Broadcom challenges Nvidia with 51.2T switch silicon • The Register

Broadcom says it has doubled the capacity of its merchant switch silicon with the launch of the 51.2 Tbps Tomahawk5 ASIC this week.

Broadcom’s Tomahawk line is aimed at hyperscale and cloud customers, and its latest ASIC promises to significantly increase port density while reducing power consumption compared to previous-generation chips. Tomahawk5 also brings the company up to speed with competitor Nvidia, which unveiled its own 51.2 Tbps Ethernet switch at GTC this spring.

Using the ASIC, the company expects OEMs to which Tomahawk5 is already shipping samples to ship switches with 64 800-Gbps ports or 128, 400-Gbps, or 256 200-Gbps ports by early next year /s ports will begin.

“Every two years we doubled the bandwidth of the silicon,” said Pete Del Vecchio, Product Line Manager The registry. “Since 2010, we’ve now increased bandwidth by 8x, and with each generation we’ve also improved power efficiency. So we are about 95 percent more efficient now than we were 12 years ago.”

However, it should be noted that Broadcom’s latest chip, like the 25.6 Tbps Tomahawk4 it replaces, is still on top of a 100 Gbps PAM4 serializer/deserializer (SerDes). This effectively limits per-port throughput to 800 Gbps when using QSFP-DD optical pluggables. So while Broadcom has managed to double the capacity of its switch silicon, it hasn’t actually doubled port speeds. Not that customers are already clamoring for more speed.

According to Broadcom executives, adoption of 400 Gbps modules is still in its infancy, even among power-hungry hyperscalers, which account for just 15 percent of the total Ethernet market by revenue. Broadcom expects 400G ports to surpass 50 percent of Ethernet revenue by 2026.

These numbers are roughly consistent with the results of a recent Dell’Oro panel report, although analysts put market penetration for 400 Gbps switching at closer to 10 percent. In the first quarter of 2021, the group reported that 400Gbps switch shipments had exceeded 800,000 ports, with that number expected to increase further over the next year, driven by strong demand from cloud providers.

However, the Tomahawk5 requires more than twice the switching capacity. Improvements to the chip’s architecture, including a move to a 5nm manufacturing process, allow the monolithic switching chip to achieve significant power savings.

According to Broadcom, the chip consumes less than one watt per 100 GB of capacity. This means the chip draws less than 500W at full tilt, which Broadcom says will allow OEMs to continue air-cooling switches powered by the chip.

“By doubling the bandwidth, you actually get a 6x reduction in cost, performance and complexity,” Del Vecchio said, comparing the chip to the previous-generation Tomahawk4.

The ASIC also has a number of features tailored for Hyperscape HPC workloads, including network virtualization and segmentation, single-pass VxLAN routing and bridging, and “cognative routing” features designed to support the Shorten job execution times by avoiding overloads.

“The traffic characteristics you have for AI/ML tend to be different than what you would have for standard compute and memory traffic,” explained Del Vecchio, adding that by redirecting potential sources of congestion, the switch reduces latency and can improve performance for AI/ML workloads.

In summary, Broadcom says that the Tomahawk5 is the highest performing single-switch ASIC available on the market, but that claim is not without caveats. At the GTC this spring, Nvidia showed off its 51.2 Tbps Spectrum-4 Ethernet switch.

Spectrum-4 is based on technology acquired with the 2019 acquisition of Mellanox, and the switch shares many of the same features as Broadcom’s Tomahawk5, including support for up to 64 800 Gbps ports on one single housing. The switch and Nvidia’s BlueField 3 DPUs are scheduled to ship later this year.

So while Broadcom can claim to have launched Nvidia with a 51.2 Tbps ASIC – it’s technically sampling – these chips have yet to be integrated into OEM packages before they ever make their debut in the give data center. This raises some doubts as to which will first get into the hands of the customers, especially given the current state of the supply chain. ® Broadcom challenges Nvidia with 51.2T switch silicon • The Register

Laura Coffey

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