What is a Gigabit Ethernet?

Kurt Inman

Gigabit Ethernet is a network technology for exchanging data at speeds of up to 1 Gigabit per second (Gbps). Several types of fiber optic and copper cables can be used to connect these devices. Specific lasers and single-mode optic cables can transmit high-speed data for miles (kilometers) over a single cable. Gigabit Ethernet is often used by servers to connect to routers, switches and storage area networks. It is also frequently used for high-speed connections between buildings on corporate campuses.

Cat 5 cable with RJ45 plug.
Cat 5 cable with RJ45 plug.

In 1998, Gigabit Ethernet was introduced to provide higher device bandwidths than 100 Megabit per second (Mbps) Fast Ethernet. Originally an optical-only technology, it was upgraded in 1999 to include the 1000BASE-T copper twisted-pair standard. This allows the use of Gigabit devices with existing American National Standards Institute (ANSI) Category (CAT) 5 cables. Many Gigabit routers, switches and network interface cards can negotiate connection speed automatically. Gigabit devices can use this feature to operate with slower 100 Mbps or 10 Mbps interfaces instead of replacing the existing infrastructure.

Ethernet cables plugged into an Internet switch.
Ethernet cables plugged into an Internet switch.

Most of the standards for Gigabit Ethernet devices were developed by the Institute of Electrical and Electronics Engineers (IEEE). The 1000BASE-T standard created by IEEE utilizes all four copper-twisted pairs in a CAT 5 or better cable. A competing standard was designed around the same time by the Telecommunications Industry Association (TIA). Called 1000BASE-TX, this less popular specification utilizes only two twisted pairs but requires CAT 6 or better cable. Some vendor confusion and marketing has led to some 1000BASE-T devices being promoted incorrectly as 1000BASE-TX.

The 1000BASE-T and 1000BASE-TX standards can both utilize cables up to 328 feet (100 meters) long. An earlier unpopular copper specification called 1000BASE-CX utilizes a balanced and shielded cable. Its single twisted pair design limits cable length to 82 feet (25 meters).

Four IEEE Gigabit standards exist for optic fiber-based Ethernet. 1000BASE-SX can communicate with multi-mode fiber for 721-1,804 feet (220 to 550 meters). 1000BASE-LX can use multi-mode fiber for up to 1,804 feet (550 meters) or single-mode fiber for up to 3.1 miles (5 kilometers). 1000BASE-LX10 and 1000BASE-BX10 can utilize single-mode fiber with 1,310 to 1,490 nanometer lasers for up to 6.2 miles (10 kilometers). An informal standard called 1000BASE-ZX may reach up to 43 miles (70 kilometers) with single-mode fiber and a 1,550 nanometer laser.

Some Gigabit network cards provide great flexibility by allowing connection of a Gigabit Interface Converter (GBIC). This is a hot-pluggable device with a network transceiver and cable interface specific to a particular 1 Gbps technology. GBICs exist for several Fiber Channel technologies as well as copper and optical Gigabit Ethernet. Using a GBIC-based network card, a technician can replace a link without powering down or reconfiguring a running system. A copper Gigabit Ethernet GBIC could be unplugged from a network card and replaced with a 1 Gbps Fiber Channel GBIC, for example.

During the 2000s Gigabit technology evolved to include even faster data transmission speeds. 10 Gigabit Ethernet was first introduced in 2002. Work began on standards for 40 and 100 Gigabit Ethernet in 2007, which were finally approved by IEEE in 2010. These technologies usually require cable upgrades from existing 100 Mbps or 1 Gbps infrastructure to accommodate the higher speeds.

Gigabet ethernet technology allows for network connections at speeds up to 1 gigabit per second.
Gigabet ethernet technology allows for network connections at speeds up to 1 gigabit per second.

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