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Gigabit Ethernet

Gigabit Ethernet networking, which is becoming increasingly common as a backbone connection method and for a server to switch connectivity, is achieved using either copper-based media or fiber optic cabling. The two IEEE standards that specify Gigabit transfer are 802.3z and 802.3ab.


Three distinct standards are specified under the 802.3z standard; they are referred to collectively as 1000BaseX.

The three standards are 1000BaseLX, 1000BaseSX, and 1000BaseCX. 1000BaseLX and 1000BaseSX use long wavelength laser and short wavelength laser, respectively. Both 1000BaseSX and 1000BaseLX can be supported over two types of multimode fiber62.5 and 50 micron-diameter fibers. Only long wave lasers support the use of single-mode fiber.

The 1000BaseCX standard specifies Gigabit Ethernet over STP cabling. Segment length of 1000BaseCX is extremely limited, reaching a maximum of 25 meters. 1000BaseCX is not widely implemented.


The 802.3ab standard specifies Gigabit Ethernet transfer over Category 5 UTP cable. To achieve the 1000Mbps speeds, each of the four pairs of wires in a twisted-pair cable can transmit 250Mbps. Table 5 summarizes the characteristics of the Gigabit standards.

Table 5 Gigabit Ethernet


Cable Type

Segment Length



Multimode/single-mode fiber

550/multimode 5000/single-mode

Fiber connectors


Multimode fiber

550 meters using 50 Micron multimode fiber

Fiber connectors



25 meters

9-pin shielded connector, 8-pin fiber channel type 2 connector



75 meters


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