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Magnum 8000X Mixed-Media Fiber Hubs Installation and User Guide (05/ 02)
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4. For Port #1, if the LINK LED is not illuminated, change to port 1X. If this does
not help, ensure that the cable is connected properly and that the device on the
other end is powered on and is not defective.
3.6.1 100Mbps Collision Domain Diameter, Cable Distances and PDV
Calculations
The 100Mbps Collision Domain Diameter is the length of the longest path
between any two devices in a single collision domain. A collision domain is defined as
a cluster of network devices which are connected by means of a repeater or repeaters
such that no bridging devices are present between any two devices in the cluster. In
order to install an IEEE 802.3u compliant Fast Ethernet network, the collision domain .
. regardless of the actual network topology . . must be less than 512 BT (Bit Times).
Bit Times are related to media type as shown in Table 3.6.1a.
Table 3.6.1a: Worst case round-trip delay for Fast Ethernet media*
Media Type Round-trip delay in
Bit Time per Meter (BT/m)
Fiber Optic 1.000
Shielded TP cable 1.112
Category 5 Cable 1.112
Category 3, 4 Cable 1.140
*Worst case delays taken from IEEE Std 802.3u-1995, actual delays may be less for a particular
cable. Contact your cable supplier for exact cable specifications.
Each Fast Ethernet device component also has an associated BT delay which
depends on the physical signaling system employed. Table 3.6.1b shows each Fast
Ethernet device component and the associated BT delay. A “DTE” is an end node, such
as a user station. Note that there is only one DTE pair associated with any device-to-
device path.
Table 3.6.1b: Worst case round-trip delay for Fast Ethernet device components*
Component Round-trip delay in Bit Times (BT)
2 TX DTEs 100
2 FX DTEs 100
1 FX and 1 TX DTE 100
1 T4 and 1 TX or FX DTE 127
Class I Repeater 140
Class II Repeater with any
combination of TX and FX ports
92 **
**Note, the delay is only 80 Bit Times for
the 8000X, front-port-to-front-port.
*Worst case delays taken from IEEE Std 802.3u -1995.