Power over Ethernet technology
This article will look at aspects of the application and purpose of PoE technology, the principles of power supply to the line and the impact of the implementation on the power supply network.
Adopted in July 2003, the IEEE 802.3af standard regulates the method of powering devices connected to an Ethernet network, which involves the use of a cable designed for data transmission.
Wikipedia defines PoE as follows:
From where it immediately becomes clear why this technology was invented - who wants to drag the power cable to the webcam or VoIP device, thereby increasing the cable management of the office or home.
True to throw PoE everywhere and everywhere must be carefully, because this implementation requires a revision of the issues of power supply and cooling (of course it comes to industrial implementation)
If you do not take into account the increased power requirements for power supply and cooling, you should be prepared for unexpected outages and equipment malfunctions. Since PoE is commonly used in communication and access control systems, the negative effect of such outages is especially noticeable.
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The following methods are available for powering the Ethernet:
The maximum allowable power level of about 15-16 W per port at a current of 350mA and a voltage of 48V, based on these restrictions, a list of devices that can be powered by this technology emerges.
A typical IP phone uses up to 5 watts of power, a video-enabled IP phone, like a RFID tag reader or a fixed security camera, is 10-12 watts, a wireless access point, a card reader or an electromechanical lock from 8 to 12 watts.
The PoE + (IEEE 802.3at) standard version that is under development will allow connecting devices with power consumption up to 30 W when transmitting data over two pairs (10BaseT and 100BaseTX) and equipment up to 60 W in the case of transmission over all four pairs (for Gigabit Ethernet 1000BaseT) . Thus, Wireless Mesh Network access points with a capacity of up to 50 W, managed video surveillance cameras with power consumption of up to 20 W and other sufficiently powerful devices will be able to receive power through a single wire.
Suppose our office has 50 machines. There are two 48-port switches and an “injector” for supplying voltage to PoE-enabled devices. And suppose that our devices require no more than 7W of power.
Without the use of PoE technology, the power consumption of switching equipment in a small office will not exceed 90 watts. To support such a load is enough UPS with a capacity of 500 W / 750 VA.
However, if we power all telecommunications equipment, webcams and other additional equipment from the UPS, then we will have to take into account the increased load (for a small office with 50 active devices, it will increase about 6 times) with the UPS, which may entail replacing the UPS with more powerful analog.
Also, you may have to perform the calculation of heat dissipation, because A new UPS in battery mode will generate more heat.
via wikipedia lan mag
Adopted in July 2003, the IEEE 802.3af standard regulates the method of powering devices connected to an Ethernet network, which involves the use of a cable designed for data transmission.
Wikipedia defines PoE as follows:
Power over Ethernet, or PoE, is a technology that allows electric power to be transmitted to a remote device along with data through a standard twisted pair over an Ethernet network. This technology is intended for IP-telephony, access points of wireless networks, Web-cameras, network hubs and other devices to which it is undesirable or impossible to conduct a separate electrical cable.
From where it immediately becomes clear why this technology was invented - who wants to drag the power cable to the webcam or VoIP device, thereby increasing the cable management of the office or home.
True to throw PoE everywhere and everywhere must be carefully, because this implementation requires a revision of the issues of power supply and cooling (of course it comes to industrial implementation)
If you do not take into account the increased power requirements for power supply and cooling, you should be prepared for unexpected outages and equipment malfunctions. Since PoE is commonly used in communication and access control systems, the negative effect of such outages is especially noticeable.
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How is power supplied to the line?
The following methods are available for powering the Ethernet:
- switch with voltage supply to the line;
- “Power injector” installed between the switch and the cross;
- cross with voltage supply to the line;
- “Power injector” for one line (the latter provides power for PoE-compatible devices in networks lacking such support)
PoE technology does not affect data transmission quality. The properties of the physical Ethernet layer are used for its implementation:
A) The use of high-frequency transformers at both ends of the line with a central tap from the windings. A constant supply voltage is supplied to the central taps of the secondary windings of these transformers, and also removed from the central taps at the receiving side. The use of central taps of signal transformers allows, without mutual influence, to transmit one pair of wires and high-frequency data and a constant supply voltage.
B) Use free pairs for power supply. Modern cable networks Ethernet, conforming to the standard 100Base-TX, consist of four pairs, two of which are not involved.
Accordingly, there are two options for powering the PSE device:
- A - for twisted pairs for which the data goes
- B - for unused pairs in the cable
PSE devices (injectors) differ, depending on options A or B, while splitters, that is, PD devices, are universal. A PD device must be able to receive power in any way, including when the polarity is reversed (for example, when using a computer-to-computer cross cable). It is important that the PSE device supplies power to the cable only if the device being connected is a PD device. Thus, equipment that does not support the PoE standard and is accidentally connected to a PSE device will not be disabled. The procedure for applying and disconnecting power to a cable consists of several steps.
The maximum allowable power level of about 15-16 W per port at a current of 350mA and a voltage of 48V, based on these restrictions, a list of devices that can be powered by this technology emerges.
A typical IP phone uses up to 5 watts of power, a video-enabled IP phone, like a RFID tag reader or a fixed security camera, is 10-12 watts, a wireless access point, a card reader or an electromechanical lock from 8 to 12 watts.
The PoE + (IEEE 802.3at) standard version that is under development will allow connecting devices with power consumption up to 30 W when transmitting data over two pairs (10BaseT and 100BaseTX) and equipment up to 60 W in the case of transmission over all four pairs (for Gigabit Ethernet 1000BaseT) . Thus, Wireless Mesh Network access points with a capacity of up to 50 W, managed video surveillance cameras with power consumption of up to 20 W and other sufficiently powerful devices will be able to receive power through a single wire.
What should I look for when implementing PoE in a corporate network?
Suppose our office has 50 machines. There are two 48-port switches and an “injector” for supplying voltage to PoE-enabled devices. And suppose that our devices require no more than 7W of power.
Without the use of PoE technology, the power consumption of switching equipment in a small office will not exceed 90 watts. To support such a load is enough UPS with a capacity of 500 W / 750 VA.
However, if we power all telecommunications equipment, webcams and other additional equipment from the UPS, then we will have to take into account the increased load (for a small office with 50 active devices, it will increase about 6 times) with the UPS, which may entail replacing the UPS with more powerful analog.
Also, you may have to perform the calculation of heat dissipation, because A new UPS in battery mode will generate more heat.
via wikipedia lan mag
Source: https://habr.com/ru/post/45992/
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