[c-nsp] NPE-G1s don't want to talk to each other over copper?

[Lukas Tribus]

Hi,



> There is nothing to "switch". GigE on copper will use all 4 pairs *in both
> directions at the same time*, unlike 10/100 (2 pairs, with one for RX only
> and one for TX only).

True - once AN completes; but I still don't buy that as a final conclusion.



Here is my understanding:

> Actually during auto-negotiation one pair transmits fast link pulses
> and another pair receives them. The same basic AN protocol is used
> for 10/100/1000, gigabit just has some additional pages.

Exactly. Fast link pulses is used for AN in 1000BASE-T as well, not
only 10/100, as per IEEE 802.3-2012 section 3, 34.1.5 ("Auto-Negotiation,
type 1000BASE-T"):

> [...]
> Auto-Negotiation is performed upon link startup through the use of
> a special sequence of fast link pulses.

But fast link pulses based AN still needs a transmit pair and a receiver
pair (because thats what we did with 10/100) and cannot work in a MDI(X)
mismatch situation, *unless* auto-mdix hops in, which is still optional
in 1000BaseT, although 99% of the gear has it (NPE-G1 likely not).

So while its true that 1000BaseT uses 4 pairs, the problem is that
AN doesn't complete and the port will never come up.



> So gigabit phys generally do support MDI/MDIX as well as auto-mdix

Generally yes (in 99% of the cases).



> the need goes away when link comes up at 1G.

My point is that the link will not come up at all.


This may not be the case with 1000BaseT-only stuff like certain copper SFPs,
but it is when you use 10/100/1000 ports.


2 copper 10/100/1000 ports (no SFPs) configured with "no mdix auto" will
not come up if you use the wrong cable.

Heres the output of a recent platform when doing this test:
http://pastebin.com/avfYQqch




Regards,

Lukas