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Gigabit Ethernet

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Gigabit Ethernet

In computer networking, Gigabit Ethernet (GbE or 1 GigE) is the term applied to transmitting 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 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.

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 (Mbit/s). Gigabit Ethernet was the next iteration, increasing the speed to 1000 Mbit/s.

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 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, but the specification has not been maintained and full-duplex operation with switches is, in practice, used exclusively.

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.

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