inference/research
verifiedhigh · 0.90updated 2026-10-11

Broadcom BCM78919 102.4-Tb/s CPO Switch

25 GB/s

Fields

id
interconnect/broadcom-bcm78919-cpo
Kind
ethernet
Version
BCM78919 (Tomahawk 6 family CPO, 3nm Condor SerDes)
Bandwidth (GB/s, per link, unidirectional)
25
Bandwidth basis
PER DUPLEX FIBER, PER DIRECTION. Broadcom's product page states: 'The integrated optical engines enable direct high-speed I/O to the BCM78919 using 512 duplex single-mode optical fibers to the front panel in a variety of different port configurations. Each optical engine is directly driven from the Condor SerDes, providing the lowest-power and lowest-cost optical interconnect solution. Each duplex fiber is capable of supporting 200GbE, 100GbE, or 50GbE using a single wavelength at 1310 nm.' 200 GbE line rate per duplex fiber = 200 / 8 = 25 GB/s in each direction. Total device capacity is published as '102.4-Tb/s Multilayer CPO Switch with 200G SerDes', which is the bidirectional aggregate across all 512 duplex fibers: 512 x 200 Gb/s = 102,400 Gb/s = 102.4 Tb/s (= 12,800 GB/s bidirectional aggregate, or 6,400 GB/s per direction).
Link count
512
Topology
Switched fabric with direct co-packaged optical front-panel connectivity via 512 duplex single-mode fibers. Supports arbitrary topologies including Clos, rail-optimized, rail-only, and scale-up cluster topologies up to 512 XPUs, or scale-out up to 1M+ XPUs.
Scale-up
yes
Scale-out
yes
Switching
Single-chip 102.4 Tb/s multilayer switching with 64 Condor 3-nm SerDes cores (512 x 212.5-Gb/s PAM4 SerDes transceivers driving integrated optical engines). Supports up to 64 x 1.6TbE, 128 x 800GbE, 256 x 400GbE, or 512 x 200GbE ports. Cut-through and store-and-forward switching modes with enhanced dynamic load balancing, telemetry, and TCP Incast burst absorption.
notes
BCM78919 is Broadcom's 102.4 Tb/s co-packaged optics (CPO) switch ASIC, representing the optical variant of the Tomahawk 6 generation built on 3nm silicon. Each Condor SerDes directly drives co-packaged silicon photonics engines, eliminating high-speed pluggable transceivers and reducing I/O power dissipation by up to 50% compared to standard pluggable optical links.\n\nJERICHO4 AND TOMAHAWK 6 OPTICAL STATUS AUDIT (2026-10-11): Industry rumors and early launch roadmaps speculated on optical switching across both Jericho4 and Tomahawk 6. First-party documentation check reveals: (1) Tomahawk 6 has a dedicated CPO SKU in the BCM78919 with 512 duplex optical fibers directly attached, while standard Tomahawk 6 (BCM78910/BCM78914) remains copper/pluggable-SerDes. (2) Jericho4 (BCM99450, 51.2 Tb/s StrataDNX) publishes NO co-packaged optics or optical switching SKUs whatsoever; it relies entirely on electrical SerDes (50GE to 1.6TE) and DNX fabric interfaces to Ramon4 elements with HBM deep packet buffers. Rumors of optical Jericho4 are unfounded in verified vendor publications.\n\nINFERENCE RELEVANCE: Scale-out and scale-up fabrics for large-language model inference are intensely bandwidth- and power-constrained. In multi-node distributed inference (such as DeepSeek-V3 or Llama-3.1-405B split across multiple racks with tensor parallelism or expert parallelism), traditional pluggable optics consume 15-30 W per 800G optical transceiver module, easily consuming 20-30% of total rack power. Co-packaged optics reduces I/O power significantly while providing high radix (up to 512 200GbE or 64 1.6TbE ports per 1RU chassis), minimizing network tier hops and tail latency during all-reduce and all-to-all collective communication phases.
way
each

Notes

BCM78919 is Broadcom's 102.4 Tb/s co-packaged optics (CPO) switch ASIC, representing the optical variant of the Tomahawk 6 generation built on 3nm silicon. Each Condor SerDes directly drives co-packaged silicon photonics engines, eliminating high-speed pluggable transceivers and reducing I/O power dissipation by up to 50% compared to standard pluggable optical links.\n\nJERICHO4 AND TOMAHAWK 6 OPTICAL STATUS AUDIT (2026-10-11): Industry rumors and early launch roadmaps speculated on optical switching across both Jericho4 and Tomahawk 6. First-party documentation check reveals: (1) Tomahawk 6 has a dedicated CPO SKU in the BCM78919 with 512 duplex optical fibers directly attached, while standard Tomahawk 6 (BCM78910/BCM78914) remains copper/pluggable-SerDes. (2) Jericho4 (BCM99450, 51.2 Tb/s StrataDNX) publishes NO co-packaged optics or optical switching SKUs whatsoever; it relies entirely on electrical SerDes (50GE to 1.6TE) and DNX fabric interfaces to Ramon4 elements with HBM deep packet buffers. Rumors of optical Jericho4 are unfounded in verified vendor publications.\n\nINFERENCE RELEVANCE: Scale-out and scale-up fabrics for large-language model inference are intensely bandwidth- and power-constrained. In multi-node distributed inference (such as DeepSeek-V3 or Llama-3.1-405B split across multiple racks with tensor parallelism or expert parallelism), traditional pluggable optics consume 15-30 W per 800G optical transceiver module, easily consuming 20-30% of total rack power. Co-packaged optics reduces I/O power significantly while providing high radix (up to 512 200GbE or 64 1.6TbE ports per 1RU chassis), minimizing network tier hops and tail latency during all-reduce and all-to-all collective communication phases.

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