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Power over Ethernet, or PoE, describes any of several standards or
ad hoc Ad hoc is a Latin phrase meaning literally 'to this'. In English, it typically signifies a solution for a specific purpose, problem, or task rather than a generalized solution adaptable to collateral instances. (Compare with ''a priori''.) Com ...
systems that pass
electric power Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions o ...
along with data on
twisted-pair Ethernet Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers. Early Ethernet used various grades of coaxial cable, but in 1984, StarL ...
cabling. This allows a single cable to provide both data connection and electrical power to devices such as
wireless access point In computer networking, a wireless access point (WAP), or more generally just access point (AP), is a networking hardware device that allows other Wi-Fi devices to connect to a wired network. As a standalone device, the AP may have a wired ...
s (WAPs), Internet Protocol (IP) cameras, and voice over Internet Protocol (VoIP) phones. There are several common techniques for transmitting power over Ethernet cabling. Three of them have been standardized by Institute of Electrical and Electronics Engineers (IEEE) standard IEEE 802.3 since 2003. These standards are known as ''alternative A'', ''alternative B'', and ''4PPoE''. For 10BASE-T and 100BASE-TX, only two of the four signal pairs in typical Cat 5 cable are used. Alternative B separates the data and the power conductors, making troubleshooting easier. It also makes full use of all four twisted pairs in a typical Cat 5 cable. The positive voltage is applied to pins 4 and 5, and the negative to pins 7 and 8. Alternative A transports power on the same wires as data for 10 and 100 Mbit/s Ethernet variants. This is similar to the
phantom power Phantom power, in the context of professional audio equipment, is DC electric power transmitted through microphone cables to operate microphones that contain active electronic circuitry. It is best known as a convenient power source for con ...
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 Differential signalling is a method for electrically transmitting information using two complementary signals. The technique sends the same electrical signal as a differential pair of signals, each in its own conductor. The pair of conduc ...
, this does not interfere with data transmission. The common-mode voltage is easily extracted using the
center tap In electronics, a center tap (CT) is a contact made to a point halfway along a winding of a transformer or inductor, or along the element of a resistor or a potentiometer. Taps are sometimes used on inductors for the coupling of signals, and ...
of the standard Ethernet
pulse transformer A variety of types of electrical transformer are made for different purposes. Despite their design differences, the various types employ the same basic principle as discovered in 1831 by Michael Faraday, and share several key functional part ...
. For
Gigabit Ethernet In computer networking, Gigabit Ethernet (GbE or 1 GigE) is the term applied to transmitting Ethernet frames at a rate of a gigabit per second. The most popular variant, 1000BASE-T, is defined by the IEEE 802.3ab standard. It came into use ...
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. 4PPoE provides power using all four pairs of a twisted-pair cable. This enables higher power for applications like
pan–tilt–zoom camera PTZ is an abbreviation that stands for pan-tilt-zoom. The term "Panning (camera), pan" refers to the horizontal movement of the lens, "Tilt (camera), tilt" refers to the vertical movement of the lens, and "Zoom lens, zoom" refers to the adjustment ...
s (PTZ), high-performance WAPs, or even charging laptop batteries. 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 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.


Standards development


Two- and four-pair Ethernet

The original IEEE 802.3af-2003 PoE standard provides up to 15.4 W of DC power (minimum and 350 mA) on each port. Only 12.95 W is assured to be available at the powered device as some power dissipates in the cable. The updated IEEE 802.3at-2009 PoE standard also known as PoE+ or PoE plus, provides up to 25.5 W of power for Type 2 devices. The 2009 standard prohibits a powered device from using all four pairs for power. Both of these standards have since been incorporated into the IEEE 802.3-2012 publication. The IEEE 802.3bt-2018 standard further expands the power capabilities of 802.3at. It is also known as PoE++ or 4PPoE. The standard introduces two additional power types: up to 51 W delivered power (Type 3) and up to 71.3 W delivered power (Type 4). Each pair of twisted pairs needs to handle a current of up to 600  mA (Type 3) or 960 mA (Type 4). Additionally, support for 2.5GBASE-T, 5GBASE-T and 10GBASE-T is included. This development opens the door to new applications and expands the use of applications such as high-performance
wireless access point In computer networking, a wireless access point (WAP), or more generally just access point (AP), is a networking hardware device that allows other Wi-Fi devices to connect to a wired network. As a standalone device, the AP may have a wired ...
s and surveillance cameras.


Single-pair Ethernet

The IEEE 802.3bu-2016 amendment introduced ''single-pair'' Power over Data Lines () for the single-pair Ethernet standards 100BASE-T1 and 1000BASE-T1 intended for automotive and industrial applications. On the two-pair or four-pair standards, the same power voltage is applied to each conductor of the pair, so that within each pair there is no differential voltage other than that representing the transmitted data. With single-pair Ethernet, power is transmitted in parallel to the data. PoDL initially defined ten power classes, ranging from 0.5 to 50 W (at PD). Subsequently, PoDL was added to the single-pair variants 10BASE-T1,IEEE 802.3cg-2019 2.5GBASE-T1, 5GBASE-T1, and 10GBASE-T1 and includes a total of 15 power classes with additional intermediate voltage and power levels.


Uses

Examples of devices powered by PoE include: *
VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...
phones *
IP camera An Internet Protocol camera, or IP camera, is a type of digital video camera that receives control data and sends image data via an IP network. They are commonly used for surveillance, but, unlike analog closed-circuit television (CCTV) camera ...
s including PTZs * WAPs * IP TV (IPTV) decoders * Network routers * A mini
network switch A network switch (also called switching hub, bridging hub, and, by the IEEE, MAC bridge) is networking hardware that connects devices on a computer network by using packet switching to receive and forward data to the destination device. A netw ...
installed in distant rooms, to support a small cluster of Ethernet ports from one
uplink In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or sha ...
cable. PoE power is fed into the PD (or PoE in) port. These switches may in turn power remote PoE devices using PoE pass through. *
Intercom An intercom, also called an intercommunication device, intercommunicator, or interphone, is a stand-alone voice communications system for use within a building or small collection of buildings which functions independently of the public telephon ...
and
public address system A public address system (or PA system) is an electronic system comprising microphones, amplifiers, loudspeakers, and related equipment. It increases the apparent volume (loudness) of a human voice, musical instrument, or other acoustic sound sou ...
s and hallway speaker amplifiers * Wall clocks in rooms and hallways, with time set using Network Time Protocol (NTP) * Outdoor roof mounted radios with integrated antennas, 4G/LTE, 802.11 or 802.16 based wireless CPEs (customer premises equipment) used by wireless ISPs * Outdoor point to point microwave and millimeter wave radios and some Free Space Optics (FSO) units usually featuring proprietary PoE *
Industrial control system An industrial control system (ICS) is an electronic control system and associated instrumentation used for industrial process control. Control systems can range in size from a few modular panel-mounted controllers to large interconnected and in ...
components including sensors, controllers, meters etc. * Access control components including help-points, intercoms, entry cards, keyless entry, etc. * Intelligent lighting controllers and Light-Emitting Diode (LED) Lighting fixtures * Stage and Theatrical devices, such as networked audio breakout and routing boxes * Remote Point Of Sale (POS) kiosks * Inline Ethernet extenders * PoE Splitters that output the power, often at a different voltage (e.g. 5V), to power a remote device or charge a
mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whil ...


Terminology


Power sourcing equipment

''Power sourcing equipment'' (PSE) are devices that provide (''
source Source may refer to: Research * Historical document * Historical source * Source (intelligence) or sub source, typically a confidential provider of non open-source intelligence * Source (journalism), a person, publication, publishing institute o ...
'') power on the Ethernet cable. This device may be a network switch, commonly called an ''endspan'' (IEEE 802.3af refers to it as ''endpoint''), or an intermediary device between a non-PoE-capable switch and a PoE device, an external PoE ''injector'', called a ''midspan'' device.


Powered device

A ''powered device'' (PD) is any device powered by PoE, thus consuming energy. Examples include
wireless access point In computer networking, a wireless access point (WAP), or more generally just access point (AP), is a networking hardware device that allows other Wi-Fi devices to connect to a wired network. As a standalone device, the AP may have a wired ...
s,
VoIP phone A VoIP phone or IP phone uses voice over IP technologies for placing and transmitting telephone calls over an IP network, such as the Internet. This is in contrast to a standard phone which uses the traditional public switched telephone network ...
s, and
IP camera An Internet Protocol camera, or IP camera, is a type of digital video camera that receives control data and sends image data via an IP network. They are commonly used for surveillance, but, unlike analog closed-circuit television (CCTV) camera ...
s. Many powered devices have an auxiliary power connector for an optional external power supply. Depending on the design, some, none, or all of the device's power can be supplied from the auxiliary port,IEEE 802.3-2008, section 2, clause 33.3.5IEEE 802.3at-2009, clause 33.3.7 with the auxiliary port also sometimes acting as backup power in case PoE-supplied power fails.


Power management features and integration

Advocates of PoE expect PoE to become a global long term DC power cabling standard and replace a multiplicity of individual AC adapters, which cannot be easily centrally managed. Critics of this approach argue that PoE is inherently less efficient than AC power due to the lower voltage, and this is made worse by the thin conductors of Ethernet. Advocates of PoE, like the
Ethernet Alliance The Ethernet Alliance was incorporated in the US state of California in August 2005 and officially launched in January 2006 as a non-profit industry consortium to promote and support Ethernet. The objectives were to provide an unbiased, industry ...
, point out that quoted losses are for worst case scenarios in terms of cable quality, length and power consumption by powered devices. In any case, where the central PoE supply replaces several dedicated AC circuits, transformers and inverters, the power loss in cabling can be justifiable.


Integrating EEE and PoE

The integration of PoE with the IEEE 802.3az
Energy-Efficient Ethernet In computer networking, Energy-Efficient Ethernet (EEE) is a set of enhancements to twisted-pair, twinaxial, backplane, and optical fiber Ethernet physical-layer variants that reduce power consumption during periods of low data activity. The ...
(EEE) standard potentially produces additional energy savings. Pre-standard integrations of EEE and PoE (such as Marvell's EEPoE outlined in a May 2011 white paper) claim to achieve a savings upwards of 3 W per link. This saving is especially significant as higher power devices come online.


Standard implementation

Standards-based Power over Ethernet is implemented following the specifications in IEEE 802.3af-2003 (which was later incorporated as clause 33 into IEEE 802.3-2005) or the 2009 update, IEEE 802.3at. The standards require category 5 cable or better for high power levels but allow using category 3 cable if less power is required.IEEE 802.3at-2009, clause 33.1.1c Power is supplied as a
common-mode signal Common-mode signal is the voltage common to both input terminals of an electrical device. In telecommunication, the common-mode signal on a transmission line is also known as longitudinal voltage. In most electrical circuits the signal is transferr ...
over two or more of the differential pairs of wires found in the
Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
cables and comes from a power supply within a PoE-enabled networking device such as an
Ethernet switch A network switch (also called switching hub, bridging hub, and, by the IEEE, MAC bridge) is networking hardware that connects devices on a computer network by using packet switching to receive and forward data to the destination device. A netw ...
or can be injected into a cable run with a ''midspan'' power supply, an additional PoE power source that can be used in combination with a non-PoE switch. A
phantom power Phantom power, in the context of professional audio equipment, is DC electric power transmitted through microphone cables to operate microphones that contain active electronic circuitry. It is best known as a convenient power source for con ...
technique is used to allow the powered pairs to also carry data. This permits its use not only with 10BASE-T and 100BASE-TX, which use only two of the four pairs in the cable, but also with 1000BASE-T (gigabit Ethernet), 2.5GBASE-T, 5GBASE-T, and 10GBASE-T which use all four pairs for data transmission. This is possible because all versions of Ethernet over twisted pair cable specify differential data transmission over each pair with transformer coupling; the DC supply and load connections can be made to the transformer center-taps at each end. Each pair thus operates in common mode as one side of the DC supply, so two pairs are required to complete the circuit. The polarity of the DC supply may be inverted by crossover cables; the powered device must operate with either pair: spare pairs 4–5 and 7–8 or data pairs 1–2 and 3–6. Polarity is defined by the standards on spare pairs, and ambiguously implemented for data pairs, with the use of a
diode bridge A diode bridge is a bridge rectifier circuit of four diodes that is used in the process of converting alternating current (AC) from the input terminals to direct current (DC, i.e. fixed polarity) on the output terminals. Its function is to con ...
. Notes:


Powering devices

Three modes, A, B, and 4-pair are available. Mode A delivers power on the data pairs of 100BASE-TX or 10BASE-T. Mode B delivers power on the spare pairs. 4-pair delivers power on all four pairs. PoE can also be used on 1000BASE-T, 2.5GBASE-T, 5GBASE-T and 10GBASE-T Ethernet, in which case there are no spare pairs and all power is delivered using the phantom technique. Mode A has two alternate configurations (MDI and MDI-X), using the same pairs but with different polarities. In mode A, pins 1 and 2 (pair #2 in
T568B ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunications ...
wiring) form one side of the 48 V DC, and pins 3 and 6 (pair #3 in T568B) form the other side. These are the same two pairs used for data transmission in 10BASE-T and 100BASE-TX, allowing the provision of both power and data over only two pairs in such networks. The free polarity allows PoE to accommodate for crossover cables, patch cables and
Auto MDI-X A medium dependent interface (MDI) describes the interface (both physical and electrical/optical) in a computer network from a physical layer implementation to the physical medium used to carry the transmission. Ethernet over twisted pair also d ...
. In mode B, pins 4–5 (pair #1 in both
T568A ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunications I ...
and T568B) form one side of the DC supply and pins 7–8 (pair #4 in both T568A and T568B) provide the return; these are the "spare" pairs in 10BASE-T and 100BASE-TX. Mode B, therefore, requires a 4-pair cable. The PSE, not the PD, decides whether power mode A or B shall be used. PDs that implement only mode A or mode B are disallowed by the standard. The PSE can implement mode A or B or both. A PD indicates that it is standards-compliant by placing a 25 kΩ resistor between the powered pairs. If the PSE detects a resistance that is too high or too low (including a short circuit), no power is applied. This protects devices that do not support PoE. An optional ''power class'' feature allows the PD to indicate its power requirements by changing the sense resistance at higher voltages. To retain power, the PD must use at least 5–10 mA for at least 60 ms at a time. If the PD goes more than 400 ms without meeting this requirement, the PSE will consider the device disconnected and, for safety reasons, remove power. There are two types of PSEs: endspans and midspans. Endspans (commonly called PoE switches) are Ethernet switches that include the power over Ethernet transmission circuitry. Midspans are power injectors that stand between a regular Ethernet switch and the powered device, injecting power without affecting the data. Endspans are normally used on new installations or when the switch has to be replaced for other reasons (such as moving from
10/100 Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers. Early Ethernet used various grades of coaxial cable, but in 1984, Sta ...
 Mbit/s to 1 Gbit/s), which makes it convenient to add the PoE capability. Midspans are used when there is no desire to replace and configure a new Ethernet switch, and only PoE needs to be added to the network. IEEE 802.3at capable devices are also referred to as ''Type 2''. An 802.3at PSE may also use LLDP communication to signal 802.3at capability. Class 4 can only be used by IEEE 802.3at (Type 2) devices, requiring valid Class 2 and Mark 2 currents for the power up stages. An 802.3af device presenting a class 4 current is considered non-compliant and, instead, will be treated as a Class 0 device.IEEE 802.3-2008, section 2, clause 33.3.4


Configuration via Ethernet layer 2 LLDP

Link Layer Discovery Protocol The Link Layer Discovery Protocol (LLDP) is a vendor-neutral link layer protocol used by network devices for advertising their identity, capabilities, and neighbors on a local area network based on IEEE 802 technology, principally wired Ether ...
(LLDP) is a layer-2 Ethernet protocol for managing devices. LLDP allows an exchange of information between a PSE and a PD. This information is formatted in
type–length–value Within communication protocols, TLV (type-length-value or tag-length-value) is an encoding scheme used for optional informational elements in a certain protocol. A TLV-encoded data stream contains code related to the record type, the record val ...
(TLV) format. PoE standards define TLV structures used by PSEs and PDs to signal and negotiate available power. The setup phases are as follows: * PSE (provider) tests PD (consumer) physically using 802.3af phase class 3. ** PSE powers up PD. * PD sends to PSE: I'm a PD, max power = X, max power requested = X. * PSE sends to PD: I'm a PSE, max power allowed = X. ** PD may now use the amount of power as specified by the PSE. The rules for this power negotiation are: * PD shall never request more power than physical 802.3af class * PD shall never draw more than max power advertised by PSE * PSE may deny any PD drawing more power than max allowed by PSE * PSE shall not reduce power allocated to PD that is in use * PSE may ''request'' reduced power, via conservation mode


Non-standard implementations


Cisco

Some Cisco WLAN access points and
VoIP phone A VoIP phone or IP phone uses voice over IP technologies for placing and transmitting telephone calls over an IP network, such as the Internet. This is in contrast to a standard phone which uses the traditional public switched telephone network ...
s supported a proprietary form of PoE many years before there was an IEEE standard for delivering PoE. Cisco's original PoE implementation is not software upgradeable to the IEEE 802.3af standard. Cisco's original PoE equipment is capable of delivering up to per port. The amount of power to be delivered is negotiated between the endpoint and the Cisco switch based on a power value that was added to the Cisco proprietary
Cisco Discovery Protocol Cisco Discovery Protocol (CDP) is a proprietary data link layer protocol developed by Cisco Systems in 1994 by Keith McCloghrie and Dino Farinacci. It is used to share information about other directly connected Cisco equipment, such as the operati ...
(CDP). CDP is also responsible for dynamically communicating the Voice VLAN value from the Cisco switch to the Cisco VoIP Phone. Under Cisco's pre-standard scheme, the PSE (switch) will send a fast link pulse (FLP) on the transmit pair. The PD (device) connects the transmit line to the receive line via a
low-pass filter A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filter des ...
. The PSE gets the FLP in return. The PSE will provide a common mode current between pairs 1 and 2, resulting in 2010-01-12 ciscopress.com and 2010-01-12 conticomp.com default of allocated power. The PD must then provide Ethernet link within to the auto-negotiation mode switch port. A later CDP message with a TLV tells the PSE its final power requirement. A discontinuation of link pulses shuts down power. 2010-01-12 cisco.com In 2014, Cisco created another non-standard PoE implementation called (UPOE). UPOE can use all 4 pairs, after negotiation, to supply up to 60 W.


Linear Technology

A proprietary high-power development called LTPoE++, using a single Cat 5e Ethernet cable, is capable of supplying varying levels at 38.7, 52.7, 70, and 90 W.


Microsemi

PowerDsine, acquired by
Microsemi Microsemi Corporation was an Aliso Viejo, California-based provider of semiconductor and system solutions for aerospace & defense, communications, data center and industrial markets. In February 2018, it was announced that Chandler, Arizona-bas ...
in 2007, has been selling midspan power injectors since 1999 with its proprietary ''Power over LAN'' solution. Several companies such as
Polycom Poly, formerly Polycom, a part of HP Inc., is an American multinational corporation that develops video, voice and content collaboration and communication technology. Polycom was co-founded in 1990 by Brian L Hinman and Jeffrey Rodman. In 2018 ...
,
3Com 3Com Corporation was an American digital electronics manufacturer best known for its computer network products. The company was co-founded in 1979 by Robert Metcalfe, Howard Charney and others. Bill Krause joined as President in 1981. Metcalfe ex ...
,
Lucent Lucent Technologies, Inc. was an American multinational telecommunications equipment company headquartered in Murray Hill, New Jersey. It was established on September 30, 1996, through the divestiture of the former AT&T Technologies business u ...
and
Nortel Nortel Networks Corporation (Nortel), formerly Northern Telecom Limited, was a Canadian multinational telecommunications and data networking equipment manufacturer headquartered in Ottawa, Ontario, Canada. It was founded in Montreal, Quebec, ...
utilize PowerDsine's Power over LAN.


Passive

In a passive PoE system, the injector does not communicate with the powered device to negotiate its voltage or wattage requirements, but merely supplies power at all times. Common 100 Mbit/s passive applications use the pinout of 802.3af mode B (see )with DC positive on pins 4 and 5 and DC negative on 7 and 8 and data on 1–2 and 3–6, but polarization may vary. Gigabit passive injectors use a transformer on the data pins to allow power and data to share the cable and are typically compatible with 802.3af Mode A. Passive midspan injectors with up to 12 ports are available. Devices needing 5 volts cannot typically use PoE at 5 V on Ethernet cable beyond short distances (about ) as the voltage drop of the cable becomes too significant, so a 24 V or 48 V to 5 V DC-DC converter is required at the remote end. Passive PoE power sources are commonly used with a variety of indoor and outdoor wireless radio equipment, most commonly from Motorola (now Cambium), Ubiquiti Networks,
MikroTik MikroTik (officially SIA "Mikrotīkls") is a Latvian network equipment manufacturer. The company develops and sells wired and wireless network routers, network switches, access points, as well as operating systems and auxiliary software. The com ...
and others. Earlier versions of passive PoE 24 VDC power sources shipped with 802.11a, 802.11g and 802.11n based radios are commonly 100 Mbit/s only. Passive DC-to-DC injectors also exist which convert a 9 V to 36 V DC, or 36 V to 72 V DC power source to a stabilized 24 V 1 A, 48 V 0.5 A, or up to 48 V 2.0 A PoE feed with '+' on pins 4 & 5 and '−' on pins 7 & 8. These DC-to-DC PoE injectors are used in various telecom applications.


Power capacity limits

The
ISO/IEC ISO/IEC JTC 1, entitled "Information technology", is a joint technical committee (JTC) of the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). Its purpose is to develop, maintain and p ...
TR 29125 and
Cenelec CENELEC (french: Comité Européen de Normalisation Électrotechnique; en, European Committee for Electrotechnical Standardization) is responsible for European standardization in the area of electrical engineering. Together with ETSI (telecommun ...
EN 50174-99-1 draft standards outline the cable bundle temperature rise that can be expected from the use of 4PPoE. A distinction is made between two scenarios: # bundles heating up from the inside to the outside, and # bundles heating up from the outside to match the ambient temperature. The second scenario largely depends on the environment and installation, whereas the first is solely influenced by the cable construction. In a standard unshielded cable, the PoE-related temperature rise increases by a factor of 5. In a shielded cable, this value drops to between 2.5 and 3, depending on the design.


Pinouts


References


External links


Buy the IEEE 802.3 standards

ieee802.org: IEEE 802.3af Task Force

ieee802.org: IEEE 802.3at Task Force

ieee802.org: IEEE 802.3bt Task Force
{{DEFAULTSORT:Power Over Ethernet Ethernet Networking hardware Network appliances Electric power IEEE standards Power supplies