[Tfug] Switch problem

[Louis Taber]

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

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.

Fiber will always be wonderful in the right environment.  2 miles off the
paved road 15 miles from Ukiah is not the place for a 1200 foot link.  The
fiber is not usually the problem.  It is the connectors on the ends of the
fibers.  If you have a fusion splicer, it is not a problem.  Oh, then there
is the cost of the NICs.  The original plan was to get rid of a second
satellite link costing about $100 a month.  Low data rates anyway.  They
currently are using a long haul Wi-Fi connection down to Ukiah.  The
10Base-T connection has been in place about ten years now.

So far as "pushing-my-luck"  --  from Wikipedia:  (
http://en.wikipedia.org/wiki/10BASE-T#Cabling)

Unlike earlier Ethernet standards using
broadband<http://en.wikipedia.org/wiki/Broadband>
 and coaxial cable <http://en.wikipedia.org/wiki/Coaxial_cable>, such as
10BASE5 <http://en.wikipedia.org/wiki/10BASE5>
(thicknet<http://en.wikipedia.org/wiki/Thicknet>)
and 10BASE2 <http://en.wikipedia.org/wiki/10BASE2>
(thinnet<http://en.wikipedia.org/wiki/Thinnet>),
10BASE-T does not specify the exact type of wiring to be used, but instead
specifies certain characteristics that a cable must meet. This was done in
anticipation of using 10BASE-T in existing twisted-pair wiring systems that
may not conform to any specified wiring standard. Some of the specified
characteristics are attenuation
<http://en.wikipedia.org/wiki/Attenuation>,characteristic
impedance <http://en.wikipedia.org/wiki/Characteristic_impedance>, timing
jitter <http://en.wikipedia.org/wiki/Jitter>, propagation
delay<http://en.wikipedia.org/wiki/Propagation_delay>,
and several types of noise <http://en.wikipedia.org/wiki/Signal_noise>.
Cable testers are widely available to check these parameters to determine
if a cable can be used with 10BASE-T. These characteristics are expected to
be met by 100 meters of
24-gauge<http://en.wikipedia.org/wiki/American_wire_gauge> unshielded
twisted-pair cable. However, with high quality cabling, cable runs of 150
meters or longer are often obtained and are considered viable by most
technicians familiar with the 10BASE-T specification.[*citation
needed<http://en.wikipedia.org/wiki/Wikipedia:Citation_needed>
*]

Note there is no specific distance in the 10Base-T specification (150m is
about 500ft).  The location, being will off the grid & on the ocean side of
the ridge, also provided a very low noise environment.

  - Louis

On Thu, Mar 14, 2013 at 11:35 AM, Bexley Hall <bexley401 at yahoo.com> wrote:

> Hi Louis,
>
>
> On 3/13/2013 10:09 PM, Louis Taber wrote:
>
>> It is worth noting that the auto-negotiation signaling uses a VERY
>> different protocol and line frequencies than the subsequent data
>> transmission.  My guess is two GigaBit interfaces will auto-negotiate to 1
>> GigaBit on a physical connection that will only support 10MegaBit.  I
>>
>
> Interesting.  How did you come to that conclusion?  (I have never
> bothered trying to understand the magic involved -- the folks who
> specify these things are way smarter than me!)  And, what do you mean
> by "physical connection that will only support 10Megabit"?  I.e., as
> a consequence of the *cables* being used?  (since you've already
> stipulated that it is delimited by a pair of Gb interfaces)
>
> The problem (IMO) with the SOHO devices is they don't tell you
> much (by way of indications) -- and don't *expect* you to
> understand what they are not telling you!  :-/
>
>
>  haven't seen that one, bit I have seen an auto-negotiation to 100MegaBit
>> on
>> a line 600ft link that worked fine when forced to 10MegaBit.  The topology
>> I used for a 1200ft link was a 10MegaBit (custom POE) hub in the halfway
>> point.  It has worked fine for years (except when the hub got wet<sigh>).
>>
>
> Kinda pushing your luck on that one!  :>  Why not use fibre?
>
>
> ______________________________**_________________
> Tucson Free Unix Group - tfug at tfug.org
> Subscription Options:
> http://www.tfug.org/mailman/**listinfo/tfug_tfug.org<http://www.tfug.org/mailman/listinfo/tfug_tfug.org>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://tfug.org/pipermail/tfug_tfug.org/attachments/20130317/71ffb238/attachment-0002.html>