Juniper Networks EX8208 manual Calculating the EX8200 Switch Fiber-Optic Cable Power Budget

Complete Hardware Guide for EX8208 Ethernet Switches

NOTE: We recommend that you maintain N +1 or N+N power supplies in your switch at all times. Replace failed power supplies immediately to prevent unexpected failures. Power management raises a minor alarm if the number of online power supplies in your switch is less than the number required to maintain the configured power redundancy (N+1 in Junos OS Release 10.1 or earlier; N+1 or N+N in Junos OS Release 10.2 or later). If the problem is not corrected in 5 minutes, a major alarm is issued.

Power management raises a major alarm if the number of online power supplies in your switch is less than N power supplies. If your switch is running Junos OS Release 10.1 or earlier, all line cards are powered off. If your switch is running Junos OS Release 10.2 or later, power management provides power to line cards in priority order until power is exhausted. The remaining line cards are powered off.

If a new line card is installed in an operational switch, power management does not poweronthelinecardiftheincreasedpowerdemandexceedsthetotalavailablepower, including redundant power. If redundant power is used to power on the line card, a minor alarm is raised, which becomes a major alarm in 5 minutes if the condition is not corrected.

Related Topics • AC Power Supply in an EX8200 Switch on page 40

•DC Power Supply in an EX8200 Switch on page 48

•Understanding Power Management on EX Series Switches

Calculating the EX8200 Switch Fiber-Optic Cable Power Budget

Calculate the link's power budget when planning fiber-optic cable layout and distances to ensure that fiber-optic connections have sufficient power for correct operation. The power budget is the maximum amount of power the link 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 for fiber-optic cable power budget (P ) for the

B

link:

1.Determine values for the link's minimum transmitter power (P ) and minimum

T

receiver sensitivity (P ). For example, here, (P ) and (P ) are measured in decibels,

RTR

and decibels are referred to one milliwatt (dBm).

P= –15 dBm

T

P= –28 dBm

R

NOTE: See the specifications for your transmitter and receiver to find the minimum transmitter power and minimum receiver sensitivity.

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