Hi MikroTik-Forum!
I’ve just bought a CRS112-8P-4S-IN to switch, route and power my home network/ components.
Unfortunately the CRS seems to be not able to power my IP based doorbell/ cam (Doorbird D202), which needs PoE 802.3af Mode-A (Specs: http://www.doorbird.com/poe.
Powering the device via different ports, cables and PoE configs: auto detect, force on, and so on don’t work. I also tried a separate 48V PSU instead and parallel with the 28V PSU shipped with the CRS. The Power-Indicating LEDs work 28+48V, the GUI shows the different voltages - but it seems that no current is consumed - just 2mA in 48V / high voltage mode.
The doorbird works well with my UniFi Switch 8-60W (I want to replace) as well as with a Netgear GS118TP-200EUS ProSafe.
Is it possible that the CRS112 or other MikroTik CRS and Doorbird D202 are incompatible although both support PoE 802.3af ? Is it the “Mode-A” 4-wire thing?
I won’t use a separate PoE Injector as a workaround, because I’ve just bought the CRS with PoE therefore…
Any help appreciated.
I cant’t find the concrete power consumption in the data sheets. UniFi Switch shows just 3W PoE consumption when the doorbird is connected and Running.
However in this case it seems that Doorbird is not fully compatible with the standard, because:
PDs that implement only Mode A or Mode B are specifically not allowed by this IEEE 802.3at-2009 standard.
The PD shall be implemented to be insensitive to the polarity of the power supply and shall be able to
operate per the PD Mode A column and the PD Mode B column in Table 33–13.
MikroTik PSE would still allow you to use a crossover cable, but in this case it would only allow to pass DC current (not data)
Thank you PaulsMT for your fast reply!
So it seems, that the competitor switches just have a more good-natured or mor fault-tolerant PoE behaviour why the Doorbird works with them.
If I’ve got you right, with the CRS and a standard crossover cable or crossowver adapter, only powering the device via the ethernetcable is possible - data can’t be suppied via the same cable and has to go via WLAN for instance?
Can I maybe build a customized plug/ strand layout to get both (data and PoE) work via one ethernet cable?
IMHO it’s unlikely you could construct a customized cable to overcome ModeA/ModeB mismatch. In modeA (obviously supported by your doorbell device) both data and power use same wires. Unless you use some smart power injector (which, according to your initial post, you don’t want to use), you can’t simply get data to two pairs of wires and DC to other two pairs.
This kind of hokus-pokus can be done in ModeB (using pins 4,5,7,8 for power) because for 100BaseTX, only pins 1,2,3 and 5 are used for data, thus you can get 100Mbps ethernet to one plug and PoE to another plug.
Probably you could get your doorbell gadget working with other vendor’s PoE switches because those support either both variants or only ModeA, while MT seems to support only ModeB.
Both standards have their pros and cons and affect only non-standard PD which support only one of these modes.
If PSE supports only mode B (non-standard mode-A PD will not receive power)
If PSE supports only mode A (non-standard mode-B PD will not receive power)
In the same way, by using another vendor mode-A PSE, there could be the same questions why mode-B PD does not power up.
Our suggestion to avoid such problems would be no matter which PSE would you use, make sure that PD is af/at standard compatible device.
