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Power Over Ethernet (PoE) Operation for the Series 2600-PWR Switches
General PoE Operation
links. Thus, you can connect either a non-PoE device or a PD to a PoE-enabled
port without reconfiguring the port.
PD Support
The switch must have a minimum of 15.4 watts of unused PoE power available
when you connect an 802.3af-compliant PD, regardless of how much power
the PD actually uses. On the Switch 2626-PWR, there will always be enough
power available to connect and support 802.3af PoE operation on all 24 10/
100-TX ports. On the Switch 2650-PWR, however, it is possible to oversub-
scribe the available PoE power. In this case, one or more PoE devices
connected to the switch will lose power. That is:
■ Sufficient PoE Power Available: When a Switch 2650-PWR detects
a new PD, and if the switch has a minimum of 15.4 watts of PoE power
available, the switch supplies power to the port for that PD.
■ Insufficient PoE Power Available: When a Switch 2650-PWR
detects a new PD, and if the switch does not have a minimum of 15.4
watts of unused PoE power available:
• If the new PD is connected to a port “X” having a higher PoE priority
than another port “Y”, the switch removes PoE power from port “Y”
and delivers it to port “X”. In this case the PD on port “X” receives
power and the PD on port “Y” is denied power.
• If the new PD is connected to a port “X” having a lower priority than
all other PoE ports currently providing power to PDs, then the switch
does not deliver PoE power to port “X”.
Note that once a PD connects to a port and begins operating, the port retains
only enough PoE power to support the PD’s operation. Unneeded power
becomes available for supporting other PD connections. Thus, while 15.4
watts must be available for the switch to begin supplying power to a port with
a PD connected, 15.4 watts per port is not continually required if the connected
PD requires less power. For example, with 20 watts of PoE power remaining
available on the switch, you can connect one new PD without losing power to
any currently connected PDs. If that PD draws only 3 watts, then 17 watts
remain available and you can connect at least one more PD without interrupt-
ing power to any other devices. If the next PD you connect draws 5 watts, then
only 12 watts remain unused. With only 12 watts available, if you connect yet
another PD, the lowest-priority port will lose PoE power until the switch once
again has 15.4 or more watts available. (For information on power priority,
refer to
“Power Priority” on page 11-7.)
11-5