HP 100BaseT Guide de l'utilisateur télécharger pdf (Page 41)

HP 100Base-T Hubs Installation and Reference Guide

Installing the System 2-9

Distance Limit and Power Loss in Fiber Optics - When using fiber

optic cabling, the maximum length between two hubs can be up to

2 kilometers. However, you must consider power loss when

calculating the actual length of cable that can be used with your

system. You can calculate power loss with the following formula:

m =

(p dB - i dB)

c dB/km

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cable length (kilometers)

p dB

power bud

i dB intervening devices

(e.g., patch cables and splices)

c dB/km

loss per kilometer of cable

Table 2.2 Calculating the Power Budget for Fiber Optic Devices

Note: To determine the power loss incurred by intervening devices and

specific cable type, inquire with the manufacturer. The power budget

depends on the gauge of cable as shown below.

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50/125 m

9.2 dB

62.5/125 m

13 dB

Table 2.3 Power Budget for Common Fiber Optic Devices

For a sample calculation, assume the following values:

• cable gauge - 62.5/125 mm, which means a 13 dB power budget,

• 2 patch panels along the path, each with 1.5 dB power loss,

• 1 splice with 1 dB power loss, and

• inherent power loss in the cable is 4 dB/km

The maximum cable length is therefore:

m =

13 dB - 4 dB

2.25 km

4 dB/km

Note: Even though your calculations for power loss may indicate a longer

permissible length based on signal strength (as seen in the preceding

example), we advise remaining within the recommended limits.

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HP 100BaseT Guide de l'utilisateur Page 41