We've got a quick and to the point video for you today, and it's all about power.
Imagine you need to connect a few desk phones,
wireless access points and security cameras to your network.
They will require power, of course, but you don't necessarily
want to put a big power socket next to each device.
They take up a lot of space.
They can look a bit ugly and the cabling can get messy.
Fortunately, we have an alternative, which is power over Ethernet.
That is where we supply power over a regular network cable.
Any device that connects to our network that we can power
using power over Ethernet is called a powered device, or PD.
The generally smaller devices like this phone that only require
a few watts of power to start.
We simply connect the network cable
to the back of our phone, and we'll see that it starts booting up automatically .
No extra power needed.
Cisco originally introduced powered interfaces over 20 years ago.
It was called Cisco inline power, and it could deliver up
to seven watts of power per port.
The maximum port speed for this standard was 100 Meg.
This was a Cisco only technology,
so if you wanted it, you needed to have a Cisco switch.
It was a pretty good idea, though.
So since then, the IEEE has released
several PoE standards that any vendor can use.
The original PoE standard was 802.3af
which is now known as type one PoE
It uses two powered wires, and provides
15.4 watts of power per port.
Type one PoE is still used quite commonly, and is really good
for powering small appliances like desk phones and small wireless access points.
You probably know that we measure power in Watts.
Like any power solution, there is a little power loss as power runs over the cable.
It's no different with network cables.
So type one PoE supplies 15.4 watts at the port,
but only guarantees 12.95 watts at the powered device.
Just to explain this terminology a bit.
Any device that supplies power is called a PSE or power sourcing equipment.
Any device that consumes the power
is called a PD or power device.
There are some other devices that simply need more power in order to run.
These include things like a four in one security camera,
tablets, LCD screens and plenty
more. So, PoE+ was developed.
This supplies 30 watts of power per port.
But why stop there?
We now have two additional PoE++ standards called type three and type four.
And they can deliver 60 and 100 watts per port.
Cisco have their own versions
of these called UPoE and UPoE+
Most notably, these standards power up
to two pairs of wires in the network cable.
These higher powered standards are good for teleconferencing solutions.
Kiosk terminals, small switches, laptops and small TV screens.
Each of these standards is a power class
powered devices can change their power class over time if needed.
For example, a device may need only type one to power up. Later on,
It might need to turn on a screen, so it might signal a switch
that needs a change to type two, three or four.
The next question is, does it matter what kind of cabling we use?
Yeah, a bit.
It obviously has to be copper cabling.
You simply can't supply power over fiber.
Also, it should be no longer than 100 meters long,
and ideally it needs to be cat-5e or better.
But here's the really big question,
is PoE safe?
Well, it is a much smaller amount of power than you would have in your average
wall socket.
Also, it uses DC power, not AC,
which makes it much safer at small power levels.
Additionally, the IEEE Standard says that a PSE
will only supply power to a device that requests it.
So if you plug in a device that doesn't have a need for PoE, it won't get fried.
So, while it's relatively safe,
It is still power, so you still should use appropriate caution.
Don't go licking your network cables or anything like that,
although to be fair,
if you're the kind of person that licks power cables, you're probably in
the wrong industry.
OK, we have a few quiz questions, but they're pretty easy in this video,
I'm sure you're happy for a break.
We've been talking
about using switches as power sourcing equipment.
This is the nicer solution, but there are other options.
For example, this PoE injector.
This is a separate device that combines the network signal from the switch
with power from some other power source.
So if you have a switch that doesn't support PoE.
This might be a suitable alternative.
one common use of this PoE injector
would be to power an outdoor wireless access point,
which are often too far away from the switch for regular PoE to work.
Similar to an injector, you can also get a PoE splitter.
This is where you have something providing power,
but the device doesn't natively support being powered through PoE.
For example, a Raspberry Pi
It has a power source that's separate to the network interface,
so a PoE splitter will separate the power
from the data, allowing you to plug in both cables separately.
The advantage to this is that you don't need a wall socket
to power all your devices, even if they don't support PoE.
But please remember, there isn't a bottomless pit of power available to you.
Each switch has a power budget.
The power budget is the maximum amount
of power that it can supply with PoE, for example, one switch I've used in
past is a small twelve port switch and has a power budget of about 100 watts.
This means I could enable PoE on only six ports
or I could have power plus on up to three ports.
Or some
combination thereof that is less than 100 watts.
So keep this in mind when you're buying a new switch.
Generally, you can get the switch's datasheet like the one shown here
from the switch vendor, which gives you this information.
I think the interesting takeaway from this is how the power budget is calculated.
Let's say you have a desk phone connected to an interface.
You enable PoE on the interface,
which can supply up to 15.4 watts.
However, a simple desk phone
is unlikely to draw all 15 watts.
It may draw only five watts. When calculating your power budget.
Work with the amount of power that the interface can supply.
What I mean is assume that the phone will consume all 15.4 watts of power.
If you had that switch with a budget of 100 watts,
you wouldn't assume that you could run twenty phones at five watts each.
You need to assume that you can only have six
phones at 15.4 watts each.
This is because each connected device may start
drawing more power than you expect up to the limit of that port.
Also, when looking at data sheets, they may provide two values
the total power of the switch consumes and the PoE budget.
For example, a switch may consume up to 830 watts of power.
Remember, though, that it needs to consume some power itself just to turn on and run.
So while it may consume up to 830 watts of power,
720 watts, may be for PoE,
while 110 watts may be for the switch itself.
Some switches allow
you to add a second power supply, depending on the model
adding a second power supply will increase your total power budget.
So our 830 watt switch may then consume up
to 1550 watts of power,
still 110 watts for the switch itself,
but now 1440 watts of PoE budget
I hope that makes sense.
And here are the last two quiz questions.
I really hope
these quizzes have been helpful to you and you've been learning from them.
We've reached the end of our section on layer two technology and switching
in the next section, we're going to look at layer three and routing,
starting with a basic review on IP addresses and the routing table.
Please join me there.