Classification is a way to tag different terminals on the
Power over LAN network according to their power consumption.
Devices such as IP telephones, WLAN access points and others,
will be classified according to their power requirements.
The meaning of the classification labels is defined in the
IEEE specification.
This variable is valid only while a PD is being powered,
that is, while the attribute pethPsePortDetectionStatus
is reporting the enumeration deliveringPower.