach of high-speed computer networks to remote locations is crucial for many industries, such as the oil business--and to the U.S. military, which would like to be able to share information with personnel located on oil rigs or remote military posts.

But there’s no quick fix in sight, since modifying the TCP standard to make it work better with geostationary satellites could adversely affect other kinds of links.

“It gets very delicate trying to boost performance,” said Craig Partridge, division scientist at BBN Inc., a Cambridge, Mass., firm hired by NASA to develop ways to improve TCP. The standard, he said, “is remarkably sensitive to trivial changes, and we have a very delicate balancing act” in making TCP work with satellites.