What Is a 10GBASE-ER SFP Module and How Does It Differ From 10GBASE-LR and 10GBASE-SR? | 40 Km At 1550 Nm

A 10GBASE-ER SFP+ transceiver carries 10 Gb/s Ethernet about 40 km over single-mode fiber at 1550 nm, versus 10 km for LR and 300 m for SR.

Two switches 18 miles apart, one leased single-mode strand between them: a 10GBASE-LR optic will not close that hop. The ER version, running at 1550 nm, will. Whether a 10GBASE-ER SFP module fits a given link, and how it differs from 10GBASE-LR and 10GBASE-SR, comes down to two things — fiber type and distance. Wavelength, connector, and power budget follow from there.

The ER module is a pluggable 10-Gb/s Ethernet transceiver built to the IEEE 802.3ae 10GBASE-ER standard. Cisco’s standard part number is SFP-10G-ER, with SFP-10G-ER-S and SFP-10G-ER-I as related variants. Each plugs into an SFP+ cage and takes a duplex LC fiber pair. Cisco’s transceiver data sheet lists 4.0 dBm maximum and −4.7 dBm minimum transmit power, −1.0 dBm maximum and −15.8 dBm minimum receive power, and a 1530–1565 nm operating range.

10GBASE-ER SFP Module: What The 40 Km Rating Means

The 40 km figure is a nominal reach over G.652 single-mode fiber, not a promise about your span. Every splice, patch panel, and dirty connector eats into the optical budget, so the distance a link actually closes depends on measured loss, not the model name on the label.

Wavelength does the heavy lifting. Light at 1550 nm attenuates less per kilometer in standard glass than light at 1310 nm, which is the whole reason an ER optic outruns an LR optic over the same cable. Dispersion and the transceiver’s power budget set the real ceiling, and a span that tests marginal at 40 km needs a budget calculation before installation, not after. ER is also the longest reach in the standard 10GBASE family; anything longer calls for vendor-specific optics or wavelength-division gear.

These are spec-only parts. Nothing about a 10GBASE-ER module depends on an operating-system license, a service plan, or a region — the constraints are the host’s SFP+ port, its supported optic coding, firmware, and the vendor’s support policy.

How Do 10GBASE-ER, LR, And SR Compare?

ER reaches roughly 40 km on single-mode fiber at 1550 nm, LR reaches 10 km on single-mode at 1310 nm, and SR runs on multimode at 850 nm for a few hundred meters at most.

SR is the odd one out because it needs multimode glass. Cisco lists 300 m over OM3 and 26 m over FDDI-grade fiber, with some X2 implementations of the same standard documented at 400 m over OM4. The two single-mode optics are not interchangeable either: an ER port transmits at 1550 nm and an LR port at 1310 nm, and pairing them does not produce a normal Ethernet link.

All three standards use duplex LC connectors, so the cabling is identical; the differences live inside the optic. Those transmit and receive ranges come straight from Cisco’s 10GBASE SFP+ module data sheet, which lists the three standards side by side.

Model suffixes are not decoration. SFP-10G-ER-S does not support Fibre Channel over Ethernet per Cisco, so a storage-network design has to check that line before the optic goes on the order.

Matching The Optic To The Fiber And The Link

Match the transceiver to the fiber first, then confirm the host supports the module and the span’s measured loss clears the optical budget.

1. Confirm both endpoints accept a 10G SFP+ optic, and check the exact part against the hardware installation guide and release notes for the device and software version you run.
2. Choose by fiber and distance: SR for multimode, LR for single-mode up to 10 km, ER for single-mode up to 40 km.
3. Seat the optic in the SFP+ cage, connect the duplex LC pair, and watch for a solid port LED plus a link-up state in the management interface.
4. Read the device’s digital optical diagnostics — receive power should sit inside the listed range, not merely above the sensitivity floor.

Two failure modes account for most dead ER links. The first is a short span: ER transmit power is far higher than LR’s, so a few hundred meters of glass can overload the receiver, and an approved optical attenuator may be required — check the endpoint’s receive limits and the manufacturer’s attenuation guidance. The second is mismatched fiber: SR on single-mode glass, or ER on multimode, will not link reliably no matter how clean the connectors are.

The modules emit invisible laser radiation: never look into an active fiber or an open transceiver aperture, and leave dust caps on unused ports.

Compatibility is the other variable. A third-party module has to carry coding the switch accepts, and a mismatch usually shows up as an unsupported-optic alarm rather than a link fault, so match the part to the platform before you install it. Our tested 10GBASE-ER SFP module picks compare coded and OEM options.