Juniper Networks M10i manual Estimated Values for Factors Causing Link Loss

M10i Internet Router Hardware Guide

Factors that can cause link loss include higher-order mode losses, modal and chromatic dispersion, connectors, splices, and fiber attenuation. Table 23 on page 186 lists an estimated amount of loss for the factors used in the following sample calculations. For information about the actual amount of signal loss caused by equipment and other factors, refer to vendor documentation.

Table 23: Estimated Values for Factors Causing Link Loss

Link-Loss Factor	Estimated Link-Loss Value
Higher-order mode losses	Single-mode—None
	Multimode—0.5 dB
Modal and chromatic dispersion	Single-mode—None
	Multimode—None, if product of bandwidth and distance
	is less than 500 MHz–km
Connector	0.5 dB
Splice	0.5 dB
Fiber attenuation	Single-mode—0.5 dB/km
	Multimode—1 dB/km

The following example uses the estimated values in Table 23 on page 186 to calculate link loss (LL) for a 2 km-long multimode link with a power budget (PB) of 13 dB:

■Fiber attenuation for 2 km @ 1.0 dB/km= 2 dB

■Loss for five connectors @ 0.5 dB per connector = 5(0.5 dB) = 2.5 dB

■Loss for two splices @ 0.5 dB per splice =2(0.5 dB) = 1 dB

■Higher-order loss = 0.5 dB

■Clock recovery module = 1 dB

The power margin (PM) is calculated as follows:

PM = PB – LL

PM = 13 dB – 2 km (1.0 dB/km) – 5 (0.5 dB) – 2 (0.5 dB) – 0.5 dB [HOL] – 1 dB [CRM]

PM = 13 dB – 2 dB – 2.5 dB – 1 dB – 0.5 dB – 1 dB

PM = 6 dB

The following sample calculation for an 8 km-long single-mode link with a power budget (PB) of 13 dB uses the estimated values from Table 23 on page 186 to calculate link loss (LL) as the sum of fiber attenuation (8 km @ 0.5 dB/km, or 4 dB) and loss

186■ Network Cable Specifications and Guidelines