Juniper Networks M160 manual Attenuating to Prevent Saturation at SONET/SDH PICs

M160 Internet Router Hardware Guide

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 18 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.

Attenuating to Prevent Saturation at SONET/SDH PICs

SONET/SDH interfaces in the different reach classes—short reach (SR), intermediate reach (IR), and long reach (LR)—generate different output power levels and tolerate different input power levels. Interfaces that have a longer reach can transmit enough power to saturate the receivers on PICs that have a shorter reach. Specifically, LR interfaces can saturate IR PICs, and both IR and LR interfaces can saturate SR PICs. Interfaces in the same reach class can also saturate one another.

To prevent saturation, you might need to attenuate power at the PIC receiver, particularly if you know that it has a shorter reach than the interface that is sending the signal. Determine the amount of attenuation needed by measuring the power level at each receiver. Attenuate the power to bring it within the allowable range; for short lengths of fiber, with fiber and connector loss close to zero, an attenuator of 5 to 10 dB should be sufficient.

For specifications of minimum and maximum input level (receiver sensitivity and receiver saturation) and minimum and maximum output level (average launch power) for the SONET/SDH PICs supported on the M160 router, see the M160 Internet Router PIC Guide.

Routing Engine Interface Cable and Wire Specifications

For management and service operations, you connect the Routing Engine to an external console or management network through ports on the Connector

74 Routing Engine Interface Cable and Wire Specifications