Gigabit Ethernet represents an extension to the 10 Mbps and 100 Mbps IEEE 802.3 Ethernet standards. Providing a data transmission capability of 1000 Mbps, Gigabit Ethernet supports the CMSA/CD access protocol, which makes various types of Ethernet networks scalable from 10 Mbps to 1 Gbps.

Similar to 10BASE-T and Fast Ethernet, Gigabit Ethernet can be used as a shared network through the attachment of network devices to a 1 Gbps repeater hub providing shared use of the 1 Gbps operating rate or as a switch, the latter providing 1 Gbps ports to accommodate high-speed access to servers while lower operating rate ports provide access to 10 Mbps and 100 Mbps workstations and hubs. Although very few organizations can be expected to require the use of a 1 Gbps shared media network.

Similar to the recognition that Fast Ethernet would be required to operate over different types of media, the IEEE 802.3z committee recognized that Gigabit Ethernet would also be required to operate over multiple types of media.

This recognition resulted in the development of a series of specifications, each designed to accommodate different types of media. Thus, any discussion of Gigabit Ethernet involves an examination of the types of media the technology supports and how it provides this support.

There are five types of media supported by Gigabit Ethernet – single-mode fiber, multi-mode fiber, short runs of coaxial cable or shielded twisted pair, and longer runs of unshielded twisted pair.

The actual relationship of the Gigabit 802.3z reference model to the ISO Reference Model is very similar to Fast Ethernet. Instead of a Medium Independent Interface (MII), Gigabit Ethernet uses a Gigabit Media Independent Interface (GMII). The GMII provides the interconnection between the MAC sublayer and the physical layer to include the use of an 8-bit data bus that operates at 125MHZ plus such control signals as transmit and receiver clocks, carrier indicators and error conditions.

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