XO Communications Deploys Sonus Networks Solutions for Advanced Network Security

Sonus' Network Border Switch Improves Security, Peering and Transcoding Capabilities

WESTFORD, Mass., December 5, 2007 – Sonus Networks, Inc. (Nasdaq: SONS), a leading supplier of service provider IP-voice infrastructure solutions, today announced that XO Communications, has upgraded its network security by deploying Sonus' field-proven Network Border Switch (NBS). Unlike traditional peering and security products such as Session Border Controllers (SBCs), Sonus' NBS is a purpose-built IP-based solution that combines session control, PSTN gateway services and security into a single, high performance, highly scalable, carrier-class solution. The power of the NBS to protect IP-voice networks was recently validated by CT Labs, a full service testing and analysis lab, which concluded after a battery of tests that the NBS is capable of standing up to extreme denial of service attacks.

"XO is committed to providing its business customers with premium voice service, and in today's environment, that requires defending the network against a variety of security threats," said Randy Nicklas, chief technology officer, XO Communications. "In addition, more and more network operators are investing in their IP networks. With the NBS, we're able to peer directly with other networks via IP. The transcoding capabilities of the NBS have enabled us to broaden our service offerings and to drive even greater efficiency throughout our network."

The Sonus Network Border Switch is architecturally designed to improve connectivity between disparate IP networks and allow operators to gain protection, control and visibility over those accessing their networks. XO Communications has one of the United States' largest IP voice networks, carrying more than 15 billion minutes of IP voice traffic in 2006, and currently carrying approximately 1.6 billion minutes of IP voice traffic every month. With such a large IP voice deployment, scalability and reliability were two of the driving factors for migrating to the NBS.

"Like the entire Sonus product portfolio, the NBS stands out in the industry for its ability to scale while maintaining the highest levels of performance and reliability," said Hassan Ahmed, president, chairman and CEO, Sonus Networks. "We understand that security is a top concern for today's network operators, and we are committed to helping our customers protect the integrity of their networks, even under the most demanding environments."

In August, Sonus unveiled the latest version of its NBS platform, available on both the GSX(TM)9000 and GSX(TM)4000 platforms. The new version includes new features to support direct media, Denial of Service (DoS) protection for access networks and consumer VoIP deployments, advanced encryption support for call set-up, and additional Secure Real Time Protocol (RTP) to protect call content. In addition, the platform upgrade includes new features for advanced management and Operational System Support (OSS) functionality.

About Sonus Networks

Sonus Networks, Inc. is a leading provider of IP-voice infrastructure solutions for wireline and wireless service providers. With its comprehensive IP Multimedia Subsystem (IMS) solution, Sonus addresses the full range of carrier applications, including residential and business voice services, wireless voice and multimedia, trunking and tandem switching, carrier interconnection and enhanced services. Sonus' voice infrastructure solutions are deployed in service provider networks worldwide. Founded in 1997, Sonus is headquartered in Westford, 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 Item 1A "Risk Factors" of Sonus' Quarterly Report on Form 10-Q for the period ended September 30, 2007, filed with the SEC, which identifies important risk factors that could cause actual results to differ from those contained in the forward-looking statements. Risk factors include among others: the impact of material weaknesses in our disclosure controls and procedures and our internal control over financial reporting on our ability to report our financial results timely and accurately; the unpredictability of our quarterly financial results; risks and uncertainties associated with the Company's restatement of its historical stock option granting practices and accounting including regulatory actions or litigation; risks associated with our international expansion and growth; consolidation in the telecommunications industry; and potential costs resulting from pending securities litigation against the Company. 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.

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