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Tomahawk 5 Switches at 51.2Tbps

August 23, 2022

Author: Joseph Byrne

Oops, Broadcom did it again. One more time, the company has doubled data-center switching performance. Employing the same number of PAM4 serdes as its predecessor but running them twice as fast, the new Tomahawk 5 (BCM78900) delivers double the throughput and supports 800G Ethernet (800GbE). Facing heightened competition from rivals, Broadcom is sampling it now, just ahead of Nvidia’s similar Spectrum-4 switch. We expect the new chip to qualify for production by the end of 2023.

Tomahawk 5 is the company’s first 5nm merchant switch IC and its first product to support 800GbE. We estimate power consumption increases only 10% over the 7nm Tomahawk 4, reaching 500W. Once unheard of, a half-kilowatt chip is nonetheless fit for air-cooled systems. Like its predecessors, Tomahawk 5 is monolithic, avoiding the power penalty of chiplet-based architectures.

Overall switching throughput is 51.2Tbps, permitting 64x800GbE, 128x400GbE, and 256x200GbE configurations. A typical 800GbE optical-module standard is the OSFP MSA, which also allows dual-400GbE and single-800GbE configurations. In addition, Tomahawk 5 improves direct-attach-copper (DAC) support and comes in a model integrating copackaged optics for all ports.

Broadcom aims Tomahawk mainly at fixed-port data-center switches, whereas the Trident and Jericho lines target enterprise and service-provider switches. Trident is more flexible: it handles more protocols, has bigger access-control lists, and is customer programmable. To enable big, high-speed systems, Jericho has deeper packet buffers. That specialization allows Broadcom to streamline Tomahawk and maximize throughput.

Subscribers can view the full article in the Microprocessor Report.

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