POE (Power Over Ethernet) refers to some IP-based terminals (such as IP phones, WLAN access points AP, network cameras) without any changes to the existing Ethernet Cat.5 cabling infrastructure. While transmitting data signals, it can also provide DC power for such devices. POE technology can ensure the normal operation of existing networks while ensuring the security of existing structured cabling, minimizing the cost of active Ethernet
PoE is also known as Power over LAN (PoL) or Active Ethernet, and is sometimes referred to as Power over Ethernet. This is the simultaneous transfer of data using existing standard Ethernet transport cables. The latest standard specification for electrical power and maintains compatibility with existing Ethernet systems and users. The IEEE 802.3af standard is a new standard based on the Power over Ethernet (PoE) system. It adds the standard for direct power supply through the network cable based on IEEE 802.3. It is an extension of the existing Ethernet standard and the first international standard for power distribution. standard.
IEEE 802.3af
The IEEE began to develop the standard in 1999. The first vendors to participate were 3Com, Intel, PowerDsine, Nortel, Mitel and National Semiconductor. However, the shortcomings of this standard have always restricted the expansion of the market. Until June 2003, the IEEE approved the 802.3af standard, which specifies power detection and control issues in remote systems and provides access to IP phones, security systems, and wireless LANs over Ethernet cables to routers, switches, and hubs. The way in which devices are powered by points is specified. The development of IEEE 802.3af includes the efforts of many corporate experts, which also allows the standard to be tested in all aspects.
A typical Power over Ethernet system. Keep the Ethernet switch device in the wiring closet and power the twisted pair cable of the LAN with a power supply hub (Midspan HUB). At the end of the twisted pair, the power source is used to drive phones, wireless access points, cameras, and other devices. To avoid power outages, a UPS can be used.
POE system configuration and power supply characteristics
A complete POE system includes two parts: Power Sourcing Equipment (PSE) and Powered Device (PD). The PSE device is a device that powers Ethernet client devices and is the administrator of the entire POE Power over Ethernet process. The PD device is a PSE load that accepts power, that is, a client device of the POE system, such as an IP phone, a network security camera, an AP and a PDA or a mobile phone charger, etc. (actually, any power Devices up to 13W can receive the corresponding power from the RJ45 socket. Based on the IEEE 802.3af standard, the two establish information about the connection status, device type, and power consumption level of the PD of the powered device, and use this as the power supply to the PD through the Ethernet.
The main power supply characteristics of the POE standard power supply system are:
1. The voltage is between 44 and 57V, with a typical value of 48V.
2. The maximum allowable current is 550mA and the maximum starting current is 500mA.
3. The typical operating current is 10 to 350 mA, and the overload detection current is 350 to 500 mA.
4. Under no-load conditions, the maximum required current is 5 mA.
5. Provide five levels of electrical power requests for the PD device from 3.84 to 12.95W, up to a maximum of 13W.
PoE Power Supply Working Process When the PSE power supply device is deployed in a network, the POE Ethernet power supply operation process is as follows.
Detection
Initially, the PSE device outputs a small voltage on the port until it detects that the cable termination is connected to an IEEE 802.3af-compliant powered device.
2. PD device classification
After detecting the powered device PD, the PSE device may classify the PD device and evaluate the power loss required by the PD device.
3. Start powering
During the start-up period of a configurable time (typically less than 15μs), the PSE device begins to supply power from the low voltage to the PD device until a 48V DC supply is provided.
4. Power supply
The PD device is provided with a stable and reliable 48V DC power, which satisfies the power consumption of the PD device not exceeding 15.4W.
5. Power off
If the PD device is disconnected from the network, the PSE stops powering the PD device quickly (usually within 300 to 400 ms) and repeats the detection process to detect whether the terminal of the cable is connected to the PD device.
PoE is powered by cable. The standard Category 5 cable has four pairs of twisted pairs, but only two of them are used in l0M BASE-T and 100M BASE-T. IEEE80 2.3af allows two usages. When the idle pin is used for power supply, the 4 and 5 pin connections are positive, and the 7 and 8 pin connections are negative.
When the application data pin is powered, the DC power is applied to the midpoint of the transmission transformer without affecting the data transmission. In this manner, the pair 1, 2 and the pair 3, 6 can be of any polarity.
The standard does not allow the application of both cases. The power supply device PSE can only provide one usage, but the power application device PD must be able to adapt to both situations at the same time. This standard specifies that the power supply is usually 48V, 13W. It is easier for PD devices to provide 48V to low voltage conversion, but at the same time there should be a 1500V insulation safety voltage.
PoE's two power supply methods The PoE standard defines two methods for transporting DC power to a POE-compatible device using an Ethernet transmission cable:
Mid-Span
Use the idle line pair that is not used in the Ethernet cable to transmit DC power. It is applied between the common switch and the network terminal device. The network terminal device can be powered by the network cable. The Midspan PSE (mid-span power supply device) is a dedicated power management device. The device, usually placed with the switch. It has two RJ45 jacks for each port, one connected to the switch with a short wire and the other connected to the remote device.
End-Span,
The DC power is transmitted simultaneously on the core line used for transmitting data, and the transmission uses a different frequency from the Ethernet data signal. The corresponding Endpoint PSE (end-of-band device) has POE-capable Ethernet switches, routers, hubs, or other network switching devices. It is foreseeable that End-Span will be quickly promoted. This is because Ethernet data and transmission use a common line pair, thus eliminating the need for dedicated lines for independent power transmission. This is for 8-core cables and matching standard RJ- The 45 socket is of great significance.
development of
PowerDsine, a Power over Ethernet chip maker, will hold an IEEE conference to formally submit a "High Power Power over Ethernet" standard that will support powering devices such as laptops. PowerDsine will submit a white paper recommending a doubling of the 802.3af standard 48v input and 13w available power limit. In addition to notebook computers, the new standard may also provide power for LCD monitors and video phones.
Recently, the IEEE has released a new 802.3AT, which stipulates that POE can provide higher power, exceeding 13W, and can reach 50W!
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