Juniper JUNOS OS 10.3 - SOFTWARE Manual page 475

Power Priority of Line Cards
Copyright © 2010, Juniper Networks, Inc.
W in its power budget policy for redundancy. It allocates the remaining 9000 W to
normal operating power.
Specifies the rules under which components receive power. These rules are designed
to ensure the least disruption to switch operation under conditions of insufficient power.
For example, power management provides power to core system components, such
as the Routing Engine, before it provides power to line cards.
You can configure certain aspects of power management's budget policy, specifically:
The power priority of individual line cards. By assigning different power priorities to the
line cards, you can determine which line cards are more likely to receive power in the
event of insufficient power.
The power redundancy configuration. The default power redundancy configuration is
N+1; you can optionally configure N+N. For example, if you have deployed two
independent AC power feeds to the switch, configure N+N redundancy. When you
configure power management for N+N redundancy, it reserves the appropriate amount
of power in its power budget and reports insufficient power conditions accordingly.
These configurable items are discussed further in:
Power Priority of Line Cards on page 379
Power Supply Redundancy on page 380
Power management powers line cards on or off based on the power priority of the slots
they occupy:
When a switch powers on, power management provides power to the line cards in the
order of their slot priority, with line cards in high priority slots receiving power first. Thus
if available power (including redundant power) is exhausted before all line cards receive
power, higher priority cards are powered on while lower priority cards remain powered
off.
If the switch starts receiving insufficient power because of power supply failure or some
other problem, power management powers off the line cards in reverse-priority order
until power (including redundant power) is sufficient for the remaining cards. Thus
higher priority line cards are more likely to retain power in power shortage conditions
than are lower priority line cards.
Power management responds to changes in power availability and line card operating
status by powering line cards on or off as appropriate. For example, if you add a power
supply, lower priority cards that were powered off due to insufficient power are powered
on in priority order.
If you take a line card offline, power management no longer allocates power to it. If
power to the switch is insufficient when you take a line card offline, power management
allocates the freed power to a lower priority card that was offline due to lack of power
and brings it online. Restarting a line card, however, does not affect the power allocated
to it. Thus when power is insufficient, restarting a line card does not change its operating
status or the operating status of other line cards.
Chapter 18: Power Management Overview
379