Juniper PTX Series Hardware Guide

document GR-253-CORE (Section 4.3) and International Telecommunications Union
(ITU) document G.957.
When chromatic dispersion is at the maximum allowed, its effect can be considered as
a power penalty in the power budget. The optical power budget must allow for the sum
of component attenuation, power penalties (including those from dispersion), and a
safety margin for unexpected losses.
Related
Documentation
Calculating Power Budget and Power Margin for Fiber-Optic Cables on page 269•
• Network Cable and Transceiver Overview for PTX Series Packet Transport Switches
on page 267
• Network Cable and Transceiver Overview for M Series, MX Series, and T Series Routers
Calculating Power Budget and Power Margin for Fiber-Optic Cables
1.
Calculating Power Budget for Fiber-Optic Cable on page 269
2.
Calculating Power Margin for Fiber-Optic Cable on page 269
Calculating Power Budget for Fiber-Optic Cable
To ensure that fiber-optic connections have sufficient power for correct operation, you
need to calculate the link's power budget, which is the maximum amount of power it
can transmit. When you calculate the power budget, 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 the worst-case levels. To calculate the worst-case estimate of power budget (P
B
),
you assume minimum transmitter power (P
T
) and minimum receiver sensitivity (P
R
):
P
B
= P
T
– P
R
The following hypothetical power budget equation uses values measured in decibels
(dB) and decibels referred to one milliwatt (dBm):
P
B
= P
T
– P
R
P
B
= –15 dBm – (–28 dBm)
P
B
= 13 dB
Calculating Power Margin for Fiber-Optic Cable
After calculating a link's power budget you can calculate the power margin (P
M
), which
represents the amount of power available after subtracting attenuation or link loss (LL)
from the power budget (P
B
). A worst-case estimate of P
M
assumes maximum LL:
P
M
= P
B
– LL
A P
M
greater than zero indicates that the power budget is sufficient to operate the receiver.
Factors that can cause link loss include higher-order mode losses (HOL), modal and
chromatic dispersion, connectors, splices, and fiber attenuation. Table 50 on page 270
lists an estimated amount of loss for the factors used in the following sample calculations.
269Copyright © 2012, Juniper Networks, Inc.
Appendix E: Packet Transport Switch Cable, Wire, and Pinout Specifications and Guidelines

Juniper PTX Series Specifications

General

Product Series	PTX Series
Operating System	Junos OS
Port Density	High-density
Forwarding Performance	Billions of packets per second
Use Case	Service provider core, peering, and transit networks; data center interconnect (DCI)
Power Supply	Redundant, hot-swappable power supplies
Dimensions	Varies by model
Weight	Varies by model