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Power over Ethernet
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Power over Ethernet
Power over Ethernet (PoE) describes any of several standards or ad hoc systems that pass electric power along with data on twisted-pair Ethernet cabling. This allows a single cable to provide both a data connection and enough electricity to power networked devices such as wireless access points (WAPs), IP cameras and VoIP phones.
There are several common techniques for transmitting power over Ethernet cabling, defined within the broader Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard since 2003.
The three techniques are:
Alternative A transmits power on the same wires as data for common 10 and 100 Mbit/s Ethernet variants. This is similar to the phantom power technique commonly used for powering condenser microphones. Power is transmitted on the data conductors by applying a common voltage to each pair. Because twisted-pair Ethernet uses differential signaling, this does not interfere with data transmission. The common-mode voltage is easily extracted using the center tap of the standard Ethernet pulse transformer. For gigabit Ethernet and faster, both alternatives A and B transmit power on wire pairs also used for data since all four pairs are used for data transmission at these speeds.
4PPoE provides power using all four pairs of the connectors used for twisted-pair Ethernet. This enables higher power for applications like pan–tilt–zoom cameras (PTZ), high-performance wireless access points (WAPs), or even charging laptop batteries.
In addition to standardizing existing practice for common-mode data pair (Alternative A), spare-pair (Alternative B), and four-pair (4PPoE) transmission, the IEEE PoE standards provide for signaling between the power sourcing equipment (PSE) and powered device (PD). This signaling allows the presence of a conformant device to be detected by the power source and allows the device and source to negotiate the amount of power required or available while avoiding damage to non-compatible devices.
The original PoE standard, IEEE 802.3af-2003, now known as Type 1, provides up to 15.4 W of DC power (minimum 44 V DC and 350 mA) on each port. Only 12.95 W is guaranteed to be available at the powered device as some power dissipates in the cable.
The first update to PoE, IEEE 802.3at-2009, introduced Type 2, also known as PoE+ or PoE plus. It provides up to 25.5 W and prohibits the use of four pairs simultaneously for power.
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Power over Ethernet
Power over Ethernet (PoE) describes any of several standards or ad hoc systems that pass electric power along with data on twisted-pair Ethernet cabling. This allows a single cable to provide both a data connection and enough electricity to power networked devices such as wireless access points (WAPs), IP cameras and VoIP phones.
There are several common techniques for transmitting power over Ethernet cabling, defined within the broader Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard since 2003.
The three techniques are:
Alternative A transmits power on the same wires as data for common 10 and 100 Mbit/s Ethernet variants. This is similar to the phantom power technique commonly used for powering condenser microphones. Power is transmitted on the data conductors by applying a common voltage to each pair. Because twisted-pair Ethernet uses differential signaling, this does not interfere with data transmission. The common-mode voltage is easily extracted using the center tap of the standard Ethernet pulse transformer. For gigabit Ethernet and faster, both alternatives A and B transmit power on wire pairs also used for data since all four pairs are used for data transmission at these speeds.
4PPoE provides power using all four pairs of the connectors used for twisted-pair Ethernet. This enables higher power for applications like pan–tilt–zoom cameras (PTZ), high-performance wireless access points (WAPs), or even charging laptop batteries.
In addition to standardizing existing practice for common-mode data pair (Alternative A), spare-pair (Alternative B), and four-pair (4PPoE) transmission, the IEEE PoE standards provide for signaling between the power sourcing equipment (PSE) and powered device (PD). This signaling allows the presence of a conformant device to be detected by the power source and allows the device and source to negotiate the amount of power required or available while avoiding damage to non-compatible devices.
The original PoE standard, IEEE 802.3af-2003, now known as Type 1, provides up to 15.4 W of DC power (minimum 44 V DC and 350 mA) on each port. Only 12.95 W is guaranteed to be available at the powered device as some power dissipates in the cable.
The first update to PoE, IEEE 802.3at-2009, introduced Type 2, also known as PoE+ or PoE plus. It provides up to 25.5 W and prohibits the use of four pairs simultaneously for power.
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