Need High-Speed Network Testing? Who You Gonna Call?
By Dr. Eric Bogatin
www.BeTheSignal.com
November 2006
“We are the Switzerland of the networking industry,” says Andy Baldman, member of the senior technical staff at the InterOperability Lab at the University of New Hampshire (www.iol.unh.edu). The InterOperability Lab (UNH-IOL) is the largest and most extensive independent testing lab for the high-speed networking industry.
The lab focuses on 20 different network technologies or “consortia," encompassing wire-line, wireless and optical fiber (ranging from 10baseT to 10 Gbit Ethernet), and an alphabet soup of protocols such as DSL, SAS, SATA, and IPv6.
Established in 1988 and affiliated with the University of New Hampshire, the lab operates as a nonprofit, independent, and transparent test service. The lab's portfolio of tests spans all the important IEEE 802.x communications specs.
With close ties to the IEEE committees that create the specs, the staff of the UNH-IOL is expert at interpreting and creating compliance tests based on those specs. In addition, because virtually all leading providers of network products are their clients, the lab has examples of all the popular last generation, current generation, and some of the next generation network products. These are available to test interoperability with other products.
Over the years, some of the tests have required the creation of specialized testing tools. For example, to evaluate fast Ethernet systems operating at 125 Mbps, the team needed to re-create the entire range of signal quality, from best to worst case attenuation and distortion, for cables 1 m to 100 m long. The bitstream signal after passing through these cables is the input to test the receiver quality of attached devices.
Figure 1 shows Andy Baldman, MTS, with his custom design test for the serial ATA (SATA) interface between a PC and a disk drive. Baldman started in the lab as a sophomore 10 years ago and never left. After receiving his BS degree, he continued working at the lab while pursuing an MS degree and is now a full-time staff member.
Figure 1. Andy Baldman, MTS
Instead of sifting through hundreds of cables and storing the best and worst ones as golden standards, the staff emulated cable performance in MatLab code. By modeling the delays, distortions, and losses of a cable with a few parameters, they were able to synthesize the transfer function for any cable.
A precision, distorted 125 Mbps bit pattern is then turned into a real voltage signal with a fast arbitrary function generator and fed into the network device under test.
Like many of the lab's tests, the details of the procedure and even the software are available so members can duplicate all the tests at their own facilities.
“We are more than a test house,” Baldman says. “Our mission is to help the industry and train the next generation of engineers.” The expert staff works closely with member companies to help debug their products.
Member companies send their product designers to the lab to perform real-time product development. “We often have the designer testing their product in our lab during the day and re-writing the code at night to spin multiple designs in a week,” Baldman says.
For an annual fee, a company can join one of the specific network protocol consortia and have access to extensive compliance testing, the valued UNH-IOL test report, and an invitation to participate in “plugfests.”
A plugfest is a free-for-all “party” where 10 to 50 companies get together in one room and test the compatibility of their network products with the products of other participating companies. Of the 32,000 square feet of total lab space, the UNH-IOL allocates 7,500 square feet to a “Group Test Period” lab with identical set-ups of optical and wired cables in each station. This lab is neutral territory where competitors can evaluate the compatibility and interoperability of their specific products with a wide variety of network hardware and software.
Figure 2 shows the well equipped 7,500 square foot test floor where many plugfests are held.
Figure 2. 7,500 Square Foot Test Floor
Perhaps the most valuable function of the UNH-IOL and what makes it unique, is the number of students involved in the testing. According to Kristin Harris, the lab's Customer Relations and Marketing Manager, there are more than 100 undergraduate students and 20 graduate students working on staff in the lab. Over the 18 year history of the lab, more than 600 students have graduated with hands-on, practical experience.
“We provide practical applications and real-world experience to all of our students,” Harris says. And this real-world experience has high value to the students. According to Harris, the placement rate for their students in industry jobs upon graduation is 95 to 100 percent.
With an 18 year track record and a base of 157 member companies, the UNH-IOL has established a solid technical reputation and willingly shares their expertise with the current generation of network engineers and contributes a significant fraction of the next generation of network-aware engineers.
This and other signal integrity topics are covered in Eric’s public classes and online lectures, available from his website, www.BeTheSignal.com. Send your signal integrity technical questions to DoctorIsIn@BeTheSignal.com
Reader Q & A
If you have a question for the SI Doctor, please send it to DoctorIsIn@bethesignal.com.
Question from Rick in Laurel, MD: What is TX and active RX equalization?
Answer: TX equalization is the generic term for the signal processing on the transmitted signal. This is also referred to as pre-emphasis or multi-tap pre-emphasis. It usually consists of adding or subtracting a small voltage to each bit to counteract the influence of the interconnect. RX active equalization is a gain curve on the receiver channel that typically has higher gain with increasing frequency. This increasing gain “equalizes” and balances out the increasing insertion loss of a typical, lossy interconnect.
Question from Jeff in Santa Rosa, CA: Doesn’t increasing microstrip line width lead to frequency-dependent propagation because frequency is close to higher order evanescent waveguide modes?
Answer: While you are absolutely correct that microstrip shows transverse modes, which cause dispersion, excessive loss, and frequency-dependent impedance, these modes do not become apparent until the line width is comparable to a fraction of the wavelength of the highest frequency component of the signal. For a 10-mil-wide line, the wavelength is about 50 mils, which corresponds to a frequency of about 100 GHz. If the line width is 250 mils, the turn on of transverse modes is 4 GHz. As long as line widths are narrower than 50 mils, you will never see transverse mode effects below 20 GHz. This is a great example of how we can separate myth from reality by “putting in the numbers.”
Bio: Eric Bogatin is president of Bogatin Enterprises. Many of his papers are available on his website, www.BeTheSignal.com. He is the author of Signal Integrity - Simplified, published by Prentice Hall.
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