[TriLUG] IP Network Camera/PoE
glenn.hennessee at gmail.com
Wed Jan 16 14:11:49 EST 2008
We have PoE wireless units at NCSU, Cisco brand, that are connected and
powered by Cisco Catalyst 3560 PoE 24 units so the power originates with
the router and goes directly to the wireless unit.
Joseph Mack NA3T wrote:
> On Wed, 16 Jan 2008, James Tuttle wrote:
>> I'm buying a wired network camera (that runs Linux!) and
>> want to buy a Power over Ethernet adapter, but am not sure
>> how the adapters work. I guess I'm not sure how the
>> camera gets power from the adapter.
> I haven't used PoE so I don't know all the details. Here's a
> first pass.
> All ethernet cables have 4 pairs of wires. Ethernet only
> uses 2 of these pairs (why people are selling 4-pair wires
> when they could sell cheaper, thinner and lighter 2-pair
> wires I have no idea). The other 2 pairs of wire are free to
> for whatever you want, provided that neither end gets a
> surprise when two random devices are connected. One
> convention is for one of the spare pairs to be used to
> supply power to low power devices at the other end.
> Presumably if you're applying power at one end, the voltage
> has to be agreed upon by the receiving end. Maybe there's an
> agreed upon voltage (I don't know).
> I'd assumed that the device at the receiving end would pick
> the power directly off the ethernet cable (I still think
> this is right). It looks as if the device pair in the URL
> splices into the ethernet cable, supplying power at one end
> which only appears on the outgoing cable. The receiving end
> picks off the power, which is made available via small power
> plug, and the ethernet is passed on, with no power on the
> ethernet cable. This setup is for remoted devices which
> aren't PoE ready.
> I expect what you want is power to be applied on the
> computer end - whether you need an external device to do
> this I don't know (do NICs/hubs/switches exist which apply
> power to ethernet cables?). Your camera being PoE ready will
> just pull the power directly off the ethernet cable.
Department of Chemistry
NC State University
Raleigh, NC 27606
Voice: (919) 515-2947 FAX: (919) 515-8909
Email: Glenn_Hennessee at ncsu.edu
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