Installation manual

Fast EtherHub-8se User’s Guide
2-4 Installing the System
Simplified Cable Length Constraints
The Fast EtherHub-8se is a Class II repeater. IEEE recommends that Class II
repeaters be limited to a cascade of two hubs. The simplest rule is that
workstation connections be limited to 100 meters (328 feet) for twisted-pair
cabling and that interhub cabling be limited to 5 meters (16 feet). If you are
stacking hubs in a wiring closet, this is good advise. When a hub is located in a
central wiring closet, connections to end users tend to be very long. Using
these assumptions, the maximum cable lengths depend on the device type you
want to attach to the hub, as shown in the following table:
Device Cable Length
Workstation 100 meters (328 feet)
Another Hub 5 meters (16 feet)
Switch 100 meters (328 feet)
When connecting to another hub, traffic is confined to a single collision
domain. However, when connecting to a collapsed backbone (e.g., a switch or
router), the collision domain is broken up, enabling the use of longer cable
lengths as illustrated in the preceeding table.
Precise Cable Length Budgeting
If you plan on installing a network for a small office, it may not be convenient
to place hubs within 5 meters (16 feet) of each other, and then run up to 100
meters (328 feet) of cabling for each end user. This kind of installation can be
very messy and wastes a lot of cabling. Depending on how your users are
spread out, it may be more convenient to run a longer length of inter-hub
cabling (say 50 meters or more), and then run shorter lengths of cable from
each hub to the end users. Depending on the inherent delay in the hub and the
maximum cable lengths required, it may even be possible to cascade up to three
Fast Ethernet hubs.