Editing Fast Ethernet (section)

=== 100BASE-TX ===
[[File:3Com 3C905B.jpg|300px|thumb|right|3Com 3C905B-TX 100BASE-TX [[Peripheral Component Interconnect|PCI]] network interface card]]
'''100BASE-TX''' is the predominant form of Fast Ethernet, and runs over two pairs of wire inside a [[Category 5 cable|Category 5]] or above cable. Cable distance between nodes can be up to {{convert|100|m|ft|0}}. One pair is used for each direction, providing [[full-duplex]] operation at {{nowrap|100 Mbit/s}} in each direction.

Like [[10BASE-T]], the active pairs in a standard connection are terminated on pins 1, 2, 3 and 6. Since a typical Category 5 cable contains four pairs and the performance requirements of 100BASE-TX do not exceed the capabilities of even the worst-performing pair, one typical cable can carry two 100BASE-TX links with a simple wiring adaptor on each end.<ref>{{cite web|url=http://www.trinetusa.com/images/catalog/pages31-40.pdf |title=CAT5E Adapters |access-date=2012-12-17 |url-status=dead |archive-url=https://web.archive.org/web/20140707221928/http://www.trinetusa.com/images/catalog/pages31-40.pdf |archive-date=2014-07-07 }}</ref> Cabling is conventionally wired to one of [[ANSI/TIA-568]]'s termination standards, T568A or T568B. 100BASE-TX uses pairs 2 and 3 (orange and green).

The configuration of 100BASE-TX networks is very similar to 10BASE-T. When used to build a [[local area network]], the devices on the network (computers, printers etc.) are typically connected to a [[Ethernet hub|hub]] or [[Network switch|switch]], creating a [[star network]]. Alternatively, it is possible to connect two devices directly using a [[Ethernet crossover cable|crossover cable]]. With today's equipment, crossover cables are generally not needed as most equipment supports auto-negotiation along with [[auto MDI-X]] to select and match speed, duplex and pairing.

With 100BASE-TX hardware, the raw bits, presented 4 bits wide clocked at 25&nbsp;MHz at the MII, go through [[4B5B]] binary encoding to generate a series of 0 and 1 symbols clocked at a 125&nbsp;MHz [[symbol rate]]. The 4B5B encoding provides DC equalization and spectrum shaping. 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&nbsp;MHz. The procedure is borrowed from the ANSI X3.263 [[FDDI]] specifications, with minor changes.<ref name="mlt3">"The 100BASE-TX PMD (and MDI) is specified by incorporating the FDDI TP-PMD standard, ANSI X3.263: 1995 (TP-PMD), by reference, with the modifications noted below." (section 25.2 of IEEE802.3-2002).</ref>