Juniper MX10008, Руководство по оборудованию

Страница: 122 / 361

Calculating the Fiber-Optic Cable Power Margin for an MX10008 Router
Calculate the link's power margin when planning fiber-optic cable layout and distances to ensure that
fiber-optic connections have sufficient signal power to overcome system losses and still satisfy the minimum
input requirements of the receiver for the required performance level. The power margin (P
M
) is the
amount of power available after attenuation or link loss (LL) has been subtracted from the power budget
(P
B
).
When you calculate the power margin, you use a worst-case analysis to provide a margin of error, even
though all the parts of an actual system do not operate at worst-case levels. A power margin (P
M
) greater
than zero indicates that the power budget is sufficient to operate the receiver and that it does not exceed
the maximum receiver input power. This means the link will work. A (P
M
) that is zero or negative indicates
insufficient power to operate the receiver. See the specification for your receiver to find the maximum
receiver input power.
Before you begin to calculate the power margin:
•
Calculate the power budget. See “Calculating the Fiber-Optic Cable Power Margin for an MX10008
Router” on page 123 .
To calculate the worst-case estimate for the power margin (P
M
) for the link:
1. Determine the maximum value for link loss (LL) by adding estimated values for applicable link-loss
factors; for example, use the sample values for various factors as provided in Table 47 on page 123 (here,
the link is 2 km long and multimode, and the (P
B
) is 13 dBm).
Table 47: Estimated Values for Factors Causing Link Loss
Sample Link Loss (LL) Calculation Values Estimated Link Loss Value Link-Loss Factor
0.5 dBm Multimode—0.5 dBm Higher-order mode
losses
0 dBm Single-mode—None
0 dBm Multimode—None, if product of
bandwidth and distance is less
than 500 MHz/km
Modal and chromatic
dispersion
0 dBm Single-mode—None
This example assumes five connectors. Loss for five
connectors: 5 (0.5 dBm) = 2.5 dBm.
0.5 dBm Connector
This example assumes two splices. Loss for two
splices: 2 (0.5 dBm) = 1 dBm.
0.5 dBm Splice
123