1.4 Fast Ethernet

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The 100BaseT is the IEEE standard for providing 100-Mbps Ethernet performance and functionality over ubiquitously available UTP wiring. Like 10BaseT Ethernet, this standard specifies a star topology. The need for 100 Mbps came about as a result of the emergence of data-intensive applications and technologies such as multimedia, groupware, imaging, and the explosive growth of high-performance database software packages on PC platforms. All of these tax today’s client-server environments and demand even greater bandwidth for improved response time.

1.4.1 Compatibility

Also known as Fast Ethernet, 100BaseT uses the same contention-based MAC method—CSMA/CD—that is at the core of IEEE 802.3 Ethernet. The Fast Ethernet MAC specification simply reduces the “bit time”—the time duration of each bit transmitted—by a factor of 10, enabling a 10-fold boost in speed over 10BaseT. Fast Ethernet’s scaled CSMA/CD MAC leaves the remainder of the MAC unchanged. The packet format, packet length, error control, and management information in 100BaseT are all identical to those used in 10BaseT.

Since no protocol translation is required, data can pass between 10BaseT and 100BaseT stations via a hub equipped with a 10/100-Mbps bridge module. Both technologies are also full-duplex capable, meaning that data can be sent and received at the same time. This compatibility enables existing LANs to be inexpensively upgraded to the higher speed as demand warrants.

1.4.2 Media Choices

To ease the migration from 10BaseT to 100BaseT, Fast Ethernet can run over Category 3, 4 or 5 UTP cables, while preserving the critical 100-meter (330-foot) segment length between hubs and end stations. The use of fiber allows even more flexibility with regard to distance. For example, the maximum distance from a 100BaseT repeater to a fiber-optic bridge, router, or switch using fiber-optic cable is 225 meters (742 feet). The maximum fiber distance between bridges, routers, or switches is 450 meters (1,485 feet). The maximum distance between a fiber bridge, router, or switch—when the network is configured for half-duplex—is 2 km (1.2 miles). By interconnecting repeaters with other internetworking devices, large well-structured networks can be easily created with 100BaseT. The type of media used to implement 100-Mbps Ethernets is summarized as follows:

  • 100BaseTX: A two-pair system for data grade (EIA 568 Category 5) UTP and shielded twisted-pair (STP) cabling.

  • 100BaseT4: A four-pair system for both voice and data grade (Category 3, 4, or 5) UTP cabling.

  • 100BaseFX: A multimode two-strand fiber system.

Together, the 100BaseTX and 100BaseT4 media specifications cover all cable types currently in use in 10BaseT networks. Since 100BaseTX, 100BaseT4, and 100BaseFX systems can be mixed and interconnected through a hub, users can retain their existing cabling infrastructure while migrating to Fast Ethernet.

The 100BaseT also includes a media-independent interface (MII) specification, which is similar to the 10-Mbps AUI. The MII provides a single interface, which can support external transceivers for any of the 100BaseT media specifications.

Unlike other high-speed technologies, Ethernet has been installed for over 20 years in business, government, and educational networks. The migration to 100-Mbps Ethernet is made easier by the compatibility of 10BaseT and 100BaseT technologies, making it unnecessary to alter existing applications for transport at the higher speed. This compatibility allows 10BaseT and 100BaseT segments to be combined in both shared and switched architectures, allowing network administrators to apply the right amount of bandwidth easily, precisely, and cost-effectively. Fast Ethernet is managed with the same tools as 10BaseT networks, and no changes to current applications are required to run them over the higher speed 100BaseT network.



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LANs to WANs(c) The Complete Management Guide
LANs to WANs: The Complete Management Guide
ISBN: 1580535720
EAN: 2147483647
Year: 2003
Pages: 184

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