Autonegotiation @ 100 / 1000BASE-T - why in another sublayer of PHY


little question, that does not find it's answer in google (no matter of what angle I strike it) - in 100BASE-TX, autonegotiation function is placed just before the RJ-45 (MDI), under the PMD (physical medium dependent - at the bottom of PHY), and then - in 1000BASE-T it is defined as a functional block of PCS (physical coding sublayer - at the top of PHY).

Simple q: W H Y ? ? ?

Does anyone has an answer? Or does anybody has skills to dig this simple info from the web?

thanks in advance, banan

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I'm not sure it is an/the answer, but autoneg in 100BT was (at least initially) optional. I don't think it was ever optional in 1000BT. Perhaps that has something to do with where it is placed? I suspect the folks over in comp.dcom.lans.ethernet would know.

rick jones

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Rick Jones

Thanks, will go there and check out.


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I don't believe that it existed at the beginning of 100baseTX.

I used to have a 3C250 (bought cheap on eBay), one of the original

100baseTX repeaters. No 10baseT mode, but it does make a good door stop.

-- glen

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glen herrmannsfeldt Forums website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.