[Tfug] Switch problem

[Kramer Lee]

Oh, Looks like the lightning problem was already discussed, sorry.

On 5/5/13, Louis Taber <ltaber at gmail.com> wrote:
> On Sun, Mar 17, 2013 at 1:44 PM, Bexley Hall <bexley401 at yahoo.com> wrote:
>
>> Hi Louis,
>>
>>
>> On 3/17/2013 12:37 PM, Louis Taber wrote:
>>
>>> I set up a test bed in my shop with 600 ft of Cat-5.  It
>>> quite happily auto-negotiated to 100MBit/sec, but would move no data at
>>
>>  all.  Put an old hub at one end to force it to 10MBit/sec and it worked
>>> fine.  See: http://en.wikipedia.org/wiki/**Autonegotiation#Electrical_**
>>> signals
>>> <http://en.wikipedia.org/wiki/Autonegotiation#Electrical_signals>
>>>
>>
>> OK, so in each case, you get a "go" for the "Link" (LED) but the
>> first case just leaves you with no *legitimate* signal at the far
>> end. So, in Erich's case, the machine can think the link "up" and just
>
> never see any "in band" data (e.g., DHCP traffic)  (?)
>>
> Yep.  That is easy to believe.
>
>
>> In which case, forcing the interface to a specific configuration
>> (my original suggestion) should work?  I.e., don't *let* the switch
>> "think" the link (end to end) is capable of anything that it *isn't*!
>>
> That should work.
>
>>
>> [Though he stated that the slower/older NIC's seemed to be manifesting
>> the most problems...  :-/ ]
>>
>>
>>  A side note: I have contended for years that the SOHO market needed to
>>> handle miss-wired cables and mid-x to reduce returns and customer
>>> service
>>> costs.
>>>
>>
>> I think AutoMDIX adds another set of issues.  E.g., I suspect that was
>> the problem I was having with my two Gb switches (separated by 8 ft
>> of cable).  Powering them up *singly* would work but if they both
>> came up together, they just sat staring at each other...
>>
>> But I agree with your observation.  A wise manufacturer would design
>> in a way that would discourage the user from even *suspecting* the
>> kit (assuming it most usually is NOT the culprit!).  Or, at the very
>> least, provide a reassuring means by which the user can convince
>> himself that the kit *is* or is *not* the (part of) problem!
>>
>> Gb Ethernet is inherently AutoMDIX.  It uses all 4 pairs full duplex.
>> All
> pairs have both a receiver and transmitter that do work at the same time.
>
>
>>
>>
>>>
>> I'd be more worried about its exposure to lightning strikes
>> (not *direct* but, rather, *induced*) over such a long distance.
>> The galvanic isolation afforded by the coupling transformers
>> would be no match for an induced voltage spike from such a strike
>> (No idea how far into the machine any potential damage would
>> propagate).  I've lost (wired) phones from nearby strikes (the
>> surge takes out the protection diodes across the line) -- and
>> you *know* the phone company designs with this sort of thing
>> in mind!
>>
>> But, I'm typically overly pessimistic about these things.  I
>> don't like *fixing* things if I can figure out a way to prevent
>> them from *breaking*, instead!
>>
>> Base-T network connections are ground isolated at both ends with a
> coupling transformers.   Many of the older units also had a spark gap if
> enough voltage is induced.   Not that lightning is not a problem.  At Pima
> one strike caused $27,000 in damages when it hit a grounded metal building.
>  (I did learn it is better to wind excess cable in figure-8s than just
> round loops.)   Fortunately, in this case, Northern coastal California get
> very few lighting strikes.
> http://www.vaisala.com/VaisalaImages/Product%20and%20services/NLDN%20CG%20Flash%20Density%20Km%201997-2010.png
>
>   - Louis
>