What are the anticipated changes between the IEEE802.3at and IEEE802.3bt PoE standards?
*2/1/19 UPDATE* The IEEE802.3bt standard was published today!
The first change is the maximum power the load can consume. There will be two new types (Type 3 and Type 4) created to allow the PSE to source up to 60W and 90W(52V ~57V).
The second change is about the mutual identification. 802.3.bt expands existing 2-finger Type1(15W) & Type 2(30W) scheme:
− New long 1st class finger “informs” PD that the PSE will support the new MPS timings
− 4-Finger: Type 3 power levels up to 60W
− 5-Finger: Type 4 power levels up to 90W
The third change to the standard is about the standby power, which is related to the power signature that a PD must generate in order to maintain the PSE power. The maintain power signature (MPS) consists of a specific DC current amplitude, time duration and duty cycle. “New” lower Maintain Power Signature timings have been introduced in IEEE802.3bt in order to enable much lower standby power. A long first class event has been defined in order for the PSE to tell the PD it can use the new MPS timings.
The forth change is the Autoclass feature which will allow better power optimization by the PSE. Basically, it allows the PSE to set the power budget to the maximum PoE PD power through a power measurement, including the cable losses.
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