Example Network Cabling Implementation

See Figure 4-16 for this example. Company ABC has all UTP Category 5 cabling. Two Class II repeaters are separated by 20 meters instead of the standard 5 meters. The network administrators are trying to determine whether this configuration will work.

Figure 4-16 An Example Network Cabling Implementation for Company ABC (Showing the Two Most Distant DTEs)

Class II 100BaseTX Repeater A

75 m UTP Category 5 Link 1

100BaseTX DTE1

20m UTP Category 5 InterRepeater Link

100BaseTX DTE1

100BaseTX DTE2

Class II 100BaseTX Repeater B

75 m UTP Category 5 Link 2

100BaseTX DTE2

To ensure that the PDV does not exceed 512 bit times, the network administrators must calculate a worst-case scenario using DTE 1 and DTE 2, which are 75 meters from their repeaters.

Assume that DTE 1 starts transmitting a minimum-sized frame of 64 bytes (512 bits). DTE 2 just barely misses hearing DTE 1's transmission and starts transmitting also. The collision happens on the far-right side of the network and must traverse back to DTE 1. These events must occur within 512 bit times. If they take any longer than 512 bit times, then DTE 1 will have stopped sending when it learns about the collision and will not know that its frame was damaged by the collision. To calculate the link delays for the Category 5 cable segments, the repeaters, and DTEs, the administrators use the values from Table 4-4. (Remember that Table 4-4 uses round-trip delay values, so you need not multiply by two.)

To test whether this network will work, the network administrators filled in Table 4-5.

Table 4-5 Delays of Components in Company ABC's Network

To test whether this network will work, the network administrators filled in Table 4-5.

Table 4-5 Delays of Components in Company ABC's Network

Delay Cause

Calculation of Network Component Delay

Total (Bit Times)

Link 1

75m x 1.112 bit times/m

83.4

Link 2

75m x 1.112 bit times/m

83.4

Interrepeater link

20m x 1.112 bit times/m

22.24

Repeater A

92 bit times

92

Repeater B

92 bit times

92

DTE 1 and 2

100 bit times

100

Table 4-5 Delays of Components in Company ABC's Network (Continued)

Calculation of Network

Delay Cause

Component Delay

Total (Bit Times)

Safety margin

5 bit times

5

Grand Total

Add Individual Totals

478.04

The grand total in Table 4-5 is fewer than 512 bit times, so this network will work.

The grand total in Table 4-5 is fewer than 512 bit times, so this network will work.

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