GarrettCom DS 880 - Manual (Page 22)

Magnum DS880 Dual-Speed Stackable Hubs Installation and User Guide (05/01)
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lengths are up to 100 meters for Cat 5 twisted pair. The variable “X”, the maximum hub-to-hub
cable delay, is calculated as follows:
PDV = X + ((100) + (80 + 80 + 80 )+ (83 + 83) + 2 ) BT < 512 BT
512 > (X + 508) BT, X < 4 BT
Twisted pair user cable length, TL < (4 BT) / (1.112 m/BT)
TL < 3.6 meters for two hub-to-hub cascading cables
⇒ 2 meters (6 ft.) length max. for each of the cascade segments,
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 Magnum DS880 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 DS880 hubs
Note that the cascading
of multiple Magnum DS880 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 Magnum DS880 vs. the industry standard delay of 92 BT for Class
II repeaters. The installation flexibility and network growth potential is accordingly better with
Magnum DS880s 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
w om m
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
2 meter Cat. 5 cable
for cascading All us
via Cat
of up
er devices connected
. 5 twisted pair cable
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