If you're familiar with Ethernet switches, you've likely come across the SFP module. These modules are ubiquitous in modern fiber optic networks, playing a crucial role in connectivity. But what exactly are they?
This post serves as a comprehensive guide to the SFP module, covering its definition, working principle, various types, and applications.
Let's delve into it.

What is an SFP module?

Before discussing the SFP module, we first explain what is SFP. The “S” in SFP represents Samll, the letter “F” stands for Form-factor, and “P” stands for Pluggable. Therefore, SFP = Small Form-factor Pluggable. It is initially defined in the INF-8074i agreement by the SFF Committee.
An SFP module is a small form factor pluggable optical transceiver that fits into the SFP port of the networking switch or other device. Sometimes, It is also known as the mini-GBIC (gigabit interface converter) or SFP transceiver. However, some technicians may also mistype it as an SPF module, which is the same thing.

SFP transceivers come in various models tailored to different network technologies. Each type of SFP module is designed for specific networking standards and can be categorized as Ethernet SFP, FC SFP, SDH SFP/SONET SFP, SDI SFP, or PON SFP. The SFP (small form-factor pluggable) transceivers have derivated into multiple form factors. As the most popular package for optical modules in the market, SFP plays a vital role. Today, the optical communication industry has released multiple enhanced SFP modules based on this package—for example, CSFP, 10G SFP+, SFP56, 25G SFP28, 40G QSFP+, 100G QSFP28, 100G SFP-DD, 200G QSFP56, 400G QSFP-DD, 400G OSFP, 800G QSFP-DD, 800G OSFP.

Transceivers with different form factors support corresponding speeds. Check the equipment port types, and choose a matching form factor.

By SFP Transceiver Speed

100BASE SFP: Usually stands for 100Mbps and 155Mbps speed, widely used in fast Ethernet, SDH/SONET &ATM. Most of the devices have been upgraded to 1G or higher speed. Therefore, very few vendors still provide this type.
622M SFP: Special for SDH/SONET equipment. Similar to the above type, few manufacturers provide this type.
1000BASE SFP: Also known as 1G or Gigabit, it is the most popular transceiver in data communication and has the most supplier choices.
2G SFP: Including 2G fiber channel and 2.5G speed, suitable for 2x FC SAN switch and SDH/SONET device.
3G SFP: Including 2.97G and 3.07G speed, suitable for video transmission, CPRI (Common Public Radio Interface), OBSAI (Open Base Station Architecture Initiative)
4G SFP: Specific speed of 4.25G, suitable for 4x FC SAN switch
6G SFP: Specific speed of 6.14G, suitable for CPRI (Common Public Radio Interface) or OBSAI (Open Base Station Architecture Initiative) application
8G SFP: Specific speed of 8.5G, suitable for 8x FC SAN switch

By SFP Media Type

Copper: Transmit the signal with traditional copper cables, such as network cable or DAC cable
Multimode Fiber (MMF): Supports OM1, OM2, OM3, OM4, and OM5 cabling. Higher fiber grade provides better performance.
Singlemode Fiber (SMF): Suitable for 9/125 single mode fiber cabling, provides the max link distance.

By SFP Transceiver Distance

T: Including 100BASE-T, 1000BASE-T, 2.5GBASE-T, 5GBASE-T, 10GBASE-T. Typcial distance 100m over Cat5 cable.
SX: Stands for short reach. It is defined in the IEEE 802.3z; 1000base-SX reaches 550m on multimode fiber. The typical wavelength is 850nm.
LX: Stands for extended reach. It is defined in the IEEE 802.3z, 1000BASE-LX reaches 10km on single mode fiber. The typical wavelength is 1310nm.
EX: Stands for extended reach. It is defined in IEEE 802.3z. 1000BASE-EX reaches 40km on single mode fiber. The typical wavelength is 1310nm.
ZX: Also Stands for extended reach. It is defined in IEEE 802.3z, 1000BASE-ZX reaches 70km (or 80km) on single mode fiber.
EZX: it is not the standard type, but it is defined by some manufacturers and accepted by most customers. “E” stands for Extend, meaning it is the extended long-reach transceiver. The maximum distance can reach 120km or even 160km with a wavelength of 1550nm.
BX: refers to a bi-directional (BiDi) SFP transceiver; the typical transmission distance can be 10 km to 80 km. It adopts WDM technology to transmit two wavelengths on a single fiber. BX usually contains BX-U (upstream) and BX-D (downstream), and each direction uses opposite wavelengths, such as 1310nm-TX/1490nm-RX and 1490nm-TX/1310nm-RX.

By Connector Type

LC SFP: LC is the default connector for most transceivers. LC connectors are always found on 1G SFPs and 10G SFP+, 25G SFP28, 100G SFP-DD etc.
SC SFP: Some BiDi transceivers assemble SC connectors but share a very small shipment
RJ45 SFP: This transceiver has a female RJ45 connector to allow network cable insert.
MTP/MPO connectors are available for 40G QSFP+, 100G QSFP28 and 400G/800G QSFP-DD OSFP transceivers.

By Operating Temperature

Commercial grade: It’s the typical transceiver that supports 0~70C temperature. Usually, with the best pricing and cost ratio, and suitable for a standard indoor environment like a data center or enterprise.
Industrial grade: It’s a hardened transceiver that supports -40~85C temperature. Suitable for industrial switches in the outdoor environment. But they are offered at a much higher price.
Extended grade: This one is not the standard type. It can handle the -10~85C temperature.
In fact, there are many other ways to categorize them. However, the most common methods are classified by data speed and application.

Significantly, the same transceiver maybe with various types in different classified ways. For example, the compatible Cisco GLC-TE will be categorized in multiple charts, including 1G, Copper, T, RJ45, and industrial SFP transceiver.

How to choose the suitable SFP Module for your networking?

We help more than 1000 clients choose the suitable transceiver quickly. Here are the essential tips.

Check your switch (or other network devices) port-supported speed and then match the correct SFP.
Know your existing network cabling types. If you have a multimode fiber cabling structure, then choose the multimode SFP. If you have a single mode fiber cabling, a single mode transceiver is the only choice.
Know your target link distance and link budget. But remember, choose an SFP supporting longer transmission distances than expected. Otherwise, poor fiber optic cable or a dirty fiber end-face may cause a failed link.
Considering the operating temperature. For a typical indoor environment, using a commercial-grade transceiver is enough. While in harsh outdoor applications, you should use the industrial transceiver.
Remember to check compatibility with the supplier before ordering. Because the switch can not recognize an incompatible transceiver, that will waste your money and valuable time. So always choose a proven compatible transceiver.

Conclusion

Figure out what your networking technology is and which equipment and cables are in your system, go further to transmission speed for a matching form factor, and the transmission distance to pick a single-mode or multimode SFP with the required reach. Take cabling infrastructure into consideration for a proper SFP connector type. Give priority to industrial SFPs if you need to use the module in harsh environments for extreme temperatures. Choose a reliable vendor that ensures device compatibility.