ethernet polarity

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Are the signals on the two pairs polarity sensitive ? I never thought much
on this and I don't even know what the signals are. We are troubleshooting a
network with lots of packet errors. The customer has not noticed any
degradation yet, but our monitor keeps going into alarm. Anyway, we found
the green pair reversed, on the router to switch cable, but it must have
been for some time, and the problem is recent. This has been corrected,
cable tests out now. Not enough data yet to tell if that fixed it. Just
wondering.

TerryS




Re: ethernet polarity



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At least on 10 Base-T and 100Base-TX Ethernet system the
parctical systems are not polarity sensitive. The Ethernet
devices should be built in such way that they automatically
correct the reversed polarity situation.

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Most propably your errors are caused by some other reason.



--
Tomi Engdahl (http://www.iki.fi/then /)
Take a look at my electronics web links and documents at
http://www.epanorama.net /


Re: ethernet polarity



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troubleshooting a
found
have
corrected,
Just


The ethernet signal goes thru a transformer on each end, and that
essentially makes the signal AC, eliminating any DC component.  The
ethernet signals used in the original 10BaseT coax were manchester
encoded, which is not polarity sensitive, IIRC.  I believe the signals
on cat5 balanced twisted pair are also manchester encoded.  I will
crosspost to comp.dcom.cabling and for some other viewpoints.





Re: ethernet polarity



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That's true for Ethernet systems that use twisted pair wiring

Tere is no such transformer in original coax etherner:
Transceiver electronics is directly connected to coax,
the AUI interface from transceiver to MAC is trransformer
isolated (data and control signal manchester coded through
transformers, power isolated with DC-DC converter).

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There is no such thing at 10BaseT coax.
The 10Base-T Ethernet uses always twised pair wiring.

The Ethernet systems that use coax have different
names like 10Base5 and 10Base2. Coaxial Ethernet
uses manchester encoding. The coax system is polarity
sensitive (at least collosion detection fails if
polarity is not right).

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The signals on cat5 balanced twisted pair are also manchester encoded.
The electronics in twisted pair Ethernet transceivers are designed
in such what that they are not polarity sensitive
(transceiver IC can detect polarity reversal and correct it if needed).

--
Tomi Engdahl (http://www.iki.fi/then /)
Take a look at my electronics web links and documents at
http://www.epanorama.net /


Re: ethernet polarity


Tomi Holger Engdahl wrote:

(snip)

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Many transceivers have an LED to indicate polarity.  There is
no reason to do so, other than for marketing reasons.
Anyway, yes, manchester is polarity sensitive, but as far as I
know all transceivers detect and correct for it.

-- glen


Re: ethernet polarity


Watson A.Name - "Watt Sun, the Dark Remover" wrote:

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Why not post in comp.dcom.lans.ethernet, where Rich Seifert, one of the
ethernet creators, often posts?




Re: ethernet polarity



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signals
the

Yeah, I forgot about that one.  One time, back when we were still using
15 pin DIX connectors, I complained about them, and said something like
the person who specified those connectors should be made to live with
them for the rest of his life, or something like that. They were
constantly coming loose and causing problems.  I think it was he who
came forth and admitted that he was the one that made the decision, and
apologized.  I guess he had heard that same complaint many, many times
before!





Re: ethernet polarity




"Watson A.Name - \\"Watt Sun, the Dark Remover\\"" wrote:

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    He called it the second worst decision of his life.   He also said that

the first batch of connectors had slide latches that were machined or cast
from metal.  They changed the connector later to the flimsy stamped
sheet metal slide that we all came to despise.

    --Dale




Re: ethernet polarity



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[...]
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[...]

Which begs the question: what was the worst decision of his life? :)

--
David Magda <dmagda at ee.ryerson.ca>
Because the innovator has for enemies all those who have done well under
the old conditions, and lukewarm defenders in those who may do well
under the new. -- Niccolo Machiavelli, _The Prince_, Chapter VI


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