[Gllug] Ethernet crossover wiring

[Dan Stevens (IAmAI)]

> The result of making the standard lead in this form is that the
> appliances at each end of the lead have to be wired differently to make
> things work.  Thus NICs have a different interface from hubs and
> switches and when you want to connect to devices which are the same
> together you have to use a special lead.

Would I have to use a different cat5 cable to connect a computer to a
router, and to connect a computer directly into another computer (peer
to peer).


On 24/02/06, John Winters <john at sinodun.org.uk> wrote:
> On Thu, 2006-02-23 at 22:45 +0000, Russell Howe wrote:
> > On Thu, Feb 23, 2006 at 10:32:18PM +0000, Dylan wrote:
> > > Question is, if I put a socket in each room, can I configure the wiring
> > > between them to act as a crossover? It this likely to be stable, or
> > > should I tell him to shell out for a cheap hub?
> >
> > This would violate the Principle of Least Astonishment.
> >
> > If you're wiring sockets in, put straight wiring in place, and then if
> > you want crossover wiring, use a crossover cable between the NIC and the
> > socket.
>
> It always amazes me how often hardware engineers make this fundamental
> design mistake.  If you lay out a supposedly "straight" CAT5 patch lead
> on a bench and look at it you will quickly realise that despite its name
> it's really a crossover lead - like this:
>
> 1----------------\      /-8
> 2---------\    /--\----/--7
> 3----\  /--\--/----\--/---6
> 4-\/--\/----\/------\/----5
> 5-/\--/\----/\------/\----4
> 6----/  \--/--\----/--\---3
> 7---------/    \--/----\--2
> 8----------------/      \-1
>
> The result of making the standard lead in this form is that the
> appliances at each end of the lead have to be wired differently to make
> things work.  Thus NICs have a different interface from hubs and
> switches and when you want to connect to devices which are the same
> together you have to use a special lead.  Then you have to keep track of
> which leads are which, and eventually manufacturers start making the
> devices auto-sensing so that they can pretend to be either type of
> terminating device.
>
> The same mistake was made in the design of 5 pin DIN audio leads, in
> serial cables and I'm sure in other places.
>
> If instead one recognises that a genuinely straight through lead needs
> to be wired like this:
>
> 1-------------8
> 2-------------7
> 3-------------6
> 4-------------5
> 5-------------4
> 6-------------3
> 7-------------2
> 8-------------1
>
> Then you need only one kind of lead, all appliances have their
> interfaces them same and no messing about at all is needed.
>
> Why do designers *keep* making this same mistake?
>
> </rant>
> John
>
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