EUGENE PARK 800ZR/ZR+
Similar to how oFEC provided performance enhancement at 400G, interoperable PCS enables a solution for networks with ROADMs as well as challenging links requiring an OSNR boost.
INTEROPERABLE PCS KEY REQUIREMENT ENHANCES 800G PERFORMANCE The second noteworthy industry agreement that differs at 800G compared to 400G is the recent adoption in the OpenROADM MSA group of an interoperable probability constellation shaping (PCS) transmission capability that provides additional OSNR margin at 800G (Figure 1). The interop PCS application-expanding capability is in some way analogous to how oFEC gave a boost resulting in performance beyond 400ZR, with interop PCS providing a boost beyond the OIF 800ZR specification resulting in 800 ZR+ for enhanced performance Ethernet transmission. The PCS algorithm shapes the optical transmission by assigning a higher utilization weight to the inner constellation points compared to the outer points, resulting in improved OSNR performance with a minimal increase in overhead. While previous implementations of PCS have been used in proprietary performance-optimized transport solutions, several key DSP vendors have collaborated in 2022 and 2023 to enable the industry’s first interoperable version of PCS that is power-optimized for 800G MSA pluggables. Similar to how oFEC provided performance enhancement at 400G, interoperable PCS enables a solution for networks with ROADMs as well as challenging links requiring an OSNR boost. Interop PCS provides the additional performance which enables 800G implementations to achieve similar reaches as 400G implementations based on 16QAM transmission, allowing for a straightforward scalable network evolution from 400G coherent pluggables to 800G coherent pluggables.
In addition to defining the industry’s first interoperable PCS, the OpenROADM spec at 800G also includes definition of Ethernet optimized framing modes. At 800G, these Ethernet optimized framing modes operate at the same baud rate as OTN capable modes, but replace the OTN overhead with additional PCS overhead that allows for even higher performance. With these modes defined by OpenROADM, we have a complete set of protocols for 800G optical interconnects, as we had with 400G. Based on the activities around the recent industry approach for 800G coherent pluggable interoperability requirements, we can see how the past has shaped the future. The OIF this time around incorporated the enhanced FEC, oFEC, into the 800ZR, compared to 400G when oFEC was adopted instead by the OpenROADM MSA. And for additional OSNR performance at 800G, OpenROADM adopted interop PCS which provides enhanced performance over 800ZR similar to 400ZR+. STANDARDIZATION EFFORTS ALREADY UNDERWAY FOR 1.6T Fresh off the heels of 800ZR, the OIF continues to keep itself busy, having already launched efforts in 2023 to achieve industry consensus on 1.6T coherent optical interconnect solutions. Although interoperable 800G coherent pluggables that address both OIF 800ZR and OpenROADM interop PCS enhanced performance applications are expected to be introduced into the market this year, the OIF is already plotting the course towards interoperable 1600ZR and 1600ZR+ implementation agreements. What is different this time around compared to the industry convergence efforts at 800G? As discussed earlier, while the OIF was responsible for
800ZR, it was the OpenROADM MSA that adopted the enhanced OSNR specification for 800 ZR+ performance. However, for 1.6T, the OIF has kicked off projects to define both 1600ZR and 1600ZR+. Regardless of where they are defined, it has become clear that there is a need for solutions that are highly optimized for the metro data center interconnect use case, as well as higher performing solutions that can address a wider range of network applications. Standardization of these solutions enables broad industry adoption that benefits both network operators and vendors.
Eugene Park is a Senior Technical Marketing Manager with over 20 years of experience in the optical communications industry. He has held previous strategy and product management roles in various levels of the optical food chain from carrier to components. He is currently part of the Acacia marketing team.
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ISSUE 36 | Q1 2024
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