Initially, several Fast Ethernet standards for
twisted-pair cable were standardized, including: 100BASE-TX ( over two-pair
Cat5 or better cable), 100BASE-T4 (100 Mbit/s over four-pair
Cat3 or better cable, defunct), 100BASE-T2 ( over two-pair Cat3 or better cable, also defunct). The segment length for Ethernet over a twisted-pair link is limited to , the same limit as
10BASE-T and
gigabit Ethernet. All initial standards were approved under
IEEE 802.3 in 1995. Of those, 100BASE-TX became extremely popular, supplanting the others.
100BASE-TX network interface card
100BASE-TX is the predominant form of Fast Ethernet, and runs over two pairs of wire inside a
Category 5 or above cable. Cable distance between nodes can be up to . One pair is used for each direction, providing
full-duplex operation at 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. 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
hub or
switch, creating a
star network. Alternatively, it is possible to connect two devices directly using a
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 MHz at the MII, go through
4B5B binary encoding to generate a series of 0 and 1 symbols clocked at a 125 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 MHz. The procedure is borrowed from the ANSI X3.263
FDDI specifications, with minor changes.
100BASE-T1 In
100BASE-T1 the data is transmitted over a single copper pair, 3 bits per symbol, each transmitted as a code pair using PAM3. It supports full-duplex transmission. The twisted-pair cable is required to support 66 MHz, with a maximum length of 15 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.
100BASE-T2 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 (voice grade) rather than the Category 5 required by 100BASE-TX. Data is transmitted and received on both pairs simultaneously, 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. 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. and
Intel LinkBuilder FMS 100 T4. The same applies to
network interface controllers. Bridging 100BASE-T4 with 100BASE-TX required additional network equipment.
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. VG was similar to T4 in that it used more cable pairs combined with a lower carrier frequency to allow it to reach 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
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.{{cite web 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. == Fiber optics ==