Installation manual

Fast EtherHub-8se User’s Guide
Installing the System 2-5
However, when setting up these kinds of distributed cascades, you have to be
very careful in calculating the maximum length for each node pair. All end-
node devices (e.g., workstations or servers) must be within 100 meters (328
feet) of the connected hub when using twisted-pair cabling. However, when
linking one or more Fast Ethernet hubs together (i.e., in the same collision
domain), the overall length of cable used between any two nodes should not
exceed the limits outlined in the IEEE 802.3u standard. In precise terms, the
maximum length of cabling that can be run from end-node to end-node is
367m
≥ S(repeater equivalent length)
+ S(length of category 5 twisted-pair cable)
This repeater has an inherent delay of 90 bit time or 80 meters (262 feet) of
twisted-pair cable. Taking a daisy chain of two hubs connected with twisted-pair
cabling for an example, the maximum length from node to node is 367m - (2 x
80m) = 207m (679 feet). Therefore, if both node A and B are linked to separate
repeaters in a two hub system, each using 100 meters (328 feet) of cable to
connect to their respective hub, then the inter-hub cabling will be limited to 5
meters (i.e., 207m - (2 x 100m) = 7m, which is then reduced to 5 meters, or 16
feet, according to a common wiring rule).
A more detailed example of calculating the maximum cable length is included
in the section on “Precise Guidelines for Configuring Multiple Hubs” in
Chapter 3.