3Com 3C17203 - SuperStack 3 Switch 4400, Implementation Manual

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114 C
HAPTER
12: P
OWER
M
ANAGEMENT AND
C
ONTROL
Increased Reliability
A device powered by a Power over Ethernet Switch will be able to take
advantage of the facilities available to the Switch. The Switch can be
fitted with a redundant power supply or uninterruptible power supply,
increasing its uptime.
For example, if you run an IP telephone system using Power over Ethernet
and power the Switches using uninterruptible power supplies, you would
be able to make emergency phone calls if your building lost power.
Planning Power
Budgets
As you connect more Power over Ethernet devices to your Switch you
may need to calculate and implement a power plan. You can use a power
plan to specify which devices must always receive power and the priority
of the devices that do not need guaranteed power.
Calculating Power
Budgets
The Switch 4400 PWR can supply a maximum power of 15.4 watts to any
of its 24 ports provided that the total power delivered does not exceed
150 watts.
When you plan your network you need to calculate the maximum power
that you will need and make sure that the Switch is not expected to
supply more than its maximum capacity.
To calculate the power budget for the Switch, add together the power
requirements of the devices that will be connected at any one time. The
power requirements of 3Com Power over Ethernet compliant devices can
be displayed by logging on to the Web interface of the Switch and
selecting
Physical Interface > Power > Profile from the Device View .
To ensure that devices receive continuous power, the Switch reserves a
quantity of power for variations in the demand of connected devices.
Therefore, if the Switch is operating close to its power limit, it may not
allocate power to new devices. To see how much power is available, use
the
Physical Interface > Power > Configure operation in the Web
interface.
If the maximum power for the Switch is exceeded, the Switch follows
these rules:
1 A device that has been guaranteed power will always receive power
when it requests it, even if that means removing power from devices that