Juniper PTX5000, Hardware Manual

Page: 209 / 721

P
M
= P
B
– LL
P
M
greater than zero indicates that the power budget is sufficient to operate the receiver.
Factors that can cause link loss include higher-order mode losses, modal and chromatic dispersion,
connectors, splices, and fiber attenuation.
Table 71 on page 191 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 71: 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
Faulty connector 0.5 dB
Splice 0.5 dB
Fiber attenuation Single mode—0.5 dB/km
Multimode—1 dB/km
The following sample calculation for a 2-km-long multimode link with a power budget (P
B
) of 13 dB uses
the estimated values from Table 71 on page 191 . This example calculates link loss (LL) as the sum of
fiber attenuation (2 km @ 1 dB/km, or 2 dB) and loss for five connectors (0.5 dB per connector, or
2.5 dB) and two splices (0.5 dB per splice, or 1 dB) as well as higher-order mode losses (0.5 dB). The
power margin (P
M
) is calculated as follows:
P
M
= P
B
– LL
P
M
= 13 dB – 2 km (1 dB/km) – 5 (0.5 dB) – 2 (0.5 dB) – 0.5 dB
P
M
= 13 dB – 2 dB – 2.5 dB – 1 dB – 0.5 dB
P
M
= 7 dB
191