Bridgewater, NJ - July 22, 1998 - DSET Corporation (NASDAQ: DSET) announced today that Allegiance Telecom (NASDAQ: ALGX), a provider of local (CLEC), long distance (IXC), international calling and Internet services has chosen DSET's Service Order Administration (SOA) Gateway for its local number portability implementation. The choice of DSET's SOA Gateway solution wasbased on its ease-of-use, scalable architecture and cost-effectiveness.

"DSET has consistently been in a leadership position in the areas of LNP and OSS Interconnect Gateways," stated Bill McHale, DSET's President and CEO. "It is this leadership, coupled with the strength of our product, and our seamless integration with MetaSolv's TBS Operational Support System (OSS), that brings DSET and Allegiance Telecom together."

"The DSET SOA Gateway is built upon our OSSInterconnect Platform, a modular architecture that allows us to effectively build gateways for a variety of applications such as Trouble Administration (TA), Local Service Request (LSR), PIC/CARE, E911, LIDB, and CNAM. This architecture maintains the working concept of the Common Interconnect Gateway Platform (CIGP) as outlined by the Network Management Forum (NMF)," McHale continued.

"The DSET SOA Gateway reliably integrated with our MetaSolv TBS Operations Support Systems (OSS)," said Dan Yost, President and COO of Allegiance Telecom. "DSET has the proven experience in OSS interconnection to be picked as our gateway vendor. Our strategy is to create a 'one-stop-shop' for telecommunications services in our target markets. With MetaSolv and DSET as trusted leaders in OSS and Gateway technologies, we have the confidence to keep our eyes focused on providing our customers with high quality service and innovative business solutions."

"One major result of the Telecom Act of 1996 was the requirement that incumbent local exchange carriers (ILECs) provide local number portability in 100 Metropolitan Service Areas (MSAs) by the end of 1998, thus removing a primary barrier to competition at the local exchange level. The emerging CLECs now have the opportunity, by implementing their own LNP solution, to port numbers and exchange customer data with the incumbents," stated Phil Cavallo, DSET's Vice President of Marketing and Product Management. "DSET's technology has been used by most of the ILECs in building their LNP solution. Allegiance saw the value of this experience and we are pleased to be working with them."

ABOUT DSET: DSET, founded in 1989, is a leading provider of standards-based application development tools, custom application development services, Local Number Portability solutions and OSS Interconnect Gateway products to the telecommunications industry. The company's products are used globally by telecom equipment manufacturers and carriers to build applications that manage network devices (access, switching or transmission systems) and provision new services such as voice, data, Internet access and number portability. DSET's Professional Services organization provides development services for those customers without the internal resources to quickly build network management or carrier-to-carrier applications.

The company has offices in Bridgewater, NJ, Richardson, TX, Campbell and Fremont, CA, and Chengdu, China, and supports a network of distributors and strategic partners around the world. The Company's web address is: www.dset.com.

ABOUT ALLEGIANCE TELECOM: Allegiance Telecom is a competitive local exchange carrier headquartered in Dallas, Texas. The Company offers businesses a complete package of telecommunications services, including local, long distance, international calling, high-speed data transmission, and Internet services. Allegiance is targeting 24 major metropolitan areas in the U.S. with its "one-stop shopping" approach. In addition to the Atlanta, Dallas, and New York markets where the Company has already begun to provide service, other markets scheduled for initial service in 1998 include Boston, Chicago, Ft. Worth, Los Angeles, Northern New Jersey and San Francisco. The Company's web address is: www.allegiancetele.com.

Except for historical and factual information contained herein, all other information set forth in this news release represents forward-looking statements, including all statements about DSET's plans, beliefs, estimates and expectations. These statements are based on current estimates and projections that involve certain risks and uncertainties and could cause actual results to differ materially from those in the forward-looking statements. Investors are encouraged to consider these risks and uncertainties which are discussed in documents filed by DSET with the Securities and Exchange Commission, including, without limitation, fluctuation of quarterly operating results, dependence on a rapidly evolving telecommunications industry, and dependence on the TMN industry standard. DSET undertakes no obligation to publicly update any forward-looking statements whether as a result of new information, future events or otherwise.