What is PoE? (Power over Ethernet)

by sogrow team

What is PoE? (Power over Ethernet)

Power over Ethernet (PoE) is a network function defined by the IEEE 802.3af and 802.3at standards. PoE enables networked devices to be powered over Ethernet cables over the existing data connection. PoE -enabled devices can be used as a power source (PSE = power supply equipment), as a powered device (PD = powered device), or sometimes both. The device that provides the power is a PSE, while the device that is powered is a PD (powered device). Most PSEs are network switches or PoE injectors designed for use with switches that do not have PoE. Some common PD (powered device) examples: VoIP phones, WLAN access points, and IP cameras.


What are the advantages of PoE?

  • Because PoE allows you to use a single cable for power and data transmission, you save the cost of purchasing and implementing cables for VoIP phones and network devices.
  • PoE makes it much easier to install or expand a network and also reduces costs in buildings where installing new power supplies would be too expensive or impractical.
  • You can use PoE to mount devices in places where installing a power supply would be cumbersome, such as in false ceilings.
  • Using PoE can reduce the number of cables and plugs needed in a room cluttered with equipment or a distribution cabinet.

What is PoE +?

The latest PoE update is the IEEE 802.3at standard, also known as PoE +. The main difference between the 802.3af (PoE) and 802.3at (PoE +) standards is that PoE + PSEs can provide double power over a single Ethernet cable.

PoE + PSEs can supply power to PoE and PoE + PD (powered device) devices, but PoE PSEs can only supply power to PoE PD (powered device) devices. PoE + PD (powered devices) requires more power than PoE PSEs can provide.


How much power can PoE devices deliver? 

PoE + devices can provide a maximum of 30 watts per port, while PoE devices can provide a maximum of 15.4 watts per port. However, the length of the cable always leads to a loss of performance the longer the cabling is. The minimum guaranteed power for PD (powered device) devices is 12.95 watts per port for PoE and 25.5 watts per port for PoE +.

PSE also has a maximum energy budget; H. the total power you can deliver to the PD (powered device) at any given time, measured in watts. Most PSEs do not have enough power budget to power all PoE-enabled ports with the maximum power possible, as most users will not need as much power. When purchasing a PoE-enabled PSE, be sure to calculate the required power budget for all PD (powered device) devices that you want to connect.


What do the PoE classes mean? 

A class of 0 to 4 is assigned to devices that operate via PoE and PoE + based on the amount of power required. When a PD device (powered device) is connected to a PSE, it delivers its class to the PSE so that it can provide the correct power to it. Class 1, 2 and 3 devices require very low, low or medium power. Class 4 (PoE +) devices require high power and are only compatible with PoE + PSEs.

Class 0 devices have not been classified correctly by the manufacturer. Therefore, most PSEs must assign the same power to Class 0 devices as to Class 3 devices, although the Class 0 device consumes very little power. However, newer models of NETGEAR PoE + switches allow you to set the upper-performance limit of a PD device (powered device) regardless of its class. These models also allocate power to other Powered Device (PD) devices based on the power limits you set, rather than the theoretical power allocation determined by device class, reducing device waste.


Can I mix PoE and non-PoE devices on my network? 

PoE devices can be mixed with non-PoE devices on a network, but non-PoE devices cannot power PD or PSE devices. Non-PoE devices must have a separate power supply.