Black Box Dual-Speed Stackable Hubs Installation and User Guide
16
In the above example, 80 is the BT delay for 75m of Category 5 cable (1.112 BT/m), 80 is the
bit time delay for each LH8000A front-to-front ports, 100 is the BT delay for the TX DTE pair
in the user stations, and 2 BT is the safety margin applied.
Figure 3.2.2b: Multiple cascaded
Magnum LH8000A hubs
Note that the cascading of
multiple LH8000A hubs is a
capability beyond what industry
standards normally permit, and is
different from what competitive
Class II hub products normally
allow. This additional cascading
level and cable length is due to the
relatively shorter bit time (80 BT actually measured, for front-port-to-port) delay of the
100Mbps domain of the LH8000A vs. the industry standard delay of 92 BT for Class II
repeaters. The installation flexibility and network growth potential is accordingly better with
LH8000As than with hubs that merely meet the standard.
Table 3.2.2c shows maximum cable lengths for common network configurations
using industry standard repeater PDV numbers. Calculations such as above should be
performed using measured PDV data supplied by the equipment manufacturer in important
installations.
Table 3.2.2c: Maximum segment lengths for common network configurations
Number
of Hubs
Repeater
Hop Count
Max. User
Segment
Lengths (m)
Max. Inter-
Repeater (Cascade)
Length (m)
Notes
1
1
100.0
n.a.
All ports TX
2
2
100.0
5.0
All ports TX
2
2
92.0
20.0
All ports TX
3+
3
60.0
1.0
All ports TX
Instructions for connecting the LH8000A Dual-Speed Hubs to the various Fast
Ethernet media are given in the following sections.
2 meter Cat. 5 cable
for cascading
All user devices connected
via Cat. 5 twisted pair cable
of up to 75m length.
1 2 3 4 5 6 7 8
COL
ACT
PWR
LK
RX
BR
UPLINK
1 2 3 4 5 6
7 8
1 2 3 4 5 6 7 8
COL
ACT
PWR
LK
RX
BR
UPLINK
1 2 3 4 5 6
7 8
1 2 3 4 5 6 7 8
COL
ACT
PWR
LK
RX
BR
UPLINK
1 2 3 4 5 6
7 8
