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SFP: Complete guide to Small Form-Factor Pluggable: 7 things you need to know

POSTED 04/08/2024

1. What is Small Form-Factor Pluggable (SFP)?

Small Form-Factor Pluggable, commonly shortened to SFP, is a series of hot-pluggable network interface modules used for data communications. It is a widely used networking solution due to its long transmission distance, high-speed capabilities and ease of use; due to it being hot-pluggable.

2. Brainboxes SFP Products

Brainboxes have released a series of SFP capable products, these include:

  • SW-084 – 4x 1Gb RJ45 Ports & 1x 1000BASE-X SFP Port
  • SW-584 – Industrial 4x 1Gb RJ45 Ports & 1x 1000BASE-X SFP Port
  • SW-581 – Industrial Media Converter – 1x 1Gb RJ45 Port & 1x 1000BASE-X SFP Port
SW-084 SW-584 SW-581
SW-084 - 4x 1Gb RJ45 Ports & 1x 1000BASE-X SFP Port SW-584 - Industrial 4x 1Gb RJ45 Ports & 1x 1000BASE-X SFP Port SW-581 - 1x 1Gb RJ45 Port & 1x 1000BASE-X SFP Port

LED Indicators

The below LED indicators apply to Brainboxes SFP products only:

Gigabit – RJ45 SFP
Green LED Yellow LED Bi-Colour LED
Steady = 10/100 Link Steady = 1Gb Link Steady Green = Device Powered, No SFP Installed
Flashing = Data Flashing = Data Steady Orange = SFP Connected, No Link
  Flashing Orange = SFP Activity
  Flashing Green & Orange = SFP Disabled
By Microcontroller

An SFP module may be disabled by the microcontroller for a number of reasons, most commonly due to incompatible hardware or a short circuit. If this occurs and you require assistance, please contact: [email protected]

3. What is the Difference Between SFP & SFP+?

The main difference you will find between SFP & SFP+ is the higher transmission speeds on SFP+. SFP connections typically support data rates up to 1.25Gbps, whereas SFP+ supports higher speeds up to 10Gbps, making it more suited to higher bandwidth applications.

In most cases, SFP+ modules are backwards compatible with SFP ports, but they will be limited to 1.25Gbps. However, SFP modules generally cannot be used in SFP+ ports due to the difference in data rate support.

4. What Standard is Supported by Brainboxes SFP Products?

All Brainboxes SFP products (SW-084, SW-581 & SW-584) only support 1000BASE-X, supporting up to 1Gb transmission speeds. We do not support SFP+.

1000BASE-X is a collective identifier for three types of media segments, two fibre optic & one copper. The two types of fibre optic line are referred to as 1000BASE-SX (Short Wavelength) & 1000BASE-LX (Long Wavelength). The copper line is referred to as 1000BASE-CX, which is a shorter copper jumper, and only has a transmission distance of around 25 meters. 1000BASE-SX has a theoretical maximum transmission distance of 550 meters, while 1000BASE-LX can theoretically cover 10,000 meters (10km).

5. What are the Different SFP Interface Types?

1000BASE-T (Gigabit Ethernet)

SFP interfaces allow for Ethernet connections using specific modules. These modules connect directly into the SFP port and provide the user with an RJ45 interface with which to connect to their other device. This is supported through the 1000BASE-T standard, representing Gigabit Ethernet over copper cables (shielded twisted pairs).

Direct Attach Copper (DAC)

Direct Attach Copper (DAC) cable, is a twinaxial copper cable that comes with transmission modules from the factory, allowing it to connect directly into SFP ports. Twinax cabling is a cable type, similar to coaxial cabling, but with two inner copper conductor lines as opposed to the singular line found in coaxial cabling.

Fibre

Fibre cables are one of the fastest and most common sources of SFP data transmission, because it transfers data via pulses of light which pass along one or more plastic or glass fibres, transmitting the light to the receiving end where the data is read and converted. Fibre is also not affected by EMI due to the fact it uses light to transmit data, rather than electrical signals.

There are many different options when choosing a fibre cable, below are the specifications of each fibre standard:

Fibre Cable Type Jacket Colour Fibre Core Diameter Optical Source
OS1 Yellow 8 – 10.5µm
(Commonly 9µm)
VCSEL
OS2 Yellow 8 – 10.5µm
(Commonly 9µm)
VCSEL
OM1 Orange 62.5µm LED
OM2 Orange 50µm LED
OM3 Aqua 50µm VCSEL
OM4 Aqua 50µm VCSEL
OM5 Lime Green 50µm VCSEL
VCSEL – Vertical-Cavity Surface Emitting Laser
LED – Light Emitting Diode

6. Single Mode SFP vs Multi-Mode SFP

Single Mode SFP works using Single-Mode fibre, which has a typical core diameter of 9µm (micrometres).

It mainly works in 1310nm & 1550nm (nanometres) wavelengths, meaning it is suitable for long-distance data transmission applications, allowing distances up to 80km (providing the transceiver is capable of extended SFP).

Multi-Mode SFP works using multimode fibre, which has a core diameter of 50µm (micrometres).

The most common Multi-Mode SFP transceivers work mainly in 850nm wavelengths, which means it is more suitable for shorter transmission distances, achieving up to 500 meters, once again providing that the transceiver is capable of extended SFP.

Pros & Cons of Single-Mode vs Multi-Mode

As with most cabling, there are positives and negatives associated with their deployment, below is a comparison of Single-Mode vs Multi-Mode fibre:

Single Mode Multi-Mode
Lower Cabling Cost Higher Cabling Cost
Higher Electronics Cost Lower Electronics Cost
Low Attenuation High Attenuation
Smaller Core, Harder to Terminate Larger Core, Easier to Terminate
Longer Transmission Distances Shorter Transmission Distances
Higher Transmission Speed (100Gb/s) Lower Transmission Speed (10Gb/s)

7. What is SFP & SFP+ MSA and Why is it Important?

Multi-Source Agreement (MSA), is a standardization of SFP transceivers and receivers that ensure all ‘MSA Compliant’ SFP modules from vendors, all conform to the same formfactor. It’s an agreement between manufacturers to implement standards for optical modules.

SFP MSA importantly provides consumers with a choice of suppliers for SFP modules, and keeps costs down for customers by providing them the widest array of options.