What is Power Over Ethernet?

Power over Ethernet (PoE) is a technology that delivers DC power to network devices over copper Ethernet cabling, eliminating the need for separate power supplies or outlets. It typically supports distances up to 100 meters (328 feet) over standard Cat5e, Cat6, or Cat6a Ethernet cables.

How Does Power Over Ethernet Work?

Each network cable comprises four twisted pairs of wires, which makes eight wires. In commercial applications, Cat 5e and Cat 6 cables are used. In 100BASE-T Ethernet applications, two pairs are used for sending data and two pairs are unused. The pairs that are used for sending information are known as data pairs and the unused pairs are referred to as spare pairs.

When it comes to the power supply, two conductors are required. In PoE applications, each pair acts as a single conductor. This means you can use the two spare pairs or two data pairs for transmitting electrical current. PoE is usually injected into the cable at 48 V. Any voltage between 44 and 57 volts DC is considered ideal. The high voltage of 48 V DC enables efficient power transmission along the cable.

Although 48 V DC is neither too high nor too low and is considered safe for users, it is not safe for devices. Hence, signature detection is conducted before using a PSE device for powering a PD. The signature detection usually utilizes low voltage to detect the power class of PD devices like IP camera, and other equipment. The PD device is usually IEEE compatible.

Based on the signature detection, the three types of PoE power classes are classified as below:

• Class 1: The PSE power available is 4.0W and maximum device power is 3.84 W.
• Class 2: The PSE power available is 7.0 W and maximum device power is 6.49W.
• Class 3: The PSE power of 15.4 W is available to the device; however, it can only use up to 12.95 W.

The power loss is the difference between the actual power delivered by the PSE and the power received by the PD. The power loss happens due to the loss of thermal energy. If during the signature detection, the PD does not show any power class, then it belongs to class 0 and must be allocated only 12.95 watts.

The power is supplied to the cable after the signature detection, which mainly helps to identify the class. In live connection, PSE monitors the power delivery and will severe the power supply if there is too much power. This helps assure overload or under current situations.

Basic Components of a Power Over Ethernet System

A PoE system comprises the following components:

• Power Sourcing Equipment (PSE): The Ethernet cable helps transmit power between the power source and the device. The equipment that provides power to the cable is referred to as a power sourcing equipment or PSE. Endspans and midspans are two types of PSE.
• Powered Devices (PD): This is the term for a device that receives energy from the cable. A few examples of these devices include VoIP phones, wireless access points, and IP cameras.
• Ethernet Cable: This Ethernet cable is used for power and data transmission. It enables bi-directional communication between PSE and PD, and unidirectional power supply.
• Power Supply: The PSE is powered by a power source. Generally, a PSE is powered by a 48V DC power source.

Power over Ethernet (PoE) Implementation

PoE devices can be implemented as midspans or endspans. Powered devices (PDs) can receive power from both these types of devices.

• Endspans: They apply power directly to the device. Endspan devices can use the data pairs or spare pairs in the cable. Endspan devices need PoE-enabled switches, and are usually preferred for new installations. An L2 switch supporting PoE is one of the brilliant examples of endspans.
• Midspans: These devices utilize an injector or a powered patch panel, which is usually positioned between the PD and an Ethernet switch. The Midspan devices are located parallel to the switch and are considered to be the PSE. According to specifications, midspans only use the spare pair of the cable. PoE hub is an example of midspan.

Types of Power Over Ethernet Powering Devices

PoE powering devices are classified into different groups depending on the types of wires used in the Ethernet cable to power the device. The following are some of the common types:

• Mode A: These powering devices use the same pair of pins 1, 2, 3, & 6 for data and power transmission.
• Mode B: The devices of this type use two pairs of pins for data and power transmission. For example, pins 1, 2, 3, & 6 are used for data communication as well as pins 4, 5, 7, &8 for power transmission.
• 4-Pair: The devices use all pairs of the wire for power transmission.

Power Over Ethernet Standards

The project for standardization of PoE began in 1999, and the Institute of Electrical and Electronics Engineers (IEEE) established the standard in 2003. This standardization was important as it assured interoperability with different technologies. This standardization enables customers to purchase PSE, PD, as well as Ethernet cables from various vendors and still build a successful PoE system. The following are the standards that evolved over the years.

• IEEE 802.3af – 2003 (PoE): The devices developed to these standards provide up to 15.4 watts of DC power (at 48V DC) at each port.
• IEEE 802.3at – 2009 (PoE+): These devices can provide up to 25.5 watts at 48V DC.
• IEEE 802.3bt/UPoE: PoE devices of this type can provide up to 60 watts at 48V DC.
• IEEE 802.3bt 4PPOE: This standard has introduced two power types – up to 55 W and up to 90-100W. Of these, the power type up to 55 W is termed as Type 3 and up to 100W is termed as Type 4. In Type 3, each twisted pair must handle current up to 600 mA, while in Type 4 each pair is designed to handle current up to 960 mA.

In addition to these, the following are a few other standards that existed before and is still being used:

• IEEE 802.3u – 1995: Developed for 100BASE-T4, 100BASE-TX, and100BASE-FX fast Ethernet applications, the standard enables 100 Mbit/s (12.5 MB/s) with auto negotiation.
• IEEE 802.3ab 1999-06: This standard was developed for 1000BASE-T Gbit/s Ethernet over twisted pair with a delivery speed of 1 Gbit/s (125 MB/s)
• IEEE 802.3z   1998-07: The standard is suited for 1000BASE-X Gbit/s Ethernet over Fiber-Optic with a delivery speed of 1 Gbit/s (125 MB/s).

Benefits of Power Over Ethernet (PoE)

PoE technology has gained immense popularity over the years owing to the distinct benefits that it offers.

Cost and Time Savings

PoE technology requires less cabling than other contemporary technologies, which has led to its easy adoption across the globe. Also, it minimizes the use of accessories like AC power adapters even in electricity-powered application, thereby leading to cost savings. PoE technology also minimizes the installation time as less cabling needs to be done.

Flexibility of Network Design

PoE enables network engineers to design and plan access locations throughout the facility without being limited by electrical outlets. Like other technologies, PoE devices do not need electrical outlets nearby. This also improves the scalability of the networking architecture if it requires relocation of access points for improving the capacity or fine-tuning the coverage zones. The best example of flexibility is wireless access points as well as IP cameras, which are sometimes repositioned or relocated for better clarity.

Easy Power Management

The PoE system enables you to distribute data and power easily in different ways. The power and data can be easily distributed from a central location for easy power management in a star topology. In industrial networks, ring or mesh topologies are used. These topologies use managed switches for traffic management.

Today, many managed PoE switches utilize the simple network management protocol (SNMP) that enables network engineers to manage the power supply of devices remotely and effectively. For instance, the power supply to a PoE-enabled access point can be severed if any breach of security is noticed, and this can be easily done remotely. The SNMP features also enable teams to monitor the level of power consumption and power supply, thereby enabling efficient network operation.

Reliability

The power distribution in a PoE application can be managed from one point, so you see less of wall adapters. The PoE system can be backed with an uninterrupted and redundant power supply or it can be easily reset or disabled according to the requirement. This helps improve its reliability.

Scalability

The centralization of powerpoint assures the availability of power on the network. This means the distribution and installation of network connections is effective and simple.

Safety

PoE is intelligent technology. It can be set to avoid overload and underload conditions. Fault protection is also a standard of PoE.

Interoperability

PoE is a standards-based technology, so its interoperability with different networks is guaranteed. All network topologies including mesh and ring can be configured with PoE. Additionally, tools used for industrial networking management such as IGMP, VLANS, and RSTP/STP can be easily managed using advanced PoE switches. If the end devices are not PoE-enabled or not designed for PoE installation, still they can be converted into one using a PoE splitter or Midspan PoE injector.

Smart Power Management

The 802.3at standard, which is also known as PoE + standard enables PD and PSE devices to communicate with each other for smart power management. In a true sense, these devices enable smart power budgeting.

Power Over Ethernet Products

Below are several types of PoE products that you may need for establishing a network connection.

• PoE Switches
• PoE Media Converters
• PoE Splitters
• PoE Extenders/PoE Repeaters
• PoE Injectors
• Wireless Access Points and Bridges

To know in detail about all the above PoE products/devices, check out our blog post, A Comprehensive Guide to PoE Extenders, PoE Injectors, PoE Splitters, and PoE Switches.

Applications of Power Over Ethernet

The devices that use PoE for data and power supply are referred to as smart devices. They are commonly found in the Internet of Things (IoT). There are more than 200 types of PoE powered devices used today. The following are a few common examples of PoE:

• PoS Kiosks
• LED Lighting Systems and Intelligent Lighting Controllers
• Routing Boxes and Networked Audio Breakout
• IPTV Decoders
• Intercom and Public Address Systems
• Remote Point of Sale Clocks
• PoE Splitters
• Ethernet Extenders
• Security Access Controls
• Digital Signage
• Industrial Controls
• Network Switches
• Smart Clocks
• Routers
• VoIP Phones
• IP/Pan-Tilt Zoom Cameras
• Wireless Access Points

Conclusion

Owing to its widespread adoption, PoE technology is set to evolve further in the near future, as devices will demand more power for operation. Currently, there are PoE systems capable of supplying power up to 60W. But the technology is not standardized; thus, it is not interoperable, and may damage the device when used with non-compatible devices. This increasing demand for power is setting a precedent for the development of high power standards. For more information on VERSITRON’S PoE solutions, please explore our All PoE Products.

Disclaimer

The information provided in this white paper is intended solely for general information purposes. The practice of Engineering differs across each project, as it is driven by site-specific circumstances. Thus, any business decision based on the implementation must be taken only after consultation with a qualified and licensed professional who is capable of addressing all relevant factors, challenges, and desired outcomes. The information in these white papers is derived from various verified sources and posted after reasonable care and attention. It is possible that some information may appear incomplete, incorrect, or inapplicable considering your particular condition. In such condition, VERSITRON does not accept the liability for direct or indirect losses resulting from using, relying or acting upon the information in this white paper.