Differences Between
Classic Ethernet And Fast Ethernet
Introduction
The two
primary areas for concern when upgrading the network
from 10Mbps to 100Mbps are cabling and hubs. As
discussed on the Fast Ethernet Introduction page, in
Fast Ethernet twisted pair cabling needs either to be
category 5 or to be category 3 with proper twist on all
four pairs.
The problem
with hubs is the number of hubs allowed in a single
collision domain. Classic Ethernet allows hubs to be
cascaded up to four deep between any two stations. In
Fast Ethernet, the number of hubs allowed in a collision
domain is drastically reduced - to a single hub.
Sometimes it may be possible to have more than one hub
in a collision domain, but it will probably be easier in
the long term to design a Fast Ethernet network assuming
that only one hub is allowed.
What the
IEEE 802.3 spec does not explicitly state is that this
limitation only applies to shared 100BASE-T, not to
switched 100BASE-T. Since switches act like bridges in
defining a separate collision domain, installing Fast
Ethernet switches will allow you to work around the
single-hub problem. Even if it is not necessary to
deliver dedicated switched Fast Ethernet to each
desktop, Fast Ethernet hubs can be connected to
switches. Connecting a number of repeaters to a switch
will provide shared Fast Ethernet and allow you to
maintain the size of your network.
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