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An example of a device that uses PoE *and* runs at gigabits speed?

 
 
Ramon F Herrera
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      07-25-2008

A collegue of mine insists that it is impossible for a port to have
gigabit speed while simultaneously using 802.3af PoE.

Can anyone please confirm or deny?

There's a round of beers running on this one.

-RFH



 
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Trendkill
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      07-25-2008
On Jul 24, 10:05*pm, "Brian V" <(E-Mail Removed)> wrote:
> "Ramon F Herrera" <(E-Mail Removed)> wrote in messagenews:(E-Mail Removed)...
>
>
>
> > A collegue of mine insists that it is impossible for a port to have
> > gigabit speed while simultaneously using 802.3af PoE.

>
> > Can anyone please confirm or deny?

>
> > There's a round of beers running on this one.

>
> > -RFH

>
> Your collegue would be wrong. Done all the time and has been out for a
> couple years now. In the Cisco world the 7941G-GE and 7971G-GE phones are
> gigabit, both of them use PoE. Pretty much all switches from the 3560 on up
> offer a version of Gig PoE, ie 3560G-24PS, 3750G-24PS, etc.


I think he is saying that the port will then not push gig throughput,
not that PoE doesn't run on gig ports or something. Can anyone with
an IP phone run a ftp test to a local server and see the throughput
they get?
 
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whit3rd
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      07-25-2008
On Jul 25, 7:49*am, "Brian V" <(E-Mail Removed)> wrote:
> I believe he is refering to how in one mode of PoE it uses the "unused
> pairs" but in Gigabit there are no unused pairs so how could it work.


The third-pair differential signal and the fourth-pair differential
signal
are used by GigEthernet. Power is fed to the transformer center
tap, so is a common-mode DC level on the third-pair, and a different
common-mode DC level on the fourth pair, and the power adds
nothing to the differential signal, so does not interfere.

The Ethernet standard allows up to (?) 500V of DC on the twisted
pair wiring, I seem to recall.

Look up 'phantom power'; this was a trick of similar sort played
with microphone preamplifiers, going back to vacuum tube days.
 
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Sam Wilson
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      07-25-2008
In article <ugnik.274054$(E-Mail Removed)1.easynews.com>,
"Joel Koltner" <(E-Mail Removed)> wrote:

> "whit3rd" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> "Look up 'phantom power'; this was a trick of similar sort played
> wth microphone preamplifiers, going back to vacuum tube days."
>
> Phantom power is still very much alive and well in professional audio circles.


And amateur!

Sam
 
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Martin Griffith
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      07-25-2008
On Fri, 25 Jul 2008 17:52:09 +0100, in sci.electronics.design Sam
Wilson <(E-Mail Removed)> wrote:

>In article <ugnik.274054$(E-Mail Removed)1.easynews.com>,
> "Joel Koltner" <(E-Mail Removed)> wrote:
>
>> "whit3rd" <(E-Mail Removed)> wrote in message
>> news:(E-Mail Removed)...
>> "Look up 'phantom power'; this was a trick of similar sort played
>> wth microphone preamplifiers, going back to vacuum tube days."
>>
>> Phantom power is still very much alive and well in professional audio circles.

>
>And amateur!
>
>Sam

In what way?


martin
 
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JosephKK
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Posts: n/a
 
      07-28-2008
On Fri, 25 Jul 2008 07:49:50 -0400, "Brian V" <(E-Mail Removed)>
wrote:

>
>"Trendkill" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed)...
>On Jul 24, 10:05 pm, "Brian V" <(E-Mail Removed)> wrote:
>> "Ramon F Herrera" <(E-Mail Removed)> wrote in
>> messagenews:(E-Mail Removed)...
>>
>>
>>
>> > A collegue of mine insists that it is impossible for a port to have
>> > gigabit speed while simultaneously using 802.3af PoE.

>>
>> > Can anyone please confirm or deny?

>>
>> > There's a round of beers running on this one.

>>
>> > -RFH

>>
>> Your collegue would be wrong. Done all the time and has been out for a
>> couple years now. In the Cisco world the 7941G-GE and 7971G-GE phones are
>> gigabit, both of them use PoE. Pretty much all switches from the 3560 on
>> up
>> offer a version of Gig PoE, ie 3560G-24PS, 3750G-24PS, etc.

>
>>I think he is saying that the port will then not push gig throughput,
>>not that PoE doesn't run on gig ports or something. Can anyone with
>>an IP phone run a ftp test to a local server and see the throughput
>>they get?

>
>I believe he is refering to how in one mode of PoE it uses the "unused
>pairs" but in Gigabit there are no unused pairs so how could it work.


Take a look at the standards doofus.

 
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JosephKK
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Posts: n/a
 
      07-28-2008
On Fri, 25 Jul 2008 19:11:01 +0200, Martin Griffith
<(E-Mail Removed)> wrote:

>On Fri, 25 Jul 2008 17:52:09 +0100, in sci.electronics.design Sam
>Wilson <(E-Mail Removed)> wrote:
>
>>In article <ugnik.274054$(E-Mail Removed)1.easynews.com>,
>> "Joel Koltner" <(E-Mail Removed)> wrote:
>>
>>> "whit3rd" <(E-Mail Removed)> wrote in message
>>> news:(E-Mail Removed)...
>>> "Look up 'phantom power'; this was a trick of similar sort played
>>> wth microphone preamplifiers, going back to vacuum tube days."
>>>
>>> Phantom power is still very much alive and well in professional audio circles.

>>
>>And amateur!
>>
>>Sam

>In what way?
>
>
>martin


It is becoming common in a lot of audio equipment for performers at
all levels.

 
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Sam Wilson
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Posts: n/a
 
      07-28-2008
In article <(E-Mail Removed)>,
JosephKK <(E-Mail Removed)> wrote:

> On Fri, 25 Jul 2008 19:11:01 +0200, Martin Griffith
> <(E-Mail Removed)> wrote:
>
> >On Fri, 25 Jul 2008 17:52:09 +0100, in sci.electronics.design Sam
> >Wilson <(E-Mail Removed)> wrote:
> >
> >>In article <ugnik.274054$(E-Mail Removed)1.easynews.com>,
> >> "Joel Koltner" <(E-Mail Removed)> wrote:
> >>
> >>> "whit3rd" <(E-Mail Removed)> wrote in message
> >>> news:(E-Mail Removed)...
> >>> "Look up 'phantom power'; this was a trick of similar sort played
> >>> wth microphone preamplifiers, going back to vacuum tube days."
> >>>
> >>> Phantom power is still very much alive and well in professional audio
> >>> circles.
> >>
> >>And amateur!
> >>
> >>Sam

> >In what way?
> >
> >
> >martin

>
> It is becoming common in a lot of audio equipment for performers at
> all levels.


Condenser microphones (one of the two main types) require a power
source. They are either fitted with a battery (which needs to be
checked and renewed) or are phantom powered. Similarly DI boxes
(devices which match different signal levels and impedances) are often
powered and again it's convenient not to require a battery. I think
I've noticed other things being phantom powered recently but those are
the traditional things.

Sam
 
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Wim Lewis
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Posts: n/a
 
      07-31-2008
In article <(E-Mail Removed)>,
Brian V <(E-Mail Removed)> wrote:
>"Trendkill" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed)...
>>I think he is saying that the port will then not push gig throughput,
>>not that PoE doesn't run on gig ports or something. Can anyone with
>>an IP phone run a ftp test to a local server and see the throughput
>>they get?

>
>I believe he is refering to how in one mode of PoE it uses the "unused
>pairs" but in Gigabit there are no unused pairs so how could it work.


Ah, that makes perfect sense as the source of the OP's coworker's
disagreement: in one mode 802.3af uses the spare pairs, in the other mode
802.3af uses the data pairs (in common mode, with power being taken off
the center taps of the powered device's isolation transformer). The
"spare pairs" arrangement would also work for 1000baseT, as long as the
same sort of circuitry is used on those no-longer-spare pairs as on the
data pairs. But a midspan PoE injector probably won't do that unless
it's explicitly designed for GigE use, so the OP's coworker might
well have experience with GigE devices that don't work on PoE ports.


--
Wim Lewis <(E-Mail Removed)>, Seattle, WA, USA. PGP keyID 27F772C1
 
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