One of the most significant areas we have seen driving new test and measurement requirements has been data center interconnect – DCI. This rapidly growing area leverages the emergence of pluggable coherent optics (DCO) to allow rapid scaling of data center interconnect bandwidth based on an open, multi-vendor ecosystem. For the DCI market to grow and meet expectations, we need to build an open ecosystem which can deliver reliable interop. This interop must be centered around extremely complex and highly integrated DCO optics, like 400G QSFP-DD ZR modules, which are now becoming available from many vendors.

While the industry has a lot of experience in the widespread and open deployment of client optics based on direct detect photonics, DCI requires wide-scale deployment of DCO. On the one hand, the additional power requirements and cooling needs have been quickly recognized. On the other, the increased challenges of coherent optics and extremely complex coherent module command and control are very new.

At VIAVI Solutions, we have been intimately involved in this ecosystem from the earliest days. We have taken the lessons we have learned along the way and incorporated them into our ONT and MAP test and measurement platforms (for more on the interaction between the ONT and the MAP check out this blog). This helps our customers successfully bring integrated and inter-operable products to the market.

But what, exactly, are the keys to successful interoperations? Three areas immediately spring to mind which are critical to a successful ecosystem:

  1. Photonic interop – The modules must inter-operate over defined optical links in a reliable and consistent way. Together, the ONT and MAP can be used to create a full-featured DCO photonic test stand for R&D, validation, and production.
  2. Module-to-host electrical interface – The high-speed electrical interface – based on PAM-4 signaling – must be robust and reliable, plug and play. Advanced PHY layer tools in the ONT help to quickly fingerprint any errors, well beyond simple error counting tools.
  3. Module management and control – The complex features of a DCO must be closely orchestrated with the host system, and all the key performance monitoring metrics must be reliably delivered from the module to the host in real time. The ONT integrates module management debugging tools with full-feature traffic generation and analysis. So the close relationship between module commands and performance monitoring with live traffic status can be quickly established and debugged.

All of these must come together before a product or system can be deployed and they are all deeply intertwined. When troubleshooting and integrating modules it is not possible to ‘fix’ each of the domains – photonic, data and control– separately. They are all pulled together by highly integrated DSP within the module all wrapped in advanced software and firmware.

In taking an integrated approach to debugging and integrating DCI systems with our VIAVI ONT we provide engineers with a true multi-domain toolkit. To find out more, please contact your local VIAVI representative. Our ONT products have been used across the whole chips, modules and systems of DCI to get the ecosystem underway.

About The Author

Paul Brooks currently leads the strategy for the VIAVI Lab and Production business unit. After a career in the Royal Navy as a weapons officer he spent time in a variety of roles with the communications test and measurement industry with a particular interest in enabling the high-speed Ethernet ecosystem. Originally from Ireland, he lives in Southern Germany where he laments the lack of first-class rugby. Paul holds a Ph.D. in opto-electronics from the University of Southampton.

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