“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 strong current 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), smart city and other scenarios, and is widely used. It has low cost, convenient construction, and power supply. Stability, high operation and maintenance efficiency, etc., this article will combine Po
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 strong current 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), smart city and other scenarios, and is widely used. It has low cost, convenient construction, and power supply. Stability, high operation and maintenance efficiency, etc., this article will combine the development history of PoE technology to describe the implementation principle of PoE technology.
Without any changes to the existing Ethernet wiring structure, PoE technology can be implemented 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, there is no need 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.
Figure 1: PSE and PD connection diagram
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 to power IP phones, security systems, and wireless access points through Ethernet cables. The method is stipulated to provide no more than 15W of electric power for equipment that meets 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 was formally 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, UPoE, etc.
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 can be output by the PSE end is more selective, and the corresponding PSE end power is selected according to the needs of the PD.
The comparison of the three PoE power supply technology standards is as follows:
Table 1: Comparison of three standards
How is PoE powered
PoE power supply process description
Figure 2: PoE power supply flow chart
1. Detection: The PSE device sends out a voltage pulse of 2~10V at the port to detect whether the PD connected to the cable terminal is a standard-supported powered device. Only when it is detected that the PD is a standard device, will the next step be continued.
2. PD classification (Classification): Since there are many types of PDs, the required power is also different, so after the power supply device correctly detects the power receiving device, it is necessary to detect the power level of the opposite PD device.
When the PD is detected, the PSE will classify the PD device. The PSE applies a 15.5V~20.5V detection voltage (the current is limited to 100mA or less), the PD device will connect a grading resistor in series to the line to identify its own power, and the PSE can determine which PD device belongs to by testing the size of the characteristic current returned Classification.
Note: 0 is the default category
Table 2: The corresponding power description of the latest PD classification level
3. Power up: When the PSE detects that a standard PD is connected to the end of the cable and has classified the PD, it starts to supply power to the PD and output a DC voltage of 44~57V.
4. Power supply: PSE provides a stable and reliable DC voltage for the PD, and outputs the power of the corresponding level according to the classification result of the PD.
5. Disconnection: If the connection cable connected to the PD is unplugged or the user turns off the PoE power supply function of the switch port from the software, the PSE will quickly (usually within 30-40ms) stop as PD power supply. At any time during the entire process of PSE powering PD, if the PD device is short-circuited, the power consumed during classification exceeds the power that the PSE corresponds to, or the power consumed exceeds the rated power, the entire power supply process will be interrupted and the power supply will be restarted from the first The step detection process begins.
PoE power supply line sequence description
Taking the PoE standard as an example, the standard defines two power supply line sequences, and PSE can adapt to PD using any power supply line sequence.
Idle line power supply: Use idle line pairs (4/5, 7/8) that are not used in the Ethernet cable to transmit DC power.
Figure 3: Idle line power supply
Signal line power supply: DC power (1/2, 3/6) is simultaneously transmitted on the core wire used for data transmission, and its power transmission uses a different frequency from the Ethernet data signal to realize the multiplexing of the transmission data and the transmission current.
Figure 4: Signal line power supply
PoE+ uses the PoE line sequence, which is consistent with PoE.
How 802.3bt achieves higher power
With the development of the market, the terminal’s demand for high power is increasing. At the same time, as the power load increases, the cable temperature will also increase. When the temperature of the cable is too high, the cable may exceed its rated temperature, thereby reducing performance and reliability (may cause damage to the cable). Therefore, for devices with a power supply requirement of more than 30W, it is not possible to use only 4-core of the 8-core twisted pair for power supply like PoE and PoE+.
The IEEE 802.3bt standard defines the use of 8-core twisted pair for voltage output to meet the market’s demand for stronger and more efficient Ethernet power supply capabilities. can be realised:
(1) The highest rate is compatible with 10GBASE-T;
(2) The minimum power of 40W and the maximum of 90W can be obtained at the PD end.
Figure 5: Implementation of IEEE 802.3bt on the PSE&PD side
When the PSE end realizes 802.3bt, voltage is applied to the 8 cores of the RJ45. Load 54V positive electrode on 1/2 and 4/5 wire pairs, and load 54V negative electrode on 3/6 and 7/8 wire pairs. The PD end uses two diode bridges, and both diode bridges have current flowing. The chip at the PD end is required to control the two currents and output to the DC-DC conversion circuit.
PoE technology summary
Now that PoE technology has been widely used in smart cities, IoT and other industries, it is believed that PoE technology will have greater development and breakthroughs in the near future. With the official approval of 802.3bt this year (expected to be officially released in 2019), higher power Terminals will soon be widely used, which will help the rapid development of the IoT industry.
Ruijie Networks’ products supporting PoE technology cover various campus switches. The products are widely used in various industries such as new retail, Internet, education, medical care, transportation, energy, etc. Among them, the access switch S2910-H series also supports high-power 802.3bt Output, to achieve full scene coverage, power output is more stable and safe.