In computer networking, Gigabit Ethernet (GbE or 1 GigE) is the transmission of Ethernet frames at a rate of a gigabit per second. The most popular variant, 1000BASE-T, is defined by the IEEE 802.3ab standard. It came into use in 1999 and has largely replaced Fast Ethernet in wired local networks due to its considerable speed improvement over Fast Ethernet, as well as its use of cables and equipment that are widely available, economical, and similar to previous standards.
The first standard for faster 10 Gigabit Ethernet was approved in 2002.
History Ethernet was the result of research conducted at Xerox PARC in the early 1970s, and later evolved into a widely implemented physical and link layer protocol. Fast Ethernet increased the speed from 10 to 100 megabits per second (). Gigabit Ethernet was the next iteration, increasing the speed to .
The initial standard for Gigabit Ethernet was produced by the IEEE in June 1998 as IEEE 802.3z, and required optical fiber. 802.3z is commonly referred to as 1000BASE-X, where -X refers to either -CX, -SX, -LX, or (non-standard) -ZX. IEEE 802.3ab, ratified in 1999, defines Gigabit Ethernet transmission over unshielded twisted pair (UTP) category 5, 5e or 6 cabling, 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 GbE fiber standards: 1000BASE-LX10 (which was already widely implemented as a vendor-specific extension) and 1000BASE-BX10. This was part of a larger group of protocols known as Ethernet in the first mile.
Initially, Gigabit Ethernet was deployed in high-capacity backbone network links (for instance, on a high-capacity campus network). In 2000 and 2001, Apple's Power Mac G4 and PowerBook G4 respectively were the first mass-produced personal computers to feature the 1000BASE-T connection. It quickly became a built-in feature in many other computers.
Half-duplex GbE links connected through repeater hubs were part of the IEEE specification,A single repeater per collision domain is defined in IEEE 802.3 2008 Section 3: 41. Repeater for baseband networks but the specification has not been maintained and full-duplex operation with switches is, in practice, used exclusively.
Varieties
There are five physical layer standards for Gigabit Ethernet using optical 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 over multi-mode fiber, 1000BASE-LX for transmission over single-mode fiber, and the nearly obsolete 1000BASE-CX for transmission over shielded balanced copper cabling. These standards use 8b/10b encoding, which adds a 25% overhead, to ensure a DC balanced signal and allow for clock recovery. The symbols are then sent using NRZ line code.
Optical fiber transceivers are most often implemented as user-swappable modules in SFP form or GBIC on older devices.
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 mile later added 1000BASE-LX10 and -BX10 extended-distance fiber-optic variants.
Copper + Comparison of twisted-pair-based Ethernet physical transport layers (TP-PHYs) Name Standard Status Speed Pairs Lanes per Bits per hertz Line code rate per lane (MBd) (MHz) Max (m) Cable ( ) Cable (MHz) Usage (CL40) 1000 4 4 4 TCM 4D-PAM-5 125 62.5 100 Cat 5 100 LAN 1000 1 1 2.6 PAM-3 80B/81B RS-FEC 750 375 40 Cat 6A 500 Automotive, IoT, M2M (2001) 1000 4 2 4 PAM-5 250 125 100 Cat 6 250 1000BASE‑CX (CL39) 1000 Data centers; predates 1000BASE-T; rarely used. 1000BASE‑KX 1000 PCBs
1000BASE-CX 802.3z-1998 CL39 standardized 1000BASE-CX is an initial standard for Gigabit Ethernet connections with maximum distances of 25 meters using balanced shielded twisted pair and either DE-9 or 8P8C connector (with a pinout different from 1000BASE-T). The short segment length is due to a very high signal transmission rate. Although it was used for specific applications where cabling was 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-T
IEEE 802.3ab is the original standard for Gigabit Ethernet over twisted-pair wiring, known as 1000BASE-T.
Each 1000BASE-T network segment is recommended to be a maximum length of , and must use Category 5 cable or better.
Autonegotiation is a requirement for 1000BASE-T implementations, as minimally the clock source for the link has to be negotiated, as one endpoint must be master and the other endpoint must be slave.
In a departure from both 10BASE-T and 100BASE-TX, which use a cable pair in each direction, 1000BASE-T uses four cable pairs for simultaneous transmission in both directions through the use of echo cancellation with adaptive equalization, the resulting circuits being called hybrid circuits as used in telephone hybrids. Line coding is five-level pulse-amplitude modulation (PAM-5). The symbol rate is identical to that of 100BASE-TX (125 megabaud) 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-dimensional trellis coded modulation (TCM) to achieve a 6 dB coding gain across the four pairs.
Since autonegotiation takes place on only two pairs, if two 1000BASE-T interfaces are connected through a cable with only two pairs, the interfaces will complete negotiation and choose gigabit as the best common operating mode, but the link will never come up because, in most cases, all four pairs are required for data communications. Most 1000BASE-T implementations have a specific register to diagnose this behavior.
The data is transmitted over four pairs, eight bits at a time. First, eight bits of data are expanded into four three-bit symbols through a scrambling procedure based on a linear-feedback shift register; this is similar to what is done in 100BASE-T2, but uses different parameters. The three-bit symbols are then mapped to voltage levels that 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 configuration is specified as an optional feature in the 1000BASE-T standard,Clause 40.4.4 in IEEE 802.3-2008 and is commonly implemented meaning that straight-through cables will often work between two GbE-capable network node interfaces (both MDI) and between two switch or hub interfaces (both MDI-X). This feature eliminates the need for Ethernet crossover cables, making obsolete the uplink vs. normal port choices and manual selector switches found on many older hubs and switches and reducing wiring errors.
In order to extend and maximize the use of existing Cat-5e and Cat-6 cabling, the newer standards 2.5GBASE-T and 5GBASE-T operate at 2.5 and , respectively, on existing copper infrastructure designed for use with 1000BASE-T. They are based on 10GBASE-T but use lower signaling frequencies.
1000BASE-TX In 2001, the Telecommunications 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 four unidirectional pairs (two pairs TX and two pairs RX) instead of four bidirectional pairs.
1000BASE-KX 802.3ap-2007 CL70 standardized 1000BASE-KX as 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 to (from 100BASE-KX to 10GBASE-KX4). The 1000BASE-KX variant uses a 1.25 GBd electrical signaling speed.
1000BASE-T1
IEEE 802.3 standardized 1000BASE-T1 in IEEE Std 802.3bp-2016. It defines Gigabit Ethernet over a single twisted pair for automotive and industrial applications. It includes cable specifications for 15 meters (type A) or 40 meters (type B) reach. The transmission is done using PAM-3 at 750 MBd.
Fiber optics 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. Included are copper variants, 1000BASE‑CX and 1000BASE‑KX, which use the same 8b/10b line code as the fiber variants. 1000BASE-X is based on the physical-layer standards developed for Fibre Channel.IEEE 802.3 Clause 36.1.1
+ 1000BASE-X Gigabit Ethernet variants Name Standard Status Media Connector module Reach (m) # (⇆) # (→) # (→) Notes 802.3z-1998 (CL39) 25 4 N/A 4 Data centers; predates 1000BASE-T; rarely used. (CL70) 1 1 N/A 4 Printed circuit boards (CL38) rowspan="3" rowspan="3" rowspan="3" SFPGBICdirect-plug 2 1 1 Popular in intra-building LANs rowspan="3" rowspan="3" rowspan="3" rowspan="3" SFP 2 1 1 Vendor-specific; FP laser transmitter (CL38) rowspan="4" rowspan="4" rowspan="4" SFPdirect-plug 2 1 1 (CL59) rowspan="4" rowspan="4" rowspan="5" SFP 2 1 1 Identical with -LX but with increased power/sensitivity;commonly simply referred to as -LX or -LH prior to 802.3ah 1 Often simply referred to as -BX and BiDi SFP 2 1 1 Vendor specific 1000BASE‑ZX, ‑EZX SFP 2 1 1 Vendor specific (CL115) 1 1 1 Automotive, industrial, Home;Line code: 64b65b × PAM16Line rate: 325 MBdVariants: -RHA (50 m), -RHB (40 m), -RHC (15 m). (CL60) SFPXFP 1 1 1 EPON; FTTH;using point-to-multipoint topology. SFP 2 1 1 CWDM makes it possible to have multiple parallel channels over 2 fibers;spectral bandwidth 11 nm;capable of 18 parallel channels SFP 2 1 1 DWDM makes it possible to have multiple parallel channels over 2 fibers;spectral bandwidth 0.2 nm;capable of 45 to 160 parallel channels
1000BASE-SX 1000BASE-SX is an optical fiber Gigabit Ethernet standard for operation over multi-mode fiber using a 770 to 860 nanometer, near infrared (NIR) wavelength.
The standard specifies a maximum length of 220 meters for 62.5 μm/160 MHz·km multi-mode fiber, 275 m for 62.5 μm/200 MHz·km, 500 m for 50 μm/400 MHz·km, and 550 m for 50 μm/500 MHz·km multi-mode fiber.IEEE 802.3 Table 38–2—Operating range for 1000BASE-SX over each optical fiber type Fiber optic cable manufacturers have extended the reach of 1000BASE-SX to at least 1 km when used with more modern fiber optic grades such as OM3 and OM4. The SX interface is specified to have a minimum output power of −9.5 dBm and minimum receive sensitivity of −17 dBm.
This standard is popular for commercial intra-building links, co-location facilities and carrier-neutral Internet exchange points.
1000BASE-LSX 1000BASE-LSX is a non-standard but industry accepted term to refer to an improved 1000BASE-SX capabile of distances up to 2 km. It achieves longer distances over a pair of multi-mode fibers with the use of Fabry Perot laser transmitter and runs in the 1310 nm band.
1000BASE-LX 1000BASE-LX is an optical fiber Gigabit Ethernet standard specified in IEEE 802.3 Clause 38 which uses a long wavelength laser (1,270–1,355 nm), and a maximum RMS spectral width of 4 nm. 1000BASE-LX is specified to work over a distance of up to 5 km over 10 μm single-mode fiber.