Fast Ethernet

In computer networking, Fast Ethernet physical layers carry traffic at the nominal rate of 100 Mbit/s. The prior Ethernet speed was 10 Mbit/s. Of the Fast Ethernet physical layers, 100BASE-TX is by far the most common.

Intel PRO/100 Fast Ethernet NIC, a PCI card

Fast Ethernet was introduced in 1995 as the IEEE 802.3u standard[1] and remained the fastest version of Ethernet for three years before the introduction of Gigabit Ethernet.[2] The acronym GE/FE is sometimes used for devices supporting both standards.[3]

Nomenclature

The "100" in the media type designation refers to the transmission speed of 100 Mbit/s, while the "BASE" refers to baseband signalling. 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.) refers to the line code method used. Fast Ethernet is sometimes referred to as 100BASE-X, where "X" is a placeholder for the FX and TX variants.[4]

General design

Fast Ethernet is an extension of the 10 megabit Ethernet standard. 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. Most switches and other networking devices with ports capable of Fast Ethernet can perform autonegotiation, sensing a piece of 10BASE-T equipment and setting the port to 10BASE-T half duplex if the 10BASE-T equipment cannot perform auto negotiation itself. The standard specifies the use of CSMA/CD for media access control. A full-duplex mode is also specified and in practice all modern networks use Ethernet switches and operate in full-duplex mode, even as legacy devices that use half duplex still exist.

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 MAC is typically linked to the PHY by a four-bit 25 MHz synchronous parallel interface known as a media-independent interface (MII), or by a two-bit 50 MHz variant called reduced media independent interface (RMII). In rare cases the MII may be an external connection but is usually a connection between ICs in a network adapter or even two sections within a single IC. 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. Fast Ethernet or Ethernet hubs may use the MII to connect to multiple PHYs for their different interfaces.

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.

Copper

8P8C Wiring (TIA/EIA-568-B T568B)

Pin	Pair	Wire	Color
1	2	+/tip	white/orange
2	2	−/ring	orange
3	3	+/tip	white/green
4	1	−/ring	blue
5	1	+/tip	white/blue
6	3	−/ring	green
7	4	+/tip	white/brown
8	4	−/ring	brown

100BASE-T is any of several Fast Ethernet standards for twisted pair cables, including: 100BASE-TX (100 Mbit/s over two-pair Cat5 or better cable), 100BASE-T4 (100 Mbit/s over four-pair Cat3 or better cable, defunct), 100BASE-T2 (100 Mbit/s over two-pair Cat3 or better cable, also defunct). The segment length for a 100BASE-T cable is limited to 100 metres (328 ft) (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.

Name	Standard	Status	Medium	Line code	Specified distance
100BASE‑TX	IEEE 802.3u	current	Two Twisted-pair cabling (Cat-5, Cat-5e, Cat-6, Cat‑7)	4B5B	100 meters
100BASE‑T1	IEEE 802.3bw-2015 Clause 96	legacy	One Twisted-pair cabling (Cat-3)	PAM 3	15 meters
100BASE‑T2	IEEE 802.3y	legacy	Two Twisted-pair cabling (Cat-3)	PAM 5	100 meters
100BASE-T4	IEEE 802.3u	legacy	Four Twisted-pair cabling (Cat-3)	PAM 3	100 meters

100BASE-TX

3Com 3C905B-TX 100BASE-TX PCI network interface card

100BASE-TX is the predominant form of Fast Ethernet, and runs over two wire-pairs inside a category 5 or above cable. Each network segment can have a maximum cabling distance of 100 metres (328 ft). One pair is used for each direction, providing full-duplex operation with 100 Mbit/s of throughput 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 4 pairs, it can support two 100BASE-TX links with a wiring adaptor.[5] Cabling is conventional wired to TIA/EIA-568-B's termination standards, T568A or T568B. This places the active pairs on the orange and green pairs (canonical second and third pairs).

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 support 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.[6]

100BASE-T1

In 100BASE-T1[7] the data is transmitted over a single copper pair, 3 bits per symbol, each transmitted as code pair using PAM3. It supports only full-duplex, transmitting in both directions simultaneously. 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 BroadR-Reach before IEEE standardization.[8]

100BASE-T2

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[9] 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.[10] 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.[11]

100BASE-T4

100BASE-T4 was an early implementation of Fast Ethernet. It requires four twisted copper pairs of voice grade twisted pair, a lower performing cable compared to category 5 cable used by 100BASE-TX. Maximum distance is limited to 100 meters. One pair is reserved for transmit, one for receive, and the remaining two switch direction. The fact that 3 pairs are used to transmit in each direction makes 100BASE-T4 inherently half-duplex.

A very unusual 8B6T code is 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 are sent in parallel over 3 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.[11]

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.

Fiber optics

Legend for fibre-based TP-PHYs[11]

MMF FDDI 62,5/125 µm (1987)	MMF OM1 62,5/125 µm (1989)	MMF OM2 50/125 µm (1998)	MMF OM3 50/125 µm (2003)	MMF OM4 50/125 µm (2008)	MMF OM5 50/125 µm (2016)	SMF OS1 9/125 µm (1998)	SMF OS2 9/125 µm (2000)
160 MHz·km @850 nm	200 MHz·km @850 nm	500 MHz·km @850 nm	1500 MHz·km @850 nm	3500 MHz·km @850 nm	3500 MHz·km @850 nm & 1850 MHz·km @950 nm	1 dB/km @1300/ 1550 nm	0.4 dB/km @1300/ 1550 nm

Name	Standard	Status	Media	Connector	Transceiver module	Reach (km)	Media count	Lanes	Notes
Fast Ethernet - (Data rate: 100 Mbit/s - Line code: 4B5B × NRZ-I - Line rate: 125 MBd - Full-Duplex / Half-Duplex)
100BASE ‑FX	802.3u-1995 clause 24, 26	current	Fibre 1300 nm	ST SC MT-RJ MIC (FDDI)	N/A	FDDI: 2 (FDX)	2	1	[12] max. 412 m for half-duplex connections to ensure collision detection; specification largely derived from FDDI. Modal bandwidth: 800 MHz·km[13]
						OM1: 4
						50/125: 5
100BASE ‑LFX	proprietary (non IEEE)	current	Fibre 1310 nm	LC (SFP) ST SC	SFP	OM1: 2	2	1	vendor-specific FP laser transmitter Full-duplex Modal bandwidth: 800 MHz·km[14]
						OM2: 2
						62.5/125: 4
						50/125: 4
						OSx: 40 [13]
100BASE-SX	TIA-785 (2000)	legacy	Fibre 850 nm	ST, SC, LC	N/A	OM1: 0.3	2	1	Optics sharable with 10BASE-FL, thus making it possible to have an auto-negotiation scheme and use 10/100 fiber adapters.
						OM2: 0.3
100BASE-LX10	802.3ah-2004 clause 58	current}	Fibre 1310 nm	LC	SFP	OSx: 10	2	1	Full-duplex only commonly simply referred to as -LX[15]
100BASE-BX10		current	Fibre TX: 1310 nm RX: 1550 nm				1		Full-duplex only; Optical multiplexer used to split TX and RX signals into different wavelengths.
100BASE ‑EX	proprietary (non IEEE)	current	Fibre 1310 nm	SC LC	SFP GBIC	OSx: 40	2	1	vendor-specific[16]
100BASE ‑ZX	proprietary (non IEEE)	current	Fibre 1550 nm	SC LC	SFP GBIC	OSx: 80	2	1	vendor-specific[17]

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.[13]

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 throught 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 alternative to using 100BASE-FX, because it uses short wavelength optics which are significantly less expensive than the long wavelength optics used in 100BASE-FX. 100BASE-SX uses the same wavelength as 10BASE-FL, the 10 Mbit/s version over optical fiber. Unlike 100BASE-FX, this allows 100BASE-SX to be backwards-compatible with 10BASE-FL. Because of the shorter wavelength used (850 nm) and the shorter distance it can support, 100BASE-SX uses less expensive optical components (LEDs instead of lasers) which makes it an attractive option for those upgrading from 10BASE-FL and those who do not require long distances.

100BASE-EX

100BASE-EX is a non-standard but industry accepted[16] term to refer to Fast Ethernet transmission. It 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. It is sometimes referred to as 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[17] term to refer to Fast Ethernet transmission using 1,550 nm wavelength to achieve distances of at least 70km over single-mode fiber. Some vendors specify distances up to 160km 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.[27]

See also

• List of device bandwidths

Notes

1. It may possible for certain types of optics to work with a mismatch in wavelength.[22]

References

1. IEEE 802.3u-1995. IEEE. October 26, 1995. doi:10.1109/IEEESTD.1995.7974916. ISBN 978-0-7381-0276-4.
2. H. Frazier (2002) [1998]. "The 802.3z Gigabit Ethernet Standard". IEEE Network. IEEE. 12 (3): 6–7. doi:10.1109/65.690946.
3. "OC3/STM1 GE/FE Module Combination - ERX 10.3.x Module Guide". Juniper Networks.
4. "Cisco 100BASE-X Small Form-Factor Pluggable Modules for Fast Ethernet Applications Data Sheet". Cisco.
5. "CAT5E Adapters" (PDF). Archived from the original (PDF) on 2014-07-07. Retrieved 2012-12-17.
6. "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).
7. IEEE 802.3bw-2015 Clause 96
8. Junko Yoshida (2015-12-01). "Driven by IEEE Standards, Ethernet Hits the Road in 2016". EETimes. Retrieved 2016-10-06.
9. Robert Breyer and Sean Riley (1999). Switched, Fast, and Gigabit Ethernet. Macmillan Technical Publishing. p. 107.
10. IEEE 802.3y
11. Charles E. Spurgeon (2014). Ethernet: The Definitive Guide (2nd ed.). O'Reilly Media. ISBN 978-1-4493-6184-6.
12. "Introduction To Fast Ethernet" (PDF). Contemporary Control Systems, Inc. 2001-11-01. Retrieved 2018-08-25.
13. "Datasheet for EDS-408A-MM-ST". MOXA. 2019-08-06. Retrieved 2020-03-21.
14. "Datasheet for SFP-1FE Series" (PDF). MOXA. 2018-10-12. Retrieved 2020-03-21.
15. "Cisco GLC-FE-100LX 100BASE-LX10 SFP (mini-GBIC) Transceiver". FS.com. Retrieved 21 March 2020.
16. "GLC-FE-100EX 100BASE-EX SFP (mini-GBIC) Transceiver". FS.com. Retrieved 21 March 2020.
17. "FS-GLC-FE-100ZX 100BASE-ZX". FS.com. FS.com. Retrieved 21 March 2020.
18. "Cisco 350 Series Data Sheet". Cisco. Retrieved 22 March 2020.
19. "Cisco 100BASE-X SFP Data Sheet". Cisco. Retrieved 26 March 2020.
20. "FS GLC-GE-100FX Transceiver". FS. Retrieved 26 March 2020.
21. "Fiber incompatabilities? - Ars Technica OpenForum". arstechnica.com. 2006-06-06. Retrieved 29 March 2020.
22. "Everything You Always Wanted to Know About Optical Networking – But Were Afraid to Ask" (PDF). archive.nanog.org. Richard A Steenbergen. Retrieved 30 March 2020.
23. IEEE 802.3 clause 26.2 Functional specifications
24. "Datasheet for SFP-100FX-31". FS.com. Retrieved 2020-03-21.
25. "Knowledge Base Fiber". Fluke Networks. 28 February 2014. Retrieved 8 April 2020.
26. "Differences between OM1, OM2, OM3, OM4, OS1, OS2 fiber optic cable nomenclatures" (PDF). stl.tech. Retrieved 8 April 2020.
27. "SFP15160FE0B / SFP / 100BASE-eZX". Skylane Optics. Retrieved 21 March 2020.

This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.

External links

• Common 100 Mbit/s Hardware Variations
• Origins and History of Ethernet
• 100BASE-SX Fast Ethernet proposal site
• Fast Ethernet Chipsets Comparison
• IEEE802.3 standards free download
• ProCurve Networking 100BASE-FX Technical Brief