>>Though there is the question, why straight patch cables at all :)?
Because the hub connector is wired backward to the PC connector. The
"transmit" pin on the PC is the "receive" pin on the hub. And vice versa.
>>What is the technical reason hubs/routers weren't designed to work with
crossed-over pinnage?
I cannot think of a single technical reason the hubs could not have used the
same connector as the PC. Had they done so, all cables would have been
cross-over cables, and any device could have connected to any device. So
why didn't they do it that way? My guess:
When Synoptics created the first Ethernet-over-twisted-pair system, they did
it this way. They were in the business of selling hubs and cards. If you
wanted to connect two machines, you still had to buy their hub. The
crossover cable was considered a 'hack'. At first Synoptics said it
wouldn't work and would void the warranty...<grin>
Actually, it might have been a phone company standard to use straight
wiring. Synoptics used Cat-3 wiring, and the selling point was you could
use existing pairs already installed from old multi-line phones.
</guess>
I'm sure somebody on the list know more about phone stuff and might offer an
opinion.
Ken Elliott
=====================
-----Original Message-----
From: slug@nks.net [mailto:slug@nks.net] On Behalf Of Backward Thinker
Sent: Friday, May 28, 2004 10:26 PM
To: slug@nks.net
Cc: slug@nks.net
Subject: Re: [SLUG] Newb network question
> > 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? 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. But then, I don't
deal with it much, so I'm not a good judge. And a LOT of things would be
different, anyway, if it weren't for various historic/legacy baggage
reasons, and this might just be one of those cases?
Oh well, probably not very important... it is how it is.
~ Daniel
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