User's Manual

Chapter 1: Overview

PoE Powered

Device Classes

Powered devices are grouped into the five classes listed in Table 6. The

classes are based on the amount of power the devices require. The

switches support all five classes.

PoE Power

Budget

The AT-GS900/8PS switch has a power budget of 75 watts. This is the

maximum amount of power the switch can provide at one time to the

powered devices.

The sum of the power requirements of each of the PoE devices connected

to the switch determines the maximum number of devices that the switch

can support at one time. So long as the total power requirements of the

powered devices is less than the power budget of the switch, the switch

can supply power to all of the devices. But if the total power requirements

exceed the power budget, the switch denies power to one or more ports

using a mechanism referred to as port prioritization.

To determine whether the power requirements of the PoE devices you

plan to connect to the switch exceed its power budget, refer to the

documentation for the power requirement of each device and add the

requirements together. The switch should be able to power all of the

devices simultaneously as long as the total is below its power budget. If

the total exceeds the available power budget, you should consider

reducing the number of PoE devices so that all of the devices receive

power. Otherwise, the switch powers a subset of the devices, based on

port prioritization.

The switch can handle different power requirements on different ports.

This enables you to connect different classes of PoE equipment to the

PoE ports on the switch.

Table 6. IEEE Powered Device Classes

Class

Maximum Power

Output from a Switch

Port

PD Power Range

0 15.4W 0.44W to 12.95W

1 4.0W 0.44W to 3.84W

2 7.0W 3.84W to 6.49W

3 15.4W 6.49W to 12.95W

4 30.0W 12.95W to 25.5W