User guide

Understanding Priority Disconnect Installing and Managing Power over Ethernet (PoE)

page 3-28 OmniSwitch 7700/7800 Hardware Users Guide April 2005

Priority Disconnect is Enabled; Incoming PD Port has Lowest Priority Level

Reminder. Priority disconnect examples are only applicable when there is inadequate power remaining to

power an incoming device.

When a PD is being connected to a port with a lower priority level than all other ports in the slot, the

incoming PD will be denied power, regardless of its physical port number. Devices connected to other

higher-priority ports will continue operating without interruption.

In the example below, there are only 2 watts available in the current PoE power budget. When the addi-

tional 3.5W powered device is added to the configuration, the system software must determine whether the

device will be granted or denied power. Because the incoming device is being connected to a high priority

port, and all existing devices are connected to critical priority ports, the incoming high-priority PD is

denied power; meanwhile, the critical priority devices remain powered on. This ensures that no power

budget deficit occurs and that higher priority devices (e.g., mission-critical IP phones) are allowed to oper-

ate without interruption.

Priority Disconnect Example 3: Feature is Enabled; Incoming PD Port has Lowest Priority Level

1x 3x 5x 7x 9x 11x 13x 15x 17x 19x 21x 23x

OK1

OK2

24x2x

Incoming Powered

Device (PD) requiring

approx. 3.5 watts

High

Critical

Port 24

Port 1

Existing Powered

Devices (PDs)

Current power budget

has 2 watts available

for incoming PDs

UPS

Power Shelf