Keeping the Pulse on 400GE in the Data Center
2018-10-29 | 5 min read
At the heart of every data center is the transceiver. Large hyperscale data centers have more than 50,000 optical fibers in them. With a transceiver at each end of the fiber, these data centers house upwards of 100,000 transceivers. Once deployed in data centers, marginally performing transceivers can bring down the network link, lowering the overall efficiency of the data center as the switches and routers need to re-route the faulty link. The cost associated with failed transceivers in the data center is enormous, even a small one-tenth of one percent failure rate would equate to 100 broken links.
Traditionally, service providers were the early adopters of new technology and the first to test network transceivers for the next speed class. However, applications such as virtual reality (VR) and artificial intelligence (AI) drive the urgent need for increased networking bandwidth within the data center. Data center operators no longer have the luxury of learning from the growing pains of service providers. They need to upgrade data center network speeds from 100 gigabits per second (Gb/s) to 400 Gb/s to meet the ever-growing demand for bandwidth and high-speed access to high-density storage. Data center operators rely upon transceiver manufacturers to ensure the highest quality and performance of next-generation 400GE transceivers.
Characterization and Compliance Test
Several standards organizations, such as the Institute of Electrical and Electronics Engineers (IEEE), International Committee for Information Technology Standards (INCITS) and the Optical Internetworking Forum (OIF), govern optical transceiver specifications and define test procedures to ensure compliance to standards and interoperability with other vendors. Standards organizations define specifications and provide compliance test procedures to ensure that a receiver will operate with a worst-case transmitter and vice versa. There are different sets of optical and electrical tests for transmitters and receivers, and the tests must also include channel quality impairments. As systems become faster and more complex, it is also necessary to test receivers using non-ideal signals with different types of impairments or stressed signals. Since performance levels usually vary significantly from one generation to the next, standards and components often evolve together.
The standard configuration for 400GE transceivers is to use eight lanes of PAM4 traffic operating at 56 Gb/s per transceiver. For most standards, there are at least six different compliance tests suites to execute on each lane. It can take several hours to test a single transceiver manually. Any problems associated with the test setup or calibration found during testing can extend test time to several days. Since 400GE transceivers using PAM4 require complex circuit designs not previously used in non-return-to-zero (NRZ) based 100GE designs, it is difficult for test engineers to determine which component caused a failure. Fortunately, the methods that describe how to characterize 400GE designs are more stable, and engineers can review and follow the guidelines outlined in the standards when developing their test plan to characterize their transceivers.
Test Automation Software
Test automation software can reduce test time down from hours to minutes. Choosing automated compliance test software that is verified to test to the exact specifications of each technology standard is essential. Test automation software provides insights to the test engineer about any detected issues and can quickly pinpoint failures, saving hours of debug time. Test automation software guides the test engineer through setup, calibration and compliance measurements, and allows them to quickly run through test cases without being an expert on test procedures. By using compliance test applications, transceiver manufacturers can ensure that a test that passes in their lab will also pass in their customers' labs. More importantly, ensuring transceivers are compliant to standards will minimize the risk of interoperability issues with network switches and routers once installed in data centers around the world.
Find solutions for your data center transceiver test challenges here.