GarrettCom DS50 - Manual (Page 28)

Magnum DS50 / DS60s Dual Speed Hubs Installation and User Guide (06/02)
needs to know the total length of the Category 5 cable used to cascade the hubs. The variable
“X” is used to represent the unknown maximum cascade length.
PDV = X + ((111.2 + 111.2) + (92 + 92) + (100) + 0 ) BT < 512 BT
512 > (X + 506.4) BT
X < (512 - 506.4) BT
X < 5.6 BT
X < (5.6 BT) / (1.112 m/BT)
X < 5.03 m
⇒ 5.03 m maximum length for Category 5 cascaded cable
If the integrator uses Magnum hubs, he can increase the length of the cascaded
segment.
Additionally, as the Magnum hubs have a lower delay value (60BT rather than
92BT), the integrator can cascade three Magnum hubs with the maximum user cable lengths.
The calculation is shown below. The variable “X” is used to represent the unknown maximum
cascade length.
PDV = X + ((111.2 + 111.2) + (60 + 60 + 60) + (100) + 0 ) BT < 512 BT
512 > (X + 502.4) BT
X < (512 - 502.4) BT
X < 9.6 BT
X < (9.6 BT) / (1.112 m/BT)
X < 8.63 m
⇒ 8.63 m maximum total length for Category 5 cascading segments,
Where 111.2 is the BT delay for 100m of Category 5 cable (1.112 BT/m* 100m), 60 is the BT
delay for each of the Magnum hubs, 100 is the BT delay for the TX DTE pair, and a safety
margin of 0 was used. (Note the internal switch on port 6 does not enter into this calculation of
one collision domain’s cable lengths. If used, port 6 of the Magnum DS60C when set to 100Mb
has a PDV of 50BT, the same as a NIC or node.).
The resulting value tells us that two Category 5 cables whose combined lengths do
not exceed 8 meters may be used to cascade the three Magnum DS50 & DS60’s. Note that this
cable length may alternatively be increased by shortening the lengths of the 100m cables to
users.
Table 3.2c shows maximum cable lengths for common network configurations. The
above calculations should be performed for calculations not listed in the table.
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