DSET Application Development Tools Chosen for Aircraft Communications Project by ATOS Group.

BRIDGEWATER, NJ--(BUSINESS WIRE)--September 15, 1999--

(NASDAQ: DSET) - DSET and ATOS application development tools will play a key role in building management components for the new Aeronautical Telecommunication Network (ATN) that will support digital data communications with aircraft as part of improvements planned for global air-traffic control and service. The ATOS Group, a leading European provider of information technology services, is developing the ATN components for Aeronautical Communication International (ACI).

The ATN is the enabling technology to move airborne communications into the twenty-first century. Defined by standards from the International Civil Aviation Organization and the Airlines Electronic Engineering Committee, the ATN will facilitate new communications and traffic-management services that will provide a wide range of benefits to passengers and aircraft operators, including more efficient use of congested airspace.

ACI is developing the ATN's router protocols under contract to ATN Systems Inc., an international consortium of twelve major airlines. In addition, ACI is independently developing other elements needed to support Air Traffic Services (ATS) communications. These software products are designed for convenient use and certification with both airborne and ground-based platforms.

Under the company's contract with ACI, ATOS will initially be responsible for developing an application to facilitate validating various concepts for managing the ATN. DSET application development tools in conjunction with ATOS' proprietary OSIAM communications software will be used to power this phase of the project. Much of this work involves applying the Telecommunications Management Network (TMN) standard, an area where DSET and ATOS are recognized worldwide for their expertise.

The second project phase calls for integrating ATN management applications with an ACI system for use on aircraft. This will enable the deployment of both ground-based and airborne equipment that will help to realize all of the capabilities of the innovative Aeronautical Telecommunication Network.

"I'm very pleased that ATOS and our strategic partner DSET are leveraging their TMN experience to play a key role in improving air traffic control with ACI," said Jean-Paul Vautrey, head of ATOS' Systems Integration Division.

"It's quite exciting for DSET and ATOS software to have such a role in mission-critical operations for the aeronautical industry," added Paul Smith, senior vice president, network solutions at DSET. "We've had a very strong relationship with ATOS for over three years. Now our combined application development expertise will be helping to make air travel safer, in addition to accommodating consumer demand for more seats on virtually all international routes."

About ACI:

Formed in 1997, ACI is a joint venture of Airsys ATM, AlliedSignal, Honeywell, Sextant Avionique, and Sofreavia. ACI was organized to develop and market datalink communications products and services associated with the Aeronautical Telecommunication Network for airborne and ground-based applications, areas in which the venture's partners have substantial experience. ACI has offices in Paris and Toulouse, France as well as in Phoenix, Arizona and Redmond, Washington in the United States. More information about ACI can be found at their Web site: www.aci-llc.com

About ATOS:

The ATOS Group is DSET's strategic partner in offering TMN-based software solutions worldwide. Headquartered in France, ATOS is a leading provider of information technology services that offers clients strong expertise in such fast-growing areas as electronic commerce, customer-relationship management, and supply-chain management. The Group employs more than 9700 people in 12 European countries. Sales totaled EUR 957 million (FF 6.3 billion) in fiscal 1998, of which 33% was derived from outside France. Telecommunications, one of the Group's core businesses, represents sales in excess of EUR 150 million (FF 1 billion). For more information, visit the Group's Web site at www.atos-group.com

About DSET:

DSET Corporation is a leading provider of software solutions created specifically for the global telecommunications marketplace. Network equipment suppliers worldwide use DSET application development tools to build software applications that manage network components and support new services. The DSET suite of electronic-bonding gateways is designed to interconnect the operations support systems (OSSs) of competing service providers that must trade information and share network capabilities to provision a growing range of services for customers. DSET's local number portability solutions also play a key role in enabling business and residential customers to change service providers without changing their local phone numbers. DSET is headquartered in Bridgewater, New Jersey, and the company's Web site can be viewed at www.dset.com.

Statements regarding financial matters contained in this press release, other than historical facts, are forward-looking. Since all statements about DSET's plans, estimates, and expectations are based on current projections that involve risks and uncertainties, and are subject to change at any time, the company's actual results may differ materially from expected results. Investors should consider these risks and uncertainties, which are discussed in documents filed by DSET with the Securities and Exchange Commission. These documents identify important factors that could cause the actual results to differ materially from those contained in the projections or forward-looking statements. DSET expressly disclaims any obligation to update any forward-looking statements.

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