Ethernet physical layer

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Ethernet physical layer
EthernetCableYellow3.jpg
A standard 8P8C (often called RJ45) connector used most commonly on cat5 cable, one of the types of cabling used in Ethernet networks
Standard IEEE 802.3 (2002 onwards)
Physical media Coaxial cable, twisted pair, optical fiber
Network topology Point-to-point, star, bus
Major variants 10BASE-T, 10BASE2, 10BASE5, 100BASE-TX, 100BASE-FX, 100BASE-T, 1000BASE-T, 1000BASE-SX
Maximum distance 100 metres (328 ft) over twisted pair, up to 100 km over optical fiber
Mode of operation Differential (Balanced)
Maximum bit rate 1 Mbit/s to 100 Gbit/s
Voltage levels ± 2.5V (over twisted pair)
Available signals Tx+, Tx−, Rx+, Rx−
Common connector types 8P8C, LC, SC, ST

The Ethernet physical layer is the physical layer component of the Ethernet family of computer network standards.

The Ethernet physical layer evolved over a considerable time span and encompasses quite a few physical media interfaces and several magnitudes of speed. The speed ranges from 1 Mbit/s to 100 Gbit/s, while the physical medium can range from bulky coaxial cable to twisted pair and optical fiber. In general, network protocol stack software will work similarly on all physical layers.

10 Gigabit Ethernet was already used in both enterprise and carrier networks by 2007, with 40 Gbit/s[1][2] and 100 Gigabit Ethernet[3] ratified.[4] Higher speeds are under development.[5] Robert Metcalfe, one of the co-inventors of Ethernet, in 2008 said he believed commercial applications using Terabit Ethernet may occur by 2015, though it might require new Ethernet standards.[6]

Many Ethernet adapters and switch ports support multiple speeds, using autonegotiation to set the speed and duplex for the best values supported by both connected devices. If auto-negotiation fails, a multiple-speed device will sense the speed used by its partner,[7] but will assume half-duplex. A 10/100 Ethernet port supports 10BASE-T and 100BASE-TX. A 10/100/1000 Ethernet port supports 10BASE-T, 100BASE-TX, and 1000BASE-T.

Physical layers[edit]

The following sections provide a brief summary of official Ethernet media types (section numbers from the IEEE 802.3-2008 standard are parenthesized). In addition to these official standards, many vendors have implemented proprietary media types for various reasons—often to support longer distances over fiber optic cabling.

Early implementations[edit]

Early Ethernet standards used Manchester coding so that the signal was self-clocking and not adversely affected by high-pass filters.

Name Standard (Clause) Common connectors Description
Xerox experimental Ethernet Proprietary The original 2.94 Mbit/s Ethernet implementation had eight bit addresses and other differences in frame format and was carried on 50 Ω coaxial cable.[8]
10BASE5 802.3 (8) AUI Original standard uses a single coaxial cable into which you literally tap a connection by drilling into the cable to connect to the core and screen. Largely obsolete, though due to its widespread deployment in the early 1980s, some systems may still be in use.[9] Was known also as Thick-Ethernet. 10 Mbit/s over copper RG-8X (expensive) coaxial cabling, bus topology with collision detection.
10BASE2 802.3 (10) BNC 50 Ω coaxial cable connects machines together, each machine using a T-adaptor to connect to its NIC. Requires terminators at each end. For many years during the mid to late 1980 this was the dominant Ethernet standard. Also called Thin Ethernet, ThinNet or Cheapernet. 10 Mbit/s over RG-58 coaxial cabling, bus topology with collision detection.
10BROAD36 802.3 (11) F An early standard supporting Ethernet over longer distances. It utilized broadband modulation techniques, similar to those employed in cable modem systems, and operated over coaxial cable. 10 Mbit/s, scrambled NRZ signaling modulated (PSK) over high frequency carrier, broad bandwidth coaxial cabling, bus topology with collision detection.
1BASE5 802.3 (12) 8P8C Operated at 1 Mbit/s over twisted pair to an active hub. Although a commercial failure, 1BASE5 defined the architecture for all subsequent Ethernet evolution. Also called StarLAN. 1 Mbit/s over copper twisted pair cabling, star topology.
StarLAN 10 Proprietary 8P8C 10 Mbit/s over copper twisted pair cabling, star topology - evolved into 10BASE-T
LattisNet UTP Proprietary 8P8C 10 Mbit/s over copper twisted pair cabling, star topology - evolved into 10BASE-T
10BASE-T 802.3 (14) 8P8C Runs over four wires (two twisted pairs) on a Category 3 or Category 5 cable. A repeater hub or switch sits in the middle and has a port for each node. This is also the configuration used for 100BASE-T and gigabit Ethernet. Copper twisted pair cabling, star topology – direct evolution of 1BASE-5.
FOIRL 802.3 (9.9) ST Fiber-optic inter-repeater link; the original standard for Ethernet over fiber
10BASE-F 802.3 (15) A generic term for the family of 10 Mbit/s Ethernet standards using fiber optic cable: 10BASE-FL, 10BASE-FB and 10BASE-FP. Of these only 10BASE-FL is in widespread use. 10 Mbit/s over fiber pair
10BASE‑FL 802.3 (15&18) ST An updated version of the FOIRL standard
10BASE‑FB 802.3 (15&17) Intended for backbones connecting a number of hubs or switches; it is now obsolete.[10]
10BASE‑FP 802.3 (15&16) A passive star network that required no repeater, it was never implemented.[10]

Fast Ethernet[edit]

Main article: Fast Ethernet

All Fast Ethernet variants use a star topology.

Name Standard (Clause) Common connectors Description
100BASE‑T 802.3 (21) A term for any of the three standards for 100 Mbit/s Ethernet over twisted pair cable. Includes 100BASE-TX, 100BASE-T4 and 100BASE-T2. As of 2009, 100BASE-TX has totally dominated the market, and is often considered to be synonymous with 100BASE-T in informal usage. All of them use a star topology.
100BASE-TX 802.3 (24&25) 8P8C 4B5B MLT-3 coded signaling, CAT5 copper cabling with two twisted pairs.
100BASE-T4 802.3 (23) 8P8C 8B6T PAM-3 coded signaling, CAT3 copper cabling (as used for 10BASE-T installations) with four twisted pairs (uses all four pairs in the cable). Now obsolete, as CAT5 cabling is the norm. Limited to half-duplex.
100BASE-T2 802.3 (32) No products exist.[citation needed] PAM-5 coded signaling, CAT3 copper cabling with two twisted pairs, star topology. Supports full-duplex. It is functionally equivalent to 100BASE-TX, but supports old telephone cable. However, special sophisticated digital signal processors are required to handle encoding schemes required, making this option fairly expensive at the time. It arrived well after 100BASE-TX was established in the market. The technology developed for 100BASE-T2 was the foundation for 1000BASE-T.
100BASE‑FX 802.3 (24&26) ST/SC 4B5B NRZI coded signaling, two strands of multi-mode optical fiber. Maximum length is 400 meters for half-duplex connections (to ensure collisions are detected) or 2 kilometers for full-duplex.
100BASE‑SX TIA-785 ST/SC 100 Mbit/s Ethernet over multi-mode fiber. Maximum length is 300 meters. 100BASE-SX used short wavelength (850 nm) optics that was sharable with 10BASE-FL, thus making it possible to have an auto-negotiation scheme and have 10/100 fiber adapters.
100BASE‑BX10 802.3 (58) ST/SC/LC 100 Mbit/s Ethernet bidirectionally over a single strand of single-mode optical fiber. A multiplexer is used to split transmit and receive signals into different wavelengths allowing them to share the same fiber. Supports up to 10 km.
100BASE-LX10 802.3 (58) ST/SC/LC 100 Mbit/s Ethernet up to 10 km over a pair of Single Mode Fibers.
100Base‑VG 802.12 8P8C Standardized by a different IEEE 802 subgroup, 802.12, because it used a different, more centralized form of media access ("Demand Priority"). Championed by only HP, 100VG-AnyLAN (as was the marketing name) was the earliest in the market. It needed four pairs in a Cat-3 cable. Now obsolete (802.12 has been "inactive" since 1997) the standard has been withdrawn.

1 Gbit/s[edit]

Main article: Gigabit Ethernet

All Gigabit Ethernet variants use a star topology.

Name Standard (Clause) Common connectors Description
1000BASE‑T 802.3 (40) 8P8C PAM-5 coded signaling, At least Category 5 cable, with Category 5e strongly recommended copper cabling with four twisted pairs. Each pair is used in both directions simultaneously.
1000BASE‑TX TIA-854 Only over Cat-6 copper cabling. Unimplemented.
1000BASE‑SX 802.3 (38) ST/SC/LC 8B10B NRZ coded signaling, short-range multi-mode fiber (up to 550 m).
1000BASE‑LX 802.3 (38) SC/LC 8B10B NRZ coded signaling, multi-mode fiber (up to 550 m) or single-mode fiber (up to 2 km; can be optimized for longer distances, up to 10 km).[citation needed]
1000BASE‑LH multi-vendor SC/LC over single-mode fiber (up to 100 km). A long-haul solution.
1000BASE‑CX 802.3 (39) CX4 8B10B NRZ coded signaling, balanced shielded twisted pair (up to 25 m) over special copper cable. Predates 1000BASE-T and rarely used.
1000BASE‑BX10 802.3 (59) SC/LC up to 10 km. Bidirectional over single strand of single-mode fibre.
1000BASE‑LX10 802.3 (59) SC/LC Up to 10 km over a pair of single-mode fibres.
1000BASE‑PX10‑D 802.3 (60) SC/LC downstream (from head-end to tail-ends) over single-mode fiber using point-to-multipoint topology (supports at least 10 km).
1000BASE‑PX10‑U 802.3 (60) upstream (from a tail-end to the head-end) over single-mode fiber using point-to-multipoint topology (supports at least 10 km).
1000BASE‑PX20‑D 802.3 (60) downstream (from head-end to tail-ends) over single-mode fiber using point-to-multipoint topology (supports at least 20 km).
1000BASE‑PX20‑U 802.3 (60) upstream (from a tail-end to the head-end) over single-mode fiber using point-to-multipoint topology (supports at least 20 km).
1000BASE‑ZX Unknown SC/LC Up to 100 km over single-mode fibre.[11]
1000BASE‑KX 802.3 (70) 1 m over backplane

2.5 and 5 Gbit/s[edit]

Twisted pair copper cabling only, scaled-down variants of 10GBASE-T.

Name Standard (Clause) Common connectors Description
2.5GBASE-T 802.3bz 8P8C 100 m of Cat 5e
5GBASE-T 802.3bz 8P8C 100 m of Cat 6

10 Gbit/s[edit]

Main article: 10 Gigabit Ethernet

10 Gigabit Ethernet defines a version of Ethernet with a nominal data rate of 10 Gbit/s, ten times as fast as Gigabit Ethernet. In 2002, the first 10 Gigabit Ethernet standard was published as IEEE Std 802.3ae-2002. Subsequent standards encompassed media types for single-mode fibre (long haul), multi-mode fibre (up to 300 m), copper backplane (up to 1 m) and copper twisted pair (up to 100 m). All 10-gigabit standards were consolidated into IEEE Std 802.3-2008. As of 2009, 10 Gigabit Ethernet is predominantly deployed in carrier networks, where 10GBASE-LR and 10GBASE-ER enjoy significant market shares.

Name Standard (Clause) Common connectors Description
10GBASE‑SR 802.3 (52) SC/LC designed to support short distances over deployed multi-mode fiber cabling, it has a range of between 26 m and 82 m depending on cable type. It also supports 300 m and 400 m operation over 2000 MHz·km and respectively 4700 MHz·km multi-mode fiber.[citation needed]
10GBASE‑LX4 802.3 (53) SC/LC uses wavelength division multiplexing to support ranges of between 240 m and 300 m over deployed multi-mode cabling. Also supports 10 km over single-mode fiber.
10GBASE‑LR 802.3 (52) SC/LC supports 10 km over single-mode fiber
10GBASE‑ER 802.3 (52) SC/LC supports 40 km over single-mode fiber
10GBASE‑SW 802.3 (52) A variation of 10GBASE-SR using the WAN PHY, designed to interoperate with OC-192 / STM-64 SONET/SDH equipment
10GBASE‑LW 802.3 (52) A variation of 10GBASE-LR using the WAN PHY, designed to interoperate with OC-192 / STM-64 SONET/SDH equipment
10GBASE‑EW 802.3 (52) A variation of 10GBASE-ER using the WAN PHY, designed to interoperate with OC-192 / STM-64 SONET/SDH equipment
10GBASE‑CX4 802.3 (54) CX4 Designed to support short distances over copper cabling, it uses InfiniBand 4x connectors and CX4 cabling and allows a cable length of up to 15 m. Was specified by the IEEE Std 802.3an-2006 which has been incorporated into the IEEE Std 802.3-2008.
10GBASE‑T 802.3 (55) 8P8C Uses unshielded twisted-pair wiring.
10GBASE‑LRM 802.3 (68) SC/LC Extend to 220 m over deployed 500 MHz·km multimode fiber
10GBASE‑KX4 802.3 (71) 1 m over 4 lanes of backplane
10GBASE‑KR 802.3 (72) 1 m over a single lane of backplane

25 and 50 Gbit/s[edit]

Main article: 25 Gigabit Ethernet

An IEEE 802.3 workgroup has been formed to develop a 25-gigabit Ethernet standard based on one lane of the 4 by 25-Gbit/s 100 Gigabit Ethernet standard and is expected to progress quickly.[12] A 50-Gbit/s option is also being discussed.[13]

The IEEE 802.3cd Task Force is currently developing 50, 100, and 200 Gbit/s standards using one, two, or four lanes respectively.[14]

40 and 100 Gbit/s[edit]

Main article: 100 Gigabit Ethernet

This version of Ethernet specified two speeds and was standardized in June 2010 as IEEE 802.3ba, with one addition in March 2011 as IEEE 802.3bg.[15][16] The nomenclature is as follows:[17]

40 gigabits/second 100 gigabits/second Standard (Clause) Common connectors Description
40GBASE-KR4 802.3 (84) at least 1 m over a backplane
40GBASE-CR4 100GBASE-CR10 802.3 (85) QSFP+/CX4 approximately 7 m over copper cable assembly
40GBASE-SR4 100GBASE-SR10 802.3 (86) MPO at least 100 m over 2000 MHz·km multi-mode fiber (OM3)
at least 150 m over new 4700 MHz·km multi-mode fiber (OM4)
40GBASE-LR4 802.3 (87) SC/LC at least 10 km over single-mode fiber
100GBASE-LR4 802.3 (88) SC/LC
100GBASE-ER4 802.3 (88) SC/LC at least 40 km over single-mode fiber
40GBASE-FR 802.3 (89) SC/LC Single-mode fiber over 2 km

200 Gbit/s, 400 Gbit/s, 1 Tbit/s, and beyond[edit]

Main article: Terabit Ethernet

The standards body the Institute of Electrical and Electronic Engineers (IEEE) wants to define a new Ethernet standard capable of 200 and 400 Gbit/s, and possibly 1 Tbit/s.[18][19][20]

Initially, some believed that Terabit Ethernet may make a debut as early as 2015, and would be followed rapidly by a scaling to 100 Terabit, possibly as early as 2020. It is worth noting that these were theoretical predictions of technological ability, rather than estimates of when such speeds would actually become available at a practical price point.[21]

"First mile"[edit]

For providing Internet access service directly from providers to homes and small businesses:

Name Standard (Clause) Description
10BaseS Proprietary[22] Ethernet over VDSL, used in Long Reach Ethernet products[23]
2BASE-TL 802.3 (63) Over telephone wires
10PASS-TS 802.3 (62)
100BASE-LX10 802.3 (58) Single-mode fiber-optics
100BASE-BX10
1000BASE-LX10 802.3 (59)
1000BASE-BX10
1000BASE-PX10 802.3 (60) Passive optical network
1000BASE-PX20

Sublayers[edit]

From Fast Ethernet on, the physical layer specifications are divided into three sublayers in order to simplify design and interoperability:[24]

  • PCS (Physical Coding Sublayer) - This sublayer performs auto-negotiation and encoding such as 8b/10b
  • PMA (Physical Medium Attachment sublayer) - This sublayer performs PMA framing, octet synchronization/detection, and scrambling/descrambling
  • PMD (Physical Medium Dependent sublayer) - This sublayer consists of a transceiver for the physical medium

Twisted-pair cable[edit]

Several varieties of Ethernet were specifically designed to run over 4-pair copper structured cabling already installed in many locations. ANSI recommends using Category 6 cable for new installations.[citation needed]

8P8C wiring (TIA/EIA-568A)
Pin Pair Color telephone 10BASE-T 100BASE-TX 1000BASE-T PoE mode A PoE mode B
1 3 Pair 3 Wire 1 white/green TX+ z bidi 48 V out
2 3 Pair 3 Wire 2 green TX− z bidi 48 V out
3 2 Pair 2 Wire 1 white/orange RX+ z bidi 48 V return
4 1 Pair 1 Wire 2 blue ring bidi 48 V out
5 1 Pair 1 Wire 1 white/blue tip bidi 48 V out
6 2 Pair 2 Wire 2 orange RX− z bidi 48 V return
7 4 Pair 4 Wire 1 white/brown bidi 48 V return
8 4 Pair 4 Wire 2 brown bidi 48 V return

Combining 10Base-T (or 100BASE-TX) with "IEEE 802.3af mode A" allows a hub to transmit both power and data over only two pairs. This was designed to leave the other two pairs free for analog telephone signals.[25][not in citation given] The pins used in "IEEE 802.3af Mode B" supply power over the "spare" pairs not used by 10BASE-T and 100BASE-TX.

In a departure from both 10BASE-T and 100BASE-TX, 1000BASE-T and above use all four cable pairs for simultaneous transmission in both directions through the use of echo cancellation.

Comparison of twisted pair based ethernet technologies

Minimum cable lengths[edit]

Fiber connections have minimum cable lengths due to level requirements on received signals.[26] Fiber ports designed for long-haul wavelengths require a signal attenuator if used within a building.

10BASE2 installations, running on RG-58 coaxial cable, require a minimum of 0.5 m between stations tapped into the network cable, this is to minimize reflections.[27]

10BASE-T, 100BASE-T, and 1000BASE-T installations running on twisted pair cable use a star topology. No minimum cable length is required for these networks.[28][29]

Related standards[edit]

Some networking standards are not part of the IEEE 802.3 Ethernet standard, but support the Ethernet frame format, and are capable of interoperating with it.

  • LattisNet—A SynOptics pre-standard twisted-pair 10 Mbit/s variant.
  • 100BaseVG—An early contender for 100 Mbit/s Ethernet. It runs over Category 3 cabling. Uses four pairs. Commercial failure.
  • TIA 100BASE-SX—Promoted by the Telecommunications Industry Association. 100BASE-SX is an alternative implementation of 100 Mbit/s Ethernet over fiber; it is incompatible with the official 100BASE-FX standard. Its main feature is interoperability with 10BASE-FL, supporting autonegotiation between 10 Mbit/s and 100 Mbit/s operation – a feature lacking in the official standards due to the use of differing LED wavelengths. It is targeted at the installed base of 10 Mbit/s fiber network installations.
  • TIA 1000BASE-TX—Promoted by the Telecommunications Industry Association, it was a commercial failure, and no products exist. 1000BASE-TX uses a simpler protocol than the official 1000BASE-T standard so the electronics can be cheaper, but requires Category 6 cabling.
  • G.hn—A standard developed by ITU-T and promoted by HomeGrid Forum for high-speed (up to 1 Gbit/s) local area networks over existing home wiring (coaxial cables, power lines and phone lines). G.hn defines an Application Protocol Convergence (APC) layer that accepts Ethernet frames and encapsulates them into G.hn MSDUs.

Other networking standards do not use the Ethernet frame format but can still be connected to Ethernet using MAC-based bridging.

Other special-purpose physical layers include Avionics Full-Duplex Switched Ethernet and TTEthernet — Time-Triggered Ethernet for embedded systems.

References[edit]

  1. ^ "Consideration for 40 Gigabit Ethernet" (PDF). IEEE HSSG. May 2007. 
  2. ^ "40 gigabit Ethernet answers" (PDF). IEEE HSSG. May 2007. 
  3. ^ "HECTO: High-Speed Electro-Optical Components for Integrated Transmitter and Receiver in Optical Communication". Hecto.eu. Retrieved December 17, 2011. 
  4. ^ "IEEE P802.3ba 40Gb/s and 100Gb/s Ethernet Task Force". IEEE. 2010-06-19. 
  5. ^ Yiran Ma; Qi Yang; Yan Tang; Simin Chen; William Shieh, 1-Tb/s single-channel coherent optical OFDM transmission over 600-km SSMF fiber with subwavelength bandwidth access, retrieved 2010-07-30 
  6. ^ "Bob Metcalfe on the Terabit Ethernet". Light Reading. February 15, 2008. Retrieved August 27, 2013. 
  7. ^ "Configuring and Troubleshooting Ethernet 10/100/1000Mb Half/Full Duplex Auto-Negotiation". Cisco Systems. Retrieved 2016-08-09. ...it is possible for a link partner to detect the speed at which the other link partner operates, even though the other link partner is not configured for auto-negotiation. In order to detect the speed, the link partner senses the type of electrical signal that arrives and sees if it is 10 Mb or 100 Mb. 
  8. ^ John F. Shoch; Yogen K. Dalal; David D. Redell; Ronald C. Crane (August 1982). "Evolution of the Ethernet Local Computer Network" (PDF). IEEE Computer. 15 (8): 14–26. doi:10.1109/MC.1982.1654107. 
  9. ^ "L-com Introduces Commercial-Grade Thinnet (10Base-2) and Thicknet (10Base-5) Converters for Legacy Installs". Virtual-Strategy Magazine. 2012-06-11. Retrieved 2012-07-01. 
  10. ^ a b Zimmerman, Joann; Spurgeon, Charles (2014). Ethernet: The Definitive Guide, 2nd Edition. O'Reilly Media, Inc. ISBN 978-1-4493-6184-6. Retrieved 28 February 2016. This media system allowed multiple half-duplex Ethernet signal repeaters to be linked in series, exceeding the limit on the total number of repeaters that could be used in a given 10 Mb/s Ethernet system.... For the first few years after the standard was developed, equipment was available from a few vendors, but this equipment is no longer sold. 
  11. ^ Cisco Gigabit Ethernet Solutions for Cisco 7x00 Series Routers, undated, URL retrieved on 17 February 2008
  12. ^ Jim Duffy (2014-09-03). "25G Ethernet moving fast". Network World. 
  13. ^ Rick Merritt (2014-09-03). "50G Ethernet Debate Brewing". EE Times. 
  14. ^ "IEEE 802.3 50 Gb/s, 100 Gb/s, and 200 Gb/s Ethernet Task Force". IEEE 802.3. 2016-05-17. Retrieved 2016-05-25. 
  15. ^ Reimer, Jeremy (July 25, 2007). "New Ethernet standard: not 40Gbps, not 100, but both". Ars Technica. Retrieved December 17, 2011. 
  16. ^ "IEEE P802.3bg 40Gb/s Ethernet: Single-mode Fibre PMD Task Force". official task force web site. IEEE 802. April 12, 2011. Retrieved June 17, 2011. 
  17. ^ Ilango Ganga (May 13, 2009). "Chief Editor's Report" (PDF). IEEE P802.3ba 40Gb/s and 100Gb/s Ethernet Task Force public record. p. 8. Retrieved June 7, 2011. 
  18. ^ "IEEE P802.3bs 200 Gb/s and 400 Gb/s Ethernet Task Force". Retrieved 9 August 2016. 
  19. ^ Snyder, Bob. "IEEE Begins Work on New Ethernet Standard". Retrieved 9 August 2016. 
  20. ^ IEEE 802.3 Industry Connections Ethernet Bandwidth Assessment (PDF), IEEE, 2012-07-19, retrieved 2016-08-09 
  21. ^ author. "IEEE to introduce new Ethernet speed, up to 1Tb per second - MacNN". Retrieved 9 August 2016. 
  22. ^ "Infineon Strengthens Leadership in MDU/MTU Market with Ethernet over VDSL Technology Patent Award". News release. Infineon Technologies AG. January 8, 2001. Archived from the original on April 13, 2001. Retrieved August 27, 2011. 
  23. ^ "Infineon Announces Second Quarter Results". News release. Infineon Technologies. April 24, 2001. Retrieved August 28, 2011. ...strategic design-win with Cisco for new long range Ethernet products incorporating Infineon's 10BaseS technology 
  24. ^ IEEE 802.3 Figure 1–1—IEEE 802.3 standard relationship to the ISO/IEC Open Systems Interconnection (OSI) reference model
  25. ^ "Tech Info - LAN and Telephones". Zytrax.com. Retrieved December 17, 2011. 
  26. ^ "Cisco 100BASE-FX SFP Fast Ethernet Interface Converter on Gigabit SFP Ports". Cisco Systems. Archived from the original on 2007-10-13. 
  27. ^ "IEEE Standard for Ethernet 802.3-2008 Clauses 10.7.2.1-2" (PDF). 
  28. ^ "Troubleshooting Ethernet Collisions". Retrieved 9 August 2016. 
  29. ^ Gigabit Ethernet (PDF), retrieved 2016-08-09 

External links[edit]