[Tfug] Yet another poser

[johngalt1]

----- Original Message ----- 
From: "George Cohn" <>
To: "Tucson Free Unix Group" <>
Sent: Thursday, September 20, 2007 6:12 PM
Subject: Re: [Tfug] Yet another poser


> jblais wrote:
>>> I wonder if gigabit is just using double pairs in order to increase
>> current/reliability, or if it is splitting the signal somehow?  Kind of 
>> like
>> having 2 serial loops in parallel?  Could this kind of wire could mess up 
>> a
>> POE device?
>>
>
> Yes, gigabit does use all four pairs as sort of a double serial 
> connection.
>
> However, note that POE can also be sent over the data pairs per the
> Cisco link that I previously posted.
>
> So gigabit CAN be POE as well.

Except that if you used a gigabit crossover cable, would the power 
conductors would be reverse polarity?



>
> This is really old technology.  For years, analog telephony has been
> multiplexing power as well as analog audio on the same two pairs.
>
> It gets even worse.  Normally, telephony puts about 48 volts DC on the
> pair to power the phone, something like 40 ma maximum.  However, when
> someone calls you, they superimpose a 20 Hz 90-105 volt A/C signal on
> the same pair to ring the bell.
>
> George Cohn
>
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