Spirent Rolls out Avalanche 6.1 for Greater Testing Flexibility and Increased Network Protection.

Business Editors/High-Tech Writers

ROCKVILLE, Md.--(BUSINESS WIRE)--April 12, 2004

Newest features improve enterprise testing tools to reduce risk,

increase security and cut costs

Spirent Communications(TM) (NYSE:SPM)(LSE:SPT) today announced version 6.1 for its Avalanche(TM) product line, a comprehensive test solution that enables users to realistically test their application and network infrastructure to ensure their specific mix of products and services can excel in real-world conditions. The new features in Avalanche 6.1 offer IT users increased testing realism and more comprehensive testing capabilities designed to ensure network and application performance and to increase security.

Avalanche 6.1 removes the traditional limitations of load testing tools by giving enterprise IT managers complete flexibility to develop custom load profile descriptions that match their actual traffic. For example, Avalanche can simulate the staggered traffic peaks and varying application and network scenarios that result from a worldwide user base accessing e-mail at the start of their respective workdays.

"Avalanche 6.1 allows us to comprehensively stress-test our network and application infrastructure and has enabled us to save money by bringing our testing in-house," said Jason Moser, systems engineer of World Book Inc. "The new Flexible Load Profile feature is an extremely important part of this testing, as it helps us better replicate our diverse, worldwide user base and allows us to customize our tests to accurately reflect true user behavior."

The new testing features include:

-- Flexible Load Profile -- offering the user complete

flexibility to define load as needed. With a Flexible Load

Profile, a tester can create as many phases required and can

vary the type of each phase to include flat, stair, random,

sinusoidal and burst scenarios.

-- Expanded Security Tests -- adding Evasive UDP, Land Attack,

Ping of Death, Tear Drop and Unreachable Host to the 10

existing attacks available with Avalanche Enterprise Edition.

In addition to the new attacks, an extensible API is now

provided that can be used to script custom DDoS attacks. This

extensible architecture can be used to develop new attacks as

they are discovered. Additionally, the new release supports

sending viruses as email attachments, enabling enterprises to

verify their security defenses' ability to distinguish between

valid and malicious attachments

-- Random IP and MAC Addresses -- Avalanche can now generate

traffic using random IP and MAC addresses which increases the

realism of the traffic it generates.

-- Integration with Mercury Interactive's LoadRunner Analysis

Tool -- enabling LoadRunner users to store and retrieve

results of a test run on Avalanche and to correlate results

from LoadRunner and Avalanche (i.e., compare results of

similar tests run on Avalanche and on LoadRunner).

"The new features in 6.1 are focused on helping our enterprise customers reduce risk, increase security and save money," said Alan Newman, director of marketing for Spirent Communications' Enterprise business. "The flexible load profile addresses the requirements of enterprise customers, while allowing network equipment manufacturers to test their new devices with more realistic traffic -- ultimately helping enterprise customers too."

Spirent's Enterprise business develops network test and management products that address the unique needs of the enterprise customer. Its solutions include the Avalanche Enterprise product line, which enables customers to test their application and network infrastructure. Many leading corporations use Avalanche to ensure that their products and services excel in real-world conditions. Current Avalanche customers include Ask Jeeves, Bank of America, Cisco Systems, Costco.com, eBay, IBM, Intuit, MSNBC, NetScreen and WorldBook.

Avalanche 6.1 software is available now.

About Avalanche

Avalanche is designed for Enterprises that demand absolute realism and control under all conditions. Avalanche challenges any computing infrastructure's ability to stand up to the load and complexity of the real world. Avalanche supports HTTP/1.0, HTTP/1.1, HTTPS, RTSP/RTP (Apple QuickTime(R)), RealSystem(R) streaming, Microsoft(R) Windows Media(R) 8 and 9 Series, SMTP, POP3, DNS, Telnet and FTP. In addition, Avalanche can generate Distributed Denial of Service attack traffic inline with any mix of multi-protocol traffic. Real-world conditions are accurately replicated by simulating network error conditions and realistic user behavior. http://www.spirentcom.com/enterprise.

About Spirent Communications

Spirent Communications (www.spirentcom.com) is a global provider of integrated performance analysis and service assurance systems that enable the development and deployment of next-generation networking technology such as Internet telephony, broadband services, 3G wireless, global navigation satellite systems, and network security equipment. Spirent's solutions are used by more than 1,500 customers in 30 countries, including the world's largest equipment manufacturers, service providers, enterprises and governments. Based in Rockville, Maryland, Spirent Communications reported 2003 revenue of $394 million and has 1,800 employees worldwide. The company is the largest business group of Spirent plc, traded on the London and New York Stock Exchanges (LSE:SPT)(NYSE:SPM)(CUSIP number: 84856M209). www.spirent.com. Spirent Communications' sales to the United States government are made through Spirent Federal Systems. www.spirentfederal.com.

Spirent, Spirent Communications and the Spirent logo are trademarks of Spirent plc. All other trademarks or registered trademarks are held by their respective companies. All rights reserved.

This press release may contain forward-looking statements that are based on current expectations or beliefs, as well as assumptions about future events. By their nature, forward-looking statements are inherently predictive, speculative and involve risk and uncertainty because they relate to events and depend on circumstances that will occur in the future. You should not place undue reliance on these forward-looking statements, which are not a guarantee of future performance and are subject to factors that could cause Spirent's actual results to differ materially from those expressed or implied by these statements. These risks include the risks described from time to time in Spirent's SEC periodic reports and filings. We undertake no obligation to update our forward-looking statements, whether as a result of new information, future events or otherwise.