POE networking, what's the range?

[Chuck Robey]

perryh at pluto.rain.com wrote:
>>> ... does anyone know the range of Power Over Ethernet? I want
>>> something to go from my house to my garage apartment then hook
>>> a wireless access point in to the POE box. The garage and the
>>> house are on their own power circuit but where the lines split
>>> is in between the house and the garage. I'm thinking it'll be
>>> around 600ft plus all the wiring in the house and garage.
>>>       
>
> The garage and the house are over 1/10 of a mile apart?
>
>   
>> If your garage has power, why not just plug the access point into
>> an outlet in the garage instead of pulling power all the way from
>> the house?
>>     
>
> There can be some significant safety issues in stringing copper
> between buildings, especially over significant distances and if
> the building grounds are not interbonded.  I'd encourage the O.P.
> to first consult a local electrical inspector, or an electrician
> who is familiar with the local conditions and safety codes.  Yes,
> I know this is not mains power, but hazards exist with signal
> wiring as well.
>
>   
I don't know the numbers either, but you should let him know the basic
facts of the Ethernet environment: it's not power limited, it's TIME
limited.
The signal power goes down at a relatively low rate over distance, but
the time
that the ethernet signal takes to transit, that's a key limiter.  You
see, Ethernet
is a protocol that relies on a bunch of time-relationships, both to
support stuff
like direct error control, but of most importance, in supporting the
detection of
collision occurrence (Ethernet allows signal collisions by being VERY
good at
detecting and handling such items).

The way you figure limitations on ethernet is, you get tables of how
fast your
signal propagates over the cable you've chosen, and see if your cable
allows your
signal to get that far in that much time.

It's the time that's key.  If (now that I've probably embarrassed some
of the walking
encyclopedias we have around here) you come up with the kind of cable
you have,
 we could very easily look into a table and tell you how much your setup
will allow
you.  If you don't get an answer by tomorrow, I think I could probably
find it here
somewhere, with enough of a lookup.  Don't bother the fellows with power
numbers,
that will only confuse the issue, believe me, power has nothing to do
with it.
> One alternative would be to track down a couple of fiber
> adapters, and string (non-conductive) fiber instead of copper.
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