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What does the X in 100base-TX stand for?

Discussion in 'Windows - General discussion' started by MonkeyFat, Apr 14, 2007.

  1. MonkeyFat

    MonkeyFat Guest

    100base-TX 100=100 Mbps base=baseband T=twisted pair....what the heck is the X for? So far I've heard transmit, ten, axial, but nobody can state their source.

    Sorry if this is in the wrong forum, flame away. I'm studying for my network+ and can't find the answer to this anywhere.
     
  2. Indochine

    Indochine Regular member

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    I see you posted the same question in Yahoo Answers and got two rather useless responses.

    I think 100BaseTX means "100BaseT extended".

    IEEE 802.3 standard defines nomenclature, XBaseY, where:

    – X = LAN Speed in Mb/s

    – Base = Signaling method (baseband vs. broadband)

    – Y= LAN segment length in 100M multiples (bus topology) or T for twisted pair wire, F for fiber (star topology)

    I don't have any sources but I do know there is a sort of tradition in the IT industry of using the letter X to stand for "Extended". I mean this in the sense of stretching an already existing technology.

    The first IBM PC in the 1980s was followed up by the PC-XT which stood for "extended technology". This was not a complete new generation of hardware. That came with the PC-AT ("advanced Technology") hardware standard which was the basis for what we still use today. Later on came the ATX ("AT eXtended").

    Similarly with Ethernet. 100BaseT came first, using 2 twisted wires, then came 100BaseTX which used 2 higher quality twisted wires. Now you have 100BaseT4, with 4 wires and 100BaseFX with optical cable.

    http://www.isrl.uiuc.edu/~mwolske/lis451/fall05/presentations/LANOverview.pdf

    "Ethernet nomenclature" is a handy search phrase.
     
    Last edited: Apr 15, 2007
  3. MonkeyFat

    MonkeyFat Guest

    From Rich Seifert, one of the "designers of the commercial 10 Mb/s Ethernet, and author of the original DEC-Intel-Xerox Ethernet specifications."

    It doesn't "stand for" anything. When we were developing the 100 Mb/s Ethernet standard, a proposal was initially presented for an encoding scheme that supported both twisted pair and fiber. To facilitate discussion, it was called "100BASE-X", where the "X" was a placeholder for whatever medium would ultimately be used. The symbolism stuck and we kept the "X" designation to indicate the use of 4B/5B block encoding; -TX meant that coding on twisted pair, and -FX meant that encoding used on fiber.


    Thank goodness! That was bugging me.
     
  4. MonkeyFat

    MonkeyFat Guest

    Thanks for the link, Indochine. That had some useful info in it for me, I'm still learning networks.
     
  5. Xian

    Xian Regular member

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    I think they used the X because there already was a 100BaseT2 and 100BaseT4, where the last number referred to the number of wire pairs -100BaseT2 used 2 pairs, 100BaseT4 used 4 pairs. Both of those were for Cat 3 cable. When they wrote the spec to require the use of Cat 5 cable, since there already was a 100BaseT2 and the new spec still used 2 pairs of wires, they substituted X to make it 100BaseTX.
     
  6. Indochine

    Indochine Regular member

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    That's the other thing 'X' can be - a placeholder or symbol of an insignificant variable.
     

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