Power over Ethernet (PoE) technology allows an Ethernet system to pass electrical power safely along with data on Ethernet cabling. IEEE802.3af-2003 and IEEE802.3at-2009 are the PoE and PoE+ (PoE Plus) standards. The device providing power, whether it is a network switch or midspan hub, is referred to as the Power Sourcing Equipment (PSE) or Power over Ethernet (PoE) Injector, while the device receiving power is known as the Powered Device (PD). Here we discuss the operating principle, standards, applications, advantages of Power over Ethernet (PoE) technology.

Power over Ethernet (PoE) Power Cables

The IEEE standard for PoE requires category 5 cable or higher for high power levels, but can operate with category 3 cable for low power levels. Power is supplied in common mode over two or more of the differential pairs of wires found in the Ethernet cables and comes from a power supply within a PoE-enabled networking device such as an Ethernet switch or can be injected into a cable run with a midspan power supply.

Power over Ethernet (PoE) Standards

The original IEEE 802.3af-2003 PoE standard provides up to 15.4 W of DC power (minimum 44 V DC and 350 mA) to each device. The updated IEEE 802.3at-2009 PoE standard also known as PoE+ or PoE plus, provides up to 25.5 W of power. Some vendors have announced products that claim to comply with the 802.3at standard and offer up to 51 W of power over a single cable by utilizing all four pairs in the Category5 cable.

Power over Ethernet (PoE) Applications

Power over Ethernet (PoE) technology is especially useful for powering IP telephones, wireless LAN access points, cameras with pan tilt and zoom (PTZ), remote Ethernet switches, Network routers, Network webcams, Network Intercom, Paging, Public address systems, hallway speaker amplifiers, embedded computers, VOIP phones, Wireless access points, thin clients and LCD displays.

Power over Ethernet (PoE) Advantages

  • Cheaper cabling:— Even category 5 cable is cheaper than USB repeaters, and the AC power cabling is eliminated.
  • A Gigabit of data per second to every device is possible, which exceeds USB and the AC powerline networking capabilities.
  • Global organizations can deploy PoE everywhere without concern for any local variance in AC power standards, outlets, plugs, or reliability.
  • Direct power injection is possible from standard 48 V DC battery power arrays.
  • Symmetric distribution is possible. Unlike USB and AC outlets, power can be supplied at either end of the cable or outlet. This means the location of the power source can be determined after cables and outlets are installed.