The Power of Light - Coherent Optics Reshapes Networking
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The rise of router-based coherent optics: A new era for network efficiency
Network operators are constantly juggling a complex set of priorities. They need to boost capacity and efficiency while simultaneously slashing costs, simplifying operations, enhancing reliability and minimizing energy consumption. The relentless pursuit of lower total cost of ownership (TCO) is a constant in the networking industry. Fortunately, technological advancements continue to deliver solutions to this challenge. One such innovation, the introduction of 400G coherent pluggable optics for metro reach applications, has enabled the convergence of optical transport and IP layers, revolutionizing network architectures.
Hyperscalers quickly recognized the potential of this paradigm shift, pioneering the use of converged optical and packet for their metro data center interconnects. Service providers have followed suit, adopting 400G converged and reaping substantial cost benefits. Bell Canada, for instance, projects savings of $125 million CAD over the next decade, primarily due to a 27% reduction in capital expenditures.
These initial deployments of 400G coherent pluggables for router interconnects have led to the technology being dubbed "router-based coherent optics." Today, over 200 network operators have embraced this cost-saving approach, signaling a significant shift in network design.
The building blocks of change: 400G and open line systems
Several key factors have propelled the adoption of router-based coherent optics. The availability of 400G interoperable coherent MSA modules, which plug directly into router ports, has been instrumental. These modules enable high-capacity optical connections within a metro network without the need for traditional transponder hardware. The market has seen the emergence of two primary form factors for these 400G modules: QSFP-DD and OSFP, with QSFP-DD currently dominating shipments due to its alignment with widely adopted host platform slots.
The disaggregation of optical line systems has further accelerated the adoption of this technology. Open line systems allow for the insertion of wavelengths from router-based coherent MSA pluggable modules rather than relying solely on transponders from the same line system vendor. Most (approximately 70%) of the networks using router-based optical modules are deployed over these open-line systems.
The development of 400G coherent modules with high transmit optical power has also played a crucial role, particularly for service providers. Higher transmit power mitigates performance issues when connecting to existing ROADM architectures. These advanced modules often incorporate a tunable optical filter (TOF) to minimize adjacent channel interference, which is crucial in networks with colorless ROADMs.
While progress has been made, seamless management of coherent MSA modules remains an ongoing area of development. Industry bodies like the Optical Internetworking Forum (OIF) are actively working on solutions, with the Common Management Interface Specification (CMIS) being a key focus to further streamline the adoption of router-based optics.
Expanding the horizon: 800G and beyond
To maintain the momentum of router-based coherent optics, it was essential to expand the capabilities of interoperable MSA pluggable modules to address a broader range of network operator needs, including long-haul and ultra-long-haul reaches, and to facilitate the transition from 400G to 800G links. Recent advancements in coherent technology have made these capabilities a reality.
400G ultra-long-haul (ULH) modules, utilizing Class 3 (~120+ Gbaud data rate) technology, extend the reach of 400G from metro and regional to ultra-long-haul distances. This removes barriers for network operators deploying router-based coherent optics in virtually any network application. Successful trials of 400G ULH modules over substantial distances have demonstrated significant reductions in CAPEX and OPEX.
As switch and router chip capacities increase, I/O ports are migrating from 400G to 800G. The same Class 3 generation coherent technology also supports 800G interoperable coherent MSA modules that plug directly into these platforms. This allows operators already using 400G converged coherent optics to upgrade to 800G seamlessly. Recent trials of high-performance 800G ZR+ coherent pluggable optics in leading router platforms underscore this progress. These 800G optics enable doubling packet core capacity per link while reducing power per bit.
These advanced modules leverage state-of-the-art coherent technology, incorporating high-performance DSP ASICs and silicon photonic integrated circuits (PICs). This integration enables low power consumption, compact form factors and industry-standard compliance. Many 800G ZR+ modules feature standardized interoperable probabilistic constellation shaping (PCS) mode, enhancing performance and reach. Furthermore, vendors offer a wide range of 400ZR and OpenZR+ compliant modules, including high transmit power options for optimized performance in metro/regional IPoDWDM networks. The momentum of IPoDWDM using router-based coherent optics continues to accelerate, driven by these advancements in pluggable module technology. This trend offers substantial total cost of ownership (TCO) reductions for network operators, empowering them to build more efficient, scalable and cost-effective networks.
The adoption of router-based coherent optics for converged networks has expanded beyond hyperscalers and service providers to include research and education networks, enterprise networks, and numerous other operators seeking TCO optimization. The technology's applicability extends beyond routers to network switches for fabric extension, enabling interconnects to remote sites.
Addressing the management challenges of converged architectures
While the benefits of converging are clear, managing this new paradigm presents unique challenges. A recent Heavy Reading survey highlighted key concerns, including multi-vendor management, the coexistence of pluggables and transponders, the blurring of layer demarcation, and limitations in management capabilities.
Multi-vendor environments require consistent operational practices across coherent pluggables from different suppliers. This necessitates open optical management solutions supporting common data models and APIs, enabling vendor-agnostic control. Simultaneously, using pluggables and traditional transponders within the same DWDM line system requires a unified management approach. A single solution that provides a consolidated network view and consistent workflows for both types of optical engines is crucial.
Converged blurs the traditional separation between optical and IP layers, as coherent pluggables reside within IP devices (routers). Maintaining operational practices in this converged environment requires careful consideration of control architectures, allowing for independent management of the optical and IP domains while enabling seamless interaction.
Concerns about limited management capabilities due to gaps in specifications, interworking issues and perceived limitations in pluggable functionality are being addressed through the ongoing development of standards like CMIS and OpenConfig. These standards are evolving to keep pace with coherent technology and ensure smooth interoperation between pluggables and hosts. Host-independent management approaches, like those specified by the Open XR Optics Forum and the OIF, offer further flexibility and mitigate potential CMIS inconsistencies.
The industry is actively working to address these management challenges, with solutions to provide comprehensive support for converged deployments and flexible integration with various management architectures. Collaboration between vendors and operators is key to developing robust and tailored solutions that unlock the full potential of this convergence.
Summary
The rise of router-based coherent optics marks a significant turning point in network evolution. By enabling the convergence of IP and optical transport layers, this technology empowers network operators to achieve unprecedented levels of efficiency, scalability and cost-effectiveness. The widespread adoption of 400G and, increasingly, 800G pluggable coherent modules, coupled with advancements in open line systems and high-power optics, has fueled this transformation. While management challenges related to multi-vendor interoperability and layer convergence remain, ongoing standardization efforts and industry collaboration are paving the way for seamless integration and operation. The continued development of this technology, including higher data rates and extended reach capabilities, promises to further solidify the role of router-based coherent optics in shaping the future of networking and enabling the next generation of high-bandwidth applications.