Common Electrical Interface and 25G



In the early 2000s, there was open debate as to what building blocks would be required to develop next generation 100 Gbps port speeds. And while the initial 100 Gbps specification was complete, it was based on ten lanes of 10 Gbps and not scalable to future speeds. It soon became clear that the industry needed new standards to build 100 Gbps ports with less lanes instead of ten.

Beginning in 2004, OIF started working on the Common Electrical I/O CEI for 25/28 Gbps as a next-generation building block. Upon the project’s completion and release of OIF’s implementation agreement (IA), the use of 25/28 Gbps CEI had widespread adoption and a significant positive impact on the networking industry. The roadmap for server access, cloud networking, and almost every other networking component rapidly shifted towards 25 Gbps. Today, 25/28 Gbps is so ubiquitous that even silicon in the campus segment offers 25 Gbps uplinks instead of 10 Gbps and in the data center segment, 25 Gbps electrical lanes dominate, comprising over 50% of the volume in 2018.


Strong industry participation and initial attention from cloud providers in OIF led to a 25/28 Gbps specification that became foundational and a building block for the industry for the next 15+ years.

The 25/28 Gbps specification was challenging – the solution to physically obtaining high speeds over media in a way that could be easily manufactured took many companies and individuals to overcome. The output of the first specification, 25G-LR for 1-meter backplane distances, quickly led to several other distance specifications meant to handle shorter chip-to-chip connections as well as host to module and links inside the server/storage and NIC boards.

The 25/28 Gbps electrical link IAs were transformational to the industry, not only for the ability to drive higher speed networking at the right time for Cloud providers, but also in laying the groundwork for a repeatable process for higher speeds to come. Many industry leaders today use the methodologies and best practices that were developed and fine-tuned by OIF in creating the 25/28 Gbps specifications.

One of the most important building blocks in the IA was the very short reach (VSR) channel definition that enabled separation of host and module specifications (in a way one of the earliest forms of disaggregation). Separation of host and module specification allowed companies to build and test their systems and components independently (often the module supplier is different from the system and chip supplier) and verify, that by meeting the spec, they would be interoperable. Separation of host and module specification also allowed for faster development of products and more rapid qualification cycles at customers. Independent engineering programs also allowed for better optimization of the switch, modules and the integrated system. Additionally, robust interoperability and faster time to market allow Cloud providers to grow and have a widespread impact throughout the industry leading to robust vendor selection and product offerings for enterprises and network operators.

An additional benefit resulting from OIF’s CEI 25/28G initiative was the definition of an asymmetric channel, enabling the optimization of module and host usage of power and complexity. Much of the power and capability could be put in the host switch ASIC while allowing minimization of module complexity and power, striking a balance of performance, improved manufacturability and optimized system operation.

The industry’s ability to continue to increase port density while moving to higher speeds has benefited everyone. One of the early reasons why 10×10 Gbps lane variants of 100 Gbps didn’t see wide-spread adoption was the size, power and density of the original 10 x10G optics with line cards limited to just a handful of ports. Today, 32-port 100 Gbps switches are common, and with OIF’s IA for 25/28 Gbps, the industry can scale, as evidenced by 400 Gbps starting at the same port density as prior generations.


Cloud providers continue to rely on OIF to drive interoperability in the industry. With serial 100 Gbps electrical interfaces getting closer to completion, OIF will turn to working on the development of even higher speed interfaces. The industry is expected to quickly shift to planning 25.6 Tbps and 51.2 Tbps switches based on 100G electrical interfaces while OIF continues to work on specifications for even higher capacity solutions. System speeds beyond 800 Gbps and switch ASIC capacities topping 100 Tbps will all rely on the work OIF and its members will be doing over the next several years.


Authored by: Alan Weckel, Technology Analyst at 650 Group