RE: [10GBASE-T] Technical feasibility: AutoNegotiation
Dan,
I'd like to offer my opinion on this - as someone who has had to deal
with many AN related link issues.
> Perhaps someone can give me a quick pointer on how we are going to
address
> the issue of <100m cable plants that meet ISO 11801 specs not being
able
> to
> support 10GBASE-T.
>
> For example, I have a building full of CAT5e and CAT6 cables. The
cables
> were installed to specification. Now, all I see are patch panels and
wall
> jacks. I don't have a record of which cable is how long, or what its
> electrical specs are.
This is probably a common scenario. We're in the process of rewiring
the LBNL Berkeley site and part of the project is to keep a database of
all test results for the installed cables. I would hope this is the
case in general since most test equipment makes this relatively easy to
do.
>
> The current Auto-Negotiation protocol supports HCD resolution which
means
> that the link, if configured to 10GBASE-T, will resolve to that speed
if
> both ends of the link support it. However, if the cable (85m of CAT6)
does
> not, the link will bounce up and down as it negotiates to speed, then
> fails
> to link. Maybe even worse is the link that actually comes up, but
operates
> unreliably due to thermal variation causing changes in parametric
values
> and
> suffers excessive BER or drops link occasionally.
>
> What is the fix?
I would MUCH rather see the link fail to come up than to have it come up
and operate unreliably.
>
> Do I test the wire in advance of using 10GBASE-T?
Do you mean as a matter of installation practice or as a part of the
Auto-Negotiation process?
> Do we fix the Auto-Negotiation protocol to automatically drop speed if
the
> SNR gets too low to guarantee the BER?
Again, I would rather that it drop the link. Since AN only runs when
you try to establish the link, are you talking about continuous BER
monitoring?
>
> If these have already been addressed, please feel free to just send
the
> URL
> to the presentation.
>
I think these are good questions - and I would like to hear more about
how the speed would be negotiated for the multi-speed PHY as I never
heard any formal discussion on this. If there's a presentation on that,
I'd like the URL as well.
Thanks,
Mike