Power over Ethernet (PoE)

This topic is to discuss the following lesson:

Guys, lessons is very cool (I didn’t knew about the most recent type3/type4 standards, so it was a very good lesson to keep myself updated).

But I guess there is an issue:

1.2. Midspan

The PoE midspan method uses PoE injectors […]. These are intelligent devices, and like a PoE switch, they detect whether the PD requires power and, if so, enables power.

There are (rackmount) midspans that can power many cables

[PHOTO]

Or small PoE injectors you can use to power a single device

[PHOTO]

Then there is this image here, a single-device Ubiquity PoE injector.

The problem is that most single-device Ubiquity PoE injectors are not intelligent PoE devices (at least it was true at the time when I worked with them). They just add power on the wire, and they could “burn” a non-PoE device connected by mistake.

The explanation may make people misunderstand that the device on the photo is intelligent, although it is not.

If this is true, maybe you should update the explanation accordingly. Something like:

The PoE midspan method uses PoE injectors […].

There are (rackmount) midspans that can power many cables

[PHOTO]

These are intelligent devices, and like a PoE switch, they detect whether the PD requires power and, if so, enables power.

Or small PoE injectors you can use to power a single device

[PHOTO]

Some small PoE injectors, like the one from the image above, are not intelligent devices and just add power on the wire without previously detecting whether the connected device requires power. If not, the device may be damaged.

Does it make sense?

Update: I saw that, at some point in the lesson, you state:

There is also something called Passive PoE. This is not based on any standard and basically, this is a PoE injector that adds power immediately without negotiation. Because power is always on, it’s possible to burn out devices that don’t support PoE.

So, the explanation about Passive PoE is there. So maybe a single-line change that you can do to make the lesson accurate is:

The PoE midspan method uses PoE injectors […]. These usually are intelligent devices, and like a PoE switch, they detect whether the PD requires power and, if so, enables power.

1 Like

Hello Rarylson

Thanks for the feedback! I’ll let Rene know to take a look and consider making changes for clarity.

Thanks again!

Laz

Hi @rarylson

Thanks for the suggestion. I made some changes and moved the text around to make it clear.

Rene

Hi
the lessons are awsome
in the real world which POE we use ? different scenarios ?

is there any list of POE switch

thank you

Hello Abdul

In the past, many IP cameras, IP Phones, wireless access points would come with their own passive PoE injector. This was primarily done because such a passive injector is cheaper and more readily deployable. However, in recent years, more and more network device vendors have been incorporating active PoE using the IEEE 802.1af and other related standards, so today you will find that most good quality network devices will support this.

It is best practice to use the IEEE standards with switches because you can provide uninterruptible power to a switch, and have that switch in turn provide uninterruptible power to all of the devices it powers. This is more difficult to achieve using passive PoE injectors.

Switch vendors, including Cisco sell switches that support the IEEE PoE standards. As far as Cisco is concerned, each line of switches comes with different models, and some models support PoE. When looking at the datasheet for the 9300 series switches, for example, you can see the list of models available and which ones are PoE capable.

Switches that support passive PoE are rare, and typically not used in high-end reliable networks.

I hope this has been helpful!

Laz