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One of my ethernet cables starting malfunctioning, so I decided to replace it. The problem is, it turns out that the old cable is neither straight nor cross. It has all pairs mirrored (1-8 2-7 3-6 4-5 5-4 6-3 7-2 8-1). I narrowed the problem down to ethernet extender (like the one here: )

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which, if disassembled, has a circuit board inside that also mirrors all pairs. So the cable is mirrored basically to fix mirroring inside extender.

The question is, what is all that? Where does it come from? Is it described by some standard? The extender is factory-made, and the cables are definitely not made by trial and error.

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marked as duplicate by sblair, Michael Kjörling, Ƭᴇcʜιᴇ007, Dave M, Excellll Aug 6 at 16:38

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1 Answer 1

At first, I thought that sblair is right and I have telephone extender instead of ethernet extender. But later it turned out I was actually wrong. The extender does not swap any pairs. Circuit board inside it "mirrors" pairs to maintain them in straight order, because the sockets are themselves mirrored.

That brought me back to the question why the ethernet cable inverses pairs order. I called internet provider support and they told me that some technicians like to "invent" their own schemes of wire layouts, which they fix in the last cable. Don't ask me what's the point of this. I checked, when I insert the cable previously inserted into extender directly into laptop, it says cable not connected.

Overall: extender is ok, I was wrong to think it is inversed. Cable is indeed mirrored, because technicians messed up with the cable that goes into my apartment, and the last piece of cable "fixes" that.

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1  
Nice. (Well, not really. I'd say those technicians should adhere to the standards, or be laid off.) Any chance you can fix the cabling in some wall outlet instead? –  Arjan Aug 3 at 17:06
    
Was the wiring there before the internet service? If not, it might have been originally used for phone wiring. In the past, phone techs used cat 3 cables for phones, since it can be used for up to 4 phone lines. –  Keltari Aug 3 at 20:07
    
The wiring was laid by internet provider. I'm thinking to make a wall socket that fixes wire layout as suggested. –  Codeguard Aug 3 at 21:27
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i think they do this simply to prevent customers from using there Network together with an other Providers Services (they may be thinking that the other Provider doesn't know their Cable changings) –  konqui Aug 4 at 5:56

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