Eben King wrote:
> On Fri, 28 May 2004, Eric Jahn wrote:
>
>
>>On Fri May 28 2004 2:13 pm, Backward Thinker wrote:
>>
>>
>>>If you're in a pinch you can DIY: switch pins 1/3 and 2/6 on one
>>>end of your straight patch cable... but personally I wouldn't
>>>bother unless you can't find any crossover or they want like twice
>>>as much $ :).
>
>
>>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...
>
>
> straight:serial cable::crossover:serial cable plus null-modem adapter
>
> They're inherently different.
>
I'm pretty sure he's using CAT-5 UTP rather than serial for this.
I know the matter has already been addressed in fairly comprehensive terms (by Ian Blenke), but just in case it isn't clear:
Ethernet 10/100 usually involves using cabling called CAT-5 (category five) UTP (unshielded twisted pair). CAT-5 cabling involves a series of wires, ending at "terminators" (the plugs on both ends). Standard ethernet patch cable ("straight" CAT-5) has wires in it that are "in" wires and others that are "out" wires to allow two-way communication with a hub or switch. When attempting to connect two computers directly to one another through 10/100 network adapters (network cards), there is no hub or switch to sort out where data packets are sent, and the way the wires are connected to the terminators causes the network adapters to try to use the same wires for "out", and listens on the same wires for "in". Thus, wire alpha might be used as the "out" wire for both ends, and wire beta as the "in" wire. It's like trying to use two hoses to send water back and forth between two faucet-and-sink setups, where both faucets are connected to the same hose, and the other hose is set
to drain into both sinks. Since the faucets are both feeding into the same hose, there's nowhere for that hose to drain out, and since both sinks are prepared to receive water from the other hose, there's nothing putting water into either end of it.
A crossover cable, then, just switches the placement of the in-and-out wires on one end, so that the the wires "cross over", making the in on one side feed to the out on the other, and vice-versa.
My apologies if this is far too much explanation, but I figured I'd contribute for the benefit of anyone watching that didn't get enough information from previous explanations.
Anyone that knows cabling, feel free to correct me if I've misstated something. I've done cabling, but not for about five years (other than just going "this plugs in here"), and tend to focus more on the logical side of networking these days.
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