100G QSFP28 SR4 vs PSM4 vs CWDM4 vs LR4: Reach and Fiber Selection
Compare 100G QSFP28 SR4, PSM4, CWDM4 and LR4 by reach, fiber, connector, breakout and link-budget conditions for 100m, 500m, 2km and 10km links.
Selection Comparison
100G QSFP28 direction comparison
| Direction | Typical reach | Fiber and connector | Common link position | Confirm before ordering |
|---|---|---|---|---|
| SR4 | 100m class | OM3 / OM4 MMF, MPO-12 | Intra-data-center, ToR and Leaf access | MPO polarity, lane order, 4x25G breakout and total loss |
| PSM4 | 500m class | Parallel SMF, MPO-12 | Short-to-medium data-center and Leaf-Spine uplinks | Parallel-SMF plant, MPO polarity, FEC and breakout mode |
| CWDM4 | 2km class | Duplex SMF, duplex LC, four-wavelength WDM | Leaf-Spine, aggregation and inter-room links | Duplex fiber, wavelength plan, link budget and host FEC |
| LR4 | 10km class | Duplex SMF, duplex LC, LAN-WDM | Campus backbone, inter-building and long-reach uplinks | Receiver overload, dispersion, loss margin and temperature |
Start with fiber and connector, then select reach
100G QSFP28 SR4, PSM4, CWDM4 and LR4 are not interchangeable by reach label alone. Confirm the QSFP28 host port, electrical mode and breakout target, then match the installed MPO multimode, MPO parallel-SMF or duplex-LC single-mode plant to 100m-class SR4, 500m-class PSM4, 2km-class CWDM4 or 10km-class LR4.
SR4: 100m-class multimode and MPO-12
SR4 uses four parallel optical lanes and an MPO-12 interface for OM3 / OM4 multimode links in data-center rooms and ToR access. Confirm MPO lane order and polarity, fiber grade, connector loss and explicit 4x25G breakout support; a shared connector does not make PMDs interoperable.
PSM4: 500m-class parallel single-mode
PSM4 targets 500m-class parallel single-mode links and commonly uses MPO-12, but its fiber and link budget differ from SR4. Confirm the parallel-SMF plant, MPO polarity, FEC, remote PMD and breakout cable rather than reusing an SR4 assumption.
CWDM4: 2km-class duplex single-mode and LC
CWDM4 uses four-wavelength WDM over duplex single-mode fiber with duplex LC for approximately 2km data-center, aggregation and inter-room links. Confirm duplex fiber, wavelength direction, host FEC, EEPROM coding and remote CWDM4 support before ordering.
LR4: 10km-class budget and receiver window
LR4 targets 10km-class duplex-LC single-mode links for campus backbone, inter-building and long-reach uplinks. Check LAN-WDM band, dispersion, transmit power, receiver sensitivity, overload and temperature in addition to fiber and connector loss; short low-loss paths still require receiver-power checks.
MPO and LC are cabling decisions, not cosmetic details
MPO-12 requires lane order, polarity, breakout and patching checks; duplex LC requires two-fiber routing, Tx/Rx direction, patch-cord count and panel records. If the site only has multimode MPO, do not quote CWDM4 or LR4; if it has duplex SMF, do not ignore host port and optical budget limits.
Keep host, fiber and operating results in one acceptance record
Record device and software version, port mode, module coding, MPO or LC path, fiber grade, 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.