SFP refers to a small form-factor module that can be hot-pluggable. 10G stands for their maximum transmission rate of 10.3 Gbps suitable for 10 Gigabit Ethernet. SR, LRM, LR represent the transmission distance of the 10G optical module. The transmission distance they represent is from short to long.

The SFP-10G-SR is a 10GBASE-SR SP+ module, which can reach up to 300 meters matched with OM3 Multimode Fiber (MMF), known as the lowest-cost, lowest-power modules implemented with a VCSEL.

The SFP-10G-LR is a 10GBASE-LR SP+ module that adopts Distributed Feedback Laser (DFB). It operates at a nominal wavelength of 1310nm and can reach up to 10 km over Single Mode Fiber (SMF). It is used in wiring buildings on a large campus or even setting up a Metro Area Network (MAN).

The SFP-10G-LRM is a 10GBASE-LRM Module that supports link lengths of 220m on standard Fiber Distributed Data Interface (FDDI) grade multimode fiber. To ensure that specifications are met over FDDI-grade, OM1 and OM2 fibers, the transmitter should be coupled through a mode conditioning patch cord. No mode conditioning patch cord is required for applications over OM3 or OM4.

How does it work?

There are two aspects of technology the Ethernet.

• You have to support the local networks and provide the data connection. (An alternative to a Wi-Fi network)

• Sometimes, you have to transmit the data signals to more essential centers. (Because how can you transfer the 10G Ethernet over 100 kilometers)

10G SFP transceiver is associated with the second task of transmission.

But how does it do this job?

Simple. It uses optical fiber systems. And we all know that an optical fiber system can transmit signals while a copper system can locally provide the data rate. (A copper transceiver can be available for local data connection)

10G SFP+ transceiver uses long-range or short-range fiber optics to facilitate the spread of signals to longer distances. So, you can explore the relevant IEEE standards for this purpose.

Can 10G SFP+ Optics Run at 1G SFP Port？

Will 10Gb SFP+ run at 1Gb? The answer also depends. You need to down rate the 10G SFP+ transceiver on the switch, but practically no one will be encouraged to do that. In particular, from the economic point of view, assuming that you have one 1G switch and one 10G switch and if you connect them with two 10G fiber optic transceiver modules, what you can expect to get? 1G network connectivity! Since the 10G ports can take 1G modules, and the result remains the same, why not replace 10G modules with 1G ones?

Figure 3: FS 10Gb Switch SFP+ Port Links to Gigabit Switch SFP Port

Can SFP+ Optics Auto-negotiate Down to 1G with Gigabit Switch?

Can 10G SFP+ transceiver module plugged in one switch be connected to a 1G transceiver plugged in another switch and negotiate? It depends.

For Ethernet over copper wiring, auto-negotiation is supported. That means, only the BASE-T SFP transceivers support auto-negotiation as copper SFP modules supporting 10/100/1000 auto-sensing.

For fiber-based transceivers such as fiber SFP and SFP+ optics, auto-negotiation is not supported. As a protocol, auto-negotiation only works when it’s running on both sides of the link. The two devices connected in the link will decide together the best speed and duplex mode. Most SFP and SFP+ transceivers only run at its rated speed as they are manufactured, thus 10Gb SFP+ optics on 10Gb switch can not auto-negotiate down to 1Gb if the other end is gigabit switch.

For example, if a 10Gb SFP+ module is plugged into the 10Gb switch port, it will only run at 10Gb. In this case, if you link it to the gigabit switch port, it will not work. But when plugging a 1Gb SFP module in the 10G SFP+ port, the 10Gb switch will run at 1Gb. If so, you can link it to the Gigabit switch.

Edited in 2021: 1/10G dual-rate SFP+ transceivers are designed for use in 1-Gigabit and 10-Gigabit Ethernet links over single-mode fiber (SMF) or multi-mode fiber (MMF). It is viable to connect 1/10G dual-rate SFP+ transceivers on a 10G switch with 1G transceiver plugged in a 1G switch.