400G DR4 vs FR4 vs LR4: Reach, Fiber and Link-Budget Selection
Compare 400G QSFP-DD DR4, FR4 and LR4 by fiber, connector, reach, breakout and link-budget conditions for 500m, 2km and 10km links.
Selection Comparison
400G DR4 / FR4 / LR4 comparison
| Direction | Typical reach | Fiber and connector | Common link position | Confirm before ordering |
|---|---|---|---|---|
| DR4 | 500m class | Parallel SMF, MPO-12 | Intra-data-center links and 4x100G breakout evaluation | MPO polarity, breakout, FEC and total loss |
| FR4 | 2km class | Duplex SMF, duplex LC, four-wavelength WDM | Leaf-Spine, aggregation and inter-room links | Duplex fiber, link budget, FEC and remote PMD |
| LR4 | 10km class | Duplex SMF, duplex LC, long-reach WDM | Campus backbone, inter-building and edge uplinks | Transmit/receive window, overload, loss margin and temperature |
Start with the host and fiber plant, then select reach
400G DR4, FR4 and LR4 are not interchangeable suffixes. Confirm the QSFP-DD host port, FEC and breakout target, then use the installed fiber, connector and link loss to select 500m-class DR4, 2km-class FR4 or 10km-class LR4.
DR4: 500m-class parallel SMF and MPO-12
DR4 uses four 100G PAM4 parallel single-mode lanes and an MPO-12 interface. It fits intra-data-center links and may support 4x100G DR1 breakout when the host explicitly supports that port mode. Confirm MPO polarity, breakout mapping, remote PMD, FEC and total path loss.
FR4: 2km-class duplex SMF and LC
FR4 uses four-wavelength WDM over duplex single-mode fiber with duplex LC. It fits 2km-class data-center links, Leaf-Spine uplinks and installed duplex-SMF plants. Its PMD and cabling differ from DR4 even though both operate at 400G.
LR4: 10km-class optical budget and receiver window
LR4 targets 10km-class duplex-LC single-mode links for campus backbone, inter-building data-center links and edge uplinks. Check transmit power, receiver sensitivity, overload, temperature and system margin in addition to fiber and connector loss.
Choose by link conditions, not the reach label alone
Evaluate DR4 for 500m-class MPO parallel-SMF links, FR4 for approximately 2km duplex-LC SMF links, and LR4 for 10km-class campus or inter-building links. If host mode, fiber type or FEC is unknown, complete the equipment and link matrix before requesting a final configuration.
Keep host, cabling and operating results in one acceptance record
Record device and software version, port mode, module coding, MPO or LC path, measured loss, optical power, FEC, errors, temperature, alarms and duration. A one-time link-up result does not replace acceptance on the target host and final cabling.