Fast Ethernet
In computer networking, Fast Ethernet physical layers carry traffic at the nominal rate of 100 Mbit/s.
The letter following the dash (T or F) refers to the physical medium that carries the signal (twisted pair or fiber, respectively), while the last character (X, 4, etc.)
It runs on twisted pair or optical fiber cable in a star wired bus topology, similar to the IEEE standard 802.3i called 10BASE-T, itself an evolution of 10BASE5 (802.3) and 10BASE2 (802.3a).
Fast Ethernet devices are generally backward compatible with existing 10BASE-T systems, enabling plug-and-play upgrades from 10BASE-T.
A Fast Ethernet adapter can be logically divided into a media access controller (MAC), which deals with the higher-level issues of medium availability, and a physical layer interface (PHY).
The specs are written based on the assumption that the interface between MAC and PHY will be an MII but they do not require it.
The MII fixes the theoretical maximum data bit rate for all versions of Fast Ethernet to 100 Mbit/s.
The information rate actually observed on real networks is less than the theoretical maximum, due to the necessary header and trailer (addressing and error-detection bits) on every Ethernet frame, and the required interpacket gap between transmissions.
100BASE-TX is the predominant form of Fast Ethernet, and runs over two pairs of wire inside a Category 5 or above cable.
Just as in the 100BASE-FX case, the bits are then transferred to the physical medium attachment layer using NRZI encoding.
However, 100BASE-TX introduces an additional, medium-dependent sublayer, which employs MLT-3 as a final encoding of the data stream before transmission, resulting in a maximum fundamental frequency of 31.25 MHz.
The twisted-pair cable is required to support 66 MHz, with a maximum length of 15 m. No specific connector is defined.
[11] This is needed to flatten the bandwidth and emission spectrum of the signal, as well as to match transmission line properties.
The mapping of the original bits to the symbol codes is not constant in time and has a fairly large period (appearing as a pseudo-random sequence).
Proposed and marketed by Hewlett-Packard, 100BaseVG was an alternative design using category 3 cabling and a token concept instead of CSMA/CD.
The other was that the hubs could examine the payload types and schedule the nodes based on their bandwidth requirements.
100BASE-FX is still used for existing installation of multimode fiber where more speed is not required, like industrial automation plants.
It is very similar to 100BASE-FX but achieves longer distances up to 4–5 km over a pair of multi-mode fibers through the use of Fabry–Pérot laser transmitter[25] running on 1310 nm wavelength.
Cost and compatibility makes 100BASE-SX an attractive option for those upgrading from 10BASE-FL and those who do not require long distances.
It uses an optical multiplexer to split TX and RX signals into different wavelengths on the same fiber.
100BASE-EX is very similar to 100BASE-LX10 but achieves longer distances up to 40 km over a pair of single-mode fibers due to higher quality optics than a LX10, running on 1310 nm wavelength lasers.
100BASE-ZX is a non-standard but multi-vendor[29][better source needed] term to refer to Fast Ethernet transmission using 1,550 nm wavelength to achieve distances of at least 70 km over single-mode fiber.
