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Dual-Speed Stackable Hubs User’s Guide
Introduction 7
Network Diameter
Network diameter, which is the distance between two end-stations in the
same collision domain, is the primary difference between traditional
Ethernet and Fast Ethernet. Due to the increased speed in Fast Ethernet
and adherence to the EIA/TIA 568 wiring rules, the network diameter of a
Fast Ethernet collision domain is limited to 205 meters; in contrast, the
maximum 10BASE-T Ethernet collision domain diameter can be up to 500
meters.
Hub Types
Unlike 10BASE-T hubs, which are all functionally identical, Fast Ethernet
hubs are divided into two distinct types: Class I and Class II. A Class I
hub repeats all incoming signals on one port to the other ports by first
translating them to digital signals and then retranslating them back to line
signals. These translations are necessary when connecting various network
media to the same collision domain, such as when combining two-wire-pair
100BASE-TX media with four-wire-pair 100BASE-T4 media. Only one
Class I hub can exist within a collision domain; thus, this type of hub can-
not be directly interlinked. A Class II repeater, on the other hand,
immediately repeats all incoming line signals on one port to the other ports;
no translations are performed. This type of hub connects identical media
within the same collision domain; for example, TX to TX. At most, two
Class II hubs can exist within the same collision domain.
As mentioned earlier, stackable Class II hubs can be used to increase the
number of available nodes in a collision domain. An entire hub stack
counts as a single repeater. DFE-916 series hubs are Class II devices.