GarrettCom Magnum DS 880 Installation And User Manual page 22

Magnum DS880 Dual-Speed Stackable Hubs
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
Twisted pair user cable length, TL < (4 BT) / (1.112 m/BT)
TL < 3.6 meters for two hub-to-hub cascading cables
⇒
meters (6 ft.) length max. for each of the cascade segments,
2
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
Number Repeater
of Hubs Hop Count
1 1
2 2
2 2
3+ 3
ww w . GarrettC om
< 4 BT
PWR BR
ACT
COL
Max. User
Segment Repeater (Cascade)
Lengths (m)
100.0
100.0
92.0
60.0
. co m
Installation and User Guide (05/01)
1
PWR BR 1 2 3 4 5 6
7 8
ACT LK
COL
RX
1 2 3 4 5 6 7 8
UPLINK
1 2 3 4 5 6
7 8
LK
RX
All us er devices connected
via Cat . 5 twisted pair cable
of up to 75m length.
Max. Inter-
Length (m)
n.a. All ports TX
5.0 All ports TX
20.0 All ports TX
1.0 All ports TX
17
2 3 4 5 6 7 8
UPLINK
1 2 3 4 5
PWR BR 1 2 3 4 5 6
7 8
ACT LK
COL RX
2 meter Cat. 5 cable
for cascading
Notes
6 7 8
UPLINK