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
11
x
13x
15x
17x
19x
21x
23x
OK1
OK2
24x
2x
!
Incoming Powered
Device (PD) requiring
approx. 3.5 watts
High
Critical
Critical
Critical
Critical
Critical
Critical
Port 24
Port 1
Existing Powered
Devices (PDs)
Current power budget
has 2 watts available
for incoming PDs
UPS
UPS
Power Shelf
