In the twisted-pair cables , which are usual for a modern IT specialist , with the help of which PCs can be connected to a network, one remarkable possibility is hidden. The fact is that through them not only the digital data stream can be transmitted , but also the power supply. To do this, additional devices must be involved - PoE adapters. At the same time, there are a large number of their varieties and methods of connecting these devices to the network. What is the specifics of such equipment?
Device Basics
A PoE adapter is a device that uses the capabilities of PoE technology, which allows you to transfer power through a regular twisted-pair cable to the desired device. At the same time, the ability of an Ethernet cable to exchange digital signals is not lost, and the network remains fully functional.
Decoding of the abbreviation PoE - Power over Ethernet. That is, "power through 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. We will study the specifics of using the device in question in the context of using the capabilities of 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 may 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 that point in the building, to which it is problematic to bring electricity. The same can be said about cameras: sometimes there may be a need to monitor areas that are difficult to provide with power.
PoE technology allows you to organize the connection of devices to outlets, which can, as we noted above, simultaneously bring devices to the network and supply power to it. This approach can be used in case of modernization of the current network infrastructure. It is quite possible to bring power to existing outlets.
Technology benefits
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 the exchange of digital data;
- possible economic benefits associated with the lack of the need to install power cables and other necessary equipment;
- achieved a high level of security of the network infrastructure of the appropriate type, due to the presence of standards that provide the necessary protection of components from power surges;
- there is the possibility of modernizing the current network infrastructure, organizing communications in areas that were previously unavailable for installation due to the need to lay 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 operate.
Standards
The main protocol involved in organizing the corresponding infrastructure is IEEE 802.3af. It involves the inclusion in the network of 2 types of devices - sources of electricity and consumers. They can be, as we noted above, Wi-Fi routers, network drives. They work great in such camera systems. Among the well-known manufacturers that produce devices with which the PoE adapter can interact - Axis.
The first type of devices - sources - can be located on the initial section of the network or between the device that supplies power and the consumer. The standard under consideration allows the supply of power through a twisted pair unshielded type of various classes - in particular, it supports 5, 5e and 6 at a voltage of 48 V and power consumption within 15 watts. At the same time, there is no effect on the quality of digital data transmission by cable, and significant modernization of the current network infrastructure in terms of bandwidth is not expected.
Voltage supply methods
A Power over Ethernet-based network can be powered by two circuits.
Firstly, signal transformers, classified as high-frequency ones, can be used on the end sections of lines. Supply voltage will be supplied to their central taps. Similarly with them, but on the receiving side, the voltage will be removed. This technology allows you to use the same pair of wires for broadcasting high-frequency signals, as well as for transmitting electricity.
Secondly, it is possible to use 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 the Ethernet cable are often not used. Of course, when it comes to their compliance with 100 Base TX technology.
The noted specifics of the organization of the network in PoE format suggests that the features of the use of injectors will depend on the way in which the first or second voltage is transmitted. Thus, the capabilities of the noted 802.3af standard allow the transmission of electricity to pairs in bundles of 1.2 or, for example, 4.5 cables. In turn, the injectors can be fully compatible with 100 Base TX technology. However, when it comes to splitters, they should work with any of the power transfer circuits noted above, even if the polarity of the connection is reversed.
Types of PoE Equipment
There are several classes of equipment that can operate in power transmission mode over a twisted pair cable. The 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. We 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 resistance. The corresponding indicator is usually determined in the range of 19-26.5 kOhm. As a rule, in the structure of the system to which the consuming devices are connected, there is also a capacitor.
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 for the interaction of various devices in the conditions of possible power surges. If you do not use the PoE switch, then it is likely that due to random current fluctuations in the twisted pair cable, the consuming device will fail.
Adapters
Devices of this type, as we noted above, are classified into additional varieties. So, a PoE adapter can be powered. 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 an ordinary wire. The PoE power adapter , in fact, is sometimes called 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 stabilized voltage. The optimal indicator is 48 V, if we talk about the marked model of the device from TP Link.
Another type of PoE adapter is the receiving one. However, it is also used to provide power to devices using 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 related to the category of splitters are distinguished. In fact, they can also be attributed to consuming 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 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 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 first, they can function both with switches and with power adapters. Such devices include, for example, a splitter type DWL-P50 from D-Link. A PoE adapter classified as a device of this type can also be passive. They can only work with injectors. Moreover, they, as experts note, are often sold together with them in a single set.
Nuances of using adapters
If you correctly connect adapters that use Power over Ethernet technology, you should not have problems with the organization of the network. But some difficulties, due to the specifics of the standards used in such systems, can still appear. So, for example, a PoE-Switch can determine that the active source is not a consuming device, and the network may be temporarily de-energized due to the fact that the system uses a passive splitter. It is necessary, in turn, to replace it with an active one. Another possible problem is a power outage when trying to connect a consuming device to a switch. It can be solved 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 built, it is more profitable to use passive devices with a small number of consuming devices, and active ones with a large number of devices. Some IT experts believe that already after the number of access points exceeds 3 pieces, you can use active adapters.
Optimum Cable Type
Power over Internet technology involves the use, therefore, of 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 the 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.