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Gigabit Ethernet

In 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 1 Gbps standards have now been issued.

The strategy for Gigabit Ethernet is the same as that for Fast Ethernet. While defining a new medium and transmission specification, Gigabit Ethernet retains the protocol and frame format of its 10 Mbps and 100 Mbps predecessors. It's compatible with 100BASE-T, preserving a smooth migration path. As more organizations move to 100BASE-T, 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

Gigabit Ethernet configuration.

The current 1 Gbps specification for IEEE 802.3 includes the following physical layer alternatives:

  • 1000BASE-LX. This long-wavelength option supports duplex links of up to 550 m of 62.5-µm or 50-µm multimode fiber or up to 5 km of 10-µm single-mode fiber. Wavelengths are in the range of 1270 to 1355 nanometers(nm).

  • 1000BASE-SX. This short-wavelength option supports duplex links of up to 275 m using 62.5-µm multimode or up to 550 m using 50-µm multimode fiber. Wavelengths are in the range of 770 to 860 nm.

  • 1000BASE-CX. This option supports 1 Gbps links among devices located within a single room or equipment rack, using copper jumpers (specialized shielded twisted-pair cable that spans no more than 25 m). Each link is composed of a separate shielded twisted pair running in each direction.

  • 1000BASE-T. This option makes use of four pairs of Category 5 unshielded twisted pair to support devices over a range of up to 100 m.

The success of both Fast Ethernet and Gigabit Ethernet highlights the importance of network management concerns in choosing a network technology. The Ethernet alternatives offer compatibility with existing installed LANs, network management software, and applications. This compatibility has accounted for the survival of the 25-year-old Ethernet technology in today's fast-evolving network environment.

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