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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Overview
We know from Chap. 1 what an RJ-45 is. Colloquially, it is just a standard Ethernet jack. The word “magjack” is also often used equally colloquially and refers to a jack containing the “mag” in it—that is, its associated magnetics, in particular the pulse/data transformers. We will thus typically find tiny, toroidal transformers inside the metal housing of the magjack. (The housing is always metal for EMI reasons.) We can have various stacked versions of magjacks too: like the 2 × 4 for example. This would be 2 rows containing 4 magjacks per row. Much like a symmetrical 2-floor dormitory, with a total of 8 rooms. Or we can have a 1 × 4 magjack, which would be like a singlefloor dormitory with a total of 4 rooms. And so on. We should ...

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