HP 5300 Informacje Techniczne Pobierz pdf (Strona 208)

Power Over Ethernet (PoE) Operation

Planning and Implementing a PoE Configuration

For example, suppose you have 24 identical appliances to connect to an xl

PoE module receiving 204 watts of PoE power. For this example, each

appliance requires 8.3 watts to operate. In this case, the module would support

only 23 of these appliances at any given time because there would not be

enough unused power to meet the minimum of 15.4 watts required to support

the initial bring-up of the 24th appliance. That is, 204 - (23 x 8.3) = 13.1. Because

the module provisions power on the basis of the priority scheme described on

page

11-10 (under the interface < port-list > power [ critical | high | low ] syntax),

you can still fully populate the module with appliances. In this case, the lowest-

priority port will not receive power unless an appliance in a higher-priority

port is disconnected.

There is also a scenario where a device on a lower-priority port can experience

a power cycle (temporarily lose power) while a higher-priority port is bringing

up a PoE device. Suppose, for example, that:

1. An xl PoE module in slot B, with all ports configured at the default Low

priority, is receiving 204 watts of power from an EPS.

2. The 21 PoE devices on ports B2 - B22 draw 9.0 watts of power each (9 x

21 = 189), leaving 15.0 watts unused, which is less than the 15.4 watt

minimum needed to add another PoE device to the module. (Refer to

“PD

Support” on page 11-6.)

3. The system operator plugs a 7.0-watt PoE device into port B1, which is

the highest-priority port in slot B.

In the above scenario, there is less than 15.4 watts available to support the

initial bringup of the newly installed device on port B1. As a result, port B22

(the lowest-priority port on the module) temporarily loses power so that there

is enough power to add the new device on port B1. After the new device begins

operation, the power demand on port B1 drops to 7 watts. At this point, there

are 20 devices consuming 9 watts each, and 1 device consuming 7 watts, for

a total of 187 watts, and the module now has 17 watts of unused power

available. Since this exceeds the minimum of 15.4 watts required to bring up

any PoE device, there is now enough power available to bring back up the

device on port B22.

Assigning PoE Ports to VLANs

If your network includes VLANs, you may want to assign various PoE-config-

ured ports to specific VLANs. For example, if you are using PoE telephones

in your network, you may want to assign ports used for telephone access to a

VLAN reserved for telephone traffic.

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HP 5300 Informacje Techniczne Strona 208