How to increase power over ethernet performance?
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Have you ever thought how to increase power over ethernet performance? in today's article, we will discuss a special type of ethernet cable: the PoE cable.The full name of this cable is called Power Over Ethernet Cable. We will discuss what is PoE Cable,the power supply ,standards, precautions related to PoE cables, and how to increase power over ethernet performance.
1. What is POE?
Traditionally, power supply and data transmission for devices were handled separately. Devices connected to Ethernet required at least one PoE cable for data transmission and a power cable for power supply. The need for power cables has always been a limiting factor in device deployment, either requiring devices to be near existing power outlets or separately laying power cables and outlets for the devices. Power over Ethernet (PoE) technology solves this dilemma and makes deploying such devices much more flexible.
POE (Power Over Ethernet) refers to the technology that, without any modification to the existing Ethernet CAT5E cabling infrastructure, can transmit data signals to some IP-based terminals (such as IP phones, wireless LAN access points AP, network cameras, etc.) while also providing direct current (DC) power to such devices. POE is also known as Power over LAN (POL) or Active Ethernet, sometimes simply referred to as Ethernet power supply. This is the latest standard specification that uses existing Ethernet cables to transmit both data and power simultaneously. It maintains compatibility with existing Ethernet systems and users.
POE (Power Over Ethernet) power supply is a technology that provides power to devices through Ethernet cables. It allows the simultaneous transmission of data and power over a single Ethernet cable, simplifying wiring and cutting costs.
If you want to use POE power supply, it is recommended to use specialized POE cables. These cables usually have additional copper wires to provide power to the devices. Moreover, POE cables generally have higher quality and reliability because they are specifically designed and tested to ensure they work properly in Ethernet environments. Using ordinary ethernet cables for POE power supply may lead to unstable power supply, signal attenuation, and other issues. Therefore, if you need to use POE power supply, it is best to use specialized POE cables to ensure reliable power supply and data transmission.
2. POE cable power supply principle and method
Standard Cat5 network cables have four pairs of twisted wires, but only two pairs are used in 10M BASE-T and 100M BASE-T. IEEE 802.3AF, one of the POE standards, allows two methods: when using idle pins for power supply, pins 4 and 5 are connected as positive, and pins 7 and 8 are connected as negative.
When using data pins for power supply, the DC power is added to the midpoint of the transmission transformer without affecting data transmission. In this method, wire pairs 1, 2 and 3, 6 can be of any polarity. The standard does not permit both methods to be used at the same time. The power supply equipment PSE can only provide one method, but the power application equipment must be able to adapt to both cases simultaneously. The standard stipulates that the power supply is usually 48V, 13W. PD (Power Device: powered device) equipment provides 48V to low voltage conversion, which is relatively easy, but at the same time should have 1500V insulation safety voltage.
The POE standard defines two methods for using Ethernet transmission cables to deliver DC power to POE-compatible devices.
The first is the "Mid-Span" method, which uses an independent PoE power supply device, bridging between the ethernet switch and the terminal device with PoE function, generally using the idle wire pairs in the Ethernet cable to transmit DC power. Midspan PSE is a specialized power management device, usually placed with the switch. It has two RJ45 jacks for each port, one connected to the switch with a short cable (here referring to traditional switches without PoE function), and the other connected to the remote device.
The second method is "End-Span", which integrates the power supply device at the signal output end of the switch. This type of integrated connection generally provides "dual" power supply function for idle wire pairs and data wire pairs. The data wire pairs use signal isolation transformers and utilize center taps to achieve DC power supply. It's likely that End-Span will quickly gain popularity, as Ethernet data and power transmission use common wire pairs, thus eliminating the need for setting up independent power transmission dedicated lines, which is particularly significant for cables with only 8 cores and the corresponding standard RJ45 sockets.
3. POE device power supply process
When deploying POE power supply equipment in a network, the POE Ethernet power supply process mainly includes detection, power supply capability negotiation, start of power supply, continuous power supply, and power off.
3.1 Detect PD:
First, the PSE (power supply equipment) outputs a small voltage at the port to detect whether the link device at the cable terminal supports the IEEE 802.3af/at standard. This process is achieved by providing a current-limited small voltage to the cable to check whether the remote end has the required characteristic resistance. If a specific resistance value is detected, it indicates that the cable terminal is connected to a PD (powered device) that supports POE.
3.2 Monitor PD level/power supply capability negotiation:
After detecting the PD, the PSE device will classify the PD device and evaluate the required power loss. There are two ways of power supply capability negotiation, namely, analyzing the detected characteristic resistance and conducting power supply capability negotiation through the LLDP protocol (Link Layer Discovery Protocol).
3.3 Start power supply:
Within a configurable time (generally less than 15μs), the PSE device starts to supply power from low voltage to the PD device until it provides 48V DC voltage. If the PD device is disconnected from the network, the PSE will quickly (usually within 300-400ms) stop supplying power and repeat the detection process to check if the cable terminal is still connected to the PD device.
3.4 Continuous realtime monitoring and power supply:
Provide stable and reliable DC power to the PD device to ensure the normal operation of the device. And provide continuous realtime monitoring.
3.5 Power off:
If the PD device is disconnected from the network, the PSE will quickly (usually within 300-400ms) stop supplying power to the PD device and repeat the detection process to detect whether the cable terminal is connected to the PD device.
This process ensures the safety and efficiency of POE power supply while protecting the connected devices from damage. POE switches are designed to intelligently detect non-POE devices and avoid supplying power to them, making it even safer to use.
4. Regarding POE Power Supply Standards
Of course, POE cables cannot supply power arbitrarily; they must adhere to specific processes and methods. POE power supply cables also have relevant standards, and it's important to know which POE standard the cable supports before buying. These standards are mainly proposed and published by IEEE.
Currently, there are three POE power supply standards: 802.3af (PoE), 802.3at (PoE+), and 802.3bt (PoE++).
802.3af is the basic standard for PoE functionality, stipulating a maximum output power of 15W when using network cables for power supply. This standard typically uses pairs of wires 4,5,7,8 to transmit current, with 4,5 as positive and 7,8 as negative.
802.3at (PoE+) is an enhanced standard for PoE functionality, increasing the maximum output power to 30W. This standard uses pairs of wires 1,2,3,6 to transmit power, with flexible polarity options: 1,2 as positive and 3,6 as negative, or vice versa.
802.3bt (PoE++) is the latest standard for PoE functionality, with a maximum output power of up to 60W. This standard uses additional wire pairs to increase power supply capacity and efficiency, which means the cables must meet higher specifications.
5. About The Main Power Supply Parameters of Three POE Power Supply Standards.
5.1 IEEE 802.3af Main Power Supply Parameters:
DC voltage between 44～57V, typically 48V. Typical operating current is 10～350mA, with a typical output power of 15.4W. Overload detection current is 350～500mA. Under no-load conditions, the maximum required current is 5mA. It provides four Class levels of power requests to Powered Devices (PDs): 3.84～12.95W.
IEEE 802.3af Classification Parameters:
Class 0 devices require a maximum operating power of 012.95W;
Class 1 devices require 03.84W;
Class 2 devices require between 3.85W6.49W;
Class 3 devices require between 6.5～12.95W.
Because the IEEE 802.3af standard caps PoE power consumption at 12.95W for PDs, it limits the applications where Ethernet cable power can be used. To overcome the power limitations of PoE, IEEE introduced a new standard: IEEE 802.3at (also known as PoE+), which defines devices requiring more than 12.95W as Class 4, extending the power level to 25W or higher. Compared to 802.3af, 802.3at can output more than twice the power, with each port capable of outputting over 30W. PDs can reach up to 29.95W, with PSE providing over 30W of DC power. The PD responds with a Class 4 current signal to let the PSE know if it can handle the higher power specified by 802.3at.
5.2 IEEE 802.3at (PoE+) Main Power Supply Parameters:
DC voltage between 50～57V, typically 50V. Typical operating current is 10～600mA, with a typical output power of 30W. PDs support Class 4 classification.
5.3 IEEE 802.3bt (PoE++) Main Power Supply Parameters:
The IEEE 802.3bt specification introduces four new high-power PD classifications (Class), bringing the total number of single-feature categories to nine. Classes 58 are new to the PoE standard and translate to PD power levels from 40.0W to 71W.
IEEE 802.3bt is backward compatible with IEEE 802.3at and 802.3af. A lower power IEEE 802.3at or 802.3af PD can connect to a higher power 802.3bt PSE without any issues. Conversely, when a higher power 802.3bt PD connects to a lower power 802.3at or 802.3af PSE, the PD only needs to operate at its respective lower power state, a process known as "power downgrading."
6. About POE Power Supply Classification
IEEE 802.3 assigns various classes to PoE systems, as seen in the standards above from Class 0 to Class 7, along with Type 1/2/3/4. The class is determined by the lowest common power level supported by both the power supply equipment and the powered device. This is achieved through the power supply equipment detecting the power requirements of the powered device using the Link Layer Discovery Protocol (LLDP), which essentially analyzes bidirectional packets between the power supply equipment and the powered device.
The class ranges from 0 to 8, with Type 1 and Type 2 PoE including classes 0 to 4, covering input power for powered devices ranging from 12.95W to 25.5W. Type 3 includes Class 5 (up to 40W for powered devices) and Class 6 (up to 51W for powered devices), while Type 4 includes Class 7 (up to 62W for powered devices) and Class 8 (up to 73W for powered devices).
So, why do we have these classifications? The classification system exists to negotiate power needs and manage the power supply equipment's budget more effectively. For example, if the power supply equipment is Class 6 but the powered device is only Class 5, the system is classified as Class 5, and the power supply equipment can set the maximum output power according to the device's requirements, rather than outputting more power than needed.
Although some technicians rely on querying LLDP information to track which devices are consuming power and how much, the good news is that most people do not need to worry about classification-what you really need to know is the power required by the device to choose the correct power supply equipment to ensure the demand is met. If your powered devices have a wide range of power needs (which is normal, such as in the same environment there might be a PoE wall clock requiring less than 4W and a PoE TV requiring 70W, etc.), you do not need to worry because PoE types are backward compatible.
7. POE Power Supply System Power Calculation and How to increase power over ethernet performance.
The total power of a POE switch is a very important indicator, directly related to how many cameras it can support. Taking a 24-port PoE switch with a power supply of 400W as an example, the PoE switch's total usable power is around 370W after accounting for losses. The switch's total power consumption equals the sum of the maximum power used by all devices plus line losses.
Under the IEEE 802.3af standard, it can fully supply 24 ports (370/15.4=24), meaning it can simultaneously power 24 cameras, i.e., full load power supply. However, if calculated based on the IEEE 802.3at standard's maximum single-port power supply of 30W, it can only supply 12 ports simultaneously (370/30=12). This does not yet consider line loss. In practical use, many ordinary network cameras have lower maximum power consumption, generally not exceeding 15W. If each PoE port reserves power supply power according to the maximum power (e.g., 30W), some ports may not use up the PoE power, while others may not get enough power. For example, some PoE switches support dynamic power management to avoid this situation. When buying a PoE switch, make sure it supports dynamic power management, so each port only allocates the power actually used, thus more efficiently utilizing the PoE switch's power supply capacity.
