![]() In addition to standardizing existing practice for spare-pair ( Alternative B), common-mode data pair power ( Alternative A) and 4-pair transmission ( 4PPoE), the IEEE PoE standards provide for signaling between the power sourcing equipment (PSE) and powered device (PD). This enables higher power for applications like pan–tilt–zoom cameras (PTZ), high-performance WAPs, or even charging laptop batteries. For Gigabit Ethernet and faster, both alternatives A and B transport power on wire pairs also used for data since all four pairs are used for data transmission at these speeds.ĤPPoE provides power using all four pairs of a twisted-pair cable. The common-mode voltage is easily extracted using the center tap of the standard Ethernet pulse transformer. Because twisted-pair Ethernet uses differential signaling, this does not interfere with data transmission. Power is transmitted on the data conductors by applying a common voltage to each pair. This is similar to the phantom power technique commonly used for powering condenser microphones. The positive voltage is applied to pins 4 and 5, and the negative to pins 7 and 8.Īlternative A transports power on the same wires as data for 10 and 100 Mbit/s Ethernet variants. ![]() It also makes full use of all four twisted pairs in a typical Cat 5 cable. Alternative B separates the data and the power conductors, making troubleshooting easier. For 10BASE-T and 100BASE-TX, only two of the four signal pairs in typical Cat 5 cable are used. These standards are known as alternative A, alternative B, and 4PPoE. Three of them have been standardized by Institute of Electrical and Electronics Engineers (IEEE) standard IEEE 802.3 since 2003. There are several common techniques for transmitting power over Ethernet cabling. This allows a single cable to provide both data connection and electrical power to devices such as wireless access points (WAPs), Internet Protocol (IP) cameras, and voice over Internet Protocol (VoIP) phones. Power over Ethernet, or PoE, describes any of several standards or ad hoc systems that pass electric power along with data on twisted-pair Ethernet cabling. In another common configuration, the access point or other connected device includes internal PoE splitting and the external splitter is not necessary. The PoE connection eliminates the need for a nearby power outlet. ![]() ![]() The splitter is the silver and black box in the middle between the wiring junction box (left) and the access point (right). In this configuration, an Ethernet connection includes Power over Ethernet (PoE) (gray cable looping below), and a PoE splitter provides a separate data cable (gray, looping above) and power cable (black, also looping above) for a wireless access point (WAP). ![]()
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