800G SR8 vs VR8 vs DR8 vs 2xFR4: Reach, Fiber and Connector Selection
Compare 800G SR8, VR8, DR8 and 2xFR4 by reach, fiber, connector, breakout and host conditions for 50m, 100m, 500m and 2km AI-cluster links.
Selection Comparison
800G PMD and connector comparison
| Direction | Typical reach | Fiber and connector | Common deployment | Confirm before ordering |
|---|---|---|---|---|
| VR8 | 50m class | OM4 / OM5 MMF; exact MPO configuration depends on P/N | In-rack and adjacent-rack ultra-short links | Fiber grade, MPO polarity, host power and cooling |
| SR8 | 100m class | OM4 MMF, MPO-16 | AI clusters, data halls and short Leaf-Spine links | MPO-16 mapping, polarity, FEC and total loss |
| DR8 | 500m class | Parallel SMF, MPO-16 | Data-center fabric, AI fabric and 2x400G evaluation | Parallel SMF, breakout, FEC and path loss |
| 2xFR4 | 2km class | Duplex SMF, dual LC or Dual CS, four-wavelength WDM | Inter-room, aggregation and dense 2km links | Duplex fiber, connector form, wavelengths, power and budget |
Confirm the host form factor before selecting the PMD
800G SR8, VR8, DR8 and 2xFR4 cannot be interchanged by data rate or reach label alone. Confirm whether the switch, NIC or accelerator supports OSFP or QSFP-DD, then map the installed multimode, parallel single-mode or duplex single-mode fiber and its MPO, LC or CS connectors before selecting a 50m, 100m, 500m or 2km direction.
VR8: 50m-class ultra-short multimode
VR8 targets 50m-class OM4/OM5 links inside or between adjacent racks. Product versions may use different MPO configurations, so the VR8 name does not establish connector mapping or polarity. Confirm the ordered P/N, fiber grade, MPO plan, port power, cooling and host FEC.
SR8: 100m-class multimode and MPO-16
SR8 commonly uses eight 100G PAM4 multimode lanes and MPO-16 for 100m-class AI-cluster, data-hall and Leaf-Spine links. Its boundary from VR8 includes fiber grade, connector plan, optical budget and remote PMD. Validate polarity, lane mapping and end-face condition on the final cabling.
DR8: 500m-class parallel single-mode
DR8 uses eight parallel single-mode lanes and MPO-16 for data-center and AI-fabric links around 500m. A 2x400G or 8x100G direction is only an evaluation path when the host explicitly supports the lane mode. Match the breakout cable, remote PMD, FEC and software version.
2xFR4: 2km-class duplex single-mode and WDM
2xFR4 carries 800G through two 400G FR4 optical directions and commonly uses dual duplex LC or Dual CS over single-mode fiber. OSFP and QSFP-DD variants have different host, power and management conditions, while dual LC, Dual CS and MPO-16 are different cabling systems.
Validate 2x400G breakout against the topology
An 800G source connected to two 400G endpoints requires matching source lane mode, module optical architecture, cable mapping, remote PMDs and FEC. Treat breakout as deliverable only when the host documentation and target software version explicitly support it.
Keep thermal and link-budget results in one record
Record the host and software, port form factor, module P/N, fiber and connector, MPO polarity, measured path loss, optical power, FEC, errors, module temperature, adjacent-port occupancy and sustained-traffic results. The conclusion remains limited to the recorded host, cabling and specification conditions.