HP 5300 Informacje Techniczne Pobierz pdf (Strona 194)

Power Over Ethernet (PoE) Operation

General PoE Operation

Note The ports on a PoE module support standard networking links and PoE links.

Thus, you can connect either a non-PoE device or a PD to a PoE-enabled port

without reconfiguring the port.

PD Support

An xl PoE module 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. Depending on the amount of power the EPS

device delivers to a specific xl PoE module, there may or may not always be

enough power available to connect and support 802.3af PoE operation on all

24 10/100-TX ports. For example, if an HP 600 RPS/EPS is supporting only

one xl PoE module and no other PSEs, then there will be sufficient power

available for all ports on the module. However, if the same EPS is supporting

both an xl PoE module and another HP PSE device then, depending on the

power demand placed on the module by the PDs you connect, it is possible to

oversubscribe the available PoE power on the module. In this case, one or

more PDs connected to the module will not have power. That is:

■ Sufficient PoE Power Available: When a new PD connects to an xl

PoE module in the switch, and if the module has a minimum of 15.4

watts of unused PoE power available, the module supplies power to

the port for that PD.

■ Insufficient PoE Power Available: When a new PD connects to an

xl PoE module, and if the module does not have a minimum of 15.4

watts of unused PoE power already available:

• If the new PD connects to a port “X” having a higher PoE priority than

another port “Y” that is already supporting another PD on the same

module, then the module removes PoE power from port “Y” and

delivers it to port “X”. In this case the PD on port “Y” loses power and

the PD on port “X” receives power.

• If the new PD connects to a port “X” having a lower priority than all

other PoE ports currently providing power to PDs on the same

module, then the module does not deliver PoE power to port “X” until

one or more PDs using higher priority ports are removed.

Note that once a PD connects to a PoE 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 an xl PoE module on 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,

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HP 5300 Informacje Techniczne Strona 194