Extreme Networks Summit 300-48 Software User's Manual page 135

Port Power Management
Common Power Pool
The common power pool represents the total amount of power available on a per-slot basis, less any
power reserved or allocated to currently powered devices. When a new device is discovered, its defined
power requirements are subtracted from the common power pool. If the common pool does not have
sufficient available power, power is not supplied to the device. In this case, the port is placed in a
power-denied state. The device can be powered at a later time if more power becomes available to the
common power pool due to another device disconnecting or if previously reserved power becomes
available.
If multiple devices are in the denied state and more power becomes available, the devices are powered
in order of priority and connection.
Port Connection Order
The Summit 300-48 switch software tracks the order of connection for powered devices. The connection
order is recorded at the time a device is first discovered and classified. The connection order is reset if
the device is disconnected. This connection order is maintained even if the switch is powered down or
power is interrupted, and the device must be discovered again.
During system startup, ports are powered initially based only on the connection order. During normal
system operations, port power order is determined first based upon priority, then discovery time. Thus,
the highest priority port with the earliest discovery time is powered first.
Port Power Priorities
You can set the priority of a port to low, high, or critical. Higher priority ports are given precedence in
powering sequence.
Port Power Reset
You can set ports to experience a power-down, discover, power-up cycle without returning the power
to the common pool. This allows you to reset powered devices without losing their claim to the
common power pool or connection order.
Port Power Budgets
The standard 802.3af protocol permits a PD to be classified into one of 5 classes, each of which
determines the maximal power draw to the power sourcing equipment (PSE). Extreme PSEs, in the
default configuration, use the classification-to-power draw in performing power management and
budgeting.
Classification is optional, and many PD devices do not support it. Therefore, under normal conditions,
the Extreme PSE budgets for the maximum permitted power (15.4 watts), even though the maximum
device draw may be less. This may cause fewer devices to be powered, since the power budget is
prematurely exhausted. There is a wide variation in power consumption levels between 802.3af classes
(~8 watts). In such cases, the power level limit (operator-limit) can be set on a per port basis. If this is
done, the operator limit, rather than the discovered class limit will be used for power budgeting. It is
also necessary for the violation-precedence to be set to .
operator-limit
Regardless of how the port power limit is derived (through automatic classification or operator limit),
the port power limit is used to determine whether the overall system limit has been exceeded. Once the
Summit 300-48 Switch Software User Guide 135