Asynchronous Transfer Mode

COMMUNICATIONS GUIDE

Asynchronous Transfer Mode

ATM Running on SONET Circuits Provides Unparalleled Bandwidth

fter only four years in the commercial market, Asynchronous Transfer Mode (ATM) technology is showing up in a variety of telecommunications applications. The main advantages of this cell-switching technology are its lightning speed and high bandwidth. ATM is capable of transporting voice, data and video traffic simultaneously at speeds 100 times greater than any other communications network technology.

ATM works by breaking information into 53-byte units- known as cells-and relaying it through networks via a series of switching nodes. Since the cells are of a fixed size, they can accommodate different data rates and packet sizes. Cell-relay technology enables agencies to consolidate all types of communications onto a single network.

ATM can be used for local-area networks (LANs) or wide-area networks (WANs). The technology enables organizations to connect LANs and WANs without having to go through complex speed-conversion exercises.

In wide-area networking applications, ATM cells are transported via a high-speed, long-haul transmission system known as Synchronous Optical Network (SONET). ATM running on SONET circuits enables bulky data files, which are normally reserved for local networks, to be transmitted across WANs at unparalleled speeds. This has prompted long-distance carriers such as AT&T, MCI, Sprint and U S WEST to upgrade their fiber-optic lines to SONET circuits.

ATM is ideal for bandwidth-intensive applications such as imaging, multimedia, Internet access and on-line training. Its speed and capacity help eliminate network congestion while providing users a cost-effective alternative to private networks.

The Defense Information Systems Agency is building an ATM backbone that will consolidate all disparate Defense networks and serve as the primary means of transportation for the Global Command and Control System and the Defense Message System. The technology already is available on the Pentagon's Navy-Air Force ATM Communications Service contract, which recently was awarded to MCI. The ATM network transports critical weather and oceanographic data in real time between four defense and civilian processing centers.

The Air Force also is using ATM for on-board communications while the Army is using the technology in battlefield-simulation exercises, telemedicine applications and intelligence transmissions. In order to ensure accuracy of troop movements and on-time delivery of supplies, the Army uses ATM for processing logistics data.

GTE's Secure Prioritized ATM Network enables military theater commanders and tactical commanders to receive identical information at the same time. Satellite weather videos, for example, can be integrated with detailed maps, background text and spoken commands-and then sent over a single digital network.

Bell Atlantic uses ATM switching equipment and SONET circuits in its Advanced Technology Demonstration Network. That project, which involves six government agencies, demonstrates the interoperability between public and Defense networks.

The federal research community was one of the first to embrace ATM technology. Instead of leasing expensive, dedicated lines for their broadband applications, NASA and other science agencies tap commercial ATM services.The National Science Foundation is using ATM to link five national supercomputing centers, which transmit complex three-dimensional moving graphic images at the rate of 155 million bits per second.

Since GTE and Sprint began offering ATM products and services in 1992, more than 40 companies have jumped on the ATM bandwagon. A new generation of switches and routers from companies such as Bay Networks, Cabletron, Cisco Systems, Digital, Fore Systems and Newbridge

Networks provide seamless transportation of voice, data and video. But there is still a shortage of appropriate software that exploits ATM's features and enables the technology to coexist with legacy telecommunications networks.

Some standards are lacking as well. Although the Interim Interswitch Signaling Protocol and the LAN Emulation Standard were approved last year, vendors cannot agree on appropriate methods for congestion control or transferring ATM cells from one carrier's network to another. An equipment platform has not been chosen, though many companies support the User-Network Interface.

ATM implementation costs are also an issue. In local-area networks, the technology averages $1,500 per computer as opposed to about $300 per machine for the Fast Ethernet standard. Prices are highest for ATM voice transmissions, which require special technology to keep signals moving steadily.

But the ATM Forum, a 700-member industry consortium, is aggressively looking for ways to solve interoperability problems and to lower ATM prices. Many companies are confident that ATM will become the standard communications technology for high-speed applications.