100BASE-TX vs 100BASE-FX, What is The Difference?

Initial Published: March 3, 2023

The evolution of Ethernet technology has never stopped. From the traditional 10 megabits (Mbps) Ethernet to Fast Ethernet and Gigabit Ethernet to today’s 10 Gigabit Ethernet, the industry has created new Ethernet specifications for the ever-increasing performance requirements. This post introduces several Fast Ethernet standards, including 100BASE-T, 100BASE-TX, and 100BASE-FX.

Let’s look at what those are and their difference.

What is 100BASE-T

100BASE-T is a technical term that defines the family of physical layers (or PHYs) supporting 100 Mbps networks over twisted pair cables. It is an improved version of 10BASE-T Ethernet, offering ten times faster than conventional Ethernet. Like standard ethernet, it avoids collisions using Collision Detection / Carrier Sense Multiple Access (CD/CSMA) technologies.

In 1995, IEEE released the 802.3 standards. IEEE 802.3 defines three 100Mbps Ethernet PHYs: 100BASE-TX, 100BASE-T4, and 100BASE-T2. 

100BASE-T2 is defined in IEEE 802.3y. It requires two copper cable pairs like category 3 copper cable instead of the category 5 cable needed in 100BASE-TX.

100BASE-T4 is one of the first Fast Ethernet variants. It requires four copper cable pairs for communication and uses category 3 twisted pair wires. Signals are sent and received by one pair of the system, and the two remaining pairs are set aside for future use.

Since 100BASE-T2 and 100BASE-T4 are rarely deployed in the market, many people began using the word 100BASE-T to refer to the 100BASE-TX, rendering the terms synonymous. 

What is 100BASE-TX

100BASE-TX is the most common term for Fast ethernet, which runs over two wire pairs inside a category 5 or better cable. For each network segment, the maximum cable length is 100 meters (328 feet).

The active pairs in a typical connection are terminated on pins 1, 2, 3, and 6 just as 10BASE-T. A normal category 5 cable can support two 100BASE-TX links using a wiring adaptor because it has four pairs. Cabling is conventionally wired to TIA/EIA-568-B’s termination standards, T568A or T568B.

What is 100BASE-FX

100BASE-FX is a Fast Ethernet standard over fiber optic cables. “FX” stands for fiber, which supports 100Mbps (Megabits per second) data speed over optical fiber. 

It uses two strands of optical fiber, one for transmitting and the other for receiving the light signal from (TX). By converting the 100BASE-TX to 100BASE-FX fiber signal, the max distance can be 120km over the single mode fiber.

Based on these 100BASE-FX general standards, the industry vendor also presented more specific terms like 100BASE-SX, 100BASE-LX, 100BASE-EX, 100BASE-ZX, and 100BASE-EZX. Yet these terms are non-standard in IEEE. 

Now, let us take a brief look at those terms.

• 100BASE-SX: Fast ethernet over multimode fiber for short reach, supporting a maximum of 2km (OM2) with an 850nm wavelength. It allows the use of less expensive optical components (LEDs).
• 100BASE-LX: Fast ethernet over single fiber for long reach application, support max 10km or 20km with 1310nm wavelength. Generally, the FP laser is used as the transmitter.
• 100BASE-EX: Fast ethernet over single fiber for extended reach applications, supporting a maximum of 40km with a 1310nm wavelength. Generally, a high-output FP laser is used as the transmitter.
• 100BASE-ZX: Fast ethernet over single-mode fiber for quite a lengthy reach application, support max 80km with 1550nm wavelength. Generally, using FP or DFB laser as the transmitter.
• 100BASE-EZX: Fast ethernet over single mode fiber for ultra-long reach application, support max 120km with 1550nm wavelength. Generally, using a DFB laser as the transmitter.
• 100BASE-BX10: A 100BASE-BX10 link utilizes bi-directional single-strand fiber for up to 10km. It uses 1310nm-TX/1550nm-RX for upstream (100BASE-BX10-D) and 1550nm-TX/1310nm-RX for downstream (100BASE-BX10-D).

100BASE-TX vs. 100BASE-FX, What is the difference?

Name	Standard	Wavelength	Media	Interface	Distance	Device Type	System Cost
100BASE-TX	802.3u-1995	NA	Cat 5	RJ-45	100m	Media Converter	Low
100BASE-FX	802.3u-1995	1310nm	MMF	LC/SC/FC/ST	2km	Media Converter, Optical Transceiver	Low
100BASE-SX	TIA-785 (2000)	850nm	MMF	LC/SC/FC/ST	2km	Media Converter, Optical Transceiver	Low
100BASE-LX	802.3ah-2004	1310nm	SMF	LC/SC/FC/ST	20km	Media Converter, Optical Transceiver	Low
100BASE-EX	proprietary (non-IEEE)	1310nm	SMF	LC/SC/FC/ST	40km	Media Converter, Optical Transceiver	Medium
100BASE-ZX	proprietary (non-IEEE)	1550nm	SMF	LC/SC/FC/ST	80km	Media Converter, Optical Transceiver	High
100BASE-EZX	proprietary (non-IEEE)	1550nm	SMF	LC/SC/FC/ST	120km	Media Converter, Optical Transceiver	Highest

From the above table, we summarize the difference between 100BASE-TX and 100BASE-FX below:

• Transmission medium: 100BASE-TX uses twisted pair copper cables (typically Category 5 UTP), while 100BASE-FX uses fiber optic cables.
• Maximum distance: 100BASE-TX supports a maximum cable length of 100 meters. 100BASE-FX can reach up to 2km with multimode fiber and 120km with single-mode fiber.
• Connectors: 100BASE-TX uses RJ-45 connectors. 100BASE-FX uses fiber optic connectors like LC, SC, FC, or ST.
• Applications: 100BASE-TX suits shorter distances within buildings or local area networks. 100BASE-FX is ideal for long-distance applications, such as connecting campus buildings or larger networks.

FAQ

Q: Is 100BASE-FX single mode or multimode?

A: According to the IEEE802.3ah, 100BASE-FX is multimode. However, in some cases, many industry manufacturers and engineers may use 100BASE-FX, which stands for 100BASE fiber, so an extended reach of >10km means it is single mode.

Q: What are the advantages of 100BASE-FX?

A: Compared with 100BASE-TX, 100BASE-FX supports longer distances, enhanced security, and immunity to electromagnetic interference and noise. Therefore, it suits various networking applications, particularly in large campus environments and industrial automation.

Conclusion

Although fast ethernet was developed many years ago, it is still in use today despite the availability of Gigabit and 10-gigabit networks. There are two critical reasons: lower cost and long distance over multimode cabling compared to 1G and 10G data rates. 

Now, I hope you know the basics and differences between them. If you are searching for a 10/100BASE-TX to 100BASE-FX media converter, explore our broad category and extend your copper networking to a longer distance.

Reference:

• https://en.wikipedia.org/wiki/Fast_Ethernet

Read more:

• 1000BASE-SX, 1000BASE-LX & 1000BASE-ZX, A Simple Guide
• Standards for 10Gb Ethernet