Table 34: Estimated Values For Factors Causing Link Loss - Juniper Networks Hardware Manual

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Appendix E: Cable and Wire Guidelines and Specifications for the M120 Router
Factors that can cause link loss include higher-order mode losses (HOL), modal and
chromatic dispersion, connectors, splices, and fiber attenuation. Table 34 on page 245
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 34: Estimated Values for Factors Causing Link Loss

Link-Loss Factor
Higher-order mode losses
Modal and chromatic dispersion
Connector
Splice
Fiber attenuation
The following example uses the estimated values in Table 34 on page 245 to calculate
link loss ( ) for a 2-km-long multimode link with a power budget (
LL
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 mode loss = 0.5 dB
Clock recovery module = 1 dB
The power margin ( P ) is calculated as follows:
M
P = P – LL
M B
P = 13 dB – 2 km (1.0 dB/km) – 5 (0.5 dB) – 2 (0.5 dB) – 0.5 dB [HOL] – 1 dB [CRM]
M
P = 13 dB – 2 dB – 2.5 dB – 1 dB – 0.5 dB – 1 dB
M
P = 6 dB
M
The following sample calculation for an 8-km-long single-mode link with a power budget
( ) of 13 dB uses the estimated values from Table 34 on page 245 to calculate link loss
P
B
( ) as the sum of fiber attenuation (8 km @ 0.5 dB/km, or 4 dB) and loss for seven
LL
connectors (0.5 dB per connector, or 3.5 dB). The power margin (
follows:
Estimated Link-Loss Value
Single-mode—None
Multimode—0.5 dB
Single-mode—None
Multimode—None, if product of bandwidth and distance
is less than 500 MHz-km
0.5 dB
0.5 dB
Single-mode—0.5 dB/km
Multimode—1 dB/km
) of 13 dB:
P
B
) is calculated as
P
M
245