ATM over satellite: A bandwidth boon

Some of the many agencies that have adopted high-speed Asynchronous Transfer Mode as their backbone network technology of choice are now pushing to the next level with ATM-over-satellite communications.

For the Defense Department, this technology promises to provide remote users— such as those on ships, in Army tanks and at ad hoc military installations— with high-speed links to major command and control networks. Throughout government, users believe ATM over satellite can provide the bandwidth necessary for collaborative telemedicine projects and for multicast and broadcast applications.

Vendors and federal researchers continue to address some inherent problems with the technology— notably congestion control and error correction. But representatives from agencies that have begun experimenting with the technology say they are optimistic about its potential benefits. In particular, many view the technology as a way to extend the capability of their Internet connections while maintaining the throughput needed for advanced applications.

Richard Bibb, vice president of federal operations for switch manufacturer Fore Systems Inc., Vienna, Va., said other satellite technologies can provide remote connectivity, but ATM over satellite offers connectivity at much higher data rates, which will be a boon for various applications.

For example, intelligence agencies could use the technology to "collect and disseminate large volumes of information," such as satellite imagery to remote or mobile forces, he said. He noted that the limited ability to deliver such data to the theater during the Persian Gulf War was "one of the motivating factors for pushing ATM" in DOD.

Susan Miller, vice president of advanced applications management at Comsat Corp., Bethesda, Md., said her company has offered ATM over satellite since February. Although she reported no federal customers as yet, "the government has purchased quite a few Comsat terminals to do testing," she said.

Bob Riehl, chief of the Advanced Communications Technologies Division in the Defense Information Systems Agency, said DOD's Bosnia Command and Control Augmentation System, begun in 1995, already uses ATM over satellite. DOD uses BC2A to help locate, manage and dispatch information from stateside intelligence providers to U.S. forces deployed overseas. Because ATM integrates voice, video and data at high data rates, "it can get information flowing correctly across a wide spectrum of forces," he said.

DOD has been quick to see the promise of ATM over satellite, Riehl said. In 1995, the Joint Warrior Interoperability Demonstration (JWID) proved that the technology could be used to provide video teleconferencing to the desktop, he said.

DISA now plans to extend its network to ATM satellite terminals known as Strategic Tactical Entry Points. Riehl said the STEPs would provide links to "the mil deps," which are mobile units such as tanks or Joint Task Forces. A DOD specification laying out communications protocols will allow the military "to go out to their tactical forces and interoperate," Riehl said.

But a number of civilian agencies also are looking into the technology.

The National Institutes of Health has taken part in demonstrations of telemedicine using ATM-over-satellite technology, said George Thoma, chief of the Communications Engineering Branch at the National Library of Medicine. The Visible Human Images project used the technology to transmit images of body tissue slices; these images involved very large data sets used for research, surgical guidance and training purposes, he said. A second effort transmitted digital X-rays from coast to coast. Both experiments used Internet Protocol over ATM, he said.

"ATM protocols allow you to use as much bandwidth as necessary for real-time video-type messages," Thoma said.

Will Ivancic, a research engineer with NASA's Lewis Research Center in Cleveland, said ATM via satellite is also promising for multicast and broadcast applications. Ivancic said multicast applications could beam data via satellite to groups of users, and NASA conceivably could build architectures allowing "thousands or tens of thousands" of recipients to download information from a satellite broadcast.

Cyberspace in Outer Space

In a parallel effort, NASA is working with industry to refine the standards developed by the Internet Engineering Task Force (IETF) that would enable the ubiquitous Transmission Control Protocol/Internet Protocol to be run more efficiently over ATM via satellite. "ATM is used widely across Internet backbones," Ivancic said.

Running TCP/IP via ATM over satellite can help "to relieve the burden" on the land-based Internet as applications get more advanced and consumption increases, said Mike Zernic, experiment manager for NASA's Advanced Communications Technology Satellite (ACTS), which is hosting a number of ATM-over-satellite experiments.

Through the research it sponsors, NASA expects "to transition a large portion of our communications infrastructure to commercial services," Zernic said. "Rather than wait for commercial services to come online, we'd rather try and influence the next generation of systems and services so that the transition will be easier, less expensive and more effective," he said.

Tim Krout, a senior engineer at the Naval Research Laboratory (NRL), said the lab will use NASA's ACTS platform to communicate with ships via TCP/IP over ATM. He said the initiative will focus on smaller ships, such as cruisers and destroyers, which do not have the real estate of aircraft carriers for large communications antennas.

Driving the effort is the Navy's concept of "network-centric warfare," which stresses the interconnection of players throughout the battlefield. The smaller vessels, which previously operated according to pre-

determined "scripts," would be tied more closely to the larger group, and tactics would be more interactive and more responsive to changing situations, Krout said.

NRL plans to deploy the experiment with a commercial vessel by November and then try it aboard a Navy ship in the next fiscal year. The effort will use a Fore Systems switch operating at 45 megabits/sec alongside a Comsat ATM link enhancer. The link will operate on the Ka-band at 20 to 30 GHz, allowing ships to pick up the signal with a small antenna. NRL and the vendors are working on how to deal with interference from other shipboard electronics and how to keep the antenna pointed at the satellite accurately, given the complex motion of these smaller vessels, Krout said.

Mike Harrigan, chief of the Warfighter Information Network Engineering and Technology Branch at the Army's Communications-Electronics Command (Cecom), said Army exercises last year also tested IP over ATM via satellite, enabling transmitters at Fort Monmouth, N.J., to run video teleconferencing and whiteboarding sessions to forces in a tactical environment at Fort Irwin, Calif.

The troops in these "advanced warfighting experiments" used wireless terrestrial ATM communications to signal Fort Monmouth as to what data they wanted to receive, and that information was transmitted back via Global Broadcast Satellite, Harrigan said. ATM was designed for a "clean, fixed, fiber environment," he explained, and these experiments represented the Army's "first attempt to take [ATM] into a real field exercise."

Harrigan added that the Army is examining how ATM can support a lot of legacy, low-bandwidth tactical communications systems that are susceptible to delay and error. The command's new Radio Access Point program envisions the use of unmanned aerial vehicles as "surrogate satellites," enabling communications between mobile networks, Harrigan said.

Other experiments involve variable bit-rate voice service over ATM— a technique that takes advantage of unused ATM bandwidth. In addition, the Army's Military Satellite Communications office has developed a Triband Tactical Terminal, which is a mobile satellite terminal that accommodates ATM traffic.

Opening the Window

DISA's extension of its networks to Bosnia via the BC2A program also pioneered the concept of TCP/IP over ATM over satellite, extending the "TCP/IP window" from 64K to 512K. The window refers to the amount of data that can be received before the machine sending it demands a response from the far end confirming that the data was received correctly. As the need for bandwidth to support advanced applications grew, so did the need to extend this window.

NASA has been using ACTS to extend this window even further with a program known as 118X. Dave Beering, a principal with consulting firm Infinite Global Infrastructures, Wheaton, Ill., said the 118X project will refine the protocol stack implementations of various commercial operating systems to optimize their handling of TCP/IP over ATM via satellite. The experiment, to improve IETF specifications for enhancing the performance of TCP/IP over high-speed, long-delay networks, will extend the TCP/IP window to 36.5M, Beering said.

The project aims to optimize the point-to-point transfer of data between two locations across the satellite, using TCP/IP over ATM among multiple computer platforms and operating systems, he said. Companies such as Sun Microsystems Inc., Microsoft Corp., Digital Equipment Corp., Compaq Computer Corp. and Intel Corp. have joined with NASA, Lawrence Livermore National Laboratory and NRL to work on the 118X project.

A third ACTS experiment, known as ACTS 138, involving Cisco Systems Inc., aims to identify the issues and problems that arise when ATM data is run via satellite at high data rates, such as 155 megabits/sec or 622 megabits/sec, said Dan Shell, a systems engineer with Cisco's Federal Operations, Herndon, Va.

Shell said Cisco is looking at possible interactions between "random early detection," which is a congestion-control mechanism for routers, and ATM quality-of-service parameters. The company may need to tune its software or equipment configuration to work better over satellite, he said.

Adams is a free-lance writer based in Alexandria, Va. She can be reached at cbadams@erols.com.

AT A GLANCE

Status: The federal government has embraced ATM-over-satellite technology for military and scientific research applications. Agencies are using it to send mission-critical data to remote users and to extend their use of Internet applications.

issues: Vendors are still addressing problems such as congestion control and error correction. Federal agencies, particularly NASA, are providing ATM over satellite test beds to help with these challenges.

Outlook: Good. Early adopters are convinced that the technology can provide the speed and bandwidth necessary for their most complex and data-intensive applications.