Incomputer networking,Gigabit Ethernet(GbEor1 GigE) is a term describing various technologies for transmittingEthernet framesat a rate of agigabit per second(1,000,000,000 bits per second), as defined by theIEEE 802.3-2008standard. It came into use beginning in 1999, gradually supplantingFast Ethernetin wired local networks, where it performed considerably faster. The cables and equipment are very similar to previous standards and have been very common and economical since 2010.
Half-duplexgigabit links connected throughrepeater hubswere specified,but the specification is not updated anymore andfull-duplexusage withswitchesis used exclusively.
Ethernetwas the result of the research done atXerox PARCin the early 1970s. Ethernet later evolved into a widely implementedphysicalandlinklayerprotocol.Fast Ethernetincreased speed from 10 to 100 megabits per second (Mbit/s). Gigabit Ethernet was the next iteration, increasing the speed to 1000 Mbit/s. The initial standard for Gigabit Ethernet was produced by theIEEEin June 1998 asIEEE 802.3z, and requiredoptical fiber. 802.3z is commonly referred to as 1000BASE-X, where -X refers to either -CX, -SX, -LX, or (non-standard) -ZX. For the history behind the "X" seeFast Ethernet.
IEEE 802.3ab, ratified in 1999, defines Gigabit Ethernet transmission overunshieldedtwisted pair(UTP)category 5, 5e, or6cabling and became known as 1000BASE-T. With the ratification of 802.3ab, Gigabit Ethernet became a desktop technology as organizations could use their existing copper cabling infrastructure.
IEEE 802.3ah, ratified in 2004 added two more gigabit fiber standards, 1000BASE-LX10 (which was already widely implemented as vendor specific extension) and 1000BASE-BX10. This was part of a larger group of protocols known asEthernet in the First Mile.
Initially, Gigabit Ethernet was deployed in high-capacitybackbone networklinks (for instance, on a high-capacity campus network). In 2000,Apple'sPower Mac G4andPowerBook G4were the first mass-produced personal computers featuring the 1000BASE-T connection.It quickly became a built-in feature in many other computers.
1000BASE-T capablenetwork interface cardmade byIntel, which connects to the computer viaPCI-X
There are fivephysical layerstandards for Gigabit Ethernet usingoptical fiber(1000BASE-X),twisted pair cable(1000BASE-T), or shielded balanced copper cable (1000BASE-CX).
The IEEE 802.3z standard includes 1000BASE-SX for transmission overmulti-mode fiber, 1000BASE-LX for transmission oversingle-mode fiber, and the nearly obsolete 1000BASE-CX for transmission over shielded balanced copper cabling. These standards use8b/10b encoding, which inflates the line rate by 25%, from 1000Mbit/s to 1250Mbit/s, to ensure a DC balanced signal. The symbols are then sent usingNRZ.
IEEE 802.3ab, which defines the widely used 1000BASE-T interface type, uses a different encoding scheme in order to keep the symbol rate as low as possible, allowing transmission over twisted pair.
IEEE 802.3ap defines Ethernet Operation over Electrical Backplanes at different speeds.
Ethernet in the First Milelater added 1000BASE-LX10 and -BX10.Name / Medium / Specified distance
1000BASECX / Shielded balanced copper cable / 25 meters
1000BASEKX / Copper backplane / 1 meter
1000BASESX / Multi-mode fiber / 220 to 550 meters dependent on fiber diameter and bandwidth
1000BASELX / Multi-mode fiber / 550 meters
1000BASELX / Single-mode fiber / 5km
1000BASELX10 / Single-mode fiber using 1,310nm wavelength / 10km
1000BASEEX / Single-mode fiber at 1,310nm wavelength / ~ 40km
1000BASEZX / Single-mode fiber at 1,550nm wavelength / ~ 70km
1000BASEBX10 / Single-mode fiber, over single-strand fiber: 1,490nm downstream 1,310nm upstream / 10km
1000BASET / Twisted-pair cabling (Cat-5, Cat-5e,Cat-6,Cat7) / 100 meters
1000BASETX / Twisted-pair cabling (Cat-6,Cat7) / 100 meters
1000BASE-X is used in industry to refer to Gigabit Ethernet transmission over fiber, where options include 1000BASE-SX, 1000BASE-LX, 1000BASE-LX10, 1000BASE-BX10 or the non-standard -EX and -ZX implementations.
1000BASE-CX is an initial standard for Gigabit Ethernet connections with maximum distances of 25 meters using balanced shielded twisted pair and eitherDE-9or8P8Cconnector (with a pinout different from 1000BASE-T). The short segment length is due to very high signal transmission rate. Although it is still used for specific applications where cabling is done by IT professionals, for instance the IBM BladeCenter uses 1000BASE-CX for the Ethernet connections between the blade servers and the switch modules, 1000BASE-T has succeeded it for general copper wiring use.
1000BASE-KX is part of the IEEE 802.3ap standard for Ethernet Operation over Electrical Backplanes. This standard defines one to four lanes of backplane links, one RX and one TX differential pair per lane, at link bandwidth ranging from 100Mbit to 10Gbit per second (from 100BASE-KX to 10GBASE-KX4). The 1000BASE-KX variant uses 1.25 GBd electrical (not optical) signalling speed.
1000BASE-SX is afiber opticGigabit Ethernet standard for operation over multi-mode fiber using a 770 to 860nanometer,near infrared(NIR)lightwavelength.
The standard specifies a distance capability between 220 metres (62.5/125µm fiber with lowmodal bandwidth) and 550 metres (50/125µm fiber with high modal bandwidth). In practice, with good quality fiber, optics, and terminations, 1000BASE-SX will usually work over significantly longer distances.
This standard is highly popular for intra-building links in large office buildings, co-location facilities and carrier neutral internet exchanges.
Optical power specifications of SX interface: Minimum output power = −9.5dBm. Minimum receive sensitivity = −17dBm.
1000BASE-LX is afiber opticGigabit Ethernet standard specified in IEEE 802.3 Clause 38 which uses a long wavelength laser (1,270–1,355nm), and a maximum RMS spectral width of 4nm.
1000BASE-LX is specified to work over a distance of up to 5km over 10µm single-mode fiber.
1000BASE-LX can also run over all common types of multi-mode fiber with a maximum segment length of 550 m. For link distances greater than 300m, the use of a special launch conditioning patch cord may be required.This launches the laser at a precise offset from the center of the fiber which causes it to spread across the diameter of the fiber core, reducing the effect known as differential mode delay which occurs when the laser couples onto only a small number of available modes in multi-mode fiber.
1000BASE-LX10 was standardized six years after the initial gigabit fiber versions as part of theEthernet in the First Miletask group. It is very similar to 1000BASE-LX, but achieves longer distances up to 10km over a pair of single-mode fiber due to higher quality optics. Before it was standardized 1000BASE-LX10 was essentially already in widespread use by many vendors as a proprietary extension called either 1000BASE-LX/LH or 1000BASE-LH.
1000BASE-EX is a non-standard but industry acceptedterm to refer to Gigabit Ethernet transmission. It is very similar to 1000BASE-LX10 but achieves longer distances up to 40km over a pair of single-mode fibers due to higher quality optics than a LX10, running on 1310nm wavelength lasers.It is sometimes referred to as LH (Long Haul). Easily confused with a 1000BASE-LX10 or 1000BASE-ZX because some vendors use the LH term.
1000BASE-BX10 is capable of up to 10km over a single strand ofsingle-mode fiber, with a different wavelength going in each direction. The terminals on each side of the fibre are not equal, as the one transmitting downstream (from the center of the network to the outside) uses the 1,490nm wavelength, and the one transmitting upstream uses the 1,310nm wavelength.
1000BASE-ZX is a non-standard but multi-vendorterm to refer to Gigabit Ethernet transmission using 1,550nm wavelength to achieve distances of at least 70 kilometres (43 miles) over single-mode fiber. Some vendors specify distances up to 120 kilometres (75 miles) over single-mode fiber, sometimes called 1000BASE-EZX.
Intel82574L Gigabit EthernetNIC, aPCI Expressx1 card
1000BASE-T (also known as IEEE 802.3ab) is a standard for Gigabit Ethernet overcopperwiring.
Each 1000BASE-T network segment can be a maximum length of 100 meters (330 feet), and must useCategory 5 cableor better (includingCat 5eandCat 6).
Autonegotiationis a requirement for using 1000BASE-Taccording toSection 28D.5 Extensions required for Clause40 (1000BASE-T).At least the clock source has to be negotiated, as one endpoint must be master and the other endpoint must be slave.
In a departure from both10BASE-Tand100BASE-TX, 1000BASE-T uses all four cable pairs for simultaneous transmission in both directions through the use ofadaptive equalizationand a five-levelpulse amplitude modulation(PAM-5) technique. The symbol rate is identical to that of 100BASE-TX (125megabaud) and the noise immunity of the five-level signaling is also identical to that of the three-level signaling in 100BASE-TX, since 1000BASE-T uses four-dimensionaltrellis coded modulation(TCM) to achieve a 6dBcoding gainacross the four pairs.
Since negotiation takes place on only two pairs, if two gigabit devices are connected through a cable with only two pairs, the devices will successfully choose 'gigabit' as the highest common denominator (HCD), but the link will never come up. Most gigabit physical devices have a specific register to diagnose this behaviour. Some drivers offer an "Ethernet@Wirespeed" option where this situation leads to a slower yet functional connection.
The data is transmitted over four copper pairs, eightbitsat a time. First, eight bits of data are expanded into four three-bit symbols through a non-trivial scrambling procedure based on alinear feedback shift register; this is similar to what is done in100BASE-T2, but uses different parameters. The three-bit symbols are then mapped to voltage levels which vary continuously during transmission. An example mapping is as follows:Symbol / 000 / 001 / 010 / 011 / 100 / 101 / 110 / 111
Line signal level / 0 / +1 / +2 / −1 / 0 / +1 / −2 / −1
Automatic MDI/MDI-X Configurationis specified as an optional feature in the 1000BASE-T standard,meaning that straight-through cables will often work between gigabit-capable interfaces. This feature eliminates the need forcrossover cables, making obsolete the uplink/normal ports and manual selector switches found on many older hubs and switches and greatly reduces installation errors.
TheTelecommunications Industry Association(TIA) created and promoted a standard similar to 1000BASE-T that was simpler to implement, calling it 1000BASE-TX (TIA/EIA-854).The simplified design would have, in theory, reduced the cost of the required electronics by only using two unidirectional pairs in each direction instead of 4 bidirectional. However, this solution has been a commercial failure, likely due to the required Category 6 cabling and the rapidly falling cost of 1000BASE-T products.
1000BASE-T products are sometimes marketed as 1000BASE-TX despite the difference in standards. The confusion possibly stems from the most popular form of Fast Ethernet (100 Mbit/s) is known as100BASE-TX, leading to many products supporting multiple speeds of 10/100/1000Mbit/s marketed as "10/100/1000BASE-TX".[note 1]