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What is PoE?

Power over Ethernet (PoE) is a standard technology that offers both network access and electrical power to the connected devices through the same ethernet cable (e.g. with CAT-5/5e cable up to 100m). In other words, PoE enables electrical power necessary for devices that are carried by RJ45 cables (unshielded twisted-pair wires) instead of standard electrical power cords and wiring. The network devices powered by PoE are referred to as powered devices (PDs). PoE is mostly utilized for VoIP phones, IP cameras, and wireless access points (APs).

Because PoE transports both data and electrical power, less wiring is necessary. Thus, PoE saves cost and installation time. PoE's popularity has increased dramatically in recent years as a result of these and other benefits.

PoE has been initially developed in response to the need to use existing Ethernet cable infrastructure to power devices in areas where AC power outlets were not readily available. Over the last two decades, many different PoE implementations have been employed. The numerous implementations of PoE can be grouped into two categories in general: standardized and proprietary.

What are the Standards of the PoE?

Before it was regulated, PoE was typically referred to as "power injection." Those "power injectors" just supplied energy through Ethernet cabling, either AC or DC, with no sophisticated protocol or safety concerns. The technique was largely used in corporate settings when adding more AC outlets would be prohibitively expensive. Furthermore, because this technique can harm or damage equipment that isn't built to absorb the power, it can't be considered a long-term solution for sending power over data-communications cable. The IEEE later realized that there was a utilitarian necessity for a technology like this and that a standard was required.

In 2003, the initial PoE standard (IEEE 802.3af) - also called Data Terminal Equipment Power through Media Dependent Interface (MDI or RJ-45) - was set up to the definition of the power transmission over Ethernet infrastructure. Before then, different types of proprietary PoE were employed by different companies to give PoE capabilities. Today, some of these customized PoE modules are still in use. Installers of PoE products must establish where these older, customized devices are placed because they may be incompatible with later standard PoE devices.

The IEEE released an updated PoE standard towards the end of 2018 to address the demand for higher power and notably expand capacity. IEEE 802.3bt supports up to 60 W to 100 W of power at the supplier by distributing power over four pairs of wires (as opposed to two pairs in earlier technology).

With today's standard PoE modules, AP installations are easier and more adaptable, especially in ceilings that may be difficult to wire for electrical power. The level of power that can be supplied via Ethernet cable has increased as PoE technology has progressed. IEEE-compliant PoE switches can supply power per port varying from 12 watts to over 70 watts.

While previous standards have a maximum speed of 1-Gbps, the new standard will handle 2.5GBASE-T, 5GBASE-T, and 10GBASE-T. This new feature will allow for data speeds that are intermediate between existing standards.

The power outputs of the PoE standards are listed below.

  • IEEE 802.3af: Type-1, 2003, standard named as PoE (supported modes A & B), power output is 15.4 W, dc output voltage is 44 - 57 Vdc.
  • IEEE 802.3at: Type-2, 2009, standard named as PoE+ (supported modes A & B), power output is 30 W, dc output voltage is 50 - 57 Vdc.
  • IEEE 802.3bt: Type-3, 2018, standard named as PoE++ (supported modes A, B, and 4PPoE), power output is 60 W, dc output voltage is 42.5 - 57 Vdc.
  • IEEE 802.3bt: Type-4, 2018, standard named as UPoE+ (supported mode 4PPoE), power output is 100 W, dc output voltage is 41.1 - 57 Vdc.

There are three types of power transmission for network devices over Ethernet cabling:

  • Mode A(common-mode data pair power): The power is provided on the same cable pair as the data pairs (data pair pins 1,2 & 3,6; electrical power pins 1,2 dc- & 3,6 dc+) used in a 10Base-T or 100Base-TX transmission.
  • Mode B (spare-pair power): The spare pairs (data pins 4,5 & 7,8; electrical power pins 4,5 for dc- & 7,8 for dc+) are used and with 4PPoE all 4-pairs of the Ethernet cable are used for power transmission.
  • 4PPoE: This type of connection necessitates 8-pin network wiring. While almost all networking cabling is 8-pin, some low-cost cables may only have 4-pins. They've grown increasingly scarce as they can only be used for Fast-Ethernet connections.

Cable types of the PoE are as follows:

  • IEEE 802.3af: Type-1, CAT-5, 4-pins / 2-pairs, supported modes A & B.
  • IEEE 802.3at: Type-2, CAT-5, 4-pins / 2-pairs, supported modes A & B.
  • IEEE 802.3bt: Type-3, CAT-5, 8-pins / 4-pairs, supported mode 4-pair.
  • IEEE 802.3bt: Type-4, CAT-5, 8-pins / 4-pairs, supported mode 4-pair.

There is still a lot of (mis)information concerning the disadvantages of the PoE cables out there. The aluminum core of Copper-Clad Aluminum (CCA) cable is bonded with copper. A standard network cable, on the other hand, has a 100% copper core.

Clearly explained, aluminum is a poor conductor of electricity. Because it has a higher electrical resistance than copper, it loses and dissipates more power as heat. We do not advocate utilizing them with PoE injectors or switches since they cause higher power loss on the cable, which is a big concern in PoE applications.

What is a PoE Port?

PoE port is a physical network (ethernet) port with built-in PoE functionality for connecting PoE-capable devices.

How does PoE Work?

It works straightforwardly. Ethernet cable that satisfies CATx specifications has four twisted pairs, and PoE transmits power to PoE-enabled devices over these pairs. First, two twisted pairs are utilized to send data, while the remaining two pairs are just used to transfer power. Power and data are both delivered over all four twisted pairs under the new PoE standards.

The power and data transmissions do not collide with each other when the same pairings are used for both. Because energy and data travel at opposite extremes of the frequency spectrum, this is the case. Data transmissions have frequencies ranging from 10 to 1000 (MHz) million Hz, while electricity has a low frequency of 50/60 Hz.

Power and data are received by a PoE extender from the PSE to which it is connected. It consumes some of the power to run itself, and the rest is passed on to the next PoE device. A Gigabit PoE extender typically consumes 4 to 5 W of power. If you plug it into an IEEE 802.3at PSE that can give about 25 W of power to the extender, your PD will have about 20-21 W available. If you cascade PoE extenders, each extender will waste 4 to 5 W, leaving you less power for the next PD.

What are the Benefits of PoE?

PoE technology brings several benefits as listed below:

1. Safety: There are fewer points of failure using PoE technology in general. When you connect your PoE switch or PoE injector to a UPS, you can ensure that your PoE-powered devices receive consistent power, which is vital for operation-critical PoE edge devices. If your LAN is protected from power outages by a UPS, the PoE devices that are linked to it are likewise protected.

2. Reliability: The option to remotely restart connected PoE devices is available in PoE deployments that use managed PoE switches. This can be done manually, automatically, or according to a set schedule. Modern PoE switches provide watchdog capability (i.e. Powered Device Manager [PDM]), which cuts power to offline devices and then resupplies it, causing them to reboot. This feature significantly reduces the amount of time your connected devices are unavailable. Since the power for PoE is supplied from a universally compatible supplier, it could be backed up with an uninterruptible power supply (UPS) or used to disable or reset PDs.

3. Scalability: You can install your PoE-powered devices anywhere and relocate them easily if needed. The PoE cable provides significant flexibility while maintaining a controlled system. PoE can also be used for video surveillance, building management, retail video kiosks, smart signage, vending machines, and retail point-of-information systems.

4. Time-Saving: Conventional Ethernet cables are relatively affordable and are frequently already placed in the location. You can also transfer an appliance with little to no disruption.

5. Cost Saving: Utilizing a single set of twisted-pair cables for both data and low-power appliances instead of the electrical wire reduces cost. The delivery of data and transmission of power over a standard Ethernet cable eliminates the necessity for AC/DC power supplies and outlets to give power to PoE-enabled devices. Because you don't need an electrician to install power if there isn't someplace you want to put your new PDs, the cost of adding or installing appropriate network devices is reduced.

How to Use PoE?

Power Sourcing Equipment (PSE) and Powered Devices are two components of a typical PoE system. The PD is the link's natural endpoint, receiving power, and might be an IP phone, a WLAN access point, or any other IP device that consumes power. The end-point hub and the mid-span hub are the two forms of PSE deployment.

The mid-span is the most preferred type. Mid-span-hub is referred to as a "PoE injector". The mid-span hub is located adjacent to a network switch, and each cable from the switch is connected to the hub, then out to the PD. Single port midspan hubs are also commonly found close to the PD.

Mid-span Hub Figure 1. Mid-span Hub

The only difference between an end-span-hub and a mid-span-hub is that the switch is built-in.

End-span Hub Figure 2. End-span Hub

What Devices Use PoE?

Most access points received enough power from equipment according to the 2003 PoE standard, but other types of installed devices, such as video surveillance cameras, received insufficient power. The Institute of Electrical and Electronics Engineers (IEEE) and several suppliers have tried to fix the power problem throughout the years, but the interoperability issue has persisted. The IEEE 802.3 committee defines the rules that PoE devices must follow.

  • PoE Splitters: PoE Splitters receive data and power transmission from a PoE source. To support non-PoE devices, they divide data and power onto two independent lines.

  • PoE Repeaters/ PoE Extenders: Allow PoE connections to be extended beyond the 100-meter restriction, allowing access to far-flung PoE devices like access points, cameras, and VoIP phones.

  • PoE Media Converters: PoE Media Converters are a viable approach to extend your network over fiber or copper while also powering remote PoE devices through long-distance data lines. They serve as both a copper-to-fiber converter and a power source in one device.

  • Other PoE enabled PDs: PoE is usable with the following modules and devices that need less than 30 watts (W) of power:

  • Voice over IP and video telephones;

  • Wireless AP devices or nodes;

  • Pan, tilt, and zoom robotic cameras;

  • Thin-client computers, remote computer terminals;

  • Computer monitors, large display screens, and large TVs;

  • Door access systems and video signing displays;

  • Network audio.

What is the Maximum Distance of PoE?

Unless PoE extenders or other means are utilized to supply power, PoE power transmission is limited to 100 meters with CAT-5 cables.

What is PoE+?

PoE+ is the upgraded IEEE 802.3 at-2009 PoE standard that allows Type-2 devices to consume up to 30 W of power. Which is plenty of power for VoIP phones, wireless access points, and IP cameras, among other things. However, technologies such as flat-screen displays, LED lighting, and retail POS systems are insufficient. The "Minimum power for PD" setting is the most important for most users since it determines which PoE standard offers enough power for the requested application.

What is the Difference Between PoE and PoE+?

The initial PoE standard (IEEE 802.3af-2003) - PoE allows each physical port to receive up to 15.4 W of DC power. Because of the increased power, consumers may use PoE for a wider range of devices and applications. In addition, the new standard will improve energy efficiency by reducing power loss in the cable, potentially reducing the overall power loss. Thus, PoE+ is the upgraded version (@ 2009) of PoE. PoE+ allows devices to consume up to 30 W of power.

The differences between PoE and PoE+ are listed below:

StandardPSE dc output voltagePoE standard voltagePSE output powerPD power levelSupported Modes
PoEIEEE 802.3af44-57 V37-57 V15.40 W12.95 WMode A&B
PoE+IEEE 802.3at50-57 V42.5-57 V30 W25.5 WMode A&B

Table 1. Differences between the PoE and PoE+

What is PoE for the Internet?

PoE is an advanced technology, data and power are carried over a single Ethernet cable. Thus it provides the fundamental things - data connection and power - for internet connection.

What is PoE Switch?

PoE switch is a network switch with built-in PoE functionality for connecting PoE-capable devices. A PoE injector is not required with a PoE switch because it already supports PoE. Data and power are carried over a single Ethernet cable by a PoE switch.

If your existing network switch does not offer PoE or cannot provide adequate power to your devices, an injector can be used to safely connect PoE devices to the switch. A PoE injector is also known as a mid-span injector. Using a PoE injector, you may upgrade and PoE-enable all of your existing LAN setups. This technique is especially useful when the network's devices demand fewer PoE ports.

Several VoIP phones, wireless network access points, security system cameras, Bluetooth access points, and other 802.3af-compatible equipment are all supported by these injectors. It saves you money and time by eliminating the need to install electrical power at remote cameras, access points, or thin clients. Equipment can be moved from one room to another without the need for costly and time-consuming rewiring.

Aside from their regular functions, PoE Ethernet switches can also serve as power sources. They supply power to the Ethernet connection to power PoE-enabled devices like wireless access points and security cameras that are connected to it.

What is the Difference Between LAN and PoE?

PoE is a concept that provides both network access and electrical power to the connected devices through the same ethernet (CAT-5) cable with PoE-enabled switches. PoE uses your LAN (Local Area Network) infrastructure to supply power to devices plugged into your network (/docs/network-basics/what-is-wlan).

Does PoE Harm the Computer?

PoE technology that adheres with IEEE 802.3af/at/bt is safe. Even if the hardware is not meant for PoE applications, PoE injectors and switches will not harm it. Before supplying any power to a connected PD, the PSE performs a handshake operation to determine how much power is required by the attached device. This method requires very little power and is safe for any connected device, regardless of whether it is PoE or not. If the handshake is successful, the PoE injector or switch supplies power to the PD, allowing it to turn on. The PSE never supplies any voltage if that handshake is not accomplished for whatever reason. All IEEE 802.3af/at/bt-compliant appliances have this built-in functionality, which makes PoE technology fundamentally safe for computers.

What are the Challenges of PoE?

PoE isn't a cure-all. While there have been a few instances where power over ethernet has caused issues, this should not be seen as a rejection of the PoE design concept. The following are some examples of issues to be concerned about:

  • Interference: Power over ethernet implementations are typically DC and supply a constant voltage and current to the PD. The inductance is restricted and no EMI is generated if there is no current fluctuation. However, if the load is turned ON or OFF frequently or uses switch-mode power supplies, the EMI might cause noise on the data cables. Furthermore, power and signal lines are often segregated in many applications to prevent signal integrity loss. However, design practice is impacted when power and signal lines are combined into a single cable.
  • Electrical Contacts: The electrical contacts used in ground-based ethernet cable applications are made for low-current purposes with minimal physical damage. When the voltage and current connections for power applications are raised in PoE applications, the contacts are stressed and degrade faster. Some people in the aerospace industry have tried to use ground-based ethernet connectors and discovered that the vibrations produce Sequential Sparking on the contacts and rapid contact damage. In addition, the heat generated by arc flash might harm the cable and any surrounding components.
  • Power Limits: The Ethernet switch typically has 16 to 48 ports however the external power adaptor cannot provide full power to all of them. In a 24-port arrangement, for example, each load attached to a port can consume up to 30 W. As a result, the PSE can consume up to 720 W of total electricity. Most manufacturers do not ship systems with AC power supplies rated to handle a need for full power from all ports to save money. The issue is supplying as many PDs as possible while limiting PD power cycling and keeping high-priority ports operational in the case of a power outage. With port power management, there are several options for dealing with load changes. The most widely used method is adaptive control, which is based on each port's real-time required power. This method is efficient since no power is wasted.
  • Higher Switch Costs: While integrating power and data signals saves money, PoE switches are more expensive than standard switches.