[Tfug] Yet another poser

[johngalt1]

----- Original Message ----- 
From: "jblais" <>
To: "Tucson Free Unix Group" <tfug at tfug.org>
Sent: Thursday, September 20, 2007 8:33 AM
Subject: Re: [Tfug] Yet another poser


>
> >>
>> >>
>> >> Unless someone can explain a real world application of a
>> >> crossover cable using POE, I call BS. This sounds way too
>> >> hypothetical.
>> >>
>> When are you going to connect two devices supplying PoE power together?
>> (such that they require conductors 4,5,7,8) You could connect two
>> switches,
>> but why would you connect the power then?
>>
>
>
>> > real world crosssover - 2 pc's direct connected without a hub.
>> or GUI PC
>> > direct connected to a controller where you don't want the slow
>> down of the
>> > rest of the world on some network chatter.
>>
>> This answer not specified in the context of PoE.
>>
>> When connecting a PC to a PoE network camera via crossover cable with
>> conductors 4,5,7,8 properly connected, will the NIC power the
>> camera? Don't
>> think so.
>>
>> Still waiting to hear a real world example of crossover cable application
>> using the non-ethernet TX and RX pairs for PoE....
>>
>> TIA
>>
>>
>
> What a cable is actually used for -- POE for an invisible flying widget 
> that
> transmits the time of day -- I don't know.
> The thing is, it appears that crossing comm signals makes sense, crossing
> power doesn't.  So having a power crossover in your toolbox makes little
> sense. Having something that looks like an RJ45, with swapped power lines 
> or
> whatever, for things other that Ethernet (ie custom RS232 stuff) doesn't
> make sense to me.
> These lines seem to be defined .. see link below..
>
> http://www.alatec.com/info/other.html


Ok then. Now it gets deeper.

Based on that link, a crossover is a TIA568A on one end. On the other end, 
there is a TIA568B connection. This makes sense for reasons stated 
previously in the thread. The ethernet signal pairs 1,2 and 3,6 are swapped 
on the other end and the remaining pairs, 4,5 and 7,8 are not swapped.

Here is the link for the aforementioned Graybar supplied cable that omits 
4,5 and 7,8
http://www.allentel.com/page43.html

Now consider Rich's post of  Wednesday, September 19, 2007 11:55 AM.
http://www.tfug.org/pipermail/tfug_tfug.org/2007-September/016283.html


On Gigabit copper, all four pairs are swapped on a crossover cable.
http://pinouts.ru/NetworkCables/1Gbcrossover.shtml

linked from:
http://en.wikipedia.org/wiki/Gigabit_Ethernet



By the way, I strongly disagree with http://www.alatec.com/info/other.html 
where it says:

USOC RJ45 standard is not as widely used, but is an acceptable standard for 
wiring ethernet.

If you used this, send and receive conductors would not be paired as they 
should