Editing Fast Ethernet (section)

== Copper ==
'''100BASE-T''' is any of several Fast Ethernet standards for [[twisted pair cable]]s,{{dubious|Semantics of 100BASE-T|date=October 2021}} including: 100BASE-TX ({{nowrap|100 Mbit/s}} over two-pair [[Category 5 cable|Cat5]] or better cable), 100BASE-T4 (100&nbsp;Mbit/s over four-pair [[Category 3 cable|Cat3]] or better cable, defunct), 100BASE-T2 ({{nowrap|100 Mbit/s}} over two-pair Cat3 or better cable, also defunct). The segment length for a 100BASE-T cable is limited to {{convert|100|m|ft|0}} (the same limit as [[10BASE-T]] and [[gigabit Ethernet]]). All are or were standards under [[IEEE 802.3]] (approved 1995). Almost all 100BASE-T installations are 100BASE-TX.

{| class="wikitable" style="line-height:110%;"
|+Comparison of [[Ethernet over twisted pair|twisted-pair-based Ethernet]] physical transport layers (TP-PHYs)<ref name="TDG_ETH_2nd">{{cite book |title=Ethernet: The Definitive Guide |edition=2nd |author=Charles E. Spurgeon |publisher=O'Reilly Media |year=2014 |isbn=978-1-4493-6184-6}}</ref>
! Name
! Standard
! Status
! Speed {{nowrap|(Mbit/s)}}
! Pairs required
! Lanes per direction
! Bits per hertz
! [[Line code]]
! [[Symbol rate]] per lane (MBd) 
! Bandwidth (MHz)
! Max distance (m)
! Cable
! Cable rating (MHz)
! Usage
|-
| {{nowrap|[[100BASE-TX]]}}
| {{nowrap|802.3u-1995}}
| {{active|current}}
| align="right" | 100
| align="right" | 2
| align="right" | 1
| align="right" | 3.2
| align="right" | [[4B5B]] [[MLT-3]] [[NRZI]]
| align="right" | 125
| align="right" | 31.25
| align="right" | 100
| align="center" | [[Category 5 cable|Cat&nbsp;5]]
| align="right" | 100
| align="center" | LAN
|-
| {{nowrap|[[100BASE-T1]]}}
| {{nowrap|802.3bw-2015}} (CL96)
| {{active|current}}
| align="right" | 100
| align="right" | 1
| align="right" | 1
| align="right" | 2.6{{overline|6}}
| align="right" | PAM-3 4B/3B
| align="right" | 75
| align="right" | 37.5
| align="right" | 15
| align="center" | [[Category 5e cable|Cat&nbsp;5e]]
| align="right" | 66
| align="center" | Automotive, IoT, M2M
|-
| {{nowrap|[[100BASE-T2]]}}
| {{nowrap|802.3y-1997}}
| {{N/A|obsolete}}
| align="right" | 100
| align="right" | 2
| align="right" | 2
| align="right" | 4
| align="right" | LFSR PAM-5
| align="right" | 25
| align="right" | 12.5
| align="right" | 100
| align="center" | [[Category 3 cable|Cat&nbsp;3]]
| align="right" | 16
| {{N/A|''Market failure''}}
|-
| {{nowrap|[[100BASE-T4]]}}
| {{nowrap|802.3u-1995}}
| {{N/A|obsolete}}
| align="right" | 100
| align="right" | 4
| align="right" | 3
| align="right" | 2.6{{overline|6}}
| align="right" | 8B6T PAM-3 ''Half-duplex only''
| align="right" | 25
| align="right" | 12.5
| align="right" | 100
| align="center" | [[Category 3 cable|Cat&nbsp;3]]
| align="right" | 16
| {{N/A|''Market failure''}}
|-
| {{nowrap|[[100BaseVG]]}}
| {{nowrap|802.12-1995}}
| {{N/A|obsolete}}
| align="right" | 100
| align="right" | 4
| align="right" | 4
| align="right" | 1.6{{overline|6}}
| align="right" | 5B6B ''Half-duplex only''
| align="right" | 30
| align="right" | 15
| align="right" | 100
| align="center" | [[Category 3 cable|Cat&nbsp;3]]
| align="right" | 16
| {{N/A|''Market failure''}}
|}

{| class="wikitable" style="float: right; margin: 0 1em 1em 0; text-align:center;"
|+ [[8P8C]] wiring ([[ANSI/TIA-568]] T568A)
! Pin !! Pair !! Wire !! Color
|- style="background:#6f6;"
| 1 || 3 || +/tip
|  style="background:white; text-align:left;"| [[File:Wire white green stripe.svg|60px|Pair 3 Wire 1]] white/green
|- style="background:#6f6;"
| 2 || 3 || −/ring
|  style="background:white; text-align:left;"| [[File:Wire green.svg|60px|Pair 3 Wire 2]] green
|- style="background:#fc3;"
| 3 || 2 || +/tip
|  style="background:white; text-align:left;"| [[File:Wire white orange stripe.svg|60px|Pair 2 Wire 1]] white/orange
|- style="background:#69f;"
| 4 || 1 || +/ring
|  style="background:white; text-align:left;"| [[File:Wire blue.svg|60px|Pair 1 Wire 2]] blue
|- style="background:#69f;"
| 5 || 1 || -/tip
|  style="background:white; text-align:left;"| [[File:Wire white blue stripe.svg|60px|Pair 1 Wire 1]] white/blue
|- style="background:#fc3;"
| 6 || 2 || −/ring
|  style="background:white; text-align:left;"| [[File:Wire orange.svg|60px|Pair 2 Wire 2]] orange
|- style="background:#963;"
| 7 || 4 || +/tip
|  style="background:white; text-align:left;"| [[File:Wire white brown stripe.svg|60px|Pair 4 Wire 1]] white/brown
|- style="background:#963;"
| 8 || 4 || −/ring
|  style="background:white; text-align:left;"| [[File:Wire brown.svg|60px|Pair 4 Wire 2]] brown
|}
<br />
{| class="wikitable" style="float: right; margin: 0 1em 1em 0; text-align:center;"
|+ [[8P8C]] wiring ([[ANSI/TIA-568]] T568B)
! Pin !! Pair !! Wire !! Color
|- style="background:#fc3;"
| 1 || 2 || +/tip
|  style="background:white; text-align:left;"| [[File:Wire white orange stripe.svg|60px|Pair 2 Wire 1]] white/orange
|- style="background:#fc3;"
| 2 || 2 || −/ring
|  style="background:white; text-align:left;"| [[File:Wire orange.svg|60px|Pair 2 Wire 2]] orange
|- style="background:#6f6;"
| 3 || 3 || +/tip
|  style="background:white; text-align:left;"| [[File:Wire white green stripe.svg|60px|Pair 3 Wire 1]] white/green
|- style="background:#69f;"
| 4 || 1 || +/ring
|  style="background:white; text-align:left;"| [[File:Wire blue.svg|60px|Pair 1 Wire 2]] blue
|- style="background:#69f;"
| 5 || 1 || -/tip
|  style="background:white; text-align:left;"| [[File:Wire white blue stripe.svg|60px|Pair 1 Wire 1]] white/blue
|- style="background:#6f6;"
| 6 || 3 || −/ring
|  style="background:white; text-align:left;"| [[File:Wire green.svg|60px|Pair 3 Wire 2]] green
|- style="background:#963;"
| 7 || 4 || +/tip
|  style="background:white; text-align:left;"| [[File:Wire white brown stripe.svg|60px|Pair 4 Wire 1]] white/brown
|- style="background:#963;"
| 8 || 4 || −/ring
|  style="background:white; text-align:left;"| [[File:Wire brown.svg|60px|Pair 4 Wire 2]] brown
|}

=== 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>

=== 100BASE-T1 ===
{{Broader|Ethernet over twisted pair#Single-pair}}

In '''100BASE-T1'''<ref>IEEE 802.3bw-2015 Clause 96</ref> the data is transmitted over a single copper pair, 3 bits per symbol, each transmitted as code pair using PAM3. It supports full-duplex transmission. The twisted-pair cable is required to support 66&nbsp;MHz, with a maximum length of 15&nbsp;m. No specific connector is defined. The standard is intended for automotive applications or when Fast Ethernet is to be integrated into another application. It was developed as [[Open Alliance BroadR-Reach]] (OABR) before IEEE standardization.<ref>{{Cite web|url=http://www.eetimes.com/document.asp?doc_id=1328371 |title=Driven by IEEE Standards, Ethernet Hits the Road in 2016 |publisher=EETimes |author=Junko Yoshida |date=2015-12-01 |access-date=2016-10-06}}</ref>

=== 100BASE-T2 === <!-- This section is linked from [[Ethernet over twisted pair]] -->
{| class="wikitable" style="float: right; margin: 0 0 1em 1em;"
|+ 100BASE-T2 symbols to [[PAM-5]] line modulation level mapping
|-
! Symbol !! Line signal level
|-
| 000 || 0
|-
| 001 || +1
|-
| 010 || −1
|-
| 011 || −2
|-
| 100 (ESC) || +2
|}

In '''100BASE-T2''', standardized in IEEE 802.3y, the data is transmitted over two copper pairs, but these pairs are only required to be Category 3 rather than the Category 5 required by 100BASE-TX. Data is transmitted and received on both pairs simultaneously<ref name="Breyer and Riley">{{cite book |title=Switched, Fast, and Gigabit Ethernet |author=Robert Breyer and Sean Riley |publisher=Macmillan Technical Publishing |year=1999 |page=107}}</ref> thus allowing full-duplex operation. Transmission uses 4 bits per symbol. The 4-bit symbol is expanded into two 3-bit symbols through a non-trivial scrambling procedure based on a [[linear-feedback shift register]].<ref>IEEE 802.3y</ref> 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). The final mapping from symbols to [[PAM-5]] line modulation levels obeys the table on the right. 100BASE-T2 was not widely adopted but the technology developed for it is used in 1000BASE-T.<ref name="TDG_ETH_2nd" />

=== 100BASE-T4 ===
<!-- This section is linked from [[Ethernet over twisted pair]] -->
'''100BASE-T4''' was an early implementation of Fast Ethernet. It required four twisted copper pairs of [[Category 3 cable|voice grade twisted pair]], a lower-performing cable compared to [[Category 5 cable]] used by 100BASE-TX. Maximum distance was limited to 100 meters. One pair was reserved for transmit and one for receive, and the remaining two switched direction. The fact that three pairs were used to transmit in each direction made 100BASE-T4 inherently half-duplex. Using three cable pairs allowed it to reach {{nowrap|100 Mbit/s}} while running at lower carrier frequencies, which allowed it to run on older cabling that many companies had recently installed for 10BASE-T networks.

A very unusual [[8B6T]] code was used to convert 8 data bits into 6 base-3 digits (the signal shaping is possible as there are nearly three times as many 6-digit base-3 numbers as there are 8-digit base-2 numbers). The two resulting 3-digit base-3 symbols were sent in parallel over three pairs using 3-level [[pulse-amplitude modulation]] (PAM-3).

100BASE-T4 was not widely adopted but some of the technology developed for it is used in [[1000BASE-T]].<ref name="TDG_ETH_2nd" /> Very few hubs were released with 100BASE-T4 support. Some examples include the [[3com]] 3C250-T4 Superstack II HUB 100, [[IBM]] 8225 Fast Ethernet Stackable Hub<ref>{{cite web |url=https://www.ibm.com/common/ssi/cgi-bin/ssialias?appname=skmwww&htmlfid=897%2FENUS196-117&infotype=AN&mhq=IBM%20Network%20Station%208361%20Series%20100&mhsrc=ibmsearch_a&subtype=CA |title=IBM 8225 Fast Ethernet Stackable Hub Hardware Announcement |website=[[IBM]] |date=May 28, 1996}}</ref> and [[Intel]] LinkBuilder FMS 100 T4.<ref>{{cite web|url=https://techlibrary.hpe.com/docs/products/eos/3Com-End-of-Sale%20dates.pdf|title=3Com Product End of Sale dates|website=[[Hewlett Packard Enterprise]]}}</ref><ref>{{cite web | url=https://manualzz.com/doc/3244934/intel-express-100base-t4-user-s-manual | title=Intel Express 100BASE-T4 User's Manual | website=Manualzz}}</ref> The same applies to [[network interface controller]]s. Bridging 100BASE-T4 with 100BASE-TX required additional network equipment.

=== 100BaseVG ===
{{Main|100BaseVG}}
Proposed and marketed by [[Hewlett-Packard]], 100BaseVG was an alternative design using category 3 cabling and a token concept instead of CSMA/CD. It was slated for standardization as IEEE 802.12 but it quickly vanished when switched 100BASE-TX became popular. The IEEE standard was later withdrawn.<ref name=vg/>

VG was similar to T4 in that it used more cable pairs combined with a lower carrier frequency to allow it to reach {{nowrap|100 Mbit/s}} on voice-grade cables. It differed in the way those cables were assigned. Whereas T4 would use the two extra pairs in different directions depending on the direction of data exchange, VG instead used two transmission modes. In one,  control, two pairs are used for transmission and reception as in classic Ethernet, while the other two pairs are used for [[Ethernet flow control|flow control]]. In the second mode, transmission, all four are used to transfer data in a single direction. The hubs implemented a [[token passing]] scheme to choose which of the attached nodes were allowed to communicate at any given time, based on signals sent to it from the nodes using control mode. When one node was selected to become active, it would switch to transfer mode, send or receive a packet, and return to control mode.<ref name=vg>{{cite web
|url=https://standards.ieee.org/findstds/standard/802.12-1995.html
|archive-url=https://web.archive.org/web/20140419124102/http://standards.ieee.org/findstds/standard/802.12-1995.html
|url-status=dead
|archive-date=April 19, 2014
|title=ANSI/IEEE 802.12-1995
|publisher=IEEE Standards Association
|access-date=2018-07-31}}</ref>

This concept was intended to solve two problems. The first was that it eliminated the need for collision detection and thereby reduced contention on busy networks. While any particular node may find itself throttled due to heavy traffic, the network as a whole would not end up losing efficiency due to collisions and the resulting rebroadcasts. Under heavy use, the total throughput was increased compared to the other standards. The other was that the hubs could examine the payload types and schedule the nodes based on their bandwidth requirements. For instance, a node sending a video signal may not require much bandwidth but will require it to be predictable in terms of when it is delivered. A VG hub could schedule access on that node to ensure it received the transmission timeslots it needed while opening up the network at all other times to the other nodes. This style of access was known as [[demand priority]].<ref name=vg/>