Flexible net

Network elements such as routers, firewalls, gateways, and virtual private network (VPN) clients used by small businesses and home offices for access to corporate LANs and WANs. The devices contain Ethernet, Frame Relay, ATM, T1, and E1 ports.

Test the products for voice over Internet Protocol (VoIP) voice quality and for network performance. Tests must include interoperability with Frame Relay and ATM networks and edge-network switches. Make the test bed flexible enough to incorporate various network elements while maintaining stability.

• Agilent Technologies: voice quality measurement system. www.tm.agilent.com.
• Spirent Communications: network performance measurement system, bulk-call generator. www.spirentcom.com
• Ixia: network performance measurement system. www.ixiacom.com
• Radcom: WAN protocol analyzer, voice quality measurement system. www.radcom.com
• Network elements from Cisco Systems, Redback Networks, CopperCom, General Bandwidth, Marconi, Tekelec, and others.

Adtran (Huntsville, AL) makes network elements that must work with equipment from numerous manufacturers to transmit digitized voice signals using voice over Internet Protocol (VoIP). In addition, the networks may use either the H.323 protocol or the session-initiation protocol (SIP) to establish and terminate calls.To qualify a new design for the company's NetVanta product line, project engineer Chuck Rehage and others built a test network that includes elements from Adtran and several other manufacturers. While the network sends and receives voice packets, test equipment monitors network performance and calculates voice quality.

The test network (see figure), in use for three years, evolves as technology changes. Its flexible design lets Adtran test any of its NetVanta products for voice quality and network interoperability. Because Adtran's gateways and routers play different roles in a network, the test network must accommodate many configurations.

Rehage uses VoIP testers from two manufacturers to measure voice quality, packet loss, packet jitter, and throughput. "Network-element and test-equipment designers can interpret complex protocols such as H.323 and SIP differently," he notes "which can lead to interoperability problems among competing products." He also uses network-performance testers from two companies to generate 100-Mbps and 1-Gbps test packets, to test routing capabilities of the gateways, and to perform protocol analysis. "We use competitive testers because each has unique features and we can perform more comprehensive tests than are possible with one tester," He adds.

The network-performance testers generate digital data for the network, but some of Adtran's routers have analog voice ports that connect to a private branch exchange (PBX). A bulk-call generator places analog calls into the network, which simulates the way users might configure their networks.

The network lets Adtran test multiple units in the same configuration or test one unit in multiple topologies with minimal physical changes. It permits quick changes to the EUT. Engineers can test multiple units without fear of interference between tests, and the network's flexible topology promotes easy comparisons between products. It's also stable, which promotes repeatable test results that increase the engineers' confidence in the tests.