User Guide

AT-GS900/8PS Switch Installation Guide

PoE Port

Prioritization

If the power requirements of the powered devices exceed the switch’s

power budget (75 W), the switch denies power to one or more PoE ports

based on a process called port prioritization. The port priority is based on

the port number with the highest priority assigned to port 1 and the lowest

priority assigned to port 4.

For example, this occurs if your AT-GS900/8PS switch is powered off

when you connect four powered devices to the PoE ports which require

more than 75 W of combined power. When you turn the power on to the

AT-GS900/8PS switch, the lowest priority PoE port(s) are denied power so

that the total PoE power supplied does not exceed the 75 W power

budget.

You may use this mechanism to ensure that powered devices critical to

the operations of your network are given preferential treatment by the

switch. in the distribution of PoE power Should the demands of the devices

exceed the available capacity of the switch, in the distribution of PoE

power will go to those devices connected to the highest priority ports.

PoE Guard Band The PoE Guard Band is defined as the range between 70 and 75 Watts of

the total PoE power supplied to the switch ports. This power band is

reached when the total PoE power requirements of all of the powered

devices connected to the switch fall into this range. It is indicated on the

front panel when the PoE Limit LED is ON. When this condition exists, the

switch denies PoE power to any additional powered devices that may be

connected to the switch.

Note

See “Power over Ethernet LEDs” on page 22 and 23 for a detailed

description of the functions indicated by the PoE Limit LED.

Exceeding PoE

Power Budget

If a port’s POE LED is blinking, the PoE power to that port is disabled

indicating that the PoE power budget is exceeded. This condition occurs

for one of two reasons:

 The demand for PoE power from the power device connected to

the port is greater than 30 W. The maximum amount of power any

port can supply by itself is 30 W. Power demands more than 30 W

exceed the port’s ability to deliver PoE power and the PoE power

delivered by that port is shut down.

 The total demand for PoE power on all ports is exceeding the 75 W

maximum PoE power limit of the switch. This condition occurs

when you connect an additional power device to a switch port and

the switch attempts to deliver more than the maximum PoE power

limit for the switch. When this situation occurs, the lowest priority

port(s) is denied PoE power so that the combined PoE power

delivered to all the power devices connected to the switch remains

under 75 W.