Juniper Networks MX240 Bedienungsanleitung PDF herunterladen (Seite 210)

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

Estimated Link-Loss ValueLink-Loss Factor

0.5 dBSplice

Single-mode—0.5 dB/km

Multimode—1 dB/km

Fiber attenuation

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 (P

) 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

) is calculated as follows:

= P

– LL

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

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

= 6 dB

The following sample calculation for an 8 km-long single-mode link with a power

budget (P

) 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 (P

) is

calculated as follows:

= P

– LL

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

= 13 dB – 4 dB – 3.5 dB

= 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

MX240 Ethernet Services Router Hardware Guide

1 2 ... 205 206 207 208 209 210 211 212 213 214 215 ... 241 242

Keine Kommentare

Juniper Networks MX240 Bedienungsanleitung Seite 210