Technical Guide to IP Cameras- Overview, Types, Applications

Andy Chen

IP cameras, also known as Internet Protocol cameras or network cameras, are a type of security camera that utilizes an IP network to receive and transmit video data. Their primary function is to capture video footage and send it over the network. These cameras are commonly used in various sectors and environments as remote monitoring and management tools to enhance security and protect property.

How Does An IP Camera Work?

IP cameras function similarly to digital cameras in capturing high-quality images. However, what distinguishes them is their ability to compress image files and transmit them automatically to a network video recorder (NVR) through a network connection. Typically, IP cameras can be linked to the network either via an Ethernet cable connected to a broadband modem or router, or wirelessly through a Wi-Fi router.

In the case of a building already equipped with a network infrastructure, setting up IP surveillance cameras is a straightforward process. Similar to connecting your laptop or cell phone to a Wi-Fi network, you simply need to integrate the IP cameras and other devices into your existing network system. This involves establishing connections and configuring the cameras to communicate within the network.

By seamlessly integrating IP cameras into the network, you can take advantage of their features for remote monitoring and enhanced security. These cameras enable you to conveniently access and manage them from any location with network access, providing effective surveillance and peace of mind.


Once all the connections have been properly established, the cameras can begin their operation by capturing video footage and transmitting it to the network video recorder.

Four Common Types of IP Camera

There are various video surveillance solutions, in which many different types of security cameras are adopted. Among those surveillance cameras, there are four most commonly used ones, dome cameras, bullet cameras, and turret cameras.  


Four Important Specifications of IP Cameras

When selecting a security camera, it is important to consider not only the type of camera but also its specifications, as they can significantly impact performance. Here are four crucial specifications to keep in mind:


The resolution of an IP camera refers to the total number of pixels that compose an image, typically measured by its width and height. Common resolutions include 720p, 1080p, 5MP, 4K, and 8MP. Higher resolutions generally translate to a greater number of pixels per inch (PPI), resulting in sharper, high-quality images.

Field of View

The field of view (FOV) of an IP camera is determined by its lens and represents the coverage area that can be observed. Different lenses offer varying FOVs, influencing how wide an area the camera can capture. A wider FOV enables monitoring of larger areas. For instance, a large parking lot may require a different lens with a broader viewing angle compared to a small room.

Focal Length

The focal length of a camera lens, measured in millimeters (mm), determines the angle of view and the distance at which the camera can effectively capture images. There are two types of lenses commonly used: fixed focal length and varifocal lenses. Fixed focal lengths, such as 3.6mm or 8mm, provide specific viewing angles and identification distances. Varifocal lenses, like 2.8-12mm, offer adjustable focal lengths, allowing for flexibility in field of view and identification range.

Low Light Sensitivity

Low light sensitivity, often measured in Lux (lx), indicates a camera's ability to produce high-quality images in low-light environments, minimizing noise and preserving details. Factors such as pixel size, signal-to-noise ratio, and lens aperture contribute to a camera's low-light performance. Lower Lux values indicate superior performance in darker areas. For example, cameras with a range of 100-1,000lx are suitable for well-lit workspaces, while cameras with 0.0001lx are designed for moonless or overcast nights.

Most Popular IP Camera Applications


Home Use

For individuals seeking tools to enhance family connections, monitor home security, or safeguard their property, IP cameras are a must-have item. Many homeowners opt to install video surveillance systems to provide a sense of safety for themselves and their families.

IP cameras utilized in home security systems serve a multitude of purposes. They can be positioned near the front door to capture images of anyone entering or lurking around the house. They can also be installed in the backyard to preserve cherished moments with family members. Additionally, they can be placed inside rooms to ensure the well-being of babies or monitor specific areas of the house.

Business Use

Commercial security cameras are commonly employed in business premises, supermarkets, shops, restaurants, and other commercial establishments. For business owners, security cameras not only protect their property, ensuring uninterrupted operations and deterring criminal activities through real-time monitoring, but they also keep them connected to daily operations and employee safety.

Video surveillance solutions can be utilized to maintain outdoor perimeter security and monitor the surrounding areas. Compared to traditional systems, commercial IP video surveillance systems offer enhanced reliability and security with built-in encryption, data compression, network connectivity, and cybersecurity measures.

Public Safety

Surveillance cameras play a vital role in managing public order, safeguarding public safety, and protecting public property. It is common to find monitoring cameras positioned along traffic roads, parking lots, government buildings, and hospitals. Moreover, security cameras are prevalent in public areas such as schools, parks, communities, and neighborhoods.


IP cameras have become an integral part of home, business, and public surveillance systems. With the appropriate video management software, footage captured by IP cameras can be accessed from anywhere worldwide through network connectivity, be it through a laptop or a mobile phone. In many cases, IP cameras can also be remotely controlled, bringing significant convenience to our lives.

There are various types of security cameras designed for specific applications, which is why it is important to consider multiple factors when purchasing IP cameras for your security system. Before proceeding, it is advisable to determine your budget and specific requirements.

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IP Cameras vs Analog Cameras, What Are the Differences?

Andy Chen

In the realm of security and surveillance, the ongoing discussion surrounding IP cameras versus analog cameras holds significant importance for both businesses and homeowners. The choice between an IP camera system and a traditional analog setup can have a profound impact on the effectiveness and scalability of your security measures. This article aims to explore the distinctions between these two prevalent camera types, empowering you to make an informed decision that aligns with your specific surveillance requirements.

Understanding IP Cameras and Analog Cameras

Internet Protocol (IP) cameras refer to all the digital video cameras that can send and receive data via an IP network. They are widely used as video surveillance cameras, and they come in varying designs and capabilities. Some IP cameras need the support of a network video recorder (NVR) for recording and video/alarm management. However, others operate without an NVR, meaning they can record directly to a remote or local storage media. To read more: Technical Guide to IP Cameras - Overview, Types, Applications.

IP cameras encompass all digital video cameras capable of transmitting and receiving data through an IP network. They are widely employed as video surveillance cameras, available in various designs and functionalities. Some IP cameras necessitate the support of a network video recorder (NVR) for recording and managing video and alarms. However, others can operate independently without an NVR, enabling direct recording to local or remote storage media. For further information, please refer to the "Technical Guide to IP Cameras - Overview, Types, Applications."

On the contrary, analog cameras capture images, convert them into analog signals, and transmit them over a coaxial cable to a digital video recorder (DVR). The DVR then converts the analog signals into digital format, compresses the files, and stores them on a hard drive. Below, you will find a comprehensive comparison between an IP camera and an analog camera.

Advantages of IP Cameras

IP cameras provide superior resolutions and scalability, making them ideal for environments that demand comprehensive surveillance coverage over large areas. The transition towards IP-based surveillance has been predominantly influenced by the following factors:

1.Enhanced Resolution and Image Quality: IP cameras generally offer resolutions that surpass those of analog cameras by several magnitudes, resulting in sharper and more detailed images. With the availability of resolutions surpassing 4K, IP cameras deliver the level of clarity necessary for meeting stringent security requirements.

Analog Cameras VS IP Cameras

2. Seamless Integration and Advanced Functionality: By leveraging digital networks, IP cameras have the ability to seamlessly integrate with existing IT infrastructure and services, including cloud storage and sophisticated surveillance software. They offer a wide range of analytical capabilities, such as object recognition, perimeter breach alerts, and other intelligent analytics that leverage video data more efficiently. On the other hand, analog cameras generally lack support for advanced analytics but fulfill basic surveillance functions, such as video recording and live monitoring.

Human Detection
3. Scalability and Flexibility: Thanks to their network-based infrastructure, IP cameras offer effortless integration into existing systems. They support expansive and adaptable surveillance ecosystems that can expand and evolve over time without being constrained by physical connections.
4. PoE Support: IP cameras often have the capability to receive power through the same cable used for data transmission (Power over Ethernet), simplifying installation and reducing the complexity of wiring. This feature eliminates the need for additional power supply units and enables more straightforward and neater setups. In contrast, analog cameras typically require separate power connections.
5. Remote Access: One of the most desirable attributes of IP cameras is the ability to remotely view and manage surveillance footage. Users can access live and recorded videos via internet-connected devices from anywhere in the world, ensuring continuous monitoring and oversight.
6. Advanced Data Protection: IP cameras offer enhanced data protection through encryption and secure network transmission. This ensures that the crucial footage they capture is less susceptible to interception or unauthorized access, addressing a significant concern associated with the more vulnerable transmission methods of analog systems.

Advantages of Analog Cameras

  1. Cost-Effectiveness: One of the primary advantages of analog cameras is their affordability. The initial investment for analog surveillance equipment is typically lower compared to IP-based systems, making them an attractive option for budget-conscious users or smaller-scale operations.

  2. Simplicity and Ease of Use: Analog systems are often considered less complex to install and operate. With a straightforward setup that doesn't require in-depth knowledge of IT infrastructures, analog cameras can be an excellent choice for those seeking a basic yet effective surveillance system. In contrast, IP cameras may have a steeper learning curve for users who are unfamiliar with network technology.

  3. Wide Compatibility: Analog cameras have been in use for decades, leading to a widespread standard of system compatibility. This advantage is particularly valuable when upgrading existing systems, as existing wiring can be reused for new analog cameras.

  4. Low Bandwidth Requirements: Unlike IP cameras, which transmit large amounts of data over a network, analog cameras do not consume significant bandwidth. This results in a lighter load on your network infrastructure and potentially reduced ongoing operational costs.

IP Cameras vs. Analog Cameras: Which is ideal for your business?

Deciding between IP cameras and analog cameras for your business depends on finding the right balance between quality, cost, and ease of use. IP cameras may be the preferred choice if you require high-resolution footage, scalability, and integration with cutting-edge technology. However, if budget constraints are a significant factor and your current infrastructure supports it, analog cameras offer reliability without the need for an extensive overhaul. Ultimately, aligning your selection with your operational needs and financial capacity will ensure a secure and efficient surveillance environment for your business.

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Unlocking the Secrets of PoE Switches — A Complete Guide

Andy Chen

Power over Ethernet (PoE) switches have gained significant popularity as a practical solution for businesses seeking to conveniently deliver power and data through a single connection. In this comprehensive guide, we will delve into the various types of PoE switches, highlight their advantages and applications, and provide insights on selecting the most suitable PoE switch to meet your specific requirements.

What is a PoE Switch?

A PoE switch combines the functionalities of a switch and a power source into a single device. Equipped with multiple Ethernet ports, these switches facilitate seamless connections with various devices such as VoIP phones, wireless access points, and IP cameras. By integrating power delivery capabilities, PoE switches eliminate the need for separate power cables, streamlining installations. These switches prove particularly beneficial in network deployments where power outlets are limited or in scenarios where devices are situated in challenging-to-access locations.

PoE switches leverage the power over Ethernet (PoE) technology, enabling the simultaneous transmission of data and electrical power through Ethernet cables. This innovative technology employs a combination of power sources and power injectors to deliver power to connected devices. Acting as intermediaries between the power source and the devices, power injectors handle the transmission of both data and power, ensuring efficient operation. Also Check- PoE switch


Types of PoE Switches

When selecting a PoE switch, it is vital to familiarize yourself with the various types available. There exist two primary categories of PoE network switches:

The Unmanaged PoE Switch

Designed for simplicity and ease of use, the unmanaged PoE switch offers a plug-and-play solution that suits smaller setups. It requires minimal configuration and is user-friendly. However, it lacks extensive customization options, management features, and advanced security capabilities. Consequently, it is best suited for applications with uncomplicated network requirements, such as home networks or small-scale environments comprising fewer than 5-10 computers.

The Managed PoE Switch

Engineered to deliver enhanced control and comprehensive network management, managed PoE switches excel in scenarios that demand advanced functionality. With their robust security features and extensive configuration options, they prove ideal for applications like enterprise networks, data centers, and large-scale surveillance systems. These switches offer features such as VLANs (Virtual Local Area Networks), QoS (Quality of Service), port mirroring, and heightened port security, catering to complex networking requirements.

Advantages of PoE Switches

Given how PoE switches work, the benefits of PoE switches are obvious.

Simplified Installation: PoE network switches are known for their user-friendly installation and configuration. With plug-and-play functionality, these switches eliminate the need for complex wiring or intricate setup procedures. Built-in features like port mirroring, VLANs, and QoS further simplify network management tasks, enhancing overall operational convenience.

Cost Efficiency: PoE switches exhibit remarkable energy efficiency. By intelligently delivering the precise power required for each connected device, they eliminate the need for oversized power supplies. This efficient power allocation not only reduces energy consumption but also contributes to long-term cost savings, making PoE switches a financially advantageous choice.

Enhanced Flexibility: The ability to power devices through PoE enables easy relocation to areas without available power outlets. This flexibility allows PoE switches to be conveniently placed in challenging-to-reach locations or areas distant from power sources. Security cameras, for instance, can be strategically installed in optimal positions, regardless of the availability of nearby power outlets.

Future-Proofing: With the rapid growth of the Internet of Things (IoT) industry, PoE switches provide future-ready infrastructure. By incorporating PoE switches into your network, you can seamlessly accommodate the increasing number of devices designed to leverage this technology. This scalability ensures long-term compatibility and positions your network for seamless integration with emerging IoT devices.


PoE Switch Applications

This rapid expansion of network-connected devices means that PoE technology and PoE switches will grow in importance to most networking infrastructures. While PoE switches have numerous applications, we mainly discuss the three most common application scenarios.

  • VoIP Phones: VoIP phones are PoE devices, with PoE allowing for a single connection to the wall socket and the ability for remote powering down

  • IP Cameras: Security cameras can be connected to PoE switches to enable fast deployment and simple repositioning.

  • Wireless: Many wireless access points are PoE compatible. Thus, PoE switches allow for easy relocation and remote positioning.

  • Smart Home Automation: LED lighting, heating and cooling systems, appliances, voice assistants, and electric car charging stations.

How to Select the Right PoE Switch

When selecting a PoE switch, it is important to consider your application requirements, the features and limitations of the PoE network switch. Of course, the power requirements of connected devices are also important. Some PoE network switches are designed to power devices that require up to 30 watts, and some are even designed for power devices that require up to 60 watts.

Features of PoE Switches to Consider

In addition to the type of switch and power requirements, there are a number of features to consider when selecting a PoE switch. These features include port speed, port count, port types, PoE budget, power savings, and port security.

  • Port speed: Maximum speed a port can achieve. It is important to choose a switch with a port speed that can support the connected devices. The port count is the number of ports available on the switch. It is important to choose a switch with enough ports to accommodate all of the connected devices.

  • Port type: Common port types include RJ45, SFP, and SFP+. It is important to choose a switch with the right port type for connected devices.

  • PoE budget: Maximum amount of power that can be allocated to connected devices. It is important to choose a switch with a PoE budget that can accommodate all of the connected devices.

  • Power savings: Designed to conserve energy by automatically turning off unused ports. This can help to reduce energy costs. 

  • Port security: Designed to protect connected devices from unauthorized access.

Limitations of PoE Switches

Nonetheless, there are some limitations to PoE variation that you should be aware of:

  • Restrictions on distance: Typically, PoE switches can transmit over Ethernet up to a distance of up to 100 meters. The 100-meter distance restriction presents a challenge for large campuses, restaurants, and businesses implementing PoE. However, there are still devices like power extenders and powered fiber cables that can be used to extend the PoE range.

  • Power: If you require high power over poe networks, you must ensure that the power capacity of your PoE switches meets your requirements due to the power limitation imposed by PoE standards and Wattage.


FAQs about PoE Switch

Q: Non-PoE vs. PoE Switch: How do they differ?

A: Non-PoE switches cannot deliver power to connected devices, necessitating the use of midspan power sourcing equipment (PSE), such as a PoE injector. This setup adds power while transmitting data to powered devices (PDs). In contrast, PoE switches offer a simpler solution, directly delivering power and data to PDs with just a network cable and a power cable.

Also Check- PoE vs PoE+ vs PoE++ Switch: How to Choose?


Q: Do PoE Switches Require Special Cables?

A: No. The Ethernet cables that should be used for PoE network switches primarily depend on the data rate of the PoE port; for instance, Cat3 or better cables can be used for 10/100M; Cat5/Cat5e/Cat6 cables are required for 1000M. In the future, Cat6a or higher cables may be required for the installation of 2.5G/5G/10G PoE devices.


Q: Active vs Passive PoE Switch: Should I Choose Active or Passive PoE Switches?

A: Active PoE network switch complies with standard PoE. On the contrary, passive PoE network switch does not adhere to any IEEE standard. There are many ways that active and passive PoE switches differ from one another, like how the PoE power supply pinout looks and whether or not they support Ethernet.

 Also Check- Active vs. Passive PoE Switch: Which Should We Choose?


Q: Can the PoE Switch be used with a computer or other non-PoE devices? And will a PoE switch harm devices that do not use PoE?

A: Yes, a PoE switch can be used with non-PoE devices like computers. The switch automatically detects whether a connected device is PoE-compatible and will only supply power to PoE-enabled devices. So, it won't harm non-PoE devices; they just won't receive power through the switch.


Q: Is it possible to connect two PoE switches?

A: You could, yes. The PSE only supplies PD with power when it determines that the device can handle it. As PSEs, the two PoE switches will only be used for data communications.


Q: What is the maximum transmission distance of PoE? How to extend the transmission distance of PoE?

A: Whether using IEEE 802.3af (PoE) or 802.3at (PoE+), data and power transmission are limited to a distance of 100 meters over Ethernet cables in standard PoE. Media converters and PoE extenders, for example, can extend the range to up to 300 meters if you want to increase the maximum distance.


PoE switches are an effective solution for businesses looking to provide power and data over a single connection. They can simplify installation, reduce clutter, and improve energy efficiency. When selecting a PoE network switch, it is important to consider your application requirements, the power requirements of the connected devices, and the features of the switch. It is also important to consider the cost and long-term cost savings of using a PoE network switch.

If you are looking for a reliable and cost-effective PoE switch, check out Linovision PoE Switches.

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What Is Power over Ethernet and How to Add PoE to Your Network?

Andy Chen

With the wide application of VoIP phones, IP cameras, and wireless access points, Power over Ethernet (PoE) has made great strides in recent years. And PoE network is expected to expand rapidly in the future due to the increasing number of IoT applications and smart device deployments and newly ratified standards designed to support more smart devices. In this article, we will provide an introduction covering various aspects of PoE such as PoE wiki, PoE standards, PoE types, PoE classes, and PoE applications.

What Is Power over Ethernet (PoE)?

PoE is a networking technology that can transmit both data and power over one single standard Ethernet cable. It allows us to use network cables such as Cat5/Cat5e/Cat6/Cat6a cables to provide data connections and electric power to wireless access points, IP cameras, VoIP phones, PoE lighting and other powered devices (PDs). With the use of PoE technology, we can easily deliver power to indoor or outdoor PDs without the need to install additional electrical infrastructure or to deploy power outlets at every endpoint.


Benefits of PoE Network—Why Use Power over Ethernet?

Besides the above-mentioned benefits, there are several more appealing reasons for adopting PoE in networking.

Time & Cost Saving: By using PoE in the network, we do not need to deploy electrical wiring and outlets for terminal PDs. This will help to save much power cabling cost especially when there are lots of PDs in the network. Furthermore, there is no need to hire a qualified electrician for the PoE network, so you may also save both time and money on electrical installations.

Flexibility: Since Ethernet network cables are easier to deploy than electrical ones, PoE networking allows us to install PDs nearly anywhere rather than near the electrical outlets. This offers a ton of flexibility for setting up and repositioning terminal devices.

Reliability: PoE power comes from a central and universally compatible source rather than a collection of distributed wall adapters. It can be backed up by an uninterruptible power supply (UPS) or controlled to easily disable or reset devices. By doing so, the PDs will run as usual even though Power Sourcing Equipment (PSE) breaks down.

Evolutionary Path of the Power over Ethernet (PoE)

Institute of Electrical and Electronics Engineers (IEEE), Cisco, and the HDBaseT Alliance have released several standards to define PoE. These standards include IEEE 802.3af, IEEE 802.3at, IEEE 802.3bt, Cisco UPOE, and Power over HDBaseT (PoH).

Evolutionary Path of the Power over Ethernet (PoE)

PoE Types

Due to different classification standards, PoE can be divided into different types. Currently, there are 4 PoE types based on IEEE PoE Standard: Type 1(IEEE 802.3af), Type 2(IEEE 802.3at), Type 3(IEEE 802.3bt), and Type 4(IEEE 802.3bt), as shown in the following chart.

PoE Types

PoE vs. PoE+ vs. PoE++ (UPoE )vs. PoH

PoE (IEEE 802.3af), also known as PoE type 1, provides up to 15.4 watts of power per port and is used for devices like IP phones and cameras. PoE+ (IEEE 802.3at), PoE type 2, offers up to 30 watts and powers devices like PTZ cameras. PoE++ or UPoE (IEEE 802.3bt), also referred to as PoE type 3, delivers up to 60 watts and 100 watts, PoE type 4, per port for high-performance devices. Power over HDBaseT (PoH) enables power and data transmission for AV equipment over a single cable. The figure below illustrates the common applications of different PoE types for your reference.

PoE vs. PoE+ vs. PoE++ (UPoE )vs. PoH

PoE Classes

Power over Ethernet (PoE) classes define standardized power levels for different network devices. These classes ensure compatibility between Power Sourcing Equipment (PSE) and Powered Devices (PD).

The classes, ranging from Class 1 to Class 8 as the above chart shows, correspond to specific IEEE standards, indicating the maximum power output of the PSE and the maximum power input of the PD. Let’s delve into more details about each class:

PoE Classes

Class 1 is suitable for low-power devices such as IP phones, voice-over-IP (VoIP) devices, and basic sensors.

Class 2 is intended for devices that require slightly higher power, including wireless access points, small IP cameras, and IP intercom systems.

Class 3 is commonly used for devices that require moderate power, such as larger IP cameras, point-of-sale systems, and access control devices.

Class 4 provides increased power delivery capabilities and is suitable for power-hungry devices like pan-tilt-zoom (PTZ) cameras, video phones, and thin clients.

Class 5 introduces the support for four pairs of Ethernet wires, enabling higher power transmission. It is designed for devices with more demanding power requirements, including advanced PTZ cameras, multi-channel wireless access points, and small LED lighting systems.

Class 6 provides increased power delivery capabilities beyond the previous classes. It can support devices like high-power pan-tilt-zoom cameras, multi-radio wireless access points, and small LCD displays.

Class 7 offers even higher power capabilities introduced with the IEEE 802.3bt standard. It is suitable for devices like high-performance access points, large displays, and thin clients requiring substantial power.

Class 8 represents the highest power class defined by current PoE standards. It is designed for power-hungry devices such as video conferencing systems, advanced lighting systems, and digital signage

It’s important to note that the power levels specified for each class represent the maximum allowable values, and the actual power delivered or consumed by the PD may vary based on its specific power requirements and negotiation with the PSE. Besides, understanding PoE classes allows network administrators to ensure that the power requirements of their devices align with the capabilities of their PoE infrastructure, ensuring proper operation and avoiding potential power supply issues.

Passive PoE vs. Active PoE

Power over Ethernet can also be divided into passive PoE and active PoE in general. Active PoE is the standard PoE which refers to any type of PoE that negotiates the proper voltage between the PSE and the PD device. Passive PoE is a non-standard PoE technology. It can also deliver power over the Ethernet line but without the negotiation process.

How to Add PoE to Your Network?

The PoE supplied in the network generally comes from three different sources: PoE switch, PoE injector, and PoE splitter. The PoE switch is the easiest way to power up the PDs. You only need to run Ethernet cables from a PoE network switch port to the terminal PoE device. A PoE injector is used when there is no PoE switch in the network. It has an external power supply and is responsible to add power to data that is coming from a network switch that is not PoE-capable. PoE splitters also supply power, but they do so by splitting the power from the data and feeding it to a separate input that a non-PoE-compliant device can use. It is commonly used for deploying remote non-PoE devices with no nearby AC outlets in the network.


Common FAQs on PoE Network

Q: What is the voltage of Power over Ethernet?

A: Power over Ethernet is injected onto the Ethernet cable at a voltage between 44v and 57v DC, and typically 48v is used. This relatively high voltage allows efficient power transfer along the cable, while still being low enough to be regarded as safe.

Q: What data speed does PoE offer?

A: Generally, PoE can deliver data rates at 10/100/1000Mbps over Cat5, Cat5e and Cat6 cables. Now thanks to the widespread IEEE 802.3bt PoE standard and PoE++ technology, PoE is able to deliver speeds of 2.5 Gbps to 5 Gbps over 100m and reaches 10 Gbps in recent times.

Q: Are there any limitations of PoE network?

A: Yes, PoE network does have some pesky limitations. First, it has a restricted reach of 328 feet (100 meters) which limits the viable locations where users can operate a remote IP-enabled device. Second, a single PSE such as a PoE switch usually connects to multiple PDs. If the PSE broke down, all the PDs will stop working. Therefore, it is important to buy qualified switches from a reliable supplier. In addition, you may also consider connecting the PSE to an uninterruptible power supply system.

Q: What are PoE midspan and PoE endspan?

A: The PoE midspan is usually a PoE injector that serves as an intermediary device between a non-PoE switch and the terminal PoE-capable powered device. A PoE endspan, which is commonly called the PoE network switch, directly connects and supplies both PoE power and data to a PD. PoE endspan provides power over the data pairs, also known as PoE Mode A. PoE midspan provides power using the pins 4-5 and 7-8, also known as PoE Mode B.

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PoE Switch vs PoE Injector: Why Choose PoE Switch to Build Wireless Networks?

Andy Chen

Power over Ethernet (PoE) technology has transformed the way we construct wireless networks by enabling the simultaneous transmission of data and power over a single Ethernet cable. This innovative approach eliminates the need for additional modifications to the existing Ethernet infrastructure, allowing power devices (PDs) like IP cameras and wireless access points to receive power seamlessly. To gain a comprehensive understanding of PoE networks, you can consult resources such as the Demystifying PoE Network: Features, Standards, Types, and Common FAQs guide. When implementing PoE technology, you have two primary options: PoE switches and PoE injectors. In this article, we will delve into the distinctions between these two alternatives and elucidate why a PoE switch is often the superior choice for constructing wireless networks.

What Is A PoE Switch?

A PoE switch is an Ethernet switch equipped with integrated PoE capabilities, enabling it to deliver power directly to connected devices through the Ethernet cable. This eliminates the need for additional equipment, as you can directly connect PoE-enabled devices like IP cameras and wireless access points to the PoE switch using Ethernet cables. The switch seamlessly provides power to the devices, simplifying the setup process and reducing the complexity of the network infrastructure.


What is A PoE Injector?

A PoE injector is a device designed to enable PoE functionality in non-PoE network switches or routers. It acts as an intermediary between the non-PoE switch and the PoE-enabled device. By connecting the injector between these two components, it injects power into the Ethernet cable, delivering power to the device. However, it's important to note that utilizing a PoE injector adds an extra step to the installation process. You need to connect the injector to both the PoE-enabled device and the non-PoE switch, ensuring that power is properly supplied to the device.

Build Wireless Networks: PoE Switch vs PoE Injector

While both PoE switches and PoE injectors have the capability to deliver power over Ethernet cables, there are compelling reasons why a PoE switch is frequently considered the superior option when it comes to constructing wireless networks.

PoE Switches Are More Convenient and Easier to Install

PoE switches offer greater convenience and simplicity compared to PoE injectors when it comes to installation. Unlike PoE injectors, PoE switches eliminate the need for additional equipment, streamlining the installation process and reducing cable clutter. With a PoE switch, powering your devices becomes effortless since the switch itself provides power, eliminating the need for a separate injector. On the other hand, utilizing a PoE injector necessitates an additional installation step, potentially consuming more time and requiring extra equipment.

PoE Switches Are More Cost-Effective

When taking a long-term perspective into account, PoE switches provide superior cost-effectiveness. Although the initial investment in a PoE switch may be higher compared to a PoE injector, the overall cost savings over time are significant. By eliminating the need for additional injectors, you avoid the expense of purchasing and maintaining multiple devices. Moreover, the streamlined installation process and centralized power management offered by PoE switches result in time and effort savings, further contributing to cost efficiency.

PoE Switches Offer Greater Flexibility and Scalability

PoE switches provide enhanced flexibility and scalability compared to PoE injectors. With a PoE switch, you have the capability to connect multiple PoE-enabled devices to a single switch, offering the flexibility to expand your network as required. This allows for efficient network management and reduces the need for additional infrastructure. In contrast, a PoE injector can only provide power to a single device, limiting the scalability of your network and potentially requiring the installation of multiple injectors for additional devices. The ability of PoE switches to accommodate multiple devices makes them a more versatile solution for network expansion.

PoE Switches Are More Efficient for Building Wireless Networks

Deploying a wireless network using PoE switches is a more efficient approach compared to PoE injectors. When constructing an enterprise PoE wireless network, the Power over Ethernet switch serves as a connection point between the router and the Internet. This network configuration establishes seamless network connectivity between PoE wireless network devices and computers that are wired to the switch. The PoE wireless access points are directly connected to the PoE switch, receiving both power and network connectivity. These access points facilitate the connection of multiple wireless devices to the network, effectively extending its coverage and capabilities.

The picture below shows a wireless network in an office. The wireless AP is installed on the ceiling. Cat5e or Cat6 network cable delivers data and power from the nearest PoE switch. Compared with the PoE injector, using a PoE Ethernet switch to power the AP is more efficient for the wireless network because you don't need to worry about the power outlets. In addition, you don't have to specifically buy a Cat5e or Cat6 Ethernet cable for power transmission.

Wireless Network in an Office

PoE Switches Offer Better Management and Control Features

PoE switches provide superior management and control capabilities compared to PoE injectors. They come in a wide range of options, catering to various applications, from simple unmanaged edge switches with a few ports to advanced rack-mounted units with extensive management features. With a PoE switch, you gain the ability to easily monitor and control the power usage of connected devices. This allows you to optimize the performance of your network and reduce energy costs by efficiently managing power allocation.

In contrast, PoE injectors lack these management and control features. They simply deliver power to PoE devices without offering the same level of monitoring and control functionality. Furthermore, PoE switches adhering to the IEEE 802.3af standard provide Gigabit speeds, ensuring both power and data transmission over a single cable. This eliminates the need for additional wiring, power sources, or adapters, streamlining the network setup process.

Endspan PoE Switch

How to Choose a PoE Switch for a Wireless Network?

When planning to choose a PoE switch, we recommend that you should take the following three aspects into consideration.

  • The number of ports of PoE switch, which can affect the number of powered devices that can be connected to a PoE switch.

  • The power budget and PoE Standard of a PoE switch are two important points that cannot be ignored, both have an impact on PoE switch's power consumption.

  • In terms of managed or unmanaged PoE switch, one thing is that when connecting with PoE devices like IP cameras, smart managed PoE switches can detect whether they are PoE-compatible and supply power automatically for the remote-powered devices.

For more detailed information about how to choose a PoE switch, you can click: PoE vs PoE+ vs PoE++ Switch: How to Choose? 


In conclusion, while both PoE switches and PoE injectors can provide power over Ethernet cables, a PoE switch is often the better choice for building wireless networks. PoE switches are more convenient, easier to install, efficient, offer greater flexibility and scalability, and provide better management and control features than PoE injectors. By choosing a PoE switch, you can build a more efficient and effective wireless network that meets your needs and helps you achieve your goals. PoE switch is available in Linovision, where you can find a wide selection of PoE switches. For detailed information and product availability, please visit our website at or contact us.

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Troubleshooting Common PoE Errors and Solutions

Andy Chen


In a PoE power supply system, the essential components are the Power Sourcing Equipment (PSE), the Powered Device (PD), and the PoE cables. When issues arise with PoE, it often manifests as the PoE switch failing to provide power, resulting in the powered devices ceasing to function. These failures can stem from various factors, including hardware and software-related issues. This article aims to help you accurately identify the root causes of PoE errors and minimize troubleshooting time. We will discuss three common PoE faults and provide troubleshooting methods for Power over Ethernet.

PoE Error 1: PoE Switch Fails to Provide Power

One of the most frequently encountered PoE errors is when a PoE-powered device (PD) fails to boot up due to issues with PoE components or incorrect configuration commands. Follow the steps below to address this problem:

Step 1: Verify PoE IEEE Standards and Power Modes of PSE and PD

Ensure that both the Power Sourcing Equipment (PSE) and PD comply with PoE IEEE standards. It's important to note that non-standard PoE switches, also known as passive PoE switches, deliver power over Ethernet lines at a fixed voltage, regardless of whether the terminal device supports PoE or not. Improperly prepared passive PoE switches may damage the terminal devices. Additionally, the power modes of PSE and PD can contribute to PoE faults. There are three PoE modes: Alternative A, Alternative B, and 4-pair delivery. If a PD supports only PoE mode B power delivery while the PoE switch is based on Alternative A, they will not work together. Confirm the power supply modes of PSE and PD with the vendor.

Step 2: Check the PoE Cabling

Mismatched Ethernet cables and PoE ports can result in network failures. Furthermore, PoE failures can occur if the cable has hardware faults or fails to meet necessary standards. Therefore, it's highly recommended to ensure that the Ethernet cable supports PoE and is functioning properly before connecting the powered device.

Step 3: Verify Sufficient PoE Power

In theory, the PSE device interface can automatically detect the connected PD. If the power supply is insufficient, the PD will not receive power. Make sure that the power required to run the PDs does not exceed the power budget of the PoE network switch. If a PSE detects that the PD's power class falls within its capacity, it will power on the PD.

Step 4: Check PoE Power Management Configuration

Verify whether the switch interface has automatic PoE power management configuration enabled. If not, you will need to manually deliver PoE power to the connected PDs through the PoE network switch interfaces.

PoE Error 2:  Intermittent Power Loss or Reloads of a PoE PD

What if a functioning PD experiences intermittent power loss or reloads? These situations may arise due to insufficient power supply and poor-quality PoE cables.

Step 1: Check Whether PoE Power Is Sufficient

A PD can power off or reload intermittently if the PSE's output power is insufficient to support all PDs operating at full power consumption. This can cause the PoE switch to fail to provide power. Take IP cameras as an example. During testing of extended functions such as Pan-Tilt-Zoom, heaters, or wipers, the PD may consume significantly more power than during normal operation. If no additional power is available, the camera may get stuck in a continuous boot cycle. To troubleshoot this PoE fault, measure the power requirements of the IP camera during startup and use an appropriate PSE to provide sufficient power.

Step 2: Check the PoE Cabling

If the Ethernet cable used in a PoE link is over 100 meters or has power loss due to the material and resistance of the cable itself, the PD would not get sufficient power, causing issues like network failure or latency. If the cables are not qualified, it will lead to PoE faults as well.

PoE Error 3: Inconsistent Powering of PDs on the Same PSE

If some PDs are receiving power while others connected to the same PSE are not, follow the tips below:

Step 1: Check if PDs Are Available on Other Ports

Determine whether the issue lies with specific ports on the PSE. Disconnect the PoE cable between the Ethernet switch port and the non-powered PDs. If the PDs receive power when connected to other PoE ports, it indicates a problem with specific ports. Verify if the port is shut down or error-disabled using configuration commands. If so, enable PoE functions through the appropriate command.

Step 2: Check the PoE Power

If newly added PDs to PSE ports are not powering on, it may indicate that the PoE switch's power budget is depleted. Ensure that the remaining PoE power in the PSE is equal to or greater than the maximum output required by the connected PDs. Additionally, limit the per-port current to safe levels and consider using additional PSE devices if necessary.

PoE Error 4: PoE Cameras Not Powered

If your camera cannot be powered on while using a PoE Switch or PoE injector, you may follow the tips below to solve your problems.

Step 1: Verify Camera Compatibility with PoE Switch/Injector

Check the compatibility requirements of your camera with the PoE switch or PoE injector. Ensure that the specifications of the PoE switch or injector align with the camera's requirements.

Step 2: Check if the Camera Is Fully Connected to the PoE Switch/PoE Injector

Inspect the PoE port lights on thePoE switch or PoE injector to confirm if the camera is fully connected. If the lights are not illuminated, try plugging the camera into other ports and using a different Ethernet cable. Also, check if the PoE port of the switch is damaged or rusty. You can test this by connecting the camera to other functioning PoE ports.

Step 3: Check if the PoE Module of the Camera Gets Power

If the camera's PoE module is not receiving power, use a DC adapter with the correct output voltage to power the camera. Make sure the DC/AC adapter is available and compatible. Typically, the adapter has an indicator light that indicates the presence of power. Some IP cameras support both DC and AC power supply ports, such as DC12V/2A and AC 24V/3A. Verify that the adapter's specifications match those of the camera.


The four errors mentioned above basically cover the problems that PoE switches are often prone to. If you meet other problems in the process of using PoE switches, you can contact Linovision IT experts for answers. Linovision not only provides you with cost-effective and excellent quality PoE switches but also provides a series of technical support services to ensure your after-sales worry-free.

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How to Connect Linovision LoRaWAN Gateway to HTTP(s) Server?

Andy Chen


Linovision LoRaWAN gateways support sending data packets to third party MQTT/HTTP/HTTPS server. We can create a new application on gateway, which can define the method of decoding the data sent from LoRaWAN end-device and choosing HTTP(S) data transport protocol to send data to HTTP(s) server.





  • Linovison LoRaWAN Gateway: IOT-G6x, IOT-G8x
  • HTTP/HTTPS Server



Step1. Enable the gateway built-in network server.

Go to Packet Forwarder > General to enable the localhost server address.



Enable the Network server on Network Server > General page.




Step2. Add an Application and Profiles.

Go to Network Server > Applications to add a new application, then click save.

Name: user-defined, arbitrary value

Description: user-defined, arbitrary value

Payload Codec: None or custom your decoder



Go to Network Server>Profiles to add a new profile, then click save.

Name: user-defined, arbitrary value

Max TXPower: default value

Other parameters can be checked from LoRaWAN nodes user guides or you can keep all settings by default.




Step3. Add LoRaWAN nodes to the gateway.

Go to Network Server > Device, add a new device, click save&apply.

Device Name: user-defined, arbitrary value

Description: user-defined, arbitrary value

Device-Profile: choose one of corresponding profiles added before.

Application: choose one of corresponding applications added before.

Other values can be confirmed with the LoRaWAN node manufacturers.


When the status of it is “activated”, that’s mean above steps are done correctly.




Step4. Forward data to HTTP(s) server.

Go to Network Server > Applications to add a “data transmission” for the application.



Fill in the HTTP(s) URL information for each data type, click save.

Uplink data: the URL address to receive all uplink data.

Join notification: the URL address to receive join notification.

ACK notification: the URL address to receive all ACK notification.

Error notification: the URL address to receive all error notification.



Note: If there is user credentials when we access to HTTP(s) server, please add HTTP header, and fill in correct account and password.



If we get data packet on the corresponding URL of HTTP server like below, that’s mean we have connected with HTTP server successfully.



Note: The difference of forwarding data to HTTPS server is that you need upload related gateway certification on your HTTPS server (Contact Linovision to get certification).

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How to Remotely Control Devices via MQTT on Linovision Gateway

Andy Chen


When working as embedded network server, Linovision LoRaWAN gateways support both sending data packets to third party MQTT/HTTP/HTTPS server or receiving the downlink commands to transfer to LoRaWAN end devices.



  • Linovision LoRaWAN Gateway: IOT-G56, IOT-G63 V1, IOT-G65, IOT-G67, IOT-G8x (Firmware version or later)
  • MQTT Server/Broker
  • MQTT Client tool: take MQTT Explorer as example



Step1Connect gateway to MQTT broker.

Refer article How to Connect LoRaWAN Gateway to MQTT Broker?to connect gateway to MQTT broker and ensure the broker and MQTT client can receive uplinks from devices.


Step2Send Downlink Command from Gateway

Set the gateway to send downlink commands to device directly to check if the device can receive the downlink commands and take actions.

Device EUI: the device EUI to send downlink commands

Type: downlink command type. For Linovision devices, please select hex type.

Payload: downlink command content (get from device manufacturer). For Linovision devices, please refer to downlink command contents on corresponding user guides

Port: application port of device. It is 85 by default for Linovision devices.

Confirmed: after enabled, the device will send confirmed packet back to gateway if it receives the command. If not receive, the gateway will resend the downlink command 3 times at most.

Note: for class A type devices, the gateway will add the command to queue and send it when the class A device send uplinks.




Step3. Publish Topic on MQTT Explorer to send downlink data to device. 

Set a Downlink Data topic. If you need to send MQTT downlink to specific device, please add “$deveui” on the topic.

Example: /linovision/downlink/$deveui



Publish Topic Format :


Example :

From the gateway, we can get the device EUI about the device we want to control:



So we can publish a topic on the MQTT Explorer like below:

Topic: /linovision/downlink/24e124126a148401

Format: json


send as below format and replace the data content as downlink command

{"confirmed": true, "fport": 85, "data": "CQEA/w=="}


After click Publish, we can go to Network Server > Packets to check. If the gateway have subscribe corresponding downlink topic data successfully, there will be at least one grayed message packet record.



Linovision Device Command Examples

The MQTT downlink command format is fixed as below:

"confirmed": true,       //Set as true or false
"fport": 85,            //application port of device
"data": "BwAA/w=="    //base64 format downlink command

For Linovision devices, click here to convert hex format command to base64 format. Here are Linovision controller common commands:



Command (Hex)

Command (base64)


Set GPIO1 low

Set GPIO1 high

Set GPIO2 low

Set GPIO2 high







Set DO1 low

Set DO1 high

Set DO2 low

Set DO2 high







Set DO1 low

Set DO1 high

Set DO2 low

Set DO2 high








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How to Connect LoRaWAN Gateway to MQTT Broker?

Andy Chen


When working as embedded network server, Linovision LoRaWAN gateways support sending data packets to third party MQTT/HTTP/HTTPS server. We can create a new application on gateway, which can define the method of decoding the data sent from LoRaWAN end-device and choosing MQTT data transport protocol to send data to MQTT server.




  •  LoRaWAN Gateway: IOT-G8x (Firmware version or later), IOT-G65, IOT-G67, IOT-G56, IOT-G63 V1
  • MQTT Server/Broker
  • MQTT client tool: take MQTT Explorer as example



Step1. Enable the gateway built-in network server.

Go to Packet Forwarder > General to enable the localhost server address.



Enable the Network server on Network Server > General page.




Step2. Add an Application

Go to Network Server>Applications to add a new application, click save.

Name: user-defined, arbitrary value

Description: user-defined, arbitrary value





Step3. Connect gateway to MQTT broker.

Go to Network Server > Applications to add a “data transmission” for the application. One application can add only one MQTT integration.






Fill in the MQTT broker information and create topic to store different data type, click save.

Broker Address: IP address/domain of MQTT broker

Broker Port: communication port of MQTT broker

Client ID: user-defined, a unique ID identity of the client to the server.

User Credentials and TLS should be enabled and configured as required.

Note: if MQTT broker is HiveMQ, please do enable TLS and set the option as CA signed server certificate.



After MQTT configuration complete, you can check connection status here:



Step4. Add LoRaWAN nodes to the gateway.

Go to Network Server>Profiles to add a new profile, then click save. You can also use pre-defined profiles.

Name: user-defined, arbitrary value

Max TXPower: default value

Other parameters can be checked from LoRaWAN nodes user guide or you can keep all settings by default.




Go to Network Server>Device to add a new device, click Save&Apply.

Device Name: user-defined, arbitrary value

Description: user-defined, arbitrary value

Device-Profile: choose one of corresponding profiles added before.

Application: choose one of corresponding applications added before.

Other parameters can be confirmed with the LoRaWAN node manufacturers.



When the status shows as below, that’s mean above steps are done correctly.




Step5. Add uplink data topic.

Customize the uplink data to publish to MQTT broker and save the settings. If you add “$deveui” on your topic, you can replace it as real device EUI when subscribing topics. 

Example: /linovision/uplink/$deveui





Step6. Subscribe topic from MQTT client to get uplinks.

MQTT explorer is a comprehensive MQTT client and it can be replaced to other kinds of MQTT client tools(MQTT.fx, MQTT Box, etc.)

Open the MQTT Explorer, and fill in related MQTT server information in the popup window.

Name: user-defined

Protocol: mqtt://

Host: MQTT broker address

Port: broker port

User name/Password: if there is user credentials, please fill in it. If not, keep them blank.



Click ADVANCED,copy the Uplink data topic on the gateway, and paste it on the MQTT explorer, click +ADD.




Keep MQTT client ID by default,then click BACK and click CONNECT.



After while, the data will be forwarded to MQTT broker and the MQTT Exploerer can receive the data from MQTT server.


The uplink format is fixed as json and the content is as below.


  "applicationID": 1,                   // application ID
  "applicationName": "cloud",           // application name
  "deviceName": "24e1641092176759",     // device name
  "devEUI": "24e1641092176759",         // device EUI
  "time": "2020-0327T12:39:05.547336Z", // uplink receive time
  "rxInfo": [                           // lorawan gateway information related to lora
      "mac": "24e124fffef021be",        // ID of the receiving gateway
      "rssi": -57,                      // signal strength (dBm)
      "loRaSNR": 10,                    // signal to noise ratio
      "name": "local_gateway",          // name of the receiving gateway
      "latitude": 0,                    // latitude of the receiving gateway
      "longitude": 0,                   // longitude of the receiving gateway
      "altitude": 0                     // altitude of the receiving gateway
  "txInfo": {                           // lorawan node tx info
    "frequency": 868300000,             // frequency used for transmission
    "dataRate": {
      "modulation": "LORA",             // LORA module
      "bandwidth": 125,                 // bandwidth used for transmission
      "spreadFactor": 7                 // spreadFactor used for transmission
    "adr": false,                       // device ADR status
    "codeRate": "4/5"                   // code rate
  "fCnt": 0,                            // frame counter
  "fPort": 85,                          // application port
  "data": "AWcAAAJoAA=="                // base64 encoded payload (decrypted)



If you need to send downlink commands from MQTT client, please refer to article How to Remotely Control Devices via MQTT on Linovision Gateway.




Q1.How to send decoded or customize uplink content to MQTT broker?

A1:  Yes, this needs to use Payload Codec feature on the gateway. Reference articles:

IOT-G56/G65/G67: How to Use Payload Codec on Linovision Gateway

IOT-G63 V1/G8x: How to Use Payload Codec on Linovision Gateway (Old)


Q2.What’s the troubleshooting when the status of MQTT server connection is “Disconnected”.




1) Go to Maintenance > Tools >Ping , check if the gateway can ping to the broker address successfully.




2) Check if your MQTT client tool can connect to MQTT broker well, then follow the settings of MQTT client tool to configure the gateway.
3) Check if the gateway MQTT client ID is conflict with other MQTT clients.
4) Check if CPU load is too high, and if there is little available RAM and eMMC.
5) Change the log severity to Debug and replicate the disconnection problem, then download all log files and send them to




Q3.Why the connection status shows “connected” but MQTT client does not receive any data?
1)Ensure the devices has been added to gateway and go to Network Server > Packets to check if there are uplink packets from devices regularly.
2) Ensure the devices has been added to the correct Application.
3) Ensure the gateway firmware is upgraded to latest version. 
4) Change the log severity to Debug and replicate the disconnection problem, then download all log files and send them to




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90W 802.3bt PoE Powering any Ethernet Device with a Single Ethernet Cable


The new IEEE 802.3bt Power over Ethernet (PoE) standard allows standard Ethernet cables to carry up to 90 W of power, opening the doors to almost any Ethernet device being powered by a single Ethernet cable. Yet despite being in the market for over a decade, PoE technology is often shrouded in a cloud of mystery and confusion.

While the latest standard adds new features beyond increased power delivery, it is also more complex than previous standards. But take heart, this article will introduce you to PoE basics and some new features in the 802.3bt standard, as well as give you enough background to make complex PoE white papers, app notes, and datasheets understandable.

The PoE Connection

“Being powerful is like being a lady. If you have to tell people you are, you aren't.” —Margaret Thatcher

On the surface, PoE sounds complex: Inject high power onto a cable designed for data without disrupting the high-speed traffic the cable is carrying. Fortunately, the Ethernet standard and the cable design greatly simplify this technology. As shown in Figure 1, inside the Ethernet cable itself are four twisted pairs of wires. Ethernet is an isolated network, so each twisted pair connects to a transformer. All PoE does is inject a dc voltage (~54 V) onto the twisted pairs of the Ethernet cable through center taps on the transformers.

1. Inside the Ethernet cable are four twisted pairs of wires. IEEE 802.3af/at powers two of the four twisted pairs and IEEE 802.3bt powers all four twisted pairs.

In a two-pair power configuration (802.3af, 802.3at), one twisted pair is positive and the other is negative. In a four-pair power configuration (802.3bt), two twisted pairs are positive and two are negative. The power-sourcing equipment (PSE) is the device putting power onto the cable, and the powered device (PD) is the device taking power off of the cable.

Finally, the PoE standards enable the PSE to power the twisted pairs in either polarity. Therefore, the PD must have input bridges (diodes or FETs) to set the polarity of the incoming power.


“Eighty percent of success is showing up.” —Woody Allen

Now we know how to put power onto the Ethernet cable, so the PSE can just blast power down the cable whenever something is connected, right? Wrong! Applying power to a non-PoE device can damage it. PoE starts with a detection phase in which the PSE determines if the connected device is a PD requesting power. The PSE applies two voltages between 2.7 and 10.1 V onto the Ethernet cable, and the PD presents a 25-kΩ resistance, signaling to the PSE that a valid PD is connected (Fig. 2).


2. The PSE injects between 2.7 and 10.7 V onto the Ethernet cable and measures the current to check for a valid detection signature of 25 kΩ


“Never sacrifice your class to someone who has none.” —Unknown

.Once a valid PD is detected, the PSE and PD then do an analog handshake known as “classification,” in which the PD requests a power “class” and the PSE then tells the PD what class is granted. PoE technology uses the terms type and class when discussing power. Type simply denotes the kind of analog handshake from the PSE. Class defines the maximum power the PSE will put onto the cable and the maximum power the PD can draw from the cable. Because PoE follows the Ethernet standard, the cable can be up to 100 meters in length, so a fair amount of power is lost in the cable. The table lists the various PoE types and classes.

The IEEE PoE standards specify the power from the PSE and the power delivered to the PD.

Let’s start with the simplest classification handshake, type 1 (Fig. 3). The PSE puts 15.5-20.5 V onto the cable and measures the PD’s current draw. Due to cable loss, the PD will see 14.5-20.5 V from the PSE during classification. Based on the PD’s current draw, the PSE determines the PD’s requested class and either powers it on or, if the PSE doesn’t have sufficient power, doesn’t apply power.

3. The voltage waveforms seen by the PD during type 1 detection, classification, and power on.

The amount of current drawn by the PD during classification is, confusingly enough, referred to as the classification signature or classification current. 802.3bt defines five classification signatures the PD can draw during classification.

Type 2 builds on type 1 by adding a second classification pulse (Fig. 4). During classification, the PD draws 40 mA (classification signature 4) to signal class 4 to the PSE. A type 1 PSE simply sees this as a request for class 3 power and proceeds to power the PD. A type 2 PSE responds to the higher current by lowering the classification voltage to a “mark” voltage to create a pulse. It then repeats this procedure to create a second classification pulse and powers the PD. The two classification pulses signal to the PD that class 4 power has been granted by the PSE.

4. The voltage waveforms seen by the PD during type 4 detection, classification, and power on.

Here’s where you come in as the PD designer. A PD requesting class 4 might not get it from the PSE. It might receive less than it asked for through “power demotion,” and your design will need to make do with less power. Keep reading—we will get there in a few more paragraphs.

Now the moment you’ve been waiting for: 802.3bt classification (Fig. 5). As you might have guessed, it’s very similar to type 1 and 2; it just adds more classification pulses. Type 3 increases the number of classification pulses to four, and type 4 uses five pulses.

5. More classification pulses are involved with 802.3bt classification.

When a PD requests type 3 or 4 power, it draws 40 mA (classification signature 4 current) for the first two pulses and then lowers its current draw to the classification signature 3, 2, 1, or 0 level for the subsequent pulses. The lower current tells the PSE how much power the PD is requesting. In fact, after the third pulse, the PSE has determined how much power the PD wants, and the additional pulses simply tell the PD how much power is being granted by the PSE.

If the PSE generates four classification pulses, then the PD is granted type 3 power. Five classification pulses signal the PSE granting type 4 power to the PD. In other words, if the PD asked for class 7 or 8 power and the PSE grants type 4, then the PD gets the power it requested. Likewise, if the PD requests class 5 or 6 and the PSE grants type 3, then the PD receives the power it requested. With this information, you now know the key aspects of 802.3bt PoE classification.

But wait, what’s this long first classification pulse, you might ask? And what happens if the PSE doesn’t grant the PD the power it requests? Hold that thought, we will get there shortly. 

Power Demotion

“Tact is the ability to tell someone to go to hell in such a way that they look forward to the trip.” —Winston Churchill

Most PoE-enabled Ethernet switches don’t have enough power capacity for full power on each PoE Ethernet port, especially at 90 W per port, which adds up quickly. The PoE standard provides a simple way for the PSE to still power a PD but with less power than the PD requested—this is called power demotion. When a PSE demotes a PD, it assigns it a lower type than the PD requests. Because PSEs can only assign type to a PD, when a PD is demoted to a lower type, it’s automatically assigned the highest power level within that type. Let’s look at two examples of how this works.

Example 1: A PD requests class 8 power, but the PSE only has class 6 power available. In this scenario, the PSE demotes the PD to type 3, and the PD receives class 6 power.

Example 1: A PSE with class 6 power available demotes a PD requesting class 8 to type 3, resulting in the PD receiving class 6 power.

Example 2: A PD requests class 8 power, but the PSE only has class 5 power available. Because the PSE can only demote the PD by type, it can’t assign the PD class 5 power. If it granted the PD type 3 power, the PD would be assigned class 6 power. Instead, it must demote the PD to class 4, type 2 power.

Example 2: A PSE with class 5 power available demotes a PD requesting class 8 to type 2, resulting in the PD receiving class 4 power.

As a system designer, you understand what’s important here is to recognize the different power demotion options available to the PSE based on the class the PD is requesting. A class 8 PD may be demoted to class 6, class 4, and class 3 power. To ensure full compatibility, the PD system needs to operate at all four power levels. Otherwise the PSE will shut down the connected PD for drawing too much power. Most PD devices on the market include some method for communicating the received type back to the main PD system controller, such as two digital pins or a comm port.

Power On

“The measure of a man is what he does with power.” —Plato

Power on is the final stage of a PD receiving power. The IEEE PoE spec includes the inrush current that a PD may draw during power up. Most modern PD devices include built-in inrush current limiting. All the designer needs to do is follow the PD device’s recommended input capacitance and let it take care of the rest.

Maintain Power Signature

“Power does not corrupt. Fear corrupts. Perhaps the fear of a loss of power.” —John Steinbeck

The previous PoE standards include the concept of Maintain Power Signature (MPS). If a PD draws less than 10 mA of current, the PSE disconnects the PD. The MPS feature enables the PD to draw short pulses of current to maintain the connection to the PSE when the PD system is in a low-power state.

The new 802.3bt standard introduces a shorter MPS pulse to maintain the PSE connection, allowing PDs to enter an even lower-power state. Remember the long first class pulse from the type 3 or 4 PSE? This signals to the connected PD that the PSE supports short MPS, and the PD may use short MPS pulses to maintain the connection.

Just like with inrush, most 802.3bt PDs automatically switch to short MPS when connected to a PSE that supports the feature. Short MPS allows the system to enter a lower-power state than with previous PoE standards.

Autoclass, LLDP, and Closing Thoughts

“You must never try to make all the money that’s in a deal. Let the other fellow make some money too, because if you have a reputation for always making all the money, you won’t have many deals.” —J. Paul Getty

There’s one last new feature in the 802.3bt standard worth mentioning—autoclass. With autoclass, a PD draws the maximum power it will ever consume shortly after power up. This allows the PSE to measure the actual power the PD will consume and adjust power allocation accordingly. A PD may request class 8 (90 W) of power, but in reality, only draw 80 W. With autoclass, the PSE can measure this and then have 10 W of power to provide to other PDs in the system.

Another advanced feature of PoE is the Link Layer Discovery Protocol (LLDP). Ethernet networks have used LLDP for years to enable switches and routers to discover various details using the data layer. PoE adds an extension to LLDP for the PSE and PD to also communicate information over the data layer. For example, LLDP allows the PSE and PD to renegotiate power in one-tenth-of-a-watt increments, possibly freeing up power for the PSE or granting the PD slightly more power.

The 802.3bt standard brings unprecedented levels of both literal and figurative power to PoE system designers. In addition, it delivers several useful new features, such as short MPS, that bring more flexibility to PoE connected systems. With the ubiquitous nature of Ethernet networks and the higher power of 802.3bt PoE, more and more systems will take advantage of this technology to eliminate external power supplies.

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