Please explain PoE to me (getting an AP)

[EngChi]

Could you please confirm/explain PoE to me - is this purely a convenience in situations when running power to the AP location is possible or there are some advantages to using this? Any speed limitations if I just connect it to power?

This is how I believe my network will look like

Cable -->
Mikrotik RB750GR3 (hex 3) as router -> TDB switch -> wiring in each room two runs for AP
ATT -->

Can I just use normal dumb switch in that role without PoE capability and
either
connect AP (unifi AC Pro) to both network and power
or
connect AP to network by installing a small PoE switch downstream of the main one.
?



Why am I asking this
- PoE capable switches seem to draw a lot of power and would be always on in the basement . I want 24 + ports of switching but only planning to have 2 APs max.
- I would love to run 'main' switch dump and only use PoE/increased power requirements where needed downstream of it. I would also love ability to 'turn off' the ports or shut down the devices automatically at schedule (with two very small kids right now, when we are asleep, there is no need for wifi in the house for APs to run and/or draw power). What would give me that capability? I see people trying running scripts on their Mikrotik devices

Please let me know if you have any questions

 

[netwrks]

Could you please confirm/explain PoE to me - is this purely a convenience in situations when running power to the AP location is possible or there are some advantages to using this? Any speed limitations if I just connect it to power?

This is how I believe my network will look like

Cable -->
Mikrotik RB750GR3 (hex 3) as router -> TDB switch -> wiring in each room two runs for AP
ATT -->

Can I just use normal dumb switch in that role without PoE capability and
either
connect AP (unifi AC Pro) to both network and power
or
connect AP to network by installing a small PoE switch downstream of the main one.
?



Why am I asking this
- PoE capable switches seem to draw a lot of power and would be always on in the basement . I want 24 + ports of switching but only planning to have 2 APs max.
- I would love to run 'main' switch dump and only use PoE/increased power requirements where needed downstream of it. I would also love ability to 'turn off' the ports or shut down the devices automatically at schedule (with two very small kids right now, when we are asleep, there is no need for wifi in the house for APs to run and/or draw power). What would give me that capability? I see people trying running scripts on their Mikrotik devices

Please let me know if you have any questions

Unifi ACP Pro's come with PoE adapters, (mine did - purchased in individual packages) which power the WAP's. So, no need for a PoE switch.

 

[CaptainSTX]

Could you please confirm/explain PoE to me - is this purely a convenience in situations when running power to the AP location is possible or there are some advantages to using this? Any speed limitations if I just connect it to power?

This is how I believe my network will look like

Cable -->
Mikrotik RB750GR3 (hex 3) as router -> TDB switch -> wiring in each room two runs for AP
ATT -->

Can I just use normal dumb switch in that role without PoE capability and
either
connect AP (unifi AC Pro) to both network and power
or
connect AP to network by installing a small PoE switch downstream of the main one.
?



Why am I asking this
- PoE capable switches seem to draw a lot of power and would be always on in the basement . I want 24 + ports of switching but only planning to have 2 APs max.
- I would love to run 'main' switch dump and only use PoE/increased power requirements where needed downstream of it. I would also love ability to 'turn off' the ports or shut down the devices automatically at schedule (with two very small kids right now, when we are asleep, there is no need for wifi in the house for APs to run and/or draw power). What would give me that capability? I see people trying running scripts on their Mikrotik devices

Please let me know if you have any questions

For just two locations think about buying a couple of POE injector pairs.. I bought a set from WiFi-Texas.com for less than $8.00 and use it to power an eight port switch located an inconvenient location for AC. It supports a full Gig of bandwidth on the link. Many inexpensive POE injectors will only support fast Ethernet 10 Mbps links. Voltage drop is an issue you have to worry about.. The 24 gauge conductors in an Cat 5e Ethernet limit your distance. Solid copper conductors and Cat6 cable which is 23 gauge will give you more range.

 

[netwrks]

For just two locations think about buying a couple of POE injector pairs.. I bought a set from WiFi-Texas.com for less than $8.00 and use it to power an eight port switch located an inconvenient location for AC. It supports a full Gig of bandwidth on the link. Many inexpensive POE injectors will only support fast Ethernet 10 Mbps links. Voltage drop is an issue you have to worry about.. The 24 gauge conductors in an Cat 5e Ethernet limit your distance. Solid copper conductors and Cat6 cable which is 23 gauge will give you more range.

As mentioned above, a PoE adpater (injector) comes with each Unifi AC Pro, if purchased as a (indivdual) separate unit. The Unifi PoE adpaters support up to 1000Mbps.

 

[System Error Message]

with POE you have to look at the protocol used and compatibility. The TDP of the switch isnt how much power it uses, its the maximum it can use. A 24 port switch can uses between 5-30W for itself so anymore watts will be available to send for POE. Essentially its just both a network device and a PSU providing DC voltage.

For a POE switch i suggest you get at least semi managed so you can see and configure the POE. active POE (or POE that follows the 802 standard) is capable of 1Gb/s networking while having POE on the same line while passive POE is a lot more limiting and will only operate at 100Mb/s.

 

[EngChi]

Thank you. what determines whether PoE is 'active' or 'passive' - actual AP, switch, both (both have to be supporting specific format)?
Cant I simply give normal power to access point (through injector or whatever) wthout messing with PoE switch support? The ceiling where AP will go to already have power installed for the track lighting.

Thank you

 

[System Error Message]

If you look at the tip of the ethernet cable you should see 8 contacts, each contact connects a pair of cables. If an ethernet cable only has 4 out of contacts than it is only capable of 100Mb/s and no POE.

The other thing with active POE is that it can negotiate what voltage to use. passive POE however will give the voltage that it gets from the source. a passive POE injector/switch will give the voltage it gets from its PSU so if it has a 12V PSU than you will only get 12V on POE out but on active POE any voltage can come out within a certain range specified by the POE out device specs and the protocol. This means if the switch has a 12V PSU and POE out with a voltage range of 6-12V than an AP connected that uses 9V can negotiate and get 9V from the switch whereas if it was passive than regardless of what specs the AP has it will get 12V regardless and could end up destroyed.

Its possible for passive POE to have gigabit ethernet but it is very rare. active POE however can negotiate both power and data (more to do with how they use the cabling pairs differently). You will need to look this up.

POE devices however do have a voltage operating range (a lot of non consumer routers do have a range too). For example the mikrotik CCR1036 has no POE in/out but can operate between 12V-30V from the PSU. with POE devices its the same thing, they will be capable of working within a range of voltages. With active POE the device can negotiate the voltage to adjust for the voltage loss on the ethernet cable. You wont see an ASUS router capable of working within a voltage range, only 1 voltage with very little tolerance in the voltage change so if the voltage increased/decreased by 1V for instance it could cause the router to hang. Its the same thing with PCs and ATX standards. If a PSU supplies power out of standards it could cause lockups or even destroy the PC. I cant remember the exact standards but i believe the 12V rail on ATX isnt allowed to fluctuate more than 0.5V or maybe 1V, If you fed your GPU 13V or 11V you could damage it. Non consumer routers or devices that have voltage ranges usually have a circuitry that adjusts the input voltage that will only be capable of changing the voltage from a range (read more about voltage regulators).

PCs have voltage regulators too (the 12V into the CPU is change to 1V for CPU itself and some of the other parts). Since PC components run at very high frequencies compared to networking hardware they are very sensitive and allow little variation in the fluctuations of DC voltage input that they need to be as DC like as possible (voltages are never perfectly straight, theres always ripple, sagging and fluctuations). This is something you can only see with an oscilloscope and not a multimeter which is why professional PSU reviews have oscilloscope graphs to show how DC or not DC like the voltage is. It will never be a perfect line. Think of active POE as a way of making the voltage as straight as possible and making sure the voltage that reaches the device is the one needed so it can be adjusted to account for losses over cabling. If you lose 1V over ethernet the device can say its receiving 11V so the switch will give 13V so that the device can get 12V.