Power Over Ethernet

[nobrainerdeals]

anyone have any experience with these things and like to share?
i'd just like to know how well they work and the pros and cons of it.

 

[phisrow]

It is a very convenient method of dealing with large scale WAP deployments, running DC over the CAT5 is easier, cheaper, and less often in violation of building codes than putting AC in the ceiling. That's pretty much it, though. The limits on power are low enough that essentially no computers or switches of any decent size can run off the stuff, and it isn't vastly more efficient to any degree worth bothering about. A good POE injecting switch in the right place can save you a lot of headaches; but that is all there is to see(that I've seen, at any rate).

 

[nweaver]

works great...I have multiple cisco AP's running on POE, then I don't have to run a power cord into my hoffman boxes.

 

[spidey07]

pros - powers devices.

cons - ?

Works great for me. You'll see more and more devices use it.

 

[Joemonkey]

Originally posted by: nweaver
works great...I have multiple cisco AP's running on POE, then I don't have to run a power cord into my hoffman boxes.

same here, works like a charm

 

[nobrainerdeals]

ok, my bad, asking the pro's and con's was kinda stupid question. but i'm trying to find out if there are any con's i guess. Like has anyone had interference on their ethernet line from it? does it slow it down? from my understanding, you get power and ethernet on the same CAT5, right? are power spikes a problem?

btw, thanks everyone for your replies

 

[spidey07]

No cons that I know of.

 

[JackMDS]

Well, unlike regular Network traffic that is based on +V or ?V that is a logic state.

The Voltage through the POE is live capable Voltage. I.e. it is much less tolerant to shorts and bad connections.

That means that while dealing with the cables for maintenance and installation there is New factor that has to be taken in consideration.

:sun:

 

[spidey07]

Originally posted by: JackMDS
Well, unlike regular Network traffic that is based on +V or ?V that is a logic state.

The Voltage through the POE is live capable Voltage. I.e. it is much less tolerant to shorts and bad connections.

That means that while dealing with the cables for maintenance and installation there is New factor that has to be taken in consideration.

:sun:

I take it Mr. Jack has never licked a cable pair and received RING current?
😀

 

[JackMDS]

Originally posted by: spidey07

I take it Mr. Jack has never licked a cable pair and received RING current?
😀

When Mr. Jack (was still Mr. 😉 ) he used to fix very Old Control Tower?s Communication Transmitters. He needed one time to measure the Voltage of a 2KW Air force transmitter. This Transmitter has a Vacuum Tubes 20? tall with 1200V.D.C at the Anode.:Q :light:

Well, it happens to be that the lead of the Voltmeter was slightly cracked, as a result 1200V.D.C closed between his right hand and the right knee (Mr. Jack was kneeling at the time near the Transmitter?s Case). If it were closing between the hand and the left knee, he probably would not post here.🙁

In any case, the 5V can do damage to the Network through rouge short wires and not to the Tech person.

:sun:

P.S. If you want to experience high voltage, this is for you.

The tool in the following link (Megger) can deliver 1000V to test coax cables. While the voltage is very high, the Current capacity is extremely low so it is not dangerous to an healthy user. It is a good simulation, for a brief second, to what it means to be shocked by high voltage.:shocked:

http://www.omnicontrols.biz/products.asp?recnumber=786

 

[spidey07]

Everybody's been hit somehow.

Glad the ticker is OK. That's a pretty big tube you are talking about.

Luckily I've been zapped by normal voltage, but low current - home AC, cars, etc. Pretty weird to have your entire body just lock up.

But swap stories with electricians working in industrial settings - man they have stories. They all have stories of some dude literally smoking. Not the cigarette, the body.

 

[cmetz]

As part of their training, many electricians I know have been asked (goaded, dared, I don't know) to touch live 110V and 220V, presumably with their right hand, to see what it feels like and to learn how to deal with that situation. Touching high voltage is survivable, as long as it doesn't arc the wrong way through your body and you have good training as to how to deal with that situation.

nobrainerdeals, there are two things to watch out for with PoE: (1) Cisco has a pre-standard PoE that is not really compatible with the 802.11af standard, and so you have to watch that all the equipment you are using is compatible with the standard (or both are Cisco pre-standard) and (2) you need to make sure all your cable guys understand that network cables and jacks carry DC current, so don't be quite so cavalier with them.

802.11af has some reasonably good safety measures in it, assuming all vendors implement these it provides a reasonable bit of protection against accidents. The Cisco pre-standard does not.

 

[p0lar]

I think you need to be aware of both types of PoE.

There's one that is inline with the ethernet signal and can operate on two pair, and the other that is OOB that rides on the two unused ports. There are some unique requirements for both.

One con is that your power requirements will be concatenated at the switch.. IOW, if the circuit your switch is on is already loaded and you throw what seems like a low-requirement switch on and it pops a breaker or doesn't have the battery backup to last, that's not a good thing.

I've worked in several companies with every phone powered through the wire, it was great! The requirements of a large deployment (200+ phones) was high at the switch (which consequently also routed the production network traffic (ack!!). I think it had 2x4k Watt power supplies. The good part is that, even on a power outage, the devices still work fine as long as the switch is on alternate power.

Be wary of EVERY vendor who claims their device will interoperate correctly on PoE, however. They very well may, but not at full ethernet specifications. We had a few high-end phones from a vendor that claimed perfect PoE interoperability with Cisco. Their lower phones worked great -- that model required alternate power past a specific cable length. No amount of adjustment on the switch helped, though we could get a few extra meters by limiting the number of patches (but that wasn't going to fly either. 🙂)