What is Power over Ethernet(PoE)?

Ⅰ. What is PoE?

1. Definition

PoE is a technique that uses an Ethernet wiring system to deliver data signals to IP-based terminal devices (such as IP telephones, wireless LAN access points, network cameras, and so on) while also providing DC power to these devices. PoE technology helps keep the old network running smoothly while also protecting the safety of the existing structured cabling and lowering costs. We can use Cat5, Cat5e, Cat6, and other network cables to concurrently supply power and transmit data to indoor/outdoor PoE-powered devices like VoIP phones, IP cameras, and wireless access points, without having to install these devices separately, thanks to this technology. Even electrical facilities are deployed using power outlets.

The power supply device and the power reception device make up a complete PoE system.

Power Supply End Equipment (PSE): Ethernet switches, routers, hubs, or other network switching equipment that support POE functions.

Power-receiving device (PD): In the surveillance system, it is mainly a network camera (IPC).

2. Types

What are the types of PoE? What are the differences between different types of PoE?

PoE may be split into five varieties based on the above-mentioned PoE power supply standards: PoE, PoE+, PoE++, UPOE, and PoH; PoE can also be divided into standard PoE and non-standard PoE based on whether the PoE power supply matches the standard.

Different standards apply to PoE: UPOE vs. PoH vs. PoE vs. PoE+ vs. PoE++ vs. UPOE vs. PoH

The earliest iteration of the IEEE 802.3af standard defines PoE, which is primarily used to enable early PoE powered devices such as VoIP phones, low-power wireless access devices, and so on. PoE+ is an improved version of PoE that meets with the IEEE 802.3at standard. Dual-band access, video telephony, and PTZ video surveillance systems are some of the higher-power uses. Future power supply methods for high-power PoE powered devices, such as video conferencing systems, are supported by both PoE++ and UPOE. The difference is that PoE++ is a widely used industry standard, whereas UPOE is a Cisco-patented technology. PoH, like PoE power supply technology, is a technology that sends data and DC power across a network cable at the same time, with a transmission distance of 100m. PoH power supply technology, on the other hand, is mostly utilized in the video industry to power video display devices and make video connections more cost-effective, efficient, and simple.

PoE can be classified into four types based on the output power: Type 1, Type 2, Type 3, and Type 4. Type 1 PoE draws 15.4 watts from the power supply device, Type 2 PoE draws 30 watts, Type 3 PoE draws 60 watts, and Type 2 PoE draws 100 watts. The four most prevalent uses of Type 1, Type 2, Type 3, and Type 4 PoE are as follows:

Non-standard vs. standard PoE

Standard PoE is the PoE power supply technology that complies with the standard, as the name implies. A PoE control chip is included in power supply equipment that fulfills the PoE standard. It will first determine whether the terminal device is a power receiving device that supports the PoE power supply before giving power. It will be powered normally if it is. There will be no power supply if this does not happen. This step is not detected by non-standard PoE power supply devices. The terminal device is activated as soon as the power is turned on, regardless of whether it supports the PoE power supply, making it very easy to burn the access device.

3. Why do you need PoE?

With the growing prevalence of IP phones, network video surveillance, and wireless Ethernet devices on the network, the need for power over Ethernet is becoming increasingly important. The terminal equipment, in most circumstances, requires DC power, and it is typically located on a ceiling higher than the ground or outdoors. It's difficult to find a convenient power outlet nearby. Even if there is a socket, finding the AC-DC converter that the terminal equipment requires is challenging. Placement. Administrators must also manage many terminal devices at the same time in many large-scale LAN systems. These gadgets require a centralized power supply and administration system. The inconvenient location of the power supply causes a lot of problems for power supply management. PoE (Power over Ethernet) is a solution to this problem.

PoE (Power over Ethernet) is a wired Ethernet power supply technique. The network cable that is used for data transmission can also provide DC power. It overcomes the problem of centralized power supply for terminals such as IP phones, wireless APs, portable device chargers, credit card machines, cameras, and data collection. PoE power supplies have the following benefits: time and cost savings, high dependability, easy connection, and unified standards:

Save time and cost: PoE power supply technology eliminates the need for socket installation, power cable deployment, line transformation, and other operations, saving time and money, as well as network deployment expenses, labor costs, and post-maintenance costs. The greater the number of PoE-powered devices in the network, the more visible this time and cost-benefit becomes.

Strong reliability: Power over Ethernet (PoE) is provided via PoE power supply equipment (PSE). There is no powerful electricity in the equipment, therefore it will not create mishaps due to power leakage, and it is completely safe. One PoE device may provide power to several terminal devices at the same time, and it can also provide power backup while providing centralized power. A UPS (uninterruptible power supply) system can also be connected to PoE power supply equipment. Normal operation of the PoE power receiving equipment can also be guaranteed if the main power supply is disrupted.

Simple and convenient connection: The deployment of PoE-powered devices is seldom limited by time, place, or environment in a PoE power supply network, and there is no need to address socket location, power cord routing, or other concerns. The terminal device simply requires a network cable and does not require an external power supply.

Uniform standard: It complies with international standards and employs a globally consistent RJ45 power interface to ensure compatibility with equipment from various manufacturers.

 4. How to realize PoE power supply?

The most prevalent PoE power supply items are PoE switches and PoE injectors. PoE splitters are also commonly used to make it easier to integrate devices that don't support PoE power into PoE networks. In PoE networks, these three products play a critical role. Role. The most convenient way to implement PoE power supply is to use a PoE switch. Only the network cable needs to be installed, and the PoE switch may power the terminal PoE powered device. When there is no PoE switch in the network, the PoE power supply is often used. Its primary duty is to inject its own power and data signals into the network cable from the common switch and transmit them to the PoE-enabled device. When the higher end is a PoE switch, PoE power supply, or other PoE power supply equipment, and the lower end is non-PoE equipment, a PoE splitter is typically utilized. Its purpose is diametrically opposed to that of a PoE power source. It separates the data signal from the power signal, then sends the data signal over the network cable and the power cord to a non-PoE device.

Ⅱ. How does PoE work?

The PoE power supply system includes the following two device functions, as indicated in the diagram below:

Equipment for obtaining power PSE (Power-sourcing Equipment): PoE devices, such as PoE switches, that provide tasks such as detection, analysis, and intelligent power management while supplying power to powered equipment through Ethernet.

Wireless AP, portable device charger, credit card machine, camera, and other powered devices are examples of powered gadgets. PDs are classified as standard or non-standard according to on whether they comply with IEEE standards.

Ⅲ. Where can we use PoE?

Security Monitoring

A universal network camera must provide sufficient power for it around the clock in addition to transmitting video signals through a network cable. However, in real-world settings, the camera's installation site may need to be changed because it is unable to provide a stable power source.

Because just one network cable is required to accomplish the operations of power supply and data transmission at the same time with POE power supply, deployment may be finished quickly while saving money.

Emergency broadcast

POE technology can also provide dependability guarantees in the event of an emergency, such as a power outage. Monitoring and broadcasting system equipment employing POE power supply, for example, will not be freed from security protection due to power interruption in a modern computer room equipped with an uninterrupted power supply system.

Ⅳ. What are the industry standards for PoE power supply technology?

According to the international standard IEEE802.3af, which was established in 2003, the PSE must have a maximum output power of 15.4 watts, with a power reaching the receiving device of 12.95 watts and a power loss of 2.45 watts.

The PSE must reach a maximum output power of 30 watts, with 25.5 watts reaching the receiving device and 4.5 watts lost, according to the international standard IEEE802.3at, which was published in 2009.

The power of these two standards has degraded over time, and they can no longer match the power supply requirements of newer, more powerful PDs. As a result, IEEE802.3bt, the most recent international standard, contains two requirements:

IEEE International Standard Parameter Table

The first type: One of them requires the PSE to reach a 60W output power, with 51W reaching the powered device (the lowest figure from the above table), and a 9W power loss.

The second type: The PSE must reach a maximum output power of 90 watts, with 71 watts reaching the powered device and 19 watts lost.

According to the above norm, as the power supply increases, the power loss is not proportional to the power supply power, but rather grows more and larger. So, how do you compute the loss of PSE in real-world applications?

Ⅴ. PoE power supply loss

1. Content

So, let's look at how physics in junior high calculates the loss of cable power.

Joule's law asserts that conduction current transfers electrical energy into thermal energy in a quantifiable manner.

The content is: The amount of heat generated by a current going through a conductor is related to the square of the current, the resistance of the conductor, and the time it takes to energize. That is the amount of time spent by employees during the calculating procedure.

Q=I2Rt (applicable to all circuits) is the mathematical version of Joule's equation, where Q is the power loss P, I is current, R is the resistance, and t is the time.

In practice, the loss has nothing to do with time because PSE and PD work at the same time. The power loss of the network cable in a POE system is proportional to the square of the current and proportionate to the amount of the resistance, according to the findings. Simply said, in order to reduce network cable power consumption, we must aim to make the wire's current as minimal as possible, hence lowering the network cable's resistance. The importance of lowering current is particularly essential among them.

Then let's take a look at the specific parameters of the international standard:

The network cable resistance is 20 in the IEEE802.3af standard, the needed PSE output voltage is 44V, the current is 0.35A, and the power loss is P=0.35*0.35*20=2.45W.

In the IEEE802.3at standard, the network cable resistance is 12.5 ohms, the required voltage is 50 volts, the current is 0.6 amps, and the power loss is P=0.6*0.6*12.5=4.5 watts.

Using this mathematical method, there are no issues with these two criteria. However, once the IEEE802.3bt standard is implemented, this calculation will be impossible to do. To attain 60W, the voltage must be 50V and the current must be 1.2A. The power loss at this point is P=1.2*1.2*12.5=18W, minus the loss to achieve PD. The device's output is merely 42 watts.

 2. Reason

What’s the reason for POE power loss?

So, what's the deal?

9W of power is less than the actual requirement of 51W. So, what went wrong with the calculation?

Let's look at the last column of this data chart again, and notice that the current in the original IEEE802.3bt standard is still 0.6A, and then look at the twisted pair for power supply, which is powered by four pairs of twisted pair (IEEE802.3af, IEEE802.3at uses two pairs of twisted pairs for power supply). The entire circuit current is 1.2A, however the total loss is twice as much as two pairs of twisted pairs for power supply.

As a result, P=0.6*0.6*12.5*2=9W is the loss. This power supply method saves 9W in comparison to two pairs of twisted pair, allowing the PSE to make the PD device receive when the output power is just 60W. The maximum power output is 51 watts.

As a result, when selecting PSE equipment, we must ensure that the current is as low as feasible while the voltage is as high as possible; otherwise, severe power loss is likely. The PSE equipment's power may appear to be useful, but it is not in practice.

For example

A specific PD device (such as a camera) requires 12V 12.95W. The output power is 24W when a 12V2A PSE is used.

When the current is 1A, the loss is P=1*1*20=20W in practice.

The loss P=2*2*20=80W when the current is 2A.

The bigger the current, the greater the loss at this point, and the majority of the power has been used. Obviously, the PD device will not be able to accept the power given by the PSE, and the camera will be unable to function normally due to a lack of power supply.

This is a problem that occurs frequently in practice. The power supply appears to be substantial enough to be used in many circumstances, but the loss is not taken into account. As a result of the insufficient power supply, the camera is unable to function normally, and the cause is never discovered.

Ⅵ. PoE power supply resistor

Of course, the resistance of the network cable when the power supply distance is 100 meters is mentioned above. This is the maximum power supply distance's available power. The resistance is only 2 when the power supply distance in real operation is relatively short, such as 10 meters. Because the loss is just ten percent of a hundred meters, it's critical to think about the real application when choosing PSE equipment.

100 meter resistance of super five twisted-pair cables of various materials:

1. Copper clad steel network cable: 75-100Ω

2. Copper-clad aluminum cable: 24-28Ω

3. Copper-clad silver network cable: 15Ω

4. Copper-clad copper wire: 42Ω

5. Oxygen-free copper network cable: 9.5Ω

It can be observed that the better the cable, the less resistance, and thus the least power loss during the power supply process, according to the formula Q=I2Rt. This is why a decent cable should be used, and Category 6 cables are recommended. Take precautions.

According to the power loss formula, Q=I2Rt, the minimal current and minimum resistance are necessary to make the complete power supply process the best in order to reduce the loss between the poe power supply from the PSE power supply terminal to the PD power reception device.