Gigabit Ethernet

Gigabit Ethernet

An Ethernet standard that transmits at 1 Gbps. Used mostly to connect high-end workstations and servers as well as for network backbones, Gigabit Ethernet transmits full duplex from point to point using switches and half duplex in a shared environment (CSMA/CD) using a hub.

The first IEEE Gigabit Ethernet standard (802.3z) was defined in 1997 for use over multimode optical fiber and two years later for copper cables.

1000Base-T and 1000Base-TX
In 1999, the IEEE 802.3ab standard (1000Base-T) enabled Gigabit Ethernet to run over Category 5 copper cable and be readily used in 10/100 Ethernet networks without changing cables. The TIA/EIA later introduced 1000Base-TX, which did not catch on. It required Category 6 cabling, but greatly simplified the circuitry by using a different transmission method. In 1000Base-T, each of four wire pairs transmits 250 Mbps in both directions. In 1000Base-TX, two pairs transmit at 500 Mbps, and two receive at 500 Mbps.

The maximum distance between nodes is based on the type of transceiver and cable used as outlined below.

    8B/10B Encoding

    Fiber           Modal
    Diameter        Bandwidth   Range
    (microns)       (MHz-km)   (meters)

    1000Base-SX (802.3z)
    62.5 multimode   160        220
    62.5 multimode   200        275
    50 multimode     400        500
    50 multimode     500        550

    1000Base-LX (802.3z)
    62.5 multimode   500        550
    50 multimode     400        500
    50 multimode     500        550
     9 singlemode    ---       5000

    1000Base-CX (802.3z)
    Shielded twisted             25
     pair copper



    1000Base-T Encoding

    1000Base-T (802.3ab)
    Category 5 UTP              100

    1000Base-TX (TIA/EIA-854)
    Category 6 UTP              100