Information Technology Reference
In-Depth Information
Ethernet without recabling to CAT 5 UTP. This implementation is not widely deployed.
The specifications are as follows:
Tran s mis s ion over CAT 3, 4, or 5 UTP w ir ing.
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Three pairs are used for transmission, and the four th pair is used for collision detection.
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No separate transmit and receive pairs are present, so full-duplex operation is not
possible.
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8B6T coding.
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100BASE-FX Fast Ethernet
The 100BASE-FX specification for fiber is as follows:
It operates over two strands of multimode or single-mode fiber cabling.
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It can transmit over greater distances than copper media.
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It uses media interface connector (MIC), Stab and Twist (ST), or Stab and Click (SC)
fiber connectors defined for FDDI and 10BASE-FX networks.
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4B5B coding.
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100BASE-T Repeaters
To m a k e 1 0 0 - M b p s E t h e r n e t w o r k , d i s t a n c e l i m i t a t i o n s a r e
much more severe than those required for 10-Mbps Ethernet. Repeater networks have no
five-hub rule; Fast Ethernet is limited to two repeaters. The general rule is that 100-Mbps
Ethernet has a maximum diameter of 205 meters (m) with UTP cabling, whereas 10-Mbps
Ethernet has a maximum diameter of 500 m with 10BASE-T and 2500 m with 10BASE5.
Most networks today use switches rather than repeaters, which limits the length of
10BASE-T and 100BASE-TX to 100 m between the switch and host.
The distance limitation imposed depends on the type of repeater.
The IEEE 100BASE-T specification defines two types of repeaters: Class I and Class II.
Class I repeaters have a latency (delay) of 0.7 microseconds or less. Only one repeater hop
is allowed. Class II repeaters have a latency of 0.46 microseconds or less. One or two re-
peater hops are allowed.
Ta ble 3-3 shows the maximum size of collision domains, depending on the type of repeater.
Ta b l e 3 - 3
Maximum Size of Collision Domains for 100BASE-T
Repeater Type
Copper
Mixed Copper and
Multimode Fiber
Multimode Fiber
DTE-DTE (or switch-
switch)
100 m
Not applicable
412 m (2000 if full
duplex)
One Class I repeater
200 m
260 m
272 m
One Class II repeater
200 m
308 m
320 m
Two Clas s II repeaters
205 m
216 m
228 m