On Sat, 29 May 2004, Backward Thinker wrote:
>
> > > Thanks, I think I'll try that. This is rhetorical question,
> > > but why can't there be just one type of cable for both patch and
> > > crossover? It still just uses IP over Ethernet...
> >
> > Try not to confuse network transport layer 3 (IP) or data link
> > layer 2 (ethernet frames) with physical layer 1 (ethernet
> > 10/100baseT).
> >
> > Electrically, two of the wires are treated as a "transmit" pair
> > on one side of the cable (tx-/tx+), and the "receive" pair
> > (rx-/rx+) on the other side of the cable. As both sides need to
> > transmit and receive data, you have two pairs of cables to this
> > end.
> >
> > If two machines try to transmit on the same pair and receive on
> > the same pair, they cannot communicate - thus the need for
> > a "crossover" cable.
>
> Though there is the question, why straight patch cables at all
> :)? What is the technical reason hubs/routers weren't designed
> to work with crossed-over pinnage?
One thing that might connect to a hub is another hub. Barring autosensing
ports, you need either a special port or a special cable for that use.
If most ports are crossover (and the cables are likewise switched), then
you still have the "odd port/cable" situation, just it'll be
straight-through cables/ports that are rarer.
> I thought maybe when cutting lengths of cable from a roll, leaving it
> all as straight patch cable is easier... but in either case you're gonna
> be slapping an RJ-45 connector on it, including feeding the wires into
> the holes, etc. Seems a crossover wouldn't have been any more
> difficult.
No, they shouldn't be more difficult to make, just rarer, because they're
less often used.
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