400G, 800G, and 1.6T Interconnect Selection Guide

Choosing the right interconnect is not only a speed decision. At 400G, 800G, and 1.6T, the cable path, switch platform, port density, power budget, thermal design, connector type, and migration plan all affect whether the deployment works in production.

Start with the actual routed cable distance, then validate platform compatibility, power, airflow, cable density, and future 1.6T requirements before the BOM is locked.

Distance picks the cable family

Measure the actual routed path, not the straight-line distance. Include service loops, rack routing, bend radius, and maintenance access before selecting the interconnect type.

0 to 2m

Passive DAC

Best fit for intra-rack links where low power, low cost, and short reach matter most.

2 to 5m

ACC / LACC

Useful for near-rack copper paths where passive DAC margin starts to tighten.

3 to 7m

AEC

Active electrical cable with signal regeneration for dense adjacent-rack 800G links.

10 to 100m

AOC / SR8

Optical reach for cross-row and hall-level paths where copper weight and airflow become limiting factors.

100m+

DR8 / FR4

Pluggable optics and single-mode fiber for longer paths, campus links, and 1.6T planning.

Distance narrows the options. Platform compatibility, port density, power draw, cooling impact, cable tray fill, and migration plans should confirm the final selection.

Where each interconnect fits in an AI fabric

Dense AI networks often use different interconnect types at each layer. Short compute-to-leaf paths may use DAC. Leaf-to-spine links often move to AEC or AOC. Longer spine and super-spine paths typically use pluggable optics over single-mode fiber.

Core

DR8 / FR4 + single-mode fiber
Longer super-spine and data center paths.

Spine

AEC or AOC
Common fit for adjacent rack and dense 800G fabric links.

Leaf / ToR

Passive DAC
Short intra-rack connectivity where distance and routing support it.

Compute

GPU systems and endpoints
Validate cable timing, port count, and installation sequence before systems arrive.

What to validate before ordering

Before approving a high-speed interconnect BOM, review the physical path, switch platform, power budget, and future migration requirements.

Distance
  • Measure the full routed cable path.
  • Add service loop allowance.
  • Map each link to a distance zone.
Platform fit
  • Confirm IHS or RHS module requirements.
  • Check switch and NIC compatibility.
  • Verify qualified cable and optic options.
Power, cooling, and density
  • Calculate port count by wattage.
  • Check airflow impact at 64-port density.
  • Review cable tray fill before final cable selection.
Future migration
  • Plan for 1.6T where density requires it.
  • Prioritize single-mode fiber for long-life links.
  • Budget copper replacement during the 1.6T transition.

Common mistakes that delay 800G deployments

Many 800G deployment problems start as small interconnect assumptions. Review these issues before hardware reaches the rack.

Mistake 1

Ordering IHS modules for RHS slots

OSFP IHS and RHS are physically different. Confirm switch and NIC requirements before ordering modules, optics, or breakout cables.

Mistake 2

Using 3m passive DAC at 800G

800G passive DAC reach is shorter than many 400G designs. Use ACC, AEC, or optical options when the path exceeds the passive DAC limit.

Mistake 3

Ignoring cable diameter

Thick DAC bundles restrict airflow in high-density racks. Calculate tray fill and airflow impact before finalizing the cable type.

Mistake 4

Mixing connector types

MPO-12, MPO-16, UPC, and APC are not interchangeable. Connector mismatch creates attenuation, instability, or link failure.

Mistake 5

Under-budgeting optic power

A fully populated 800G switch with optics adds power and cooling demand. Validate facility and platform budgets early.

Mistake 6

Ordering cable infrastructure late

Optical infrastructure should be ready before GPU systems arrive. Late cabling creates idle hardware and rushed troubleshooting.

Cables are a small part of the cluster budget, but they often determine whether the larger deployment turns up on schedule.

Review cost beyond the part price

Interconnect cost includes more than the purchase price per link. Power draw, cooling impact, reliability, spares, deployment timing, and troubleshooting risk should be reviewed together.

  • Compare capital cost per link.
  • Estimate power and cooling cost across the port count.
  • Review expected reliability and spare requirements.
  • Plan for the cost of idle systems if cabling arrives late.

Check cable diameter and tray fill

At high port density, cable thickness affects airflow, routing, bend radius, and service access. DAC bundles can create airflow restrictions in dense racks if tray fill is not reviewed early.

  • Calculate tray fill before final cable selection.
  • Reserve spare capacity for expansion and service access.
  • Review airflow impact in 40kW+ racks.
  • Use thinner optical or active cable options where density requires it.

Plan 800G builds with the 1.6T transition in mind

Some infrastructure carries forward better than others. Fiber paths are better suited for long-term planning, while copper cable assemblies are more generation-specific.

What carries forward
  • Structured single-mode fiber for long-run links.
  • OSFP cage infrastructure in many 1.6T planning scenarios.
  • Fiber designs intended to last beyond one hardware generation.
What changes
  • DAC, ACC, and AEC cable assemblies should be treated as generation-specific.
  • OSFP224 requires new switch hardware and does not fit existing OSFP cages.
  • Copper replacement should be included in the 1.6T migration budget.

Practical takeaway: use structured single-mode fiber for links expected to last more than one generation. Budget copper replacement as part of 1.6T planning.

Validate the interconnect plan before production

Send Axiom your switch platform, target speed, form factor requirements, cable paths, rack layout, port count, and deployment timeline. Axiom's networking team will help review interconnect options, platform compatibility, power and cooling requirements, and 800G to 1.6T migration needs before deployment.

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