Twisted-pair cables, which are familiar to the modern IT specialist, with the help of which PCs can be networked, hide one remarkable feature. The fact is that not only a digital data stream can be transmitted through them, but also power supply. To do this, additional devices must be used - PoE adapters. At the same time, there are a large number of their varieties and ways to connect these devices to the network. What is the specifics of such equipment?
Basic device information
PoE-adapter is a device that uses the capabilities of PoE technology, which allows you to transfer power to the required device via a conventional twisted pair cable. However, the ability of the Ethernet cable to exchange digital signals is not lost, and the network remains fully functional.
Deciphering the abbreviation PoE - Power over Ethernet. That is, "powered by the Ethernet standard." A PoE adapter is sometimes referred to as an "injector" - but the second type of device is still more correctly considered a variation of the first. Let's study the specifics of using the device in question in the context of using PoE-technology.
More about technology
Power over Ethernet technology allows you to provide power to 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 broadcasting digital signals and for supplying electricity.
As a result, when installing networks, there is no need to lay wires for sockets, as well as to install the necessary additional electrical equipment. In some cases, the installation of power cables can be complicated by the not quite optimal physical location of the network components. For example, it happens that a Wi-Fi adapter provides the best signal at a point in the building to which it is problematic to supply electricity. The same can be said about cameras: sometimes there may be a need to monitor areas that are difficult to provide power.
PoE technology allows you to organize the connection of devices to sockets, which, as we noted above, can simultaneously output devices to the network and supply power to it. This approach can be used in the case of upgrading the current network infrastructure. It is quite possible to supply power to existing outlets.
Advantages of Technology
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 feedingpower supply, and for the exchange of digital data;
- possible economic benefits associated with the absence 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 due to the presence of standards that provide the necessary protection of components against power surges;
- it is possible to modernize the current network infrastructure, organize communications in areas that were previously inaccessible for installation due to the need to lay electrical cables;
- it is possible to organize remote control over devices through network protocols.
Let's now study the main standards on the basis of which PoE networks function.
Standards
The main protocol used in organizing the corresponding infrastructure is IEEE 802.3af. It involves the inclusion of 2 types of devices in the network - sources of electricity and consumers. They can be, as we noted above, Wi-Fi routers, network drives. Cameras work great in such systems. Among the well-known manufacturing brands that produce devices with which the PoE adapter can interact is Axis.
Devices of the first type - sources - can be located on the initial section of the network or between the device that supplies power and the consumer. The standard in question allows the supply of power over unshielded twisted pair of various classes - in particular, it supports 5,5e and 6 at a voltage of 48 V and power consumption within 15 W. At the same time, there is no impact on the quality of digital data transmission over the cable, and a significant upgrade of the current network infrastructure in terms of bandwidth is not expected.
Voltage Methods
A Power over Ethernet network can be supplied with electricity through two schemes.
Firstly, signal transformers classified as high-frequency can be used at the end of the lines. The supply voltage will be applied to their central taps. Similarly, from them, but on the receiving side, the voltage will be removed. This technology allows you to use the same pair of wires for both broadcasting high-frequency signals and transmitting electricity.
Secondly, you can use the free pairs present in the cable of the corresponding type to transfer power. 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 noted specificity of the organization of the network in the PoE format suggests that the features of using injectors will depend on which way, first or second, the voltage is transmitted. So, the capabilities of the noted 802.3af standard allow the transmission of electricity to pairs in bundles 1, 2 or, for example, 4, 5 cables. In turn, injectors can befully compatible with 100 Base TX technology. However, if we are talking about splitters, then they should work with any of the power transfer schemes noted above, even if the connection polarity is reversed.
Types of PoE Equipment
There are several classes of equipment capable of operating in power-over-twisted-pair mode. A PoE adapter is 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 each of the noted types of equipment in more detail.
Consuming Devices
Consuming devices are, in fact, the same network devices that are powered by twisted pair. Their important characteristic is the input impedance. The corresponding indicator is usually determined in the range of 19-26.5 kOhm. As a rule, a capacitor is also present in the structure of the system to which consumers are connected.
Switches
The PoE switch is designed to ensure the functioning of the network in terms of recognizing the correctness of cable connections to access points. Networks of the corresponding type operate on the basis of the 802.3af protocols, which we mentioned above, as well as 802.3at. They allow you to ensure the interaction of various devices in the conditions of possible power surges. If you do not use a PoE switch, then there is a possibility that due to random current fluctuations in the twisted pair, the consumer device will go out ofbuilding.
Adapters
Devices of the type in question, as we noted above, are classified into additional varieties. So, a PoE adapter can be a power adapter. Its structure contains 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 regular wire. A PoE power adapter is actually sometimes referred to as an injector. There are a large number of solutions of this type on the Russian market. For example, the PoE TP Link 150S adapter is popular. The most important technical characteristic of a device of the corresponding type is a stabilized voltage. 48 V is considered the best indicator, if we talk about the marked device model from TP Link.
Another type of PoE adapter is the receiving one. It, however, 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 considered class of devices, devices belonging to the category of splitters are distinguished. In fact, they can also be classified as consumer devices.
If we talk about PoE adapters, which are splitters, they are designed to work with another type of device - PoE-Switch. That is, their main function is the division of network data into separate streams for the purpose of subsequent translation 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 those levels that are optimal for the final equipment - for example, these can be indicators of 5, 12 or 48 V.
In turn, splitters are also classified into two varieties - active and passive. As for the former, they can function both with switches and with power adapters. Such devices include, for example, a DWL-P50 type splitter from D-Link. A PoE adapter classified as a device of the type in question can also be passive. They can only work with injectors. At the same time, as experts note, they are often sold together with them in a single set.
Nuances of using adapters
With proper connection of adapters that use Power over Ethernet technology, there should be no problems with network organization. But some difficulties, due to the specifics of the standards used in such systems, may still appear. So, for example, the PoE-Switch can determine that the active source is not a consumer device, and the network can temporarily lose power 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 trying to connect a consumer device to the switch. You can solve it by installing an additional device - a PoE converter.
An interesting fact is that from the point of view of the costs of the enterprise in which the network is being laid, with a small number ofconsuming devices, it is more profitable to use passive devices, with a large one - active ones. Some IT professionals believe that after the number of access points exceeds 3, active adapters can be used.
Optimal cable type
Power over Internet technology involves the use of a twisted pair cable. But they are, as you know, of different types - for example, with 2 and 4 pairs. Which one is best suited for the installation of networks of the corresponding type? According to experts, the system will retain functionality when using any type of cable. But if we are talking about a heavy load on the switch - for example, if all its available ports are used, then a cable with 4 pairs is the best option.
