PoE Guard Band

PoE Port Prioritization

Exceeding PoE Power Budget

AT-GS900/8PS Switch Installation Guide

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.

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.

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.