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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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LLDP or Physical-Layer Classification for Type 2 PSEs?
We have learned that a Type 2 PSE can support either 2-event L1 classification (no data link required—good for Midspans and Endspans) or 1-event L1, followed by L2 classification (good only for Endspans). See also Fig. 4.1. Colloquially, we just say a Type 2 PSE can do either physical layer classification or LLDP-based classification. What we actually mean should, however, be clear by now. It is actually 2-event, or 1-event + LLDP.
So now we ask: Which is better (obviously from the viewpoint of Endspans)? We will discuss this once more at the end of this chapter too.
For the purpose of mutual identification between Type 2 devices, the first method (Type 2 classification completed at layer-2), ...

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