What Is An SFP Module and Why Should I Use It?

In the communications industry, size and flexibility really matter.

If you can pack more data transmission into a smaller package with more flexibility of options, you’re ahead of the game. Back in the early 2000’s, the introduction of the SFP (Small Form Pluggable) module and socket was a great success in bringing flexibility and expandability to everyday network test equipment. Not only is it still being utilized today, it’s become an industry standard used by manufacturers and providers all around the world.

So, what exactly is an SFP Module?

What does it do? Well to start, an SFP module is simply a small modular transceiver that plugs into an SFP socket on a network switch. The word transceiver means that it can both transmit and receive data. This means that the SFP module converts electrical signals to optical signals and vice versa. This is typically done over a duplex fiber optic patch cable via two LC connectors. One fiber is designated for transmit and one fiber is designated for receive, however there are certain types of SFP’s that can transmit and receive data over a single fiber by multiplexing wavelengths. We’ll discuss this more in detail later. These pluggable transceivers are used in networking devices to give the user flexibility in options and plug-and-play ease of use. There are many different types of SFP modules available today. Most can be broken down into three main categories: Transmission Speed, Range, and Compatibility.

Let’s talk about transmission speed.

The most common SFP module on the market today is the 1 Gb. These are the least expensive SFP modules to purchase and by far the most popular network speed today. But with the expansion of networks and ever increasing demand for bandwidth, the 10 Gb SFP+ module is becoming more and more popular. The “+” means that the SFP module is enhanced for 10 Gb transmission. Next is the 25 Gb SFP28, which is designed for 100 Gb switches. You can achieve the 100 Gb by utilizing (4) of these SFP28 modules. The foot print for the SFP28 module is still the same as the SFP and SFP+.

Next up, we have the QSFP (Quad Small Form Pluggable) module.

The QSFP module has a different footprint than the SFP and therefore is considered an evolution of the technology. The QSFP footprint is specifically designed for the multi fiber MPO optical connector. Typically, the QSFP utilizes 8 out of the 12 channels of the MPO connector for transmit and receive. The first speed available is for 4 Gb applications, which means that each channel can transmit 1 Gb of data. The next speed option is the 40 Gb QSFP+. Just like before, the “+” means that the QSFP is enhanced for each channel to handle 10 Gb of data transmission. The QSFP28 can handle 100 Gb, with 25 Gb of data on each channel.

Let's talk about transmission range.

Now that we have the basics covered on the transmission speeds, let’s talk about transmission range. If you’re familiar with SFP modules, you may have seen various abbreviations used in the descriptions to indicate the SFP’s transmission range. These abbreviations are just a quick reference guide on range. The first of these is “SX”. The SX indicates that the SFP module is transmitting a 1 Gb multi mode wavelength. The most common is the 850nm wavelength for a maximum of 550 meters. If there’s a need to extend the multi mode transmission distance, you can also choose a 1310nm wavelength for a maximum transmission distance of 2,000 meters.

The next five abbreviations are all used for single mode wavelengths.

X is used for 1310nm for distances up to 10,000 meters. The EX is also for the 1310nm wavelength but has an extended distance of 40,000 meters. The ZX abbreviation is used for the 1550nm wavelength and can transmit up to 80,000 meters. The EZX also uses the 1550nm wavelength but for maximum transmission distance of 160,000 meters. The last abbreviation is used for single fiber / bi-directional SFP modules. The BX means that you are using the 1490nm and 1310nm wavelengths to multiplex both wavelengths down one fiber. But what does it mean to multiplex wavelengths? Well, let me explain.

Wavelenght Division Mutiplexing (WDM)

Wavelength Division Multiplexing (WDM) is a big topic to discuss but for the sake of time, let’s just keep it simple. SFP Modules are wavelength specific devices that convert light to an electrical signal. Basically, the idea of multiplexing is sending multiple light wavelengths down the same fiber and sorting them out at the other end. The big advantage with WDM is that you are maximizing the number of channels you have in your network. So, for example, if you have a 12 fiber cable installed in your network and you are using the standard method of 6 fibers for transmit and 6 fibers for receive, you can double your capacity by using bi-directional SFP modules and multiplexing the transmit and receive wavelengths down a single fiber. So, instead of using 6 fibers for transmit/receive, you’re utilizing all 12. Make sense?

SFP compatibility

Lastly, let’s talk about SFP compatibility. As mentioned earlier, the SFP socket and module is an industry standard used all around the world. That being said, not all SFP modules will work with all SFP sockets. Most large equipment manufacturers around the world have placed their own set of programming built into their switches. The reason they do this is to ensure the end user buys their own SFP modules and not modules from a third party. Over the past few years, a lot of third party companies have developed their own tools to program SFP modules to be compatible with the OEM. This has allowed the end user to purchase SFP modules and QSFP modules for a fraction of the original OEM cost. There are also some equipment manufacturers that adhere to the MSA (Multi Source Agreement) standard. The MSA standard is a multi-source-agreement between equipment manufacturers who came together to collaborate and standardize the form, fit, and function. So when you’re in the market for a new SFP module, the question to ask is: Do I need a MSA compatible SFP or do I need it programmed to the OEM?