Detailed Explanation Of PoE Power Over Ethernet Technology

- Sep 24, 2020-

With the rapid development of the Internet of Things technology, there are more and more terminals that need to provide network services. It is becoming more and more difficult to use traditional high-voltage methods to power a variety of smart terminals. Power over Ethernet (PoE) The popularization of technology is solving the power supply problems of various smart terminals one by one.


Technical Background


With the rapid development of the Internet of Things technology, there are more and more terminals that need to provide network services. It is becoming more and more difficult to use traditional high-voltage methods to power a variety of smart terminals. Power over Ethernet (PoE) The popularization of technology is solving the power supply problems of various smart terminals one by one. At present, PoE technology has been extended from traditional WLAN, network monitoring, IP phone and other application scenarios to new retail, IoT (Internet of Things, Internet of Things), smart city and other scenarios, which are widely used, with low cost, convenient construction, and power supply. Stability, high operation and maintenance efficiency and other characteristics, this article will combine the development of PoE technology to describe the implementation principle of PoE technology.


Without any changes to the existing Ethernet wiring structure, PoE technology can be realized to transmit data signals and provide DC power supply for IP-based terminals (such as IP phones, wireless APs, network monitoring, etc.), and maintain the same level as the existing ones. Ethernet and user compatibility. In this way, it is unnecessary to increase the process of slotting, pipe laying, threading, debugging, wall and ground beautification in the construction environment, which greatly shortens the construction period and reduces the cost.


Several role definitions in PoE power supply system:


Power Supply Equipment (PSE): Power Sourcing Equipment, equipment that supplies power to the terminal;


Powered Device (PD): Power Device, a terminal that needs power supply

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PoE technology development history


PoE technology appeared earlier, but the early PoE technology has no standard to follow. The IEEE 802.3 working group standardized it in 2003, and then gradually developed to 802.3af, 802.3at and then to the latest 802.3bt. Next, let's take a look at the development process of PoE technology.


IEEE 802.3af (PoE)


The IEEE 802.3af standard, released in 2003, clearly specifies the power detection and control items in the remote system, and provides power for routers, switches, and hubs through Ethernet cables to IP phones, security systems, and wireless access points. The method is stipulated to provide no more than 15W of electric power for devices that meet the 802.3af standard.


IEEE 802.3at (PoE+)


The maximum power of PoE is difficult to meet the power supply requirements of higher-power wireless access points, video phones, video surveillance systems and other equipment. On the basis of compatibility with IEEE 802.3af, the IEEE 802.3at standard was released in 2009 and passed CAT-5 or higher Class cables can provide up to 30W of power.


IEEE 802.3bt


IEEE 802.3bt was officially approved in September 2018. This standard was mainly born to provide more power terminals. On the basis of compatibility with 802.3af and 802.3at, it can complete terminal power supply and data transmission up to 90W. , Breaking through the limitations of PoE+ power supply of 30W.


Note: 802.3bt has been approved but has not yet been officially released, nor is it officially named. Currently, it is often expressed by names such as HPoE, PoE++, PoH, and UPoE.


With greater power, developers can easily add more functions and upgrade existing products to meet the power supply requirements of high-power terminals in systems such as monitoring, access control, information release, parking, and even laptops and TVs. .


Compared with the 802.3at (PoE+) standard, 802.3bt has two new power supply types, corresponding to 60W and 90W output power. The power that the PSE can output is more selective, and the corresponding PSE power is selected according to the needs of the PD.

The comparison of the three PoE power supply technology standards is as follows:

Stanard

PSE maximum output power

PD input power

Cable length

Power supply line pair

802.3af

15.4W

12.95W

100m

2

802.3at

30W

25.5W

100m

2

802.3bt

60W

51W

100m

4

802.3bt

90W

71.3W

100m

4

Table 1: Comparison of three standards