CIENA’s CN 1000 Broadband Loop Carrier Completes Interoperability Testing with Sonus’ ASX Access Server, Moves to Next Level in OSPA

CHELMSFORD, Mass., September 27, 2004 - Sonus Networks (Nasdaq: SONS), a leading supplier of service provider voice over IP (VoIP) infrastructure solutions, today announced that CIENA^® Corporation (Nasdaq: CIEN), a member of Sonus’ Open Services Partner Alliance (OSPA), has achieved “Powered” status for proven interoperability with Sonus products. Sonus recently completed successful interoperability testing of CIENA’s CN 1000TM Broadband Loop Carrier (BLC) Next-Generation Access Platform with Sonus’ InsignusTM Softswitch, featuring the ASX Access Server.

The CN 1000 BLC is a high-density broadband access system that delivers integrated voice, data and video services. It provides broadband digital subscriber line (DSL) and VoIP capability on every line, enabling carriers to software-provision these services to any subscriber – remotely, without manual intervention. By integrating the functions of a next-generation DLC (NGDLC), a video-enabled digital subscriber line access multiplexer (DSLAM), and a media gateway, the CN 1000 greatly simplifies the access network, while dramatically reducing capital and operational costs.

“Sonus is pleased to designate the CIENA CN 1000 BLC as one of our key Powered products,” said Steve Edwards, chief marketing officer, Sonus Networks. “Having a solid BLC solution interoperable with Sonus products is critical in driving the deployment of advanced VoIP services in areas where broadband was previously limited. We very much look forward to building on what already is a successful partnership with CIENA.”

The OSPA’s mission is to help empower standards-based interoperability between applications, third-party vendors and Sonus products. Once an OSPA member demonstrates interoperability with a Sonus product, the partner becomes “Powered.” Sonus and its “Powered” partners collaborate to deliver end-to-end packet-based network solutions using best-of-breed technologies and applications.

About Sonus’ OSPA

Sonus Networks’ Open Services Partner Alliance program provides a framework that offers service providers end-to-end packet-based network solutions using best-of-breed technologies and applications. The goal of the OSPA is to empower standards-based interoperability between applications, hardware vendors, and the Sonus product family. An integral part of the Sonus OSPA, the OSPA Interoperability Laboratory verifies product interoperability, performs trial testing and ultimately produces complete solutions. To find additional information on the OSPA, including a list of all OSPA partners, log on to http://www.sonusnet.com/partners/index.html.

About Sonus Networks

Sonus Networks, Inc. is a leading provider of voice over IP (VoIP) infrastructure solutions for wireline and wireless service providers. With its Open Services Architecture (OSA), Sonus delivers end-to-end solutions addressing a full range of carrier applications, including trunking and tandem switching, residential and business access, network border switching and enhanced services. Sonus' voice infrastructure solutions, including media gateways, softswitches and network management systems, are deployed in service provider networks worldwide. Sonus, founded in 1997, is headquartered in Chelmsford, Massachusetts. Additional information on Sonus is available at http://www.sonusnet.com.

This release may contain forward-looking statements regarding future events that involve risks and uncertainties. Readers are cautioned that these forward-looking statements are only predictions and may differ materially from actual future events or results. Readers are referred to the “Risk Factors” section of Sonus’ Annual Report on Form 10-K/A dated July 28, 2004 and filed with the SEC, and the “Cautionary Statements” section of Sonus’ Quarterly Report on Form 10-Q, dated August 20, 2004 and filed with the SEC, which identify important risk factors that could cause actual results to differ from those contained in the forward-looking statements. In addition, any forward-looking statements represent Sonus’ views only as of today and should not be relied upon as representing Sonus’ views as of any subsequent date. While Sonus may elect to update forward-looking statements at some point, Sonus specifically disclaims any obligation to do so.

Sonus is a registered trademark of Sonus Networks. Open Services Architecture, GSX9000, Insignus and Sonus Insight are trademarks of Sonus Networks. All other trademarks, service marks, registered trademarks, or registered service marks are the property of their respective owners.