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Some Guy
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PoE seems DOA - how does it scale to kW?
Some Guy   1/22/2014 1:18:03 PM
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The thing I could never figure out about Power of Ethernet is how does it scale beyond 1 device. Over a 26 AWG wire in Cat6 cable I can power a device at 50W, but how do I power a whole building worth of devices to scale it to the killoWatts that an office building consumes? If I'm running 120 or 208 out to a bunch of distributed power supplies at every cubical or in parallel with every Ethernet cable ... I just don't see how it pencil's out.

Can someone help us with how you get around the conclusion that PoE may be great for 1 device, but brain-dead for a whole building's worth?

asic_pal
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Re: PoE seems DOA - how does it scale to kW?
asic_pal   1/22/2014 1:44:18 PM
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I think PoE will be a point to point connection from the Hub to Endpoint. Hub will distribute power over Ethernet Cable to the Endpoints and the Hub may be powered by the PGE Power Port. If the Endpoints ar not power hungry, I believe Hub can also be powered by Ethernet Cable like USB.

It's my assumptions, I need to read the spec though :)

 

Some Guy
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Re: PoE seems DOA - how does it scale to kW?
Some Guy   1/22/2014 2:03:54 PM
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From the energy research that I've done, the nominal you need at a minimally configured "guest" workstation is 106W for a monitor, phone (PBX-connected), cell phone charger and laptop charger. (163 if you want lights included.) You can get 100W from a USB 3.0 cable and 15-25W from PoE.

If I have to power the Ethernet hub at that workstation from AC mains to get PoE to all those devices, where does PoE help? If I have to power EVERY cubicle with AC mains to run a hub, how does that scale? That's not enough to power a single hub by USB 3.0. And if I'm going to use USB 3.0 why wouldn't I just use it for everything instead of PoE?

Bert22306
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Re: PoE seems DOA - how does it scale to kW?
Bert22306   1/22/2014 5:07:12 PM
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No magic here, Some Guy. PoE is something that only applies from one layer 2 switch port to the host attached at the other end of the cable. It's not like you're running power between switches and routers, over the network.

So, the only concern here would be how much aggregate power a single edge Ethernet switch can deliver, to its attached hosts. That's all.

If you have a building full of equipment, presumably you have more than just one edge Ethernet switch connecting to these end systems.

Some Guy
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Re: PoE seems DOA - how does it scale to kW?
Some Guy   1/22/2014 5:13:08 PM
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So then the main utility is when you are running a point to point connection to a single sensor / device directly connected to a hub that takes < 25W. OK that works.

So all the talk about powering your PC, or a workstation, or a whole building is just not practical, right? You aren't going to tap into a Cat 5/6 cable run and pull power at every drop. Got it.

Bert22306
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Re: PoE seems DOA - how does it scale to kW?
Bert22306   1/22/2014 5:17:10 PM
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Yeah, you got it. There's no big deal here. From the beginning of time, well, almost, some telephone instruments got all they needed from ma bell, and others ALSO had to be plugged into your AC mains. The automakers simply want to expand their options in PoE, to save on copper cabling.

David Ashton
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Re: PoE seems DOA - how does it scale to kW?
David Ashton   1/22/2014 5:43:59 PM
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We use POE a lot where I work.  We just put Voip phones on and the phone gets network - and power - from the wall socket and passes the network on to the PC on the same desk.   We have personal video conference units that also work with POE but so far no PCs, not even Laptops.  I can see laptops going POE if they can get the power requirements down a bit - maybe non-hard disk types that work with the cloud, like Chromebooks?  I've just been putting in a heap of wireless access points and those also work on POE - you just run a cat 6 cable to where you want them and they get power and network from it.  It's also great for sensors, security cameras, etc.

I think one advantage is that you have one beefy power supply in the ethernet switch rather than lots of little ones for the individual devices.    Better efficiency..  But then there's a fair bit of loss in the cables as well, so it's a case of "swings and roundabouts" I suppose....  I think POE works at up to 100V, so not huge currents...but ethernet cables weren't intended for power.

zewde yeraswork
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Re: PoE seems DOA - how does it scale to kW?
zewde yeraswork   1/23/2014 3:45:34 PM
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Interesting--does anuyone else see laptops going PoE?

Bert22306
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Re: PoE seems DOA - how does it scale to kW?
Bert22306   1/22/2014 5:13:42 PM
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The original purpose of PoE was to allow VoIP phone instruments to get all the power they need from the Ethernet Cat-5e cable. Rather than having to connect a separate power cable. So this is just an update, to provide more power over the Ethernet cable.

The initial iteration was really simple. It used spare conductors in the 4 twisted pair Cat-5e to carry power. This is when Ethernet only needed two of the pairs. But then starting with 1000BASE-T, where all 4 pairs are needed for data, they had to get a little more clever. So basically power becomes the DC component on those twisted pairs.

Tunrayo
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Re: PoE seems DOA - how does it scale to kW?
Tunrayo   1/24/2014 11:22:13 AM
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@Bert. Are these PoE ports compatible with NIC cards on PCs and Laptops? Could a PoE currently in use for VoIP be re-configured as a data connection?

Bert22306
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Re: PoE seems DOA - how does it scale to kW?
Bert22306   1/24/2014 3:01:06 PM
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Tunrayo, yes, in the sense that if a switch port provides PoE, it won't harm a host that doesn't use PoE.

In the case of 100BASE-TX, the power is sent over the fiur unused conductors of the Cat-5e or Cat-6 cable. In faster copper Ethernets, it is a DC component that the NIC would ignore.

Bert22306
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Re: PoE seems DOA - how does it scale to kW?
Bert22306   1/24/2014 3:06:19 PM
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Oh, on the second question, in principle those 4 conductors dedicated to power in 100BASE-TX could have been used as a second Ethernet, yes. I mean, instead of providing power. But then when 1000BASE-T came along, there were no spare conductors. All eight copper wires are used for the one GigE link already. So as of now, 10/100/1000BASE-T cards have to be set up by default the same way.

David Ashton
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Re: PoE seems DOA - how does it scale to kW?
David Ashton   1/24/2014 4:44:37 PM
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On the question of the two unused pairs for 100Base-T,  I have made - and you can buy - splitters that do exactly that - send two different ethernet signals down one cable.  Handy when you have a PC and a printer in the same room and not enough cables.  But as we move to Gig Ethernet I won't be able to use these tricks.

Bert22306
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Re: PoE seems DOA - how does it scale to kW?
Bert22306   1/24/2014 4:53:24 PM
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Hey David. I don't mean to pry, but ... did you need a soldering iron? Or just a crimp tool? :)

David Ashton
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Re: PoE seems DOA - how does it scale to kW?
David Ashton   1/24/2014 6:24:41 PM
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Hi Bert...I'm never gonna hear the end of this now, am I??   :-))

The ones I have made I've just chopped off 6 inches of a cable, and used 2 Panduit IDC sockets.  So a pair of wire cutters and a pair of water pump pliers for the IDC sockets.  Not a soldering iron in sight!!

I must admit, it's easier to just buy them, but being able to make them has got me out of trouble a few times...

Kinnar
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CEO
Very Late Start
Kinnar   1/22/2014 1:18:28 PM
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It is a very late initiative for promoting PoE, security cameras and authentication devices in the offices, industries and domestic environment are very much cluttered with network and power connections, at-least use of PoE will eliminate the power adapters and in turn the power supplies wiring. PoE is noting new but it is not promoted up-to extent it was required.

chanj0
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In Vehicle Application
chanj0   1/22/2014 1:44:55 PM
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I can certainly see the benefit of having 1 cable running between host (Internet Gateway) and a device (e.g. an Infotainment device). However, given the space of a vehicle, I am not sure the finanical and production benefit. Another question needs to address is the energy loss. It is too soon to say there is any benefit of improving the power rating but it is definitely worth following.

Arshe100
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