Both IEEE 802.3af and IEEE 802.3AT standards use Ethernet data line pairs or alternate pairs to power Ethernet devices. They break through Ethernet applications, and they are primarily a power transfer protocol, not a data protocol.

The IEEE Association approved the 802.3af standard in June 2003, which specifies power detection and control 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.

Under the IEEE802.3AF standard, the POE system consists of a complete POE system consisting of a Power Sourcing Equipment (PSE) and a 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 is powered, that is, a client device of the POE system, such as an IP phone, a network security camera, an AP, and a handheld computer (PDA) or a mobile phone charger. 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 standard five types of network cables have four pairs of twisted pairs. IEEE80 2.3af allows two line order power supply methods: one is to transmit current on the 4, 5, 7, and 8 pairs, and it is specified that 4 and 5 are positive, 7 8 is the negative electrode. Another type of power supply is to transmit power on 1, 2, 3, 6 lines, the polarity is arbitrary, 1, 2 is positive, 3, 6 is negative or 1, 2 is negative, 3, 6 is positive, of which A power supply polarity.

The working process of IEEE802.3af:

1. Detection: Before the PSE supplies power to the powered device, it first outputs a low voltage to detect whether the powered device (PD) meets the IEEE802.3af standard. If it meets the standard, it is generally used in the powered device, using 24.9K. The resistance is confirmed to comply with the IEEE802.3af power supply standard.

2. Grading: When the PSE detects the resistance value that meets the requirements, the output voltage will be further increased to classify the powered device. If the powered device does not respond to the grading confirmation current, the PSE will default to the powered device. Level 0, which provides 15.4W of output power.

3. Power supply: After confirming the classification, the PSE will output 48V DC power to the powered device and confirm that the powered device does not exceed the power requirement of 15.4W. When the powered device is overloaded or shorted, the PSE stops supplying power and re-enters Detection phase.

The main power supply characteristic parameters of the IEEE802.3af standard power supply system are:

The DC voltage is between 44 and 57V, with a typical value of 48V.

Typical operating current is 10 to 350 mA, typical output power is 15.4W.

The overload detection current is 350 to 500 mA.

Under no-load conditions, the maximum required current is 5 mA.

Provides three class level electrical power requests for the PD device from 3.84 to 12.95W.

Classification parameters of IEEE802.3af:

Class 0 equipment requires a maximum working power of 0~12.95W

Class 1 equipment requires a maximum working power of 0~3.84W;

Class 2 equipment requires a working power of 3.85W to 6.49W;

Class 3 devices have a power range of 6.5 to 12.95W.

IEEE 802.3at standard

    Due to the IEEE 802.3af specification, PoE power consumption on powered devices (PDs) is limited to 12.95W, which is sufficient for traditional network powered devices, but with IP phones and webcams, dual band access, video With the advent of high-power applications such as telephones and PTZ video surveillance systems, the 13W power supply obviously cannot meet the demand, which limits the application range of Ethernet cable power supply. In order to overcome the PoE's power budget constraints and push it to new applications, the IEEE has set up a new task force to explore ways to increase the power limit of the international power standard. The IEEE802.3 working group evaluates the possibility of IEEE802.3at implementation technically and economically. The new standard is called IEEE 802.3at. It defines a device with a power requirement higher than 12.95W as Class 4, which can expand the power level. To 25W or higher, the new standard was released in early 2009.

Compared with 802.3af, IEEE 802.3at can output more than 2 times of power, and the output power of each port can be more than 30W. As far as the standard is concerned, the two have different definitions in power and grading.

According to IEEE802.3at, the PD of the powered device can be up to 29.95W, and the PSE will provide more than 30W DC power. The PD responds with a Class 4 current response, telling the PSE if it can provide it with a higher power specified by 802.3at.

The main power supply characteristic parameters of the IEEE802.3at standard power supply system are:

The DC voltage is between 50 and 57V, with a typical value of 50V.

Typical operating current is 10 to 600 mA, and typical output power is 30W.

The powered device PD supports the classification of Class 4.