In the 70k and 75k versions of the PS2 up to the possible first version of the 79k an ethernet transformer, IC H0037RL, is used, in the other versions from the 79k to the latest version of the 90k an RJ45 Connector with an internal transformer is used, I am not aware of any project with the use of network connection on PS2 that has worked without this transformer, but I do not rule out this possibility. Below are pictures of what I'm talking about.
The transformer inside the connector:
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The transformer in what I consider to be the first version of the 79k:
View attachment 22167
this RJ45 connector has no transformer, just a connector with its pins.
Finally, this is the 79k transformer inside, see the similarity with the connector transformer of the other 79k and 90k versions.
View attachment 22169