XO Communications Selects Sonus Networks to Provide Next-Generation Switching and Softswitch Technology.

Business Editors/Hi-Tech Writers

RESTON, Va. & WESTFORD, Mass.--(BUSINESS WIRE)--Nov. 7, 2000

Leading Broadband Communications Provider to Deploy

Sonus Gear in its Nationwide Network

XO Communications, Inc. (Nasdaq:XOXO), one of the world's fastest growing providers of broadband communications services and formerly known as NEXTLINK/Concentric, has selected Sonus Networks (Nasdaq:SONS) as a non-exclusive provider of an Internet Protocol (IP)-based next-generation telecommunications switching platform, including softswitch technology.

XO plans to deploy these solutions throughout its North American fiber optic network over the next 18 months.

XO has begun the first phase of an expansive migration to packet-based switching technology, which is expected to deliver the full range of traditional and enhanced local and long distance services and to increase the company's ability to efficiently handle an increasing amount of ISP traffic.

Softswitch technology will allow XO to realize cost savings both in reduced equipment cost and reduced physical co-location space needs. Additionally, softswitches are expected to be quickly scaleable and have capabilities to launch new and enhanced services.

"We're pleased to have selected Sonus Networks as a key provider of next-generation softswitch technology. In the near term, we believe this technology will afford us an opportunity to begin off-loading our ISP traffic from circuit switches to softswitches that we believe will translate into cost savings and increased network flexibility for XO," said Doug Carter, XO senior vice president and chief technology officer. "More importantly, this marks a major milestone toward achieving XO's goal of offering unique and scaleable IP-based voice and data services across our existing and future fiber optic networks."

XO plans to use the Sonus Networks platform, which includes the GSX9000(TM) Open Services Switch, the PSX6000(TM) SoftSwitch and the SGX2000(TM) SS7 Signaling Gateway. The system is expected to act as an integral piece of XO's future network foundation, and will support a full range of local, long distance and Internet services to enterprise customers. The Sonus platform would also support the delivery of enhanced services, such as unified messaging, single number service, credit card calling, conferencing and more.

"XO Communications has gained a reputation as a technology-savvy service provider, and continues that tradition with the migration to a packet voice backbone," said Hassan Ahmed, president and CEO, Sonus Networks. "We are thrilled that XO has chosen Sonus as a part of the foundation of its next-generation voice infrastructure and we look forward to building a strong partnership."

About Sonus Networks

Sonus Networks, Inc. is a leading provider of voice infrastructure products for the new public network. Sonus' solutions enable service providers to deploy an integrated network capable of carrying both voice and data traffic, and to deliver a range of innovative, new services. The Sonus Open Services Architecture(TM) (OSA) and award-winning Packet Telephony suite cut the time-to-market for competitive new service products, allowing carriers and third-party developers to expand marketshare and build important new revenue streams.

Its highly scalable products fully interoperate with and extend the life and utility of today's public network. Sonus embodies in its management and staff decades of experience in developing carrier-class voice, data and multimedia solutions for implementation in the world's largest networks. Sonus, founded in 1997, is headquartered in Westford, Massachusetts. Additional information on Sonus is available at http://www.sonusnet.com.

About XO Communications

XO Communications is one of the world's leading providers of broadband communications services offering local and long distance voice communication services, Digital Subscriber Line (DSL) access, Web hosting and e-commerce service, Virtual Private Networks (VPNs), dedicated access, global transit and application infrastructure services for delivering applications over the Internet or a VPN.

XO has assembled an unrivaled set of facilities-based broadband networks and Tier One Internet peering relationships that, when complete, will serve much of the United States, Canada and Europe. In the United States, XO has more than 570,000 metro and intercity fiber miles in operation. The Company is also North America's largest holder of fixed broadband wireless spectrum, with licenses covering 95 percent of the population of the 30 largest U.S. cities and a partnership with licenses covering all of the top cities in Canada.

XO has also agreed in principle to acquire metro fiber networks in Europe to serve the London, Frankfurt, Brussels, Amsterdam and Paris markets and an 88,000 fiber-mile pan-European fiber network connecting 21 major European cities and transatlantic capacity that will eventually expand to 10 Gbps. Additional information is available at http://www.xo.com.

The statements contained in this release that are not historical facts are "forward-looking statements" (as such term is defined in the Private Securities Litigation Reform Act of 1995). These statements include those describing XO's plans to utilize new network switching technology and the potential benefits of that technology, its planned European and domestic networks, and its fixed wireless deployment.

Management wishes to caution the reader that these forward-looking statements are only predictions and are subject to risks and uncertainties and actual results may differ materially from those indicated in the forward-looking statements as a result of a number of factors. These factors include, but are not limited to, the ability of XO to market, sell and provision its services, to negotiate and reach definitive agreements relating to the purchase of the European network on satisfactory terms, to design and construct fiber optic networks and, install cable and facilities, including switching electronics, to develop, install and provision LMDS equipment and interconnect that equipment with its fiber networks and connect those networks to customers.

The XO business is subject to other risks and uncertainties described from time to time in its reports filed with the Securities and Exchange Commission, including its Annual Report on Form 10-K for the year ended December 31, 1999 and its Quarterly Report on Form 10-Q for the quarter ended June 30, 2000.

XO, the XO design logo are trademarks of XO Communications, Inc.

GSX9000, PSX6000, SGX2000 and Open Services Architecture is a trademark of Sonus Networks. All other company and product names may be trademarks of the respective companies with which they are associated.