PoE (Power over Ethernet) is a technology that allows power to be transmitted through network cables, enabling the simultaneous transmission of data and power to IP terminal devices (such as IP phones, APs, IP cameras, etc.) via network cables.

What is Power over Ethernet (PoE)?

PoE is a technology that can transmit power and data to devices through twisted pair cables in Ethernet.

What devices can you connect to a PoE switch?

A PoE switch comes equipped with numerous Ethernet ports that are capable of connecting various devices, including VoIP phones, wireless access points, and IP cameras.

How does PoE work?

The PoE power supply system consists of two primary equipment roles:

• Power-sourcing equipment (PSE): Typically a PoE switch, this device supplies power to the powered devices through Ethernet. It provides functions such as detection, analysis, and intelligent power management.
• Powered devices (PD): These devices include wireless APs, portable device chargers, card readers, cameras, and other powered devices. Depending on whether they comply with IEEE standards, PD can be categorized as standard or non-standard.

When should I use a PoE switch?

The increasing prevalence of the Internet of Things and smart cities has led to a surge in the number of mobile terminals, including wireless APs, cameras, and IP phones. These devices can be deployed in various locations, making it challenging to provide them with power through traditional wiring methods, which often results in high costs.

Moreover, in large-scale LAN applications, administrators often have to manage multiple terminal devices in the same time. These devices require a unified power supply and management. However, due to the limitations of power supply locations, this can create significant inconvenience in power supply management. PoE technology effectively resolves this problem.

Typical scenarios for using PoE switches:

1. VoIP phones: If your organization uses a VoIP (Voice over IP) phone system, these phones need to transmit data and power at the same time, so using a PoE switch can simplify wiring and reduce the number of devices.
2. Network cameras: When installing IP cameras, you can provide power and data connections to the camera through a single Ethernet cable without the need for additional power cables.
3. Wireless access points: PoE switches can be used to provide power to wireless access points (APs). This way, you can install the AP in the best location without being restricted by the location of the power outlet.
4. Industrial automation equipment: In industrial environments, use PoE switches to power automation equipment, sensors, and controllers.
5. Digital signage and lighting: PoE switches can provide power for devices such as digital signage or LED lighting used in offices, stores, or other places.

PoE Standards Introduction

In order to standardize the development of PoE power supply technology, and to solve the compatibility problem between power supply and powered devices from different manufacturers, IEEE Standards Committee has released three PoE standards: from 802.3af in 2003 to 802.3at in 2009, and then to the latest 802.3bt in 2018, the new standard is backward compatible.

IEEE 802.3af

IEEE 802.3af, also known as standard PoE, has a supply voltage of 44-57V and a supply current of 10-350mA. It specifies that PSE devices need to provide up to 15.4W of DC power on each port. However, some power is lost on the Ethernet cable in actual transmission. Thus, only 12.95W is available to the powered device. It can support VoIP phones, APs, etc.

IEEE 802.3at

In October 2009, in order to meet the needs of high-power terminals, the IEEE 802.3at standard was born. On the basis of being compatible with the 802.3af standard, the IEEE 802.3at standard provides up to 30W of power to meet new needs.Its supply voltage of PoE+ ranges from 50V to 57V and the supply current is about10-600mA. Due to power loss, the guaranteed minimum output power on each port is 25W. This type can support devices that require more power like tablets, alarm systems, etc.

IEEE 802.3bt

In September 2018, the IEEE Standards Committee released the IEEE 802.3bt standard to further improve PoE power .It further enhances the power supply capability, with Type 3 providing up to 51 W power supply and Type 4 providing up to 71.3W power supply. Also included support for 2.5GBASE-T, 5GBASE-T, and 10GBASE-T, expanding the use of applications such as high-performance wireless access points and surveillance cameras and other applications.

Generally, IEEE 802.3af standard is called PoE power supply, the IEEE 802.3at standard is called PoE+ power supply, and the IEEE 802.3bt standard is called PoE++ power supply, also known as 4PPoE. The parameters corresponding to the three power supply technologies are shown in the figure below.

Asterfusion Network Switches Comply with Various PoE Standards

What are the benefits of using a PoE switch?

Although PoE power supply cannot improve the quality and speed of the network, it greatly expands the deployment scenarios of Internet access devices. The PoE function also brings many other advantages, including:

● Cost reduction

Power is provided directly through the network cable, which significantly reduces the number of power sockets required for installing network devices and the resulting power wiring, which can reduce access costs and deployment costs.

● Flexibility

Without being connected to a power socket, devices such as surveillance cameras, wireless access points, and IP network phones can be placed in any ideal location, and are easy to move, which improves deployment flexibility. At the same time, the powered device can be remotely managed by controlling the PoE power supply device to perform operations such as power off and restart, which improves management flexibility.

● Security

Using standard-compliant PoE power supply can intelligently protect network devices from overload and insufficient power supply, and naturally avoid the potential risks caused by incorrect power supply installation.

● Ease of use

The relevant standards for PoE power supply are backward compatible, and standard-compliant power supply and powered devices can negotiate parameters on their own, providing a nearly “plug and play” experience.

● Reliability

The PoE power supply end can perform power redundancy backup through an uninterruptible power supply (UPS), ensuring continuous operation even during a main power failure.

Benefits of SONiC-base Layer 3 POE++ switch

PoE++ can provide up to 90 watts of power. It can meet the network requirements of industrial automation, data centers and other environments because it can achieve more efficient power transmission and reduce power loss, and supports power priority (power can be allocated to key devices first) and device discovery (allowing PSE to detect and verify connected devices). In these complex environments, three-layer switches have many advantages such as fast speed and good performance, and are highly favored by people. SONiC, as a popular open source network operating system, is also widely used in large-scale user scenarios due to its scalability and ease of use.

There are limited manufacturers on the market that can provide three-layer PoE++ switches, and even fewer manufacturers that can adapt to SONiC. Asterfusion’s self-developed 3-layer POE++ switches have excellent performance.

These open network switches are preloaded with a feature-rich SONiC NOS ( AsterNOS) which is a container-based application deployment . It makes the switch easy to expand new functionalities even by users. It supports wire-speed Layer 2 switching and Layer 3 routing with MC-LAG feature, comprehensive QoS, advanced security and complete network management .Asterfusion PoE/PoE+ /POE++ switches can power any 802.3af or 802.3at 802.3bt device of the market, enable them flexible and secure.

Asterfusion now has 8 port Gigabit /16 port Gigabit /24 port Gigabit /48 port Gigbit PoE /PoE+/POE++ switches that follow with the PoE standard for greater security and better functionality.

The Following Table lists Asterfusion 24/48 Ports Gigabit PoE/PoE+/POE++ Switches.

How to choose the right PoE switch for your needs?

There are several factors you should consider when choosing the number of PoE ports for your push button. These include the number of current and future devices, scalability, power budget, and network architecture. By evaluating these factors, you can choose a PoE switch that will perfectly match your network needs.

Other Questions and Answers

What is the difference between a Gigabit PoE switch and a PoE switch?

When considering the difference between a Gigabit PoE switch and a PoE switch, it’s important to assess the specific needs of the network. If the network environment does not require high-speed transmission and the distance is short, a PoE switch can be chosen. However, if higher transmission speed and coverage are needed, especially with future expansion plans, selecting a Gigabit PoE switch would be more appropriate. Therefore, the most suitable PoE switch should be chosen based on the actual network requirements, budget considerations, and future expansion plans to ensure stable and efficient network operation.

What is the difference between a PoE switch and a normal switch?

With PoE technology, there is no need to provide separate power supplies for terminal devices as long as there is a network environment. PoE ensures the normal operation of the terminal devices by providing power through the network cables.

In contrast, normal switch devices cannot provide power support for terminal devices. For them to operate properly, they must be powered by external sources such as power sockets or adapters.

Compared to normal switch, PoE switch significantly reduces the need for extensive power cable installation, simplifies the overall line installation process, and facilitates maintenance in the long run. However, PoE switch does require terminal devices to have the capability to receive power through network cables.

Currently, PoE switch has made significant advancements in industries such as security, IT, medical, and education, thereby promoting industry growth. Users should choose between PoE switch and normal switch based on their specific needs and industry characteristics.

There is a physical picture of Asterfusion’s PoE switches:

Can a standard PoE switch be used as a normal switch?

According to the PoE power supply principle, a standard PoE switch(Active PoE switch), can identify whether the connected device needs power supply, and can usually disable the PoE function through software, so it can be used as a normal switch. Non-standard PoE switches(Passive PoE switches), usually output a DC voltage with constant power at the port. Connecting normal devices may cause the risk of damaging the device, so such switches are not recommended for use in non-PoE scenarios.

Can a normal switch obtain PoE function through software upgrade?

The PoE function needs to rely on hardware functions to be implemented, so the PoE function of the switch cannot be obtained through software version upgrades. For application scenarios where normal switches need to access PoE devices, connecting PoE injectors between the device and the switch is a feasible transition solution. PoE Injectors require independent power supply. The input interface is connected to the normal switch through a network cable, and the output interface can output a data signal with a certain power superimposed on it, so that the non-PoE device can achieve the functions of communication and power supply.

Is the PoE device safe?

According to the principle of PoE power supply, as long as the PoE function adheres to the IEEE 802.3 af/at/bt standard, it is considered safe. For instance, even if a non-PoE device is connected when the PoE function is enabled, it will not be harmed. As mentioned earlier, after a successful “handshake,” the PSE will transmit the required power to the PD based on the agreed parameters. Otherwise, power transmission will not occur. Since this process is well-defined in the IEEE 802.3 af/at/bt standards, PoE power supply methods that conform to these standards are deemed safe and reliable. The Asterfusion PoE equipment also features a PoE detection alarm function, which stops power supply in case of PD device overload, short circuit, threshold exceedance, or chip temperature surpassing a certain threshold, offering further safety protection.

Will PoE impact network speed?

PoE allows fulfilling power supply and network transmission requirements over a single line simultaneously, without impacting network speed. Ethernet signals are differential signals, and PoE loads power on 2 or 4 pairs of differential signal lines without altering the signal level difference between the pairs. Hence, power supply and communication do not interfere with each other.

What is the maximum distance for PoE power supply?

PoE typically has distance limitations for power and data transmission. On standard Cat5e and Cat6 Ethernet cables, the maximum transmission distance is 100 meters or 328 feet. It’s essential to ensure that the distance between the power supply equipment (PSE) and the powered device (PD) does not exceed this range. If a longer distance is required, additional extension devices or technologies may be necessary to extend the power supply distance.

How to determine the required power for PoE power supply devices?

Taking a PoE switch as an example, the total power output of the switch’s PoE ports is limited. Typically, the selection is based on the PoE switch’s total power output, the rated power required by the powered devices, and the number of ports required. When connecting PD devices with multiple power requirements, it is necessary to determine in advance whether the total power output of the PoE switch can be greater than the total input power of all connected PD devices, and whether the PoE switch supports the corresponding power level standard.

To illustrate, consider a PoE switch meeting the 802.3at standard with a total output power of 130W for 8 ports. According to the 802.3af standard, a single port of the PSE device can output a maximum power of 15.4W. Hence, the device can meet the needs of all 8 ports connected to 802.3af standard PD devices. Under the 802.3at standard, the PSE device needs to provide a maximum power of 30W per port, allowing connection to a maximum of only 4 802.3at devices requiring 30W power supply. Therefore, when selecting a model, it is essential to consider standard compatibility, the number of interfaces, and whether the PoE power supply device’s total output power meets the requirements. This prevents the issue of standard compatibility but insufficient power supply due to insufficient device load capacity.

What are Active PoE and Passive PoE?

Active PoE and Passive PoE are two different types of PoE based on the compliance with IEEE 802.3 standards and the PoE power supply principle.

Active PoE(Standard PoE)

Active PoE is an Ethernet power supply technology that negotiates the appropriate voltage during device connection. Active PoE switches adhere to the IEEE 802.3 standard and perform a series of tests and checks before providing power, ensuring compatibility with the remote device (PD device). This communication negotiation process is sometimes referred to as a “handshake.” If compatibility is not established, the active PoE switch will refrain from providing power to avoid potential damage to non-PoE devices.

Taking the Asterfusion CX204Y-24GT-M-SWP2 as an example, the Asterfusion PoE switch offers a range of advanced technologies to safeguard network basic protocols against malicious attacks, such as DHCP Snooping, dynamic ARP detection, ND Snooping, IPSGv4/v6, and more. Moreover, it supports port isolation technology and ACL policies in both outbound and inbound directions, ensuring a secure and flexible networking solution for users. Additionally, the switch implements MAB authentication, which restricts unauthorized devices like printers and IP phones from illegitimately accessing the network. In summary, Active PoE presents a safer and more intelligent Ethernet power supply approach.

Passive PoE(Non-standard PoE)

Unlike Active PoE, Passive PoE functions as a straightforward Ethernet power supply (PoE) system without involving negotiations between the power supply equipment (PSE) and the powered device (PD). It delivers power continuously to the connected device through the Ethernet cable, bypassing protocol checks. Instead, the power adapter’s wires connect directly to the network cable, merging the power interface of the powered device with the network port. Although Passive PoE lacks standardized technical specifications and negotiation mechanisms, it offers a simple and direct power supply method suitable for specific application scenarios.

In summary, Passive PoE provides a straightforward and direct power supply method, which can be beneficial in certain specialized situations , a family scene with a limited budget , for example.

Refference

Asterfuison(September 14, 2022)”What is a PoE Switch and How Does It Work?“

L Shen Technical Sevices LLC (2019) “Power Over Ethernet (PoE) Technical Overview“

Morty Eisen Marcum Technology meisen@marcumtechno (2010) “Introduction to PoE and the IEEE802.3af and 802.3at Standards”

Felipe Gabriel Osorio; Ma Xinran; Yuan Liu; Paul Lusina; Edmond Cretu (2015)”Sensor network using Power-over-Ethernet“

Laxmi Khichadi; K. Nagamani (2019) “Performance Evaluation of Power over Ethernet in an Ethernet Switch“

Galit Mendelson(2004) “All You Need To Know About Power over Ethernet (PoE) and the IEEE 802.3af Standard“

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