GarrettCom manual PDV = X + 100 + 80 + 80 +, 1b Multiple cascaded Magnum 8000X Mixed-Media hubs

All user devices connected via Cat. 5 twisted pair cable of up to 75m length.

2 meter Cat. 5 cable for cascading

Magnum 8000X Mixed-Media Fiber Hubs Installation and User Guide (05/ 02)

The resulting value tells us that a Category 5 cable with a length of up to 25 meters may be used to cascade the Magnum 8000Xs. Note that this inter-repeater cable length may be increased by shortening the lengths of the 100m hub-to-user cable segments.

It is also possible to cascade a group of up to nine Magnum 8000Xs (serving up to 56 users with full-length 100m cables to each) by using short inter-repeater cable segments. The following is an example of how to calculate the maximum allowable cascade cable segment length. An illustration of this example is shown in Figure 3.6.1b, where the hub-to-user cable lengths are up to 75 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, 75 is the BT delay for 70m of Category 5 cable (1.112 BT/m), 80 is the bit time delay for each Magnum 8000X 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 3.6.1b: Multiple cascaded

Magnum 8000X Mixed-Media hubs

Note that the cascading of multiple Magnum 8000X Mixed-Media hubs is a capability beyond what industry

standards normally permit, and is different from what competitive 100Mbps 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 Magnum 8000X vs. the industry standard delay of 92 BT for Class II repeaters. The installation flexibility and network growth potential is accordingly better with Magnum 8000Xs than with hubs that merely meet the standard. Table 3.6.1c 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.

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