Juniper M40E Hardware Manual page 315

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Appendix E: Cable and Wire Guidelines and Specifications for the M40e Router
Table 31: Estimated Values for Factors Causing Link Loss (continued)
Link-Loss Factor
Fiber attenuation
The following example uses the estimated values in Table 31 on page 286 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 31 on page 286 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:
P = P – LL
M B
P = 13 dB – 8 km (0.5 dB/km) – 7(0.5 dB)
M
P = 13 dB – 4 dB – 3.5 dB
M
P = 5.5 dB
M
In both examples, the calculated power margin is greater than zero, indicating that the
link has sufficient power for transmission and does not exceed the maximum receiver
input power.
Fiber-Optic and Network Cable Specifications for the M40e Router on page 283
Signal Loss in Multimode and Single-Mode Fiber-Optic Cable for the M40e Router on
page 284
Estimated Link-Loss Value
Single-mode—0.5 dB/km
Multimode—1 dB/km
) of 13 dB:
P
B
) is calculated as
P
M
287