factors used in the following sample calculations. For information about the actual amount of signal loss
caused by equipment and other factors, see your vendor documentation.
Table 29: Estimated Values for Factors That Cause Link Loss
Estimated Link-Loss ValueLink-Loss Factor
Single-mode—None
Multimode—0.5 dB
Higher-order mode losses
Single-mode—None
Multimode—None, if product of bandwidth and distance is less
than 500 MHz–km
Modal and chromatic dispersion
0.5 dBConnector
0.5 dBSplice
Single-mode—0.5 dB/km
Multimode—1 dB/km
Fiber attenuation
The following example uses the estimated values in Table 29 on page 96 to calculate link loss (LL) for a
2 km-long multimode link with a power budget (P
B
) 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 (P
M
) is calculated as follows:
P
M
= P
B
– LL
P
M
= 13 dB – 2 km (1.0 dB/km) – 5 (0.5 dB) – 2 (0.5 dB) – 0.5 dB [HOL] – 1 dB [CRM]
P
M
= 13 dB – 2 dB – 2.5 dB – 1 dB – 0.5 dB – 1 dB
P
M
= 6 dB
The following sample calculation for an 8 km-long single-mode link with a power budget (P
B
) of 13 dB uses
the estimated values from Table 29 on page 96 to calculate link loss (LL) as the sum of fiber attenuation
96
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