IEEE 802.3cv:2021 pdf download.IEEE Standard for Ethernet-Amendment 12:Maintenance #15: Power over Ethernet.
79. IEEE 802.3 Organizationally Specific Link Layer Discovery Protocol
(LLDP) type, length, and value (TLV) information elements
79.3.2 Power Via MDI TLV
Insert the following text and Table 79—2a at the end of 79.3.2 as follows:
Power entities that implement Data Link Layer classification shall support the Power via MDI TLV DLL classification extension fields shown in Figure 79—3 after the P1 has been powered. Type 3 or Type 4 power entities that implement Data Link Layer classification and are connected to another Type 3 or Type 4 power entity shall support the Type 3 and Type 4 extension fields shown in Figure 7—3 after the P1 has been powered. Such entities, when connected to a Type I or Type 2 power entity, may support the Type 3 and Type 4 extension fields shown in Figure 79—3 after the P1 has been powered. Type I and Type 2 devices shall not include the Type 3 and Type 4 extension fields in the transmitted Power via MDI TLV.
NOTE—Some implementations of the Power via MDI TLV in Type 1 and Type 2 power entities ignore TLVs that are longer than 12 octets. In order to be interoperable with these implementations, Type 3 and Type 4 power entities are pennitted to transmit 12-octet TLVs (without the Type 3 and Type 4 extension) after first transmitting at least one valid 29-octet TLV (including the Type 3 and Type 4 extension). Table 79—2a lists the recommended Power via MDI TLV formats for each combination of power entity Types.IEEE 802.3cv pdf download.