100BASE-TX

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 100 metres (328 ft). One pair is used for each direction, providing full-duplex operation at 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.^[6] 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.^[7]

100BASE-T1

In 100BASE-T1^[8] 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 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.^[9]

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 rather than the Category 5 required by 100BASE-TX. Data is transmitted and received on both pairs simultaneously^[10] 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.^[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). 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.^[5]

100BASE-T4

100BASE-T4 was an early implementation of Fast Ethernet. It required four twisted copper pairs of 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.

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.^[5] 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^[12] and Intel LinkBuilder FMS 100 T4. ^[13][14] 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.

Fast Ethernet SFP ports

Fast Ethernet speed is not available on all SFP ports,^[18] but supported by some devices.^[19][20] An SFP port for Gigabit Ethernet should not be assumed to be backwards compatible with Fast Ethernet.

Optical interoperability

To have interoperable there is some criteria that have to be meet:^[21]

• Line encoding
• Wavelength^{[lower-alpha 1]}
• Duplex mode
• Media count
• Media type and dimension

100BASE-X Ethernet is not backward compatible with 10BASE-F and is not forward compatible with 1000BASE-X.

100BASE-FX

100BASE-FX is a version of Fast Ethernet over optical fiber. The 100BASE-FX physical medium dependent (PMD) sublayer is defined by FDDI's PMD,^[23] so 100BASE-FX is not compatible with 10BASE-FL, the 10 Mbit/s version over optical fiber.

100BASE-FX is still used for existing installation of multimode fiber where more speed is not required, like industrial automation plants.^[16]

100BASE-LFX

100BASE-LFX is a non-standard term to refer to Fast Ethernet transmission. 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^[24] running on 1310 nm wavelength. The signal attenuation per km at 1300 nm is about half the loss of 850nm.^[25][26]

100BASE-SX

100BASE-SX is a version of Fast Ethernet over optical fiber standardized in TIA/EIA-785-1-2002. It is a lower-cost, shorter-distance alternative to 100BASE-FX. Because of the shorter wavelength used (850 nm) and the shorter distance supported, 100BASE-SX uses less expensive optical components (LEDs instead of lasers).

Because it uses the same wavelength as 10BASE-FL, the 10 Mbit/s version of Ethernet over optical fiber, 100BASE-SX can be backward-compatible with 10BASE-FL. Cost and compatibility makes 100BASE-SX an attractive option for those upgrading from 10BASE-FL and those who do not require long distances.

100BASE-LX10

100BASE-LX10 is a version of Fast Ethernet over optical fiber standardized in 802.3ah-2004 clause 58. It has a 10 km reach over a pair of single-mode fibers.

100BASE-BX10

100BASE-BX10 is a version of Fast Ethernet over optical fiber standardized in 802.3ah-2004 clause 58. It uses an optical multiplexer to split TX and RX signals into different wavelengths on the same fiber. It has a 10 km reach over a single strand of single-mode fiber.

100BASE-EX

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-EX is not a formal standard but industry-accepted term.^[27] It is sometimes referred to as 100BASE-LH (long haul), and is easily confused with 100BASE-LX10 or 100BASE-ZX because the use of -LX(10), -LH, -EX, and -ZX is ambiguous between vendors.

100BASE-ZX

100BASE-ZX is a non-standard but multi-vendor^{[28][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. Some vendors specify distances up to 160 km over single-mode fiber, sometimes called 100BASE-EZX. Ranges beyond 80 km are highly dependent upon the path loss of the fiber in use, specifically the attenuation figure in dB per km, the number and quality of connectors/patch panels and splices located between transceivers.^[29]