Many times I've come across that there is an "X" added to the end of network-related names on equipment, like how copper cables have wires in them called TX and RX, and ports on switches can have names like "100BASE-FX". Why is the X there? Does it mean anything?


1 Answer 1


Source: Ethernet_Nomenclature_GA-TB-357.pdf


Optical link that uses short wavelength (850 nm) lasers over two FDDI grade multimode optical Fibers, with eXternal sourced coding. Supports up to at least 2 km.

So, F=fiber, X=external sourced coding

  • 1
    Allright, but what does "external sourced coding" mean :P? Mar 25, 2014 at 16:15
  • 1
    Did you try searching for this term in the pdf I linked? Page 5, under "Fast Ethernet (100Mbps)"
    – mulaz
    Mar 25, 2014 at 16:23

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