Table 48: Estimated Values for Factors Causing Link Loss (continued)
Sample (LL) Calculation ValuesEstimated Link-Loss ValueLink-Loss Factor
This example assumes the link is 2 km
long. Fiber attenuation for 2 km:
•
(2 km) * (1.0 dBm/km) = 2 dBm
•
(2 km) * (0.5 dBm/km) = 1 dBm
•
Multimode—1 dBm/km
•
Single mode—0.5 dBm/km
Fiber attenuation
1 dBm1 dBmClock Recovery Module (CRM)
NOTE: For information about the actual amount of signal loss caused by
equipment and other factors, see your vendor documentation for that
equipment.
2. Calculate the (P
M
) by subtracting (LL) from (P
B
):
P
B
– LL = P
M
(13 dBm) – (0.5 dBm [HOL]) – ((5) * (0.5 dBm)) – ((2) * (0.5 dBm)) – ((2 km) *
(1.0 dBm/km)) – (1 dB [CRM]) = P
M
13 dBm – 0.5 dBm – 2.5 dBm – 1 dBm – 2 dBm – 1 dBm = P
M
P
M
= 6 dBm
The calculated power margin is greater than zero, indicating that the link has sufficient
power for transmission. Also, the power margin value does not exceed the maximum
receiver input power. Refer to the specification for your receiver to find the maximum
receiver input power.
Related
Documentation
• Calculating the EX Series Switch Fiber-Optic Cable Power Budget on page 99
• Understanding EX Series Switches Fiber-Optic Cable Signal Loss, Attenuation, and
Dispersion on page 144
• Pluggable Transceivers Supported on EX Series Switches on page 132
101Copyright © 2017, Juniper Networks, Inc.
Chapter 7: Planning Power Requirements
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