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Unit 8: Data Link Protocols

8.7.2 Fast Ethernet Notes

100BaseT (Fast Ethernet)
100BaseT is a high-speed LAN standard and is considered a variation of 10BaseT. This is
standardized as IEEE 802.3u. This operates with an access mechanism as CSMA/CD and provides
a transmission speed of 100 Mbps through an Ethernet switching hub. Multiple 10 Mbps
connections are supported through multiple ports on the switch. Cat 3, 4, or 5 UTP can be used
in 4-pair configuration. Cat 5 UTP is generally used for a maximum LAN diameter of 500 meters.
Three pairs are used for transmission, with the fourth pair used for signaling and control (CSMA/
CD) in half-duplex mode. Connections to nodes, servers and other switching hubs are provided
at 100 Mbps, supporting ten 10-Mbps channels. The 100 Mbps media include fiber (up to 30 miles
or 50 Km without repeaters) and Cat 5 UTP at 100 meters.

Type of 100Base-T
The 100BaseT can be divided into 100BaseTX, 100BaseT4 and 100BaseFX, depending on the type
of transmission media used as explained above. Two pair category 5 UTP, four pair category 3
UTP and optical fiber cable are used for 100BaseTX, 100BaseT4 and 100BaseFX respectively. This
standard has been defined in IEEE802.3u.

Figure 8.8: Hardware Configuration of 100BaseTx

Figure 8.8 shows the hardware configuration of 100BaseTx. As with 100Baset, terminals are
connected to the hub with 100BaseTx. Cat5 UTPs are used for connection. 100BaseTx has been
developed based on 10BaseT to enable a higher transmission speed, vendors can readily develop
peripheral equipment for 100BaseTx. Virtually all hubs and NICs for 100BaseTx can also be used
for 10BaseT.
Figure 8.9 shows the hardware configuration of 100BaseT4. It is same as that for 100BaseTx. Cat3
UTPs are used for connection. Although originally intended for use as transmission lines at
10Mbps, cables of this type now offer a transmission speed of 100Mbps as a result of special
arrangements., including improved signal processing and simultaneous use of three out of four
pairs for transmission or reception. This enables the trouble free introduction of a 100Mbps LAN
without the need to replace 10BaseT cables. However, these cables must be four pair cables.

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