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Big Test MFG says our Ethernet Chip violates the IEEE standard - are they right?

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Ranayna:
Huh, i don't think that that is correct about auto negotiation. At least not in any implementation i ever saw. It also does not really make sense. It should be trivial to detect that pairs are missing, so that gigabit negotiation would be pointless.

It has been a while, but a couple of years ago, one of our office buildings was still wired with what we in germany like to call "Sparverdrahtung". Essentially one CAT 5 cable for a double ethernet jack, so just 2 pairs on 12 and 36.
I do not remember that we ever had to set 100 Mbit/s on any of our networking gear. And it is not that the cable itself or the jacks did not support gigabit. In several instances where speed was required we re-wired the jacks on both ends to have one gigabit capable port, and those worked fine.

nctnico:

--- Quote from: tooki on October 20, 2021, 12:24:42 pm ---- Gigabit requires Cat 5 cable, but requires 4 pairs.

--- End quote ---

AFAIK Cat 5E actually. I had to redo a lot of wiring to replace plain CAT5 because it didn't work for 1Gbit.

ve7xen:

--- Quote from: Ranayna on October 20, 2021, 07:43:25 pm ---Huh, i don't think that that is correct about auto negotiation. At least not in any implementation i ever saw. It also does not really make sense. It should be trivial to detect that pairs are missing, so that gigabit negotiation would be pointless.
--- End quote ---

It's correct. 802.3 says to always try the highest-common-denominator. The only way out is for one side to lower its advertised capabilities based on the link failures (or the administrator's awareness of the cabling limitations), to change the resolved HCD. Many 1000base-T PHYs do implement this (often called 'automatic downshift' or 'speed fallback'), kind of like AutoMDIX (though somewhat less common), but it's not part of the spec. In theory I suppose you could even do it in the driver. Many ports explicitly don't do this, particularly in networking equipment, as down link is often a better situation than a downgraded link, with the assumption that if this is desirable end-stations may implement it (and commonly do).


--- Quote from: IEEE 802.3-2018 28.1.4 ---Auto-Negotiation does not perform cable tests, such as detect number of conductor pairs (if more than two pairs are required) or cable performance measurements. Some PHYs that explicitly require use of high-performance cables, may require knowledge of the cable type, or additional robustness tests (such as monitoring CRC or framing errors) to determine if the link segment is adequate.

...

Provision has been made within Auto-Negotiation to limit the resulting link configuration in situations where the cabling may not support the highest common capability of the two end points. The system administrator/installer must take the cabling capability into consideration when configuring a repeater port’s advertised capability. That is, the advertised capability of a hub port should not result in an operational mode that is not compatible with the cabling.

--- End quote ---

ejeffrey:

--- Quote from: nctnico on October 20, 2021, 08:51:41 pm ---
--- Quote from: tooki on October 20, 2021, 12:24:42 pm ---- Gigabit requires Cat 5 cable, but requires 4 pairs.

--- End quote ---

AFAIK Cat 5E actually. I had to redo a lot of wiring to replace plain CAT5 because it didn't work for 1Gbit.

--- End quote ---

Really?  I've haven't looked a that extensively but I have never seen a cat5 cable fail at a gigabit speeds.  The initial version of 1000Base-T specifically called for cat5 but with slightly modified specs -- I think only for NEXT which was not specified in the cat5 standard but which most existing cat5 cables supported.  Cat5e was then published and cat5 withdrawn and the ethernet spec modified to call for cat5e.

metrologist:
Regarding cat5 vs. cat5e, I think it may be because the spec is guaranteed to 100m. Who here has tested this? I think short runs, 3m patch cables, is why I see reported Gbit speeds on cat3.

Some of the reporting here seems contradictory, but I am not a standards expert. Negotiating the highest common denominator is what I would expect. I only really care about what's happening at the port.

So I took a peak at the digital board and found https://www.ti.com/lit/ds/symlink/dp83867ir.pdf in qfn. I see all 16 data lines go off the backbone :-//

Edit: one thing I wanted to mention is that I had fiber installed and a new router. My PC had Gbit NIC, but I was only getting 10Mbps (simple speedtest.net). I changed the 10m patch cable and then got near the specified 1000mbps. I did not keep track of that cable.

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