What is SFP Module? An Ultimate Guide (2024)

Initial Published: December 6, 2022; Updated: November 29, 2024

You probably know the SFP module if you know the Ethernet switch. In fact, we can see it almost everywhere in modern fiber optic networks. But what is it exactly?

This post is a complete guide to this product. It will cover its definition, working principle, classified types, and applications.

Now, let’s go on.

What is an SFP module?
Why is it important?
How many SFP types are there?
SFP compatibility
SFP color code
How to choose the suitable SFP module?
FAQ

What is an SFP module?

Before discussing the SFP module, we first explain what SFP is. The “S” in SFP represents Samll, the letter “F” stands for Form-factor, and “P” stands for Pluggable. Therefore, SFP = Small Form-factor Pluggable is defined by the multi-source agreement. The SFF Committee initially defined it in the INF-8074i agreement.

An SFP module is a small, pluggable optical transceiver that fits into the SFP port of a networking switch or other device. Sometimes, it is 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.

A typical SFP fiber module consists of a cage, PCBA, chip, and TOSA+ROSA (sometimes maybe BOSA for BiDi transceiver). See the photo below.

*Figure 1: SFP module top and back view*

Although it appeared later than the GBIC and SFF form factor, SFP shares an excellent ratio in the market and is still growing. Furthermore, it replaces those two old types rapidly. We believe the most critical influence factors are:

Hot Pluggable: Plug in and Plug out without restarting the switch
Compact Size: High port density for more bandwidth
Smart real-time monitor: enhanced DDM (DOM) function makes simple operation
Lower cost: Mass production and many suppliers give them much lower pricing than the GBID and SFF formats.

To help understand the basics, we briefly introduce the SFP MSA. It stands for small form factor multi-source agreement – the critical MSA for the SFP module, including INF-8074i, SFF-8431, and SFF-8472. This agreement defines the mechanical dimensions, electronic/optical interface, and Diagnostic Monitoring Interface.

Why is the SFP module important?

Imagine your switch without an optical module. How can you achieve high speed? The answer may be through copper cable. However, it is not viable because of thickness, cost, and short-distance limitations.

That is where the SFP module plays a role. Inserting a transceiver into the switch port allows you to bridge communication with another switch for tens to hundreds of kilometers. It is an essential conversion medium for connectivity among nearly all networking switches and routers.

For example, with a 1G SFP SX, the maximum distance reaches 550m over multimode OM2 fiber. Meanwhile, with a 1G SFP LX module, the max span can be 20km at single mode fiber.

How many types of SFP modules are there?

Since there are so many SFP modules on the market, many people usually need to know the different classifications. Therefore, choosing the correct transceiver becomes a challenge.

Next, we will try to categorize them based on various standards.

By SFP 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 SFP: Transmit the signal with traditional copper cables, such as network cable or DAC cable
Multimode SFP: also known as MM SFP, supports OM1, OM2, OM3, OM4, and OM5 cabling. A higher fiber grade provides better performance.
Single mode SFP: sometimes called SM SFP, is suitable for 9/125 singlemode fiber (SMF) cabling and provides the maximum link distance. The typical distance is 10km or 20km. However, it can reach even 180km in some cases.

By SFP Distance

SFP T: Including 100BASE-T, 1000BASE-T, 2.5GBASE-T, 5GBASE-T, Typcial distance 100m over Cat5 cable.
SFP 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.
SFP 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.
SFP 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.
SFP ZX: Also Stands for extended reach. It is defined in IEEE 802.3z, 1000BASE-ZX reaches 70km (or 80km) on single mode fiber.
SFP EZX is not the standard type but is defined by some manufacturers and accepted by most customers. “E” stands for Extend, meaning it is an extended long-reach transceiver. With a wavelength of 1550 nm, the maximum distance can reach 120km or even 160km.
SFP 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.

SFP Type	Media	Wavelength	Max Distance
T	Copper	N/A	100m
SX	MMF OM1/OM2/OM3/OM4/OM5	850nm	1Gbps: 550nm 155Mbps: 2km
LX	SMF OS1/OS2	1310nm	10km or 20km
EX	SMF OS1/OS2	1310nm or 1550nm	40km
ZX	SMF OS1/OS2	1550nm	70km or 80km
EZX	SMF OS1/OS2	1550nm	160km
BX	SMF OS1/OS2 or MMF	1310/1490nm, 1310/1550nm,1490/1550nm	80km

Table 1: SFP module type by distance

By Application

Regular SFP: Most commonly, a transceiver with a duplex fiber. If not specified, when someone talks about the SFP module, it refers to this type.
CWDM SFP: Support CWDM transmission to improve the bandwidth in one fiber.
DWDM SFP: Support DWDM transmission to maximize the bandwidth while saving the fiber cabling
BiDi SFP: Bi-directional transceiver for transmitting and receiving in simplex fiber.
SDH/SONET SFP: mainly speed including 155Mbps, 622Mbps, and 2.5Gbps, suitable for SDH/SONET platform.
Fiber Channel SFP: Covers the speed of 1G, 2G, 4G, and 8G, mainly used in the storage network.
Video SFP: Support HD-SDI/3G-SDI/6G-SDI/12G-SDI, focusing on the video transmission market.
PON SFP: Include the GPON and EPON standards for Passive optical networking, mainly for the FTTX application.
SFP Cable: It is a direct attached cable with an SFP connector on two ends, a lower-cost solution for a very short length.

LC vs SC vs RJ45 SFP module — *Figure 2: LC duplex vs. SC simplex vs. RJ45 SFP module (From left to right*)

By Connector Type

LC SFP: LC is the default connector for most SFP transceivers
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.

By Operating Temperature

Commercial grade: It’s the typical transceiver that supports 0~70C temperature. Usually, the best pricing and cost ratio suits 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 may have various types classified differently. For example, the compatible Cisco GLC-TE will be categorized in multiple charts, including 1G, Copper, T, RJ45, and industrial SFP transceiver.

SFP Compatibility

In practice, the majority of users are bound to face SFP Compatibility. In the above paragraphs of this article, we mentioned that all SFPs are released based on the SFP Multi-source agreement. In other words, all SFPs must follow the same size, connector, electrical, and optical interface standards. Of course, later emerging Advanced SFPs such as SFP28, QSFP, and QSFP28 also need to follow these standards in the industry.

However, some leading manufacturers in the industry, such as Cisco®, HP®, and Juniper®, have implemented software locks on the SFP ports of their networking equipment. As a result, these ports reject SFP modules that comply with industry standards. This is why we emphasize the importance of SFP compatibility. The switch will not function properly if a port is locked, even if it inserts an MSA-compliant SFP module.

Only specially coded SFPs can be used in these locked ports. A compatible SFP must be an MSA SFP, but an MSA SFP is not necessarily compatible. The main difference lies in the SFP’s internal code.

To ensure optimal compatibility, users should purchase an original transceiver or buy third-party SFPs that have passed compatibility tests. This approach helps avoid guesswork and saves time.

How to choose the suitable SFP Module for your networking?

We help more than 1400 clients choose the suitable transceiver quickly. Here are the essential tips.

Check your switch (or other network devices) port-supported speed and ensure it matches the correct SFP.
Know your existing network cabling types. If you have a multimode fiber cabling structure, choose the multimode SFP. If you have a single-mode fiber cabling structure, a single-mode SFP is the only choice.
Know your target link distance and link budget. But remember, choose an SFP that supports 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, a commercial-grade transceiver is enough for a typical indoor environment. In harsh outdoor applications, you should use an industrial transceiver.
Remember to check compatibility with the supplier before ordering. Because the switch can not recognize an incompatible transceiver, it will waste your money and valuable time. So, always choose a proven compatible transceiver.

FURTHER READING

SFP Module Color Code

To quickly distinguish the SFP module, industry manufacturers follow general color codes based on wavelength. The table below lists the general coding for the available channels. Most manufacturers follow the same color code, but others may have different codes based on their applications.

Wavelength	Color Code
850nm	Black
1310nm	Blue
1550nm	Green
CWDM 1470nm	Gray
CWDM 1490nm	Violet
CWDM 1510nm	Blue
CWDM 1530nm	Green
CWDM 1550nm	Yellow
CWDM 1570nm	Orange
CWDM 1590nm	Red
CWDM 1610nm	Brown
1310nm-TX/1490nm-RX	Blue
1310nm-TX/1550nm-RX	Blue
1550nm-TX/1310nm-RX	Yellow
1550nm-TX/1490nm-RX	Violet

SFP Module Evolution

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 transceivers based on this package—for example, CSFP, SFP+, SFP28, SFP-DD, SFP56, DSFP, etc. All of them have a very similar appearance. If you look at them, it’s hard to tell the difference. The significant difference between them is the supported data rates.

FAQ

Q: How does the SFP differ from the GBIC module?

A: They are two different form factors and can not replace each other. GBIC is an older version of the form that is bigger. Instead, SFP utilizes a compact size, providing around double port density. In addition, it supports enhanced DDM function for easy operating status tracking.

Q: Is SFP and SFP+ compatible?

A: They are generally not compatible. Because SFP+ usually stands for enhanced SFP, it provides a high speed of 8G/10G/16G. Both modules share the same mechanical dimension.

Q: Are SFP modules vs. media converters the same?

A: Definitely different. While both serve to connect network devices and convert the copper to fiber media and vice versa, they are different. Generally speaking, the SFP transceiver can not work as a standalone device; you must install it in the SFP port of the switch and then start to work. In contrast, media converters are standalone devices that convert signals from one media type to another.

Optical Transceiver