Power-classification technology can help stretch your wiring closet power budget by leaving more power in the switch for additional devices. A switch is not required to power up all ports simultaneously. If it runs out of power budget, it can refuse to power up a device.
Devices that support power classification let the switch dole out power more granularly. A device without power classification must be supplied with a full 15.4 watts, whereas one with power classification can request a lesser amount.
Cisco takes power classification a step further, using CDP (Cisco Discovery Protocol) for its devices to specify their exact power requirements after initial power has been placed on the line. Although its approach is proprietary, Cisco can power more devices with the same power budget--a big plus if you have limited power in your wiring closet.
Whether you go with 802.af's approach or a proprietary one like Cisco's, power classification lets you support more devices on the same switch simultaneously without adding more power in the wiring closet. The catch: Not all PSEs and PDs support power classification.
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