75R Termination for PoE

[sven]

Hi,

I have a board which has Ethernet connection. Recently I wanted to extend this board with Power over Ethernet support.
Since I need direct access to J4/J5/J7/J8 of the RJ-45 connector, I started looked to for a new connector which supports PoE.

I came across two types of connectors, one having a 75R termination and some have not. Does anybody know why this might be necessary (or not)?

My old one has termination resistors: WE 74990101210 https://katalog.we-online.de/pbs/datasheet/74990101210.pdf

Bel 1840469-2 has none: https://www2.mouser.com/datasheet/2/643/dr-MAG-1840469-1541922.pdf
Pulse JXD3-0003NL has them: https://www2.mouser.com/datasheet/2/336/JXD3-0003NL-1131715.pdf
WE 7499210123 has none: https://www2.mouser.com/datasheet/2/445/7499210123-922978.pdf
This one doesn't even have a tapped transformer TE 5-2337993-2: https://www.mouser.de/datasheet/2/418/NG_CD_5-2337993-2_A-1544947.pdf

Sven