Today's testing, tomorrow's engineers

Staff and students combine to form a unique test lab that's widely respected in the data-communications industry.

Martin Rowe, Senior Technical Editor -- Test & Measurement World, 4/1/2006

READ OTHER APRIL ARTICLES:  Contents, April 2006 WEB-EXCLUSIVE TESTIMONIALS: Engineers tip their hats to the UNH-IOL SIDEBARS: Catch the Rabbit Let the students do the testing

Durham, NH—You may not think of New Hampshire as a hotbed for data-communications testing, but you should. In this town a few miles from the seacoast resides the University of New Hampshire InterOperability Laboratory (UNH-IOL, www.iol.unh.edu), part of the UNH Research Computing Center. The UNH-IOL is a testing lab that has the respect of just about every maker of data-communications equipment. Since its founding in 1988, the UNH-IOL has become known for its technology expertise and for a spirit of cooperation that helps member companies solve conformance and interoperability problems.

The UNH-IOL currently tests products in 20 technology categories, including Ethernet, DSL, IPv6, Serial Attached SCSI (SAS), Serial ATA (SATA), Fibre Channel, and Wi-Fi. Companies join the UNH-IOL to take advantage of its heavily equipped test beds and extensive technical resources. Test beds contain hardware and software tools developed at the lab for performing compliance tests, and they also contain networking equipment from member companies that the lab uses for interoperability testing. For an annual membership fee ranging from $14,000 to $20,000, a member company may reserve week-long blocks of individual testing on a test bed and participate in week-long group tests, called "plugfests." Some companies belong to more than one technology group; the lab refers to each group as a "consortium." (Editor's note, 4/21/06: This section has been amended since the article was published. The original wording implied that members were permitted to use the lab for only one week per year or attend only one plugfest per year. This is not the case.)

Students perform most of the tests, which cover components such as communications ICs, subsystems such as network-interface cards, and network elements such as switches and routers (see "Let the students do the testing"). Member companies often send an engineer to the lab for a week to work with students on standards compliance testing or interoperability testing. "Catch the Rabbit," highlights how Rabbit Semiconductor used the UNH-IOL when the company added Ethernet to its microprocessors.

Student Aarti Patel performs a test using the IPv4 Interoperability test bed.

The test beds are richly equipped, because companies that join a lab consortium must agree to contribute their products. "We have networking and communications equipment that companies won't give to each other," said Gerard Nadeau, manager of the UNH-IOL's Fast Ethernet Consortium. "We act as a buffer between companies, and we can work out problems without giving away proprietary technology."

"Some companies leave every product they bring to the lab," added Bob Noseworthy, manager of the lab's 10 Gigabit Ethernet Consortium. "But 10-Gbps products are expensive, so we may share products with the IPv6 Consortium."

Because companies provide products for the test beds, their products are continually tested against new products. "We've found interoperability problems with equipment that's been on the market for years" said staff engineer Andy Baldman. "When that occurs, we contact the manufacturer and explain how their product interacts with a new device."

UNH-IOL clients appreciate the lab's role as a technology intermediary. "The UNH-IOL gives us a neutral ground," said George Dobrowski, director of technology and product planning at Conexant, a member of the lab's DSL Consortium. "We can bring our DSL chips there for a week of intense testing." Conexant uses the DSL test bed to run interoperability tests on new designs because "the UNH-IOL has equipment combinations that we can't replicate in our own lab."

Beds and tools

Test beds contain networking equipment, test equipment, and test tools. Often, staff and graduate students develop hardware and software test tools before such tools are commercially available. "We have, on occasion, used a company's prototype or evaluation board as the basis for developing a test tool," said Nadeau. "If member companies give us the hooks into their products, we can design a somewhat automated tool for more in-depth analysis than we could achieve with standard test equipment."

The lab has several Ethernet test tools that graduate students and staff have designed in collaboration with member companies. But because the lab lacks the facilities to fabricate test boards, member companies often pitch in to design and build them.

Figure 1.  The “Tiger” board provides access to Ethernet ICs and lets students view serial data in a parallel format.

One such test tool is the "Tiger," designed by UNH-IOL and Texas Instruments (Figure 1), for testing Gigabit Ethernet (GigE) and Fibre Channel devices. The Tiger provides students with access to an Ethernet IC's signals. It provides 20 digital outputs that connect to an Agilent Technologies logic analyzer. With the tool, students testing GigE ICs can see a parallel representation of a GigE data stream—while the data is in a 10-bit format. They can view two 10-bit sequences at once on the logic analyzer. (GigE uses 8b/10b encoding that converts 8-bit data into 10-bit data. The extra bits add bit transitions to provide for clock recovery.)

Another test tool used for Ethernet testing lets students view a Fast Ethernet Auto-Negotiation sequence, which is a significant part of conformance testing. This tool consists of a custom interface board (Figure 2) that connects to a digital I/O card from Viewpoint Systems that then connects to a PC. The Auto-Negotiation sequence consists of a series of 100-ns pulses that occur at 100-ms intervals. The interface board contains one-shot flip-flops that elongate the pulses to lengths long enough for the digital I/O board to capture them. A custom software application written in LabView provides a graphical display of the sequence.

Figure 2.  An Ethernet Auto-Negotiation test tool provides a parallel representation of bits between two Ethernet devices.

When performing tests, the students follow carefully written test procedures that describe how to set up and run tests based on clauses in communications standards. The procedures, available for downloading from the UNH-IOL Web site, clarify ambiguities in standards that require measurements without specifying how to make them.

UNH-IOL engineers play an important role not only in interpreting industry standards but also in helping to develop them. For example, consortium managers Eric Lynskey (Ethernet in the First Mile) and Bob Noseworthy (10 Gbit Ethernet) and others regularly attend committee meetings of IEEE 802.3 Ethernet subcommittees, and they often edit IEEE standards documents.

Physical-layer measurements

The Tiger and Auto-Negotiation test tools let students test Ethernet products at the Ethernet physical (PHY) and data-link layers, but much of the lab's conformance testing for Ethernet and other technologies focuses on the analog signaling in the PHY layer. Jitter is perhaps the most critical PHY-layer measurement, and the UNH-IOL has been a pioneer in the area. Andy Baldman measures jitter in serial data streams by capturing them with high-bandwidth oscilloscopes from Agilent, LeCroy, and Tektronix. Although today's oscilloscopes can perform jitter analysis, the UNH-IOL staff created its own tool using Matlab when the lab started offering jitter conformance testing for Token Ring networks.

Student Matt Hersh (left) gets assistance with a Gigabit Ethernet test board from staff engineer Andy Baldman.

"Once upon a time, scope companies just made scope hardware, so we had to develop our own software tool for separating total jitter from deterministic jitter," said Baldman. Because he knows exactly how his algorithm works, he can answer questions about how the measurements were made when a product fails.

Baldman will use a scope maker's internal conformance software if he knows its algorithm. He spent the summer of 2005 working for Agilent Technologies on the company's Ethernet compliance software. He started using it because he knows how it works, but he also knows that engineers in the industry use scopes from other makers. Thus, he compares results obtained from Agilent, LeCroy, and Tektronix scopes. He's working with test-equipment makers to harmonize the methods of jitter measurement to provide more consistent results.

Baldman's relationship with test-equipment makers is typical of other UNH-IOL staff members. Much of the test equipment in the lab is donated, and staff and graduate students often develop their test procedures that use the donatedequipment.

"We can't get out of the starting gate without test-equipment makers," noted Noseworthy. "The difficulty is that we try to play evenly with all the manufacturers." Test-equipment makers also rely on the UNH-IOL for their own product testing, often bringing new equipment to the lab for evaluation.

Students and staff use test equipment for more than just measurements. The lab's DSL Consortium, managed by Matthew Langlois, uses data generators from Spirent Communications and wire-line simulators from Spirent, Telebyte, and Sparnex to test DSL modems and DSL access multiplexers (DSLAMs), which are used by service providers. Data generators create data streams and wire-line simulators simulate worst-case line conditions for each of the DSL modulations that the lab supports (ADSL1, ADSL2, ADSL2+, and VDSL2).

Figure 3.  Students use the DSL test bed to perform compliance and interoperability tests.

During a compliance test, a digitizer captures the DSL signals on a phone line and transfers them to a PC through a National Instruments digital I/O card. The PC measures longitudinal balance, transmit power, noise margin, and bit-error rate. The digitizer acts as a digital storage oscilloscope with flexible sampling clocks and an arbitrarily deep capture buffer greater than 512 Mbytes, which far exceeds that of commercially available scopes. With the digitizer card, students running a test can store as many samples as they need in the PC's hard drive and perform signal analysis offline.

The DSL test bed (Figure 3) consists of five DSLAMs and hundreds of DSL modems. DSL modem makers and chipset makers such as Conexant come to the lab because the test bed has DSLAMs from all suppliers. Modem makers can typically use the lab's standard test suite, although some will run customized tests. "The standard test suite takes about 18 hours to run," said Langlois. "It takes a week to run through all five DSLAMS."

Testing the next Internet

While the UNH-IOL focuses heavily on deployed technologies such as Ethernet and DSL, the lab is also involved in the next Internet technology, IPv6. "IPv6 is the next Internet protocol," said technical manager Erica Williamson. "With IPv6, we should never run out of IP addresses."

The UNH-IOL is a leading IPv6 test lab, with a test bed that consists of routers, firewalls, servers, cameras, a network time server from Symmetricom, and router and network testers from Agilent and Ixia. Makers of voice, video, and data-communications products come to the UNH-IOL to test their IPv6 protocol stacks. Test tools include software that lets students and staff manipulate data traffic. "We look at every 'must' and 'should' in the protocol specification to see how an equipment maker implements it," said Williamson. Testing of an IPv6 product takes from one to two weeks.

The lab's IPv6 Consortium's test bed includes a connection to the world's largest IPv6 network. Dubbed the MoonV6 project (www.moonv6.org), the IPv6 network is a joint effort led by the North American IPv6 Task Force that includes the UNH-IOL, the Department of Defense, and network service providers. Its aim is to promote the use of the IPv6 protocol. At a MoonV6 plugfest, makers of video and voice equipment, routers, and firewalls test their products for interoperability.

While IPv6 is an up-and-coming technology, 10BaseT Ethernet is mature and stable. Thus, the UNH-IOL has dropped its 10BaseT Ethernet Consortium, but the lab still tests new 10BaseT products on an individual basis for backward compatibility and conformance.

Serial-bus technologies that are gaining in popularity include SAS and SATA. The UNH-IOL has formed the SAS Consortium, which currently has five full members, but it supports SATA as a testing service only. "We're trying to convince companies to help us start an SATA consortium," said Baldman. He's currently developing test beds for both serial buses. Part of the difficulty stems from these products being so new that manufacturers often don't have many samples to contribute.

Makers of SAS and SATA disk drives and host-bus-adapter cards can use the UNH-IOL to perform interoperability tests under specified worst-case conditions. The test beds that Baldman is developing use a "golden worst case" set of cables built by Molex specifically for the lab. The cables come in three different lengths and gauges although they produce identical amounts of signal loss.

"Some companies want different lengths so they can say their products were tested with different length cables," said Baldman. "While the cables may be equivalent from a signal-loss perspective, the ability to demonstrate that you work across different length cables is still very valuable to our members from a marketing perspective."

Although the UNH-IOL is best known for testing wireline technologies, its staff and students can test IEEE 802.11 wireless devices, too. Jeremy Kent manages the lab's Wireless LAN Consortium, which contains a precompliance test bed (the UNH-IOL is a certified Wi-Fi precompliance lab). The lab has dozens of wireless devices that let students perform interoperability tests. The test bed includes wireless test systems from Azimuth Systems and VeriWave as well as a vector network analyzer and signal generator from Rohde & Schwarz. The test bed can perform measurements such as transmit power and protocol analysis. A graduate student is developing a receiver test tool as part of a master's thesis.

The UNH-IOL has gained the respect of many people in the data-communications industry. Its test tools and procedures are the envy of many engineers. IC manufacturers, card manufacturers, network-equipment manufacturers, and test-equipment makers rely on the UNH-IOL's spirit of cooperation and technical expertise to verify that their products will work in the field.

Catch the Rabbit During my visit to the UNH-IOL, I met Lynn Wood, an engineer with Rabbit Semiconductor. Rabbit is adding Ethernet to its processor ICs, and Wood spent a week at the lab running compliance tests. Wood tested receivers, transmitters, complete Ethernet subsystems, and software drivers. This was Wood's second visit to the UNH-IOL for this project. After performing basic function tests in his lab, Wood came to the lab because, "If you look at the Ethernet spec, you can't figure out what to test. UNH-IOL has worked all of that out." On his first visit, Wood worked with his device in FPGA form because he could quickly make design changes based on test results. This time, he was there to test the final FPGA design before the company commits to building it in ASIC form. Wood performed 10BaseT Ethernet transmitter and receiver PHY-layer tests under worst-case conditions. He tested his devices using long cables and used a UNH-IOL tool to create simulated signals with varying jitter, crosstalk, skin effects, return loss, and rise time. The test tool uses Matlab scripts to generate Ethernet worst-case signal conditions. Wood performed bit-error-rate measurements to verify that the receivers could maintain 10–12 BER or less under worst-case conditions. Let the students do the testing Students play a major role at the UNH-IOL. In fact, about 100 of the 120 UNH-IOL employees are students, most of whom are undergraduates majoring in electrical engineering or computer science, although some have nonengineering majors. Students do the lab's testing under guidance from a graduate student or staff member. Students learn about the UNH-IOL from open houses, through friends, or through faculty members. A professor may recommend a student to the UNH-IOL for a position. Students typically work about 15 hours per week. "We assume no knowledge of computer networks, and we assume that everything a student knows about networks is wrong," said EFM Consortium manager Eric Lynskey. The UNH-IOL usually hires first- or second-year students. After being hired, students must spend 13 weeks at "boot camp" during the summer, where they learn the basics of computer networks and become familiar with the lab's test tools. Students do most of the testing, using hardware and software test tools developed by staff engineers and graduate students. "Students will learn LabView and Matlab, and once they gain enough experience, they can tweak test code," noted Lynskey. Sometimes, a student will develop a test tool for academic credit such as a senior project or a master's thesis. In addition to gaining practical experience from their UNH-IOL jobs, the students also make industry contacts that often lead to employment after graduation.

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