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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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IEEE 802.3at Table 33-8 Explained Further
Table 33-8 on Page 42 of 802.3at-2009 summarizes some of the above-mentioned points cogently. This figure was reproduced in Fig. 4.1 with adjoining examples revealing how it should be understood and interpreted. The key conclusions are (for compliant PSEs and PDs):
1.  A Type 2 PSE is allowed to depend only on 2-finger classification to seek out Type 2 PDs, with no layer-2 /LLDP classification. But it can also opt to use 1-finger classification followed by LLDP classification. So when the data link comes up, the PSE will use LLDP protocol to communicate with the PD that it is a Type 2 PSE and is thus able to provide more than 13 W to it.
2.  A Type 2 PD must be able to accept both of the above Type ...

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