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Chapter 1: Overview
40
Power Budgeting The power for PoE is provided on the ports of the AT-SBx31GP24 Line
Cards is provided by the AT-SBxPWRPOE1 Power Supply. It can provide
up to 1200 watts of power for powered devices. You may install up to two
power supplies in the chassis for a total of 2400 watts for the powered
devices that are connected.
The number of powered devices the chassis can support at one time
depends on the number of AT-SBxPWRPOE1 Power Supplies in the
chassis and the power requirements of the powered devices in your
network. Table 4 lists the maximum number of powered devices by class,
for one or two power supplies. The numbers assume that the powered
devices require the maximum amount of power for their classes.
Note
The maximum number of PoE ports in the SwitchBlade x3112
Switch is 240 ports.
PoE Wiring The IEEE 802.3af and 802.3at standards define two methods for
delivering power to powered devices over the four pairs of strands that
comprise a standard Ethernet twisted-pair cable. The methods are called
Alternatives A and B. In Alternative A, power is supplied to powered
devices on strands 1, 2, 3, and 6, which are the same strands that carry
the 10/100Base-TX network traffic. In Alternative B, power is delivered on
strands 4, 5, 7, and 8. These are the unused strands.
Note
1000BASE-T cables carry the network traffic on all eight strands of
the Ethernet cable.
Table 4. Maximum Number of Powered Devices
Class
Maximum Number of
Ports with
One PoE PSU
(1200 W)
Maximum Number of
Ports with
Two PoE PSU’s
(2400 W)
0 77 155
1 240 240
2 171 240
3 77 155
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