Juniper Networks EX8208 manual Estimated Values for Factors Causing Link Loss

Chapter 7: Planning Power Requirements

2.Calculate the power budget (P ) by subtracting (P ) from (P ):

BRT

–15 dBm – (–28 dBm) = 13 dBm

Related Topics • Calculating the EX8200 Switch Fiber-Optic Cable Power Margin on page 121

•Optical Interface Support in EX8200 Switches on page 60

•Understanding EX8200 Switch Fiber-Optic Cable Signal Loss, Attenuation, and Dispersion on page 106

Calculating the EX8200 Switch Fiber-Optic Cable Power Margin

Calculate the link's power margin when planning fiber-optic cable layout and distances to ensure that fiber-optic connections have sufficient signal power to overcome system losses and still satisfy the minimum input requirements of the receiver for the required performance level. The power margin (P ) is the amount of power available after

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attenuation or link loss (LL) has been subtracted from the power budget (P ).

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When you calculate the power margin, you use a worst-case analysis to provide a margin of error, even though all the parts of an actual system do not operate at worst-case levels. A power margin (P ) greater than zero indicates that the power budget is sufficient

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to operate the receiver and that it does not exceed the maximum receiver input power. This means the link will work. A (P ) that is zero or negative indicates insufficient power

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to operate the receiver. See the specification for your receiver to find the maximum receiver input power.

Before you begin to calculate the power margin:

•Calculate the power budget. See “Calculating the EX8200 Switch Fiber-Optic Cable Power Budget” on page 120.

To calculate the worst-case estimate for the power margin (P ) for the link:

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1.Determine the maximum value for link loss (LL) by adding estimated values for applicable link-loss factors—for example, use the sample values for various factors as provided in Table 51 on page 121 (here, the link is 2 km long and multimode, and

the (P ) is 13 dBm):

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Table 51: Estimated Values for Factors Causing Link Loss

Link-Loss Factor	Estimated Link-Loss Value
Higher-order mode losses (HOL)	•	Multimode—0.5 dBm
	•	Single mode—None
Modal and chromatic dispersion	•	Multimode—None, if product of
		bandwidth and distance is less than
		500 MHz/km
	•	Single mode—None

Sample (LL) Calculation Values

•0.5 dBm

•0 dBm

•0 dBm

•0 dBm

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