Setting the stage
As the demand for higher network speeds and increased bandwidth continues to grow, carriers, cloud providers, and other network operators are increasingly adopting the latest advancements in optical networking, including 400G and 800G technologies.
The road to delivering faster, more reliable and more scalable networks is not without its pitfalls - challenges that could trip up even the most seasoned network engineers. Knowledge is power, however, and this article aims to provide valuable insights into the key technologies, use cases, and deployment scenarios that are driving the proliferation of 400G and 800G in modern networks. If you want to stay ahead of the curve in the fast-paced world of optical networking, this article is for you.
Advancements in 400G – a look at 400ZR and OpenZR+
The 400G OpenZR+ MSA is an open standard that provides a coherent solution for 100-400G Ethernet for distances and applications beyond that of 400ZR. Although it has many benefits over its predecessors, OpenZR+ also brings some implementation challenges to the table. To help you understand how to implement this coherent technology within your network, we will begin first by describing the differences between OpenZR+ and 400ZR. Then, we will explain the prime difficulties many network operators face when adopting OpenZR+.
To begin with,400ZR and OpenZR+ are two modern standards for pluggable, coherent 400G DWDM optics that offer the high capacity and high performance today’s network operators need. However, some significant differences have resulted in exciting capabilities and new challenges.
As an OIF standard, 400ZR [3] coherent optics provide 400Gbps of bandwidth over a single optical wavelength using DWDM. This technology enables point-to-point 400GbE Data Center Interconnect (DCI) for distances up to 80-120km, with the use of amplifiers but without the need for specialized optical transport equipment. The 400ZR standard was born from a hyperscale need for enhanced DCI performance using small form factor pluggable modules like QSFP-DD and OSFP. The OIF has done extensive work focused on the multi-vendor interoperability aspect of 400ZR optics and has held several plugfests and interoperability demonstrations [4].
In many ways, OpenZR+ can be thought of as the continuation of 400ZR, and this is one of the reasons it is also called 400G ZR+. Open, flexible and interoperable, OpenZR+ is the answer to the network operator's desire for a coherent solution that can offer greater functionalities over longer distances than 400ZR optics. In other words, communications service providers (CSPs) wanted the high-performance capabilities of 400ZR in a small form factor pluggable module but for applications and lengths beyond DCI.
According to the OpenZR+ organization’s website [5], this standard is a combination of two others – the DCI-oriented technology of 400ZR and the longer haul-oriented capabilities of Open ROADM. As a result, OpenZR+ can be used for metro, regional and long-haul purposes involving P2P extended reach and multi-hop network architectures. OpenZR+ enables operators to transform their networks towards an IP over DWDM (IPoDWDM) type of design, replacing some of the traditional transport networks. This will allow operators to drive CAPEX costs down and help automation and operations in the long run.
However, whenever advanced technology, broader capabilities and open standards meet with a network operator's need to leverage small form factors and reduce operating expenditures, implementation challenges always arise. OpenZR+ faces two major ones in particular: higher power requirements and a need for updated network management/orchestration tools.
Implementation challenges of OpenZR+
One of the most significant implementation challenges facing OpenZR+ operators is power consumption. While 100G transceivers generally consume around ~4W, and typical wideband 400G transceivers can use up to 10-12W, 400ZR optics for DCI typically need anywhere from 15-20W [6]. By contrast, OpenZR+ optics can require as much as 25W of power [7] per module.
The power consumption challenge of OpenZR+ optics creates further difficulty when it comes to implementation: the limitations of the data center operator or CSP’s host platforms. Consider a rack unit (1RU) in either a data center or a headend. With 400G, it is possibleto have up to 36 ports of 400G per 1RU [8] in a switch or router. However, with the power requirements of OpenZR+, not many host platforms will be able to handle a full 1RU of OpenZR+ at this density level.
Operators have also typically been used to having different teams dealing with IP systems and Optical/Transport systems, each with their own management and operational tools. Moving towards a network design where the Transport and IP functions are merged places increased pressure on the network teams to cooperate. This can be clearly seen with OpenZR+ since the Transport/Long-haul pluggables operate as part of the IP Routers/Switches. In addition to working more closely together, the convergence of Transport and IP functions also creates demand for a new set of management tools that can handle all the capabilities and operational requirements that the implementation of OpenZR+ pluggables require.
Transitioning to the world of 800G
As with anything in the world of technology, nothing stays the same for long. Demand for 800G is already being driven by an accelerating need for higher bandwidth in data centers and other communication networks.
The roadmap to 800G pluggables will be similar to that of 400G optics but with the potential for a few key differences. In some ways, the optical networking industry is better prepared for the transition, having already developed a plethora of standards for various 400G applications, including DR4, DR4+, FR4, LR8, SR8, ZR, and OpenZR+. We can expect that 800G optical transceivers will follow suit – in other words, we will see both pluggable grey 800G optics like SR8, DR8 and FR8 and also 800G coherent optics like ZR (among others) proliferate throughout the networks of the future. That said, the power consumption and thermal management demands of this new generation of optics will likely challenge the existing platforms of today’s network operators and shake up which models and form factors become prevalent.
For example, with 400G, the QSFP-DD form factor has become the more popular choice for network operators around the world. With 800G, however, it’s not at all clear that the journey for the QSFP-DD (800G QSFP-DD/QSFP-DD800/QSFP112) [9] and OSFP (as defined by the OSFP MSA) [10] form factors will follow the same trajectory. It all comes down to the questions of power consumption and thermal management.
Transitioning to 800G means packing even more advanced technology into form factors that have definitive size constraints. That means increased power consumption and a requirement for greater thermal resilience. This could very well mean that the advanced thermal management components (i.e., heat sinks, airflow passages) of the 800G OSFP specification become critical in enabling 800G at the level modern hyperscale cloud service providers require. How network operators choose between the 800G QSFP-DD and OSFP form factors will depend on the specific requirements of their intended applications and the industry's technological developments.
Addressing the challenges of 400G and 800G adoption
The best strategy for network operators to solve the implementation challenges of 400G and 800G is to find and work with vendors that are not only experts in manufacturing optical equipment but can also serve as a network systems integration partner. Every detail counts here - from the type of laser utilized in a transceiver, for example, to the type of metal alloy leveraged and much more. The optimal vendor partner is one that is equipped with state-of-the-art laboratories for rigorous stress testing of the optics and host platforms you rely on before they are placed within your network. The pathway to 400G and 800G is filled with questions and challenges, but it’s one that can be made simpler through effective partnerships.
Sources:
- www.oiforum.com/technical-work/hot-topics/400zr-2/
- www.oiforum.com/meetings-events/oif-ofc-2023/
- openzrplus.org/about-us/
- www.lightwaveonline.com/optical-tech/transmission/article/14188934/understanding-400zropenzr400zr-optics
- www.qsfp-dd.com/wp-content/uploads/2021/01/2021-QSFP-DD-MSA-Thermal-Whitepaper-Final.pdf
- www.arista.com/assets/data/pdf/Datasheets/Arista-400G_Optics_FAQ.pdf
- www.qsfp-dd.com/wp-content/uploads/2022/07/QSFP-DD-Hardware-Rev6.3-final.pdf
- osfpmsa.org/assets/pdf/OSFP_Module_Specification_Rev5_0.pdf
