Articles Tagged ‘100BASE-FX’

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

100Base-(T) TX/T4/FX - EthernetThe 100Base-TX (sometimes referred to 100Base-T) cable was until 2010 perhaps 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 CAT5e cable (see the CAT 1/2/3/4/5 page).There is also 100Base-T4 and 100Base-FX available, which we discuss at the end of this article.

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

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


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 Mbps. In practice though, you wouldn't get more than 4 Mbps.

Fast Ethernet

Full motion video for video conferencing requires, typically, at least 25 Mb/sec. That means that a legacy Ethernet, at 10 Mbps/sec, can only deliver poor quality real-time video. With 100 Mbps/sec, however, you can be watching a broadcast presentation in one window while you're in conference with three people in three other windows (for a total of 100 megabits of bandwidth).

Consider a file server that requires 0.6 Mb/sec (6 million bits per second; 60% utilization on a 10 Mb/sec Ethernet). With a 100 Mb/sec Ethernet this server can now utilize interface hardware that can pump data down the pipe at a greatly increased rate.

It seems clear that the evolution of the industry is moving away from 10 Mb/sec Ethernet and towards the 100 Mb/sec (or higher) rates of data transfer. This section of the compendium discusses 100 Mb/sec Ethernet technology

Virtually everyone who uses Ethernet has wished from time to time that their network had a higher bandwidth. When Ethernet was being designed in the late 1970s, 10Mbps seemed immense. With today's bandwidth-intensive multimedia applications, or even with just the departmental server, that number sometimes is barely adequate. Yes, faster network technologies were available, but they were complicated and expensive. Then came Fast Ethernet.

Anyone who understands classic Ethernet already understands much about Fast Ethernet. Fast Ethernet uses the same cabling and access method as 10Base-T. With certain exceptions, Fast Ethernet is simply regular Ethernet - just ten times faster! Whenever possible, the same numbers used in the design of 10Base-T were used in Fast Ethernet, just multiplied or divided by ten. Fast Ethernet is defined for three different physical implementations.

The Implementations of Fast Ethernet:

  • 100BASE-TX: Category 5
  • 100BASE-FX: Multimode fibre
  • 100BASE-T4: Category 3

Probably the most popular form of Fast Ethernet is 100BASE-TX. 100BASE-TX runs on EIA/TIA 568 Category 5 unshielded twisted pair, sometimes called UTP-5. It uses the same pair and pin configurations as 10Base-T, and is topologically similar in running from a number of stations to a central hub.

As an upgrade to 10Mbps Ethernet over multimode fibre (10Base-F), 100BASE-FX is Fast Ethernet over fibre. Single duplex runs are supported up to 400m and full duplex runs are supported for up to 2km.

Fast Ethernet is possible on Category 3 UTP with 100BASE-T4. There is a popular misconception that Fast Ethernet will only run on Category 5 cable. That is true only for 100BASE-TX. If you have Category 3 cable with all four pairs (8 wires) connected between station and hub, you can still use it for Fast Ethernet by running 100BASE-T4. 100BASE-T4 sends 100Mbps over the relatively slow UTP-3 wire by fanning out the signal to three pairs of wire.

This "demultiplexing" slows down each byte enough that the signal won't overrun the cable. Category 3 cable has four pairs of wire, eight wires total, running from point to point. 10Base-T only uses four wires, two pairs. Some cables only have these two pairs connected in the RJ-45 plug. If the category 3 cabling at your site has all four pairs between hub and workstation, you can use Fast Ethernet by running 100BASE-T4.

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