Power over Ethernet (PoE) 802.3af

Power over Ethernet (PoE) is a technology that allows both data and power to be transmitted over a single Ethernet cable. The 802.3af standard, also known as PoE, is a widely used standard developed by the IEEE (Institute of Electrical and Electronics Engineers) and published in 2003. Thanks to this technology, network installations become simpler and more flexible.

802.3af technical specifications
Power supply

The 802.3af standard delivers up to 15.4 W of power to each port. However, after taking into account cable losses, the effective power available to the end device (Powered Device, PD) is approximately 12.95 W. This is enough to power many network devices, such as VoIP phones or IP cameras.

Supply voltage

The 802.3af standard's power supply voltage ranges from 44V to 57V, with a typical voltage of 48V. This high voltage is necessary to overcome energy loss in long Ethernet cables while also providing safe and stable power to network devices.

Device types

802.3af PoE compliant devices fall into two main categories:

  1. PSE (Power Sourcing Equipment) – source devices such as PoE switches and PoE injectors. They supply electricity to end devices.
  2. PD (Powered Devices) – powered devices such as VoIP phones, IP cameras and Wi-Fi access points. These devices receive energy supplied by PSE.
Connection topologies

The 802.3af standard supports two power transfer methods:

  • Mode A: Power is sent together with data on pairs 1/2 and 3/6. This is made possible by using cables to transmit both the data signal and power.
  • Mode B: Power is transmitted on pairs 4/5 and 7/8, which are not used for data transmission in Cat5 cables. This allows power to be transferred without disturbing data transmission.
PoE 802.3af Applications

PoE 802.3af has been widely used in many areas, including:

  • VoIP phones: This technology eliminates the need for separate power supplies for phones, simplifying installation and reducing costs.
  • IP cameras: PoE enables simple installation of monitoring systems, especially in hard-to-reach places where it is not possible to run separate power cables.
  • Wi-Fi access points: With PoE, you can easily deploy access points without the need for external power, increasing the flexibility of your wireless network.
  • Access control systems: PoE powers electronic locks, card readers and other devices, which allows you to create more advanced security systems without the need to install additional power cables.
Advantages of PoE 802.3af

PoE 802.3af has many advantages that contribute to its popularity:

  • Simple installation: Single cabling for data and power reduces installation complexity and costs. Users can use existing Ethernet infrastructure, making it faster and easier to deploy new devices.
  • Flexibility: The ability to install devices in places where there is no access to electrical power increases the flexibility of deploying network equipment. This allows you to easily expand the network without having to rebuild the electrical infrastructure.
  • Security: PoE standards include surge detection and protection mechanisms, which increases operational safety. PSE devices can detect the presence of PD devices and deliver power only when needed, minimizing the risk of damage.

802.3af PoE technology simplifies network installations by reducing the number of cables and power supplies required. Thanks to it, you can place network devices more flexibly, which contributes to more effective use of network infrastructure. Despite the introduction of newer PoE standards such as 802.3at and 802.3bt, 802.3af still remains a popular choice in many applications due to its reliability and sufficient power for many common network devices. This technology is still used in many areas, enabling simpler, more effective and safer network installations.