In the usual modern IT specialist cablessuch as "twisted pair", with which the PC can be combined into a network, one remarkable feature is hidden. The matter is that through them not only a digital data stream can be transmitted, but also power supply. To do this, additional devices must be used - PoE adapters. In this case, there is a large number of their varieties and ways to connect these devices to the network. What is the specificity of the operation of such equipment?
A PoE adapter is a device that usesthe possibility of PoE-technology, which allows to transmit via normal twisted pair power to the desired device. The ability of the Ethernet cable to exchange digital signals is not lost, and the network remains fully functional.
Explanation of the abbreviation PoE - Power overEthernet. That is, "power supply via Ethernet standard". The PoE adapter is sometimes referred to as an "injector" - but the second type of device is still more correct to consider a variety of the first. Let's study the specifics of using the device in the context of using the capabilities of PoE-technology.
Power over Ethernet technology allowsprovide power supply for a variety of types of devices: Wi-Fi-routers, cameras, drives. The main advantage of this technology is that it involves the use of a single set of wires - both for digital broadcasting and for electricity.
As a result, when installing networks, there is no need,to lay wires for sockets, and also to install the necessary additional electrical equipment. In some cases, the installation of power cables can be complicated by not quite optimal physical location of network components. For example, it happens that the Wi-Fi-adapter provides the best signal at the point of the building, to which the electricity is problematic. The same can be said about the cameras: sometimes there may be a need for monitoring territories that are difficult to provide power.
PoE technology allows you to organizeconnection of devices to sockets, which can, as we noted above, simultaneously bring devices into the network and supply power to it. This approach can be used in case of upgrading the current network infrastructure. It is quite realistic to bring food to the already active sockets.
So, if we summarize the key advantages of the technology in question, they can form the following list:
- the use of the same cable is possible both for power supply and for digital data exchange;
- there are possible economic benefits associated with the lack of the need to install power cables and other necessary equipment;
- a high level of security of the network infrastructure of the appropriate type is achieved, thanks to the availability of standards ensuring the necessary protection of components from power surges;
- there is the possibility of upgrading the current network infrastructure, organizing communications in areas that were previously inaccessible for installation because of the need to run electrical cables;
- there is the possibility of organizing remote control of devices through network protocols.
We will now study the basic standards on the basis of which PoE networks function.
The main protocol used in the organizationThe corresponding infrastructure is IEEE 802.3af. It involves the inclusion in the network of 2 types of devices - power sources and consumers. They can be, as we noted above, Wi-Fi-routers, network drives. Excellent work in such camera systems. Among the well-known brands that manufacture devices with which the PoE adapter can communicate - Axis.
Devices of the first type - sources - canlocated on the initial part of the network or between the device, which supplies power, and the consumer. The considered standard allows the power supply over twisted pair unshielded type of different classes - in particular, supported 5, 5e and 6 at a voltage of 48 V and power consumption within 15 watts. At the same time, there is no impact on the quality of digital data transmission via cable and there is no substantial upgrade of the current network infrastructure in terms of bandwidth.
A network operating on the basis of the Power over Ethernet standard can be provided with electricity through two circuits.
First, you can use the finalSignal transformers classified as high frequency. The supply voltage will be supplied to their central outlets. Similarly from them, but at the same on the receiving side, the voltage will be removed. This technology allows you to use the same pair of wires for both high-frequency signals and for electricity transmission.
Second, you can use it to transfersupply free pairs present in the cable of the appropriate type. How is this possible? The fact is that in practice, 2 out of 4 pairs that are in an Ethernet cable are often not used. Of course, if we are talking about their compliance with 100 Base TX technology.
The specifics of the organization of the network inthe PoE format assumes that the features of the use of injectors will depend on how exactly the first or second way, the voltage is transmitted. So, the capabilities of the noted 802.3af standard allow to transfer electricity to pairs in bundles of 1,2 or, for example, 4,5 cables. In turn, the injectors can be fully compatible with the technology of 100 Base TX. However, in the case of splitters, they should work with any of the above power transfer schemes, even if the polarity of the connection is changed.
There are several classes of equipment,capable of operating in a power transfer mode over a twisted pair. PoE-adapter - one of them (the corresponding devices have a large number of varieties - we will study their specifics). Along with it, there are also PoE switches, as well as consuming devices. In many cases, they can be integrated into one system. Let's study the specifics of the operation of each of the mentioned types of equipment in more detail.
Consuming devices are, actually, thoseThe most network devices that are powered over a twisted pair. Their important characteristic is the input resistance. The corresponding figure is usually determined in the range of 19-26.5 kΩ. As a rule, a capacitor is also present in the structure of the system to which the powering devices are connected.
Коммутатор PoE предназначен для обеспечения the functioning of the network in terms of recognizing the correctness of cable connections to access points. Networks of the appropriate type operate on the basis of the 802.3af protocols, which we mentioned above, as well as 802.3at. They allow the interaction of various devices in the face of possible surges. If the PoE switch is not used, then there is a chance that, due to random oscillations of the current in the twisted pair, the consumer device will fail.
Devices of this type, as we notedabove are classified into additional varieties. So, a PoE adapter can be powering. In its structure there is a power supply, as well as a conjugation element, which can be equipped with galvanic isolation and in this case look like a small box or be a normal wire. The PoE power adapter, in fact, is sometimes referred to as the injector. There are a large number of solutions of this type in the Russian market. For example, the PoE TP Link 150S adapter is popular. The most important technical characteristic of the device of the corresponding type is stabilized voltage. The best indicator is 48 V, if we talk about the marked device model from TP Link.
Another type of PoE adapter is receiver.However, it is also used to provide power to devices using a twisted pair, but only those that do not belong to the category of consumers. In order for such equipment to function, it is desirable that its power does not exceed 24 watts. It can be noted that within the class of devices under consideration, devices belonging to the category of splitters are distinguished. In fact, they can also be attributed to consuming devices.
If we talk about PoE adapters that aresplitters, they are designed to work with a different type of device - PoE-Switch. That is, their main function is the separation of network data into separate streams for the purpose of subsequent broadcasting to devices that do not belong to the category of consuming devices. Splitters are responsible for converting the voltage that is supplied to them to levels that are optimal for the final equipment — for example, these can be 5, 12 or 48 V.
В свою очередь, сплиттеры также классифицируются into two types - active and passive. As for the first, they can function with both switches and power adapters. Such devices include, for example, the splitter type DWL-P50 from D-Link. A PoE adapter classified as a device of this type can also be passive. They can work only with injectors. At the same time, they, as experts note, are often sold with them in a single set.
With proper adapter connection,involving Power over Ethernet technology, problems with the organization of the network should not arise. But some difficulties, due to the specifics of the standards used in such systems, may still appear. For example, the PoE-Switch can determine that the active source is not a consuming device, and the network can be temporarily de-energized due to the fact that a passive splitter is used in the system. It is necessary, in turn, to replace it with an active one. Another possible problem is a power outage when attempting to connect a consumer device to a switch. You can solve it by installing an additional device - PoE-converter.
An interesting fact is that in terms of costsenterprises in which the network is being laid, with a small number of consuming devices, it is more profitable to use passive devices, with a large one - active ones. Some IT specialists believe that after the number of access points exceeds 3 units, you can use active adapters.
Power over Internet technology suggeststhus enabling the twisted pair. But they are, as you know, of different types - for example, with 2 and 4 pairs. Which one is best for installing networks of the appropriate type? According to experts, the system will retain its functionality when using any type of cable. But if we are talking about a large load on the switch - for example, if all its available ports are involved, then a cable with 4 pairs is the best option.
