ethernet polarity


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
Reply to
TerryS
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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.
Most propably your errors are caused by some other reason.
Reply to
Tomi Holger Engdahl
Why not post in comp.dcom.lans.ethernet, where Rich Seifert, one of the ethernet creators, often posts?
Reply to
James Knott
troubleshooting a
corrected,
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.
Reply to
Watson A.Name - "Watt Sun, th
Which begs the question: what was the worst decision of his life? :)
Reply to
David Magda
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
Reply to
Dale Farmer
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!
Reply to
Watson A.Name - "Watt Sun, th
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).
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).
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).
Reply to
Tomi Holger Engdahl
(snip)
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
Reply to
glen herrmannsfeldt

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