100Base-(T) TX/T4/FX - Ethernet

Introduction

The 100Base-TX (sometimes referred to 100Base-T) cable is the most popular cable around since it has actually replaced the older 10Base-T and 10Base-2 (Coaxial). The 100Base-TX cable provides fast speeds up to 100Mbits and is more reliable since it uses CAT5 cable.There is also 100Base-T4 and 100Base-FX available, which we discuss later.

So what does 100Base-TX/T4/FX mean ?

To make it simpler to distinguish cables they are categorised; that's how we got the CAT1, 2, 3 etc cables. Each category is specific for speed and type of network. But since one type of cable can support various speeds, depending on its quality and wiring, the cables are named using the "BaseT" to show exactly what type of networks the specific cable is made to handle.

We are going to break the "100Base-T?" into 3 parts so we can make it easier to understand:

100

The number 100 represents the frequency in MHz (Mega HertZ) for which this cable is made. In this case it is 100 MHz. The greater the MHz, the greater speeds the cable can handle. If you try to use this type of cable for greater frequencies (and, therefore, speeds) it will either not work or become extremely unreliable. The 100 MHz speed translates to 100Mbit per second, which in theory means 12 MBytes per second. In practice though, you wouldn't get more than 4 MBytes per second.

Base

The word "Base" refers to Baseband. Baseband is the type of communication used by Ethernet and it means that when a computer is transmitting, it uses all the available bandwith, whereas Broadband (cable modems) shares the bandwidth available. This is the reason cable modem users notice a slowdown in speed when they are connected on a busy node, or when their neighbour is downloading all the time at maximum speed ! Of course with Ethernet you will notice a slowdown in speed but it will be smaller in comparison to broadband.

TX/T4/FX

The "T" refers to "Twisted Pair" physical medium that carries the signal. This shows the structure of the cable and tells us it contains pairs which are twisted. For example, UTP has twisted pairs and this is the cable used in such cases. The 100Base-T is used sometimes to refer to the 100Base-TX cable specification. For more information, see the "UTP -Unshielded Twisted Pair" page where you can find information on pinouts for the cables. All 100Mbit rated cables, except the 100Base-FX, use CAT5 cable.

100Base-TX

The TX (sometimes refered as "T" only) means it's a CAT5 UTP straight through cable using 2 of the 4 available pairs and supports speeds up to 100Mbits. Maximum length is 100 meters

100Base-T4

The T4 means it's a CAT5 UTP straight through cable using all 4 available pairs and supports speeds up to 100Mbits. Maximum length is 100 meters.

100Base-FX

The FX means it's a 2 strand fiber cable and supports speeds up to 100Mbits.

Summary

To summarise, keep the following in mind:

• 100Base-TX/T4 works for 100Mbit networks only and uses unshielded twisted pair cable with RJ-45 connectors at each end
• All CAT5 UTP cables have 4 pairs of cables (8 wires).
• 100Base-TX (sometimes called 100Base-T) uses 2 of the 4 available pairs within the UTP cable, whereas the 100Base-T4 uses all 4 pairs.
• 100Base-FX also works for speeds up to 100Mbits but uses fibre optic cable instead of UTP.