PoE (output)
The PoE output(s) standard used by the router.
By itself, PoE (Power over Ethernet) technology allows you to transfer not only data over an Ethernet network cable, but also energy to power network devices. And
the presence of a PoE output (outputs) makes it possible to power such devices from the network connectors of the device. This eliminates the need to lay additional wires or use independent power sources, which is especially important for some equipment, such as external IP surveillance cameras. And when using the so-called splitters - devices that divide the PoE cable signal into purely network data and power power - using such outputs, you can also power equipment that does not initially support PoE (the main thing is that their power characteristics correspond to the capabilities of the switch).
As for PoE standards, they determine not just the overall power supply, but also compatibility with specific devices: the consumer must support the same standard as the router, otherwise normal operation will be impossible. Nowadays, including in the connectors of "switches", you can find two types of such standards - active (802.3af, 802.3at, 802.3bt) and passive (one, that's what it's called). The main difference between these varieties is that active PoE provides for matching the power source and load in terms of voltage and power, while passive PoE does not have such functions, and energy is supplied “as is”, witho
...ut adjustments. And here is a more detailed description of specific standards:
— 802.3af. The oldest active PoE power format in use today. It provides power at the power output up to 15 W (at the input of the consumer - up to 13 W), output voltage 44 - 57 V (at the input - 37 - 57 V) and power in a pair of supply wires up to 350 mA. Despite the "venerable age", it still continues to be widely used; so there are still quite a lot of routers that work only with 802.3af on sale (as of the end of 2021). However, it is worth considering that this standard immediately covers 4 so-called power classes (from 0 to 3), which differ in the maximum number of watts at the output and input. So when using 802.3af, it doesn't hurt to make sure that the output power will be sufficient for the selected load.
— 802.3af/at. A combination of two standards at once - the 802.3af described above and the newer 802.3at. The latter allows you to supply power up to 30 W (up to 25.5 W at the input of the powered device), uses a voltage of 50 - 57 V (42.5 - 57 V at the input), while the power in a pair of wires does not exceed 600 mA. Such a combination is relatively inexpensive, while it makes it possible to power a wide variety of external devices; so at the end of 2021, it is this type of PoE outputs that is most popular in routers.
— 802.3af/at, bt. Combination of 802.3af/at above with 802.3bt (PoE++, PoE type 3 or type 4). 802.3bt is the newest PoE power format; unlike earlier ones, it uses not 2, but 4 power wires, which allows you to supply very solid power to external devices - up to 71 V (at 90 W at the power output). Such capabilities are indispensable when supplying power to equipment with increased consumption - for example, external surveillance cameras, supplemented by heating systems. On the other hand, support for the 802.3bt standard significantly affects the cost of the device, and such a connection puts forward special requirements for the quality of cables. In addition, you need to keep in mind that this standard also includes the UPoE format created by Cisco and used in its equipment; and this standard (it is known as PoE type 3) has a more modest power - up to 60 W at the output (up to 51 W at the consumer's input). Yes, and the general standard 802.3bt includes two power classes - class 8, at which maximum performance is achieved, and class 7, where 75 watts are supplied to the output, and about 62 watts reach the consumer. So if you plan to use 802.3bt equipment, when choosing a router from this category, you must make sure that the power supply is enough for the connected devices to work properly.
— Passive. As already mentioned, the key difference between passive PoE and the active standards described above is that in this case the power output produces a strictly fixed power, without any automatic adjustments and adjustments for a specific device. The main advantage of this standard is its low cost: its implementation is much cheaper than active PoE, so such ports can be found even in entry-level routers. On the other hand, the aforementioned lack of auto-tuning makes it much more difficult to coordinate the equipment with each other - especially in light of the fact that different devices can differ markedly in the output / consumption of voltage and power (power). Because of this, when using passive PoE, you need to pay special attention to the compatibility of the source and load in these parameters. If there is no match, then in the best case (if the output voltage / power is lower than required), the power simply will not work, and in the worst case (with excess voltage / power), there is a high probability of overloads, overheating, and even breakdowns with fires - and such troubles may not occur immediately, but after a fairly long time. And it is definitely impossible to connect devices with active inputs to passive PoE outputs - for the same reasons.
In conclusion, it should be said that if the router has both an input with PoE support and several outputs with this function, then all the possibilities of such outputs, as a rule, can only be realized when the switch itself is powered from the outlet, and not from the PoE input. See "PoE Outputs" for details.PoE outputs
The number of PoE-enabled outputs (see above) provided in the design of the router.
In theory, this number corresponds to the maximum number of network devices that can be powered via PoE. However, in practice, two more points should be taken into account. The first and foremost is the total power delivered by such ports; most often it is indicated in the item "Total PoE power", and for models with one output - in the item "Power per PoE output". In any case, if the power consumption of the connected equipment is higher than this value, at best, the power from the switch simply “does not start”, and at worst, overloads and equipment breakdowns are possible.
The second nuance concerns routers, which themselves can be powered using Power over Ethernet. Recall that the power of such a power supply is very limited, so when it is used, most of the power usually goes to the operation of the switch itself, and there is little (if any) left to supply the PoE outputs. So when a device is powered via PoE, its own PoE outputs, at best, greatly “sag” in terms of capabilities (maximum power decreases, the number of simultaneously powered devices decreases), and at worst, they completely turn into ordinary network ports, without additional power. So if you plan to fully use the PoE outputs, you should take care to connect the switch itself to the network; this is especially true for models where there is more than one such output.
