Juniper Networks MX240 manual Estimated Values for Factors Causing Link Loss

MX240 Ethernet Services Router Hardware Guide

Table 38: Estimated Values for Factors Causing Link Loss (continued)

Link-Loss Factor	Estimated Link-Loss Value
Splice	0.5 dB
Fiber attenuation	Single-mode—0.5 dB/km
	Multimode—1 dB/km

The following example uses the estimated values in Table 38 on page 181 to calculate link loss (LL) for a 2 km-long multimode link with a power budget (PB) 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 (PM) is calculated as follows:

PM = PB – LL

PM = 13 dB – 2 km (1.0 dB/km) – 5 (0.5 dB) – 2 (0.5 dB) – 0.5 dB [HOL] – 1 dB [CRM]

PM = 13 dB – 2 dB – 2.5 dB – 1 dB – 0.5 dB – 1 dB

PM = 6 dB

The following sample calculation for an 8 km-long single-mode link with a power budget (PB) of 13 dB uses the estimated values from Table 38 on page 181 to calculate link loss (LL) as the sum of fiber attenuation (8 km @ 0.5 dB/km, or 4 dB) and loss for seven connectors (0.5 dB per connector, or 3.5 dB). The power margin (PM) is calculated as follows:

PM = PB – LL

PM = 13 dB – 8 km (0.5 dB/km) – 7 (0.5 dB)

PM = 13 dB – 4 dB – 3.5 dB

PM = 5.5 dB

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.

182■ Network Cable Specifications and Guidelines