GoKawiilAs AI clusters grow larger, they begin to use optical interconnects for scale-out connectivity. However, the day when they require optical interconnects for scale-up connectivity may be approaching soon. To prep for that day, hyperscalers Microsoft, Meta, and OpenAI teamed up with hardware designers AMD, Broadcom, and Nvidia to develop a protocol-agnostic scale-up interconnection technology for AI clusters.
To do so, the group of companies this week established the Optical Compute Interconnect (OCI) Multi-Source Agreement (MSA) group to define an open optical connectivity specification for scale-up interconnections used inside large AI systems and racks to enable hyperscalers to use optical cables instead of copper to connect more accelerators at high speed and predictable power. In practice, this means the consortium will develop a common optical physical layer (PHY) and unified components to support various protocols, such as UALink for AMD and Broadcom, and NVLink for Nvidia.
The OCI connectivity technology for short-reach optical links used in AI racks and scale-up clusters will define a common PHY based on NRZ signaling and wavelength-division multiplexing (WDM), starting at four wavelengths × 50 Gb/s (200 Gb/s per direction) and scaling all the way to 800 Gb/s per fiber. Over time, the roadmap is expected to expand both wavelength counts and signaling rates, targeting 3.2 Tb/s per fiber and beyond as the ecosystem evolves. The technology will support pluggable optical modules, on-board optics, and co-packaged optics (CPO) integrated directly with compute silicon.
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"The growing need for optical scale-up interconnect to support large AI systems later this decade is clear," said Brian Amick, Senior Vice President, Technology & Engineering at AMD. "AMD is a founding member and strong supporter of the OCI MSA as it establishes an open specification for the industry to foster a robust, multi-vendor optical scale-up interconnect ecosystem."
The common optical layer will enable different processors and interconnect protocols to operate over the same fiber infrastructure and switches from different suppliers, ensuring flexibility for hyperscalers while retaining the competitive advantages of the protocols used by developers of AI accelerators, AI GPUs, XPUs, and other processors. In addition, the standardized OCI roadmap is meant to simplify system integration, reduce development risk, and shorten deployment cycles for new generations of AI hardware.
"Broadcom is proud to draw upon our multi-generational CPO platform and industry partnerships to drive the OCI specification forward," said Near Margalit, Vice President & General Manager, Optical Systems Division at Broadcom. "The OCI-MSA allows for seamless integration with existing electrical SerDes-based ASICs while providing a clear path to direct ASIC integration, ensuring the ecosystem remains flexible and high-performing."
While the OCI MSA group is headed by AMD, Broadcom, and Microsoft, which are known supporters of open industry standards, this is clearly not a traditional standard body like the Ultra Ethernet Consortium or UALink Consortium, which will have an impact on how the technology is developed.
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Firstly, the OCI MSA is hyperscaler-driven rather than vendor-driven. The arrangement is unlike most industry consortia, which are organized and led by independent hardware vendors (IHVs), IP companies, and networking suppliers.
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