JAJSES8B October 2017 – November 2018 TPS2372
Autoclass is a classification mechanism that allows a PD to communicate its effective maximum power consumption to the PSE. This happens in such a way that the PSE will be able to set the power budget to the effective maximum PD power including the effective channel losses and additional margin. This new feature was introduced in the IEEE802.3bt standard to allow a more efficient use of the available power since only the effectively used power needs to be budgeted.
A Type 3 or Type 4 PD may optionally support Autoclass whereas a Type 3 or Type 4 PSE may make use of it to optimize its power management.
A PSE implementing Autoclass uses the first class event to inquire if the PD supports Autoclass, looking for the class current to fall to class 0 current level after a time tACS, as shown in Figure 17. If it is the case, the PSE can then proceed to Autoclass measurement immediately after power up, the PD being required to draw its highest power throughout the period bounded by the next 1.35 second to 3.65 seconds. Note that the average power is calculated using any sliding window with a width in the range of 150 to 300 ms .