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Gigabit and 10-Gigabit Ethernet

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Bill Stallings discusses the latest high-speed Ethernet standards.
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Gigabit Ethernet

In late 1995, the IEEE 802.3 committee formed a High-Speed Study Group to investigate means for conveying packets in Ethernet format at speeds in the gigabit per second (Gbps) range. A set of 1000 Mbps standards have now been issued.

While defining a new medium and transmission specification, Gigabit Ethernet retains the protocol and frame format of its 10 Mbps and 100 Mbps predecessors, making it compatible with the slower Ethernets to provide a smooth migration path. As more organizations move to 100 Mbps Ethernet, putting huge traffic loads on backbone networks, demand for Gigabit Ethernet has intensified.

Figure 1 shows a typical application of Gigabit Ethernet. A 1 Gbps LAN switch provides backbone connectivity for central servers and high-speed workgroup switches. Each workgroup LAN switch supports both 1 Gbps links (to connect to the backbone LAN switch and to support high-performance workgroup servers) and 100 Mbps links (to support high-performance workstations, servers, and 100 Mbps LAN switches).

Figure 1 Sample Gigabit Ethernet configuration.

The protocol architecture for Gigabit Ethernet consists of a medium access control (MAC) layer on top of a physical layer. The MAC layer is an enhanced version of the basic 802.3 MAC algorithm. A separate gigabit medium-independent interface (GMII) has been defined and is optional for all of the medium options except unshielded twisted pair (UTP). The GMII defines independent 8-bit parallel transmit and receive synchronous data interfaces. It's intended as a chip-to-chip interface that lets system vendors mix MAC and physical layer components from different manufacturers.

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