Gigabit Ethernet is defined in the IEEE 802.3z extension to the IEEE 802.3 standard. The media speed is 1000Mb or 1Gb. It uses the same frame and MAC address formats as Ethernet. It operates in either half- or full-duplex mode. There is also an optional IEEE 802.3x flow control standard.
There are several different media types at the Physical layer:
1000BASE-LX using long-wave laser over single-mode or multimode fiber
1000BASE-SX using short-wave laser over multimode fiber
1000BASE-CX using balanced shielded 150-ohm copper cable
1000BASE-T using Unshielded Twisted Pair (UTP)
Gigabit Ethernet allows you to choose on a port-by-port basis what physical media type you will use via a Gigabit Ethernet Interface Carrier (GBIC). There are different GBICs for each physical media type. GBICs plug directly into the router.
Gigabit Ethernet supports existing Ethernet frame formats and encapsulations. This means no changes to applications that already support Ethernet.