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Power over Ethernet what is it and why is it needed? PoE technology and video switches

Video cameras and video recorders connected to various network switches with and without POE, routers, have firmly established themselves in the video surveillance market. It is too early to speak about the widespread transition to digital equipment. However, the trend towards consistent market conquest and displacement of coordinate-matrix structures has been observed over the past five years.

Manufacturers have emerged in the relevant trade industry that specialize only in video surveillance devices operating over the Internet. In turn, the demand for specialized equipment has increased to create the stability of the system.

It is often possible to come across the point of view that IP video surveillance devices connected to the world wide web can be connected to an already functioning network of an organization, which guarantees savings in installation costs. However, in practice, the efficiency of such a system is not of high quality. Typical network devices cannot handle the increased load on them. As a result, malfunctions arise not only in the functioning of video surveillance devices, but also in the entire enterprise network.

For this reason, you should focus on network switches for video surveillance systems, since these devices impose the main burden of redirecting the array of information.

What is a CCTV switch?

Internet Protocol video tracking structures often use standard network switches, more commonly known as switches. They are also called switches (from the English "switch"). Such devices create an association of connecting elements of the local network. During operation, the switch analyzes the MAC addresses of all connected equipment and creates a special table of input correspondence, which makes it possible to restrict the transfer of information to the local network.

In the course of developing the structure of video control connected to the Internet, attention is focused on the combination of the technical parameters of the switch to the mounted video surveillance devices and the general requirements for the functioning of the system.

Switch Bandwidth

Each network switch for video surveillance is endowed with certain information processing capabilities. In other words, this is the real amount of information that devices are able to process over a given period of time. In addition, the ability to process the data of each connector is also taken into account. The most common indicators are ten - one hundred megabits per second and one gigabits per second.

Be aware that it is not uncommon for the total processing capacity of a switch array to be less than the combined value of all inputs. If such a device is installed in full, then the structure is not capable of functioning in proper quality. In particular, the user will encounter video filming slowdown. In addition, the signal will disappear from time to time.

Number of LAN ports

This switch characteristic reflects the limit on the number of connected video surveillance devices or other network components. For home video control, switches with a small number of inputs (from 4) are often used. For specialized structures, equipment with eight, sixteen or twenty-four connectors is used. Taking into account the number of inputs, it is necessary to keep in mind the compatibility of the overall ability to process information per unit of time.

Degree of protection

As well as video surveillance devices with Internet Protocol, switches can be designed for external (street) and internal video control networks. Switches for outdoor use must provide a guarantee of functioning regardless of weather conditions. For this reason, the devices are manufactured in reinforced enclosures with a protection level of at least IP66.

For structures mounted inside buildings, switches for video tracking devices in common production are used. Portable devices that can be mounted on a DIN rail are widespread. But they have a small number of connectors.

Power over Ethernet Switch

The presence of Power over Ethernet makes it much easier to set up the video control structure, since the power is routed over a regular network cable (). It should be noted that a switch with POE is used in conjunction with video surveillance devices that support this option (this is necessarily reflected in the technical parameters).

Specificity of Power over Ethernet Switches

PoE is a technology for organizing a data channel together with power supply for ip video cameras using an ordinary Ethernet connection. Taking into account the difficulty of installing ip video control structures, power supply and image transmission over a single wire is the best option. For this reason, it is not uncommon for power users to prioritize Power over Ethernet devices.

The maximum transmission distance of the video signal of an ip video camera over a twisted pair cable without using additional devices is 100 meters. It should be noted that it is necessary to power the camera at such a distance directly near the video camera. POE Switch allows transmitting both signal and voltage over a single cable over a distance of up to 150 meters.

POE switch is an excellent solution in the field of IP video surveillance in 99% of cases, except (the same 1%) when, for example, current cameras with panning, zooming and ptz control with a power of about ninety watts are not able to function without laying an extra power cable, i.e. .to. the usual twenty-five watts of Power over Ethernet switch is definitely not enough.

But in recent years, manufacturers have been creating profile solutions with increased power, which makes it possible to use fairly powerful video monitoring devices with, as well as power additional devices (such as infrared illuminators). But you shouldn't rely on them too much. In any situation, it is necessary to carefully calculate the power consumption of the structure, correlating it with the capabilities of the switch.

UPLINK

A poe switch has not only a certain number of Power over Ethernet ports, but also an uplink port, thanks to which the device can be combined with various network components: routers, computers, DVRs, etc.

In the video: Choosing a switch for video surveillance

All commercially available switches are classified into Fast Ethernet and Gigabit Ethernet. A parameter that must be taken into account when choosing. This is the characteristic of the bandwidth: Fast Ethernet - 10/100 Mbps, Gigabit Ethernet - 10/100/1000 Mbps.

Symmetrical and asymmetric switches

Symmetry and asymmetry characterize a network switch in terms of the bandwidth of each port. A symmetric switch connects ports with the same bandwidth — 10 Mbps, 100 Mbps, or 1000 Mbps. An asymmetric switch connects ports with different bandwidths - 10 Mbps with 100 Mbps, 100 Mbps with 1000 Mbps. Such devices are used when there are large network flows "client-server": users simultaneously exchange data with the server, and this requires a wide bandwidth for the port. When streaming from a 100 Mbps port to a 10 Mbps port, the switch uses a memory buffer to avoid congestion. The size of the memory buffer is an important selection criterion.

Unmanaged and Managed PoE Switches

The unmanaged switch is simpler to use — ready to install out of the box with no configuration required. Ideal for typical systems. The managed switch provides fine tuning of many parameters. The devices are designed to solve complex problems, build branched out large systems, including equipment of different technical characteristics. A modern PoE switch is a complete element of a comprehensive security system.

The very name "PoE switch" means that the device performs communication tasks and simultaneously distributes energy. But connecting several nodes to a network and powering devices over twisted pair are far from all functions. PoE switches in functionality are not inferior to network switches, on board:

Setting the bandwidth of each port.
Bandwidth reservation for applications.
Traffic prioritization.
Static routing.
Network storm protection.
Port mirroring.
Aggregation.
Supports SSL and SSH encryption.
Detection of loops in the network with further isolation of the port and cable diagnostics.
Quantitative limitation of learned mac addresses.
Access list and the like.

Most of these functions are also present in unmanaged models, but they do not have the ability to customize (it is not always needed - it depends on the tasks).

Voltage

At the output, the PoE switch provides 48 V. The voltage of the powered device is 12 V. This is due to inevitable electrical losses during transmission over long cables. Thus, the required amount of energy reaches the consumers, which would not have happened if the output of the switch was 12 V. When the distance between devices is small, the losses are minimal. For such a case, each end device is equipped with a converter that adapts the voltage level, and there are switches on sale that operate in several modes.

Number of ports

The number of ports is an ambiguous characteristic. 4-port, 8-port, 16-port, 24-port are common names that do not indicate the number of PoE-enabled connectors. When you need to connect 8 CCTV cameras to the switch, you need 8 PoE ports, but in fact there are at least one more ports: in addition to RJ-45 with PoE, there is also Ethernet without PoE support, SFP, combined. When buying a switch, keep in mind that 4 devices need exactly 4 PoE ports, for 16 - 16. 4, 8, 24, 48 is an international standard. 16 ports are a Russian invention. Customer-focused manufacturers produce switches with 2, 5, 6, 7, 9, 10 or more ports with PoE support.

PoE budget

PoE Budget is a characteristic of each port and its aggregate. Please note: the budget for each port separately is higher than the budget for the same port, but at maximum load (using all connectors). Example: 15W port, total 8 ports, total budget 100W. In case of excessive consumption, energy is not supplied to one of the ports - according to the sequence set (manually or provided by the manufacturer). When purchasing a PoE switch, consider your overall PoE budget.

You can buy Netis, Osnovo, TP-Link, Hikvision, Trassir, Hikvision PoE switches from us. Trassir products are ours, the rest are our partners. On sale Netis, Osnovo, TP-Link, Hikvision at manufacturer prices.

PoE (Power over Ethernet) switch is a switch that uses a technology to transmit data and power over the same wires, using a twisted pair. Switches are required to connect several nodes of a computer network.

This is what a POE switch looks like, it is also called a switch (switch)

Computers are connected using an Ethernet cable to the switch. This device can receive and transmit data, determining its source and destination and transmitting packets of information only to those nodes in the network for which they are intended. For this, switches use switching tables - the scheme of correspondence of the MAC address of the computer in the network to the switch port The switch just powered on has an empty table. While transmitting data over the network, it analyzes the MAC addresses of the sending device and enters them into a table located in the associative memory. If the device then receives data assigned to a computer whose MAC address is in the table, the switch will send a signal only through the port associated with this node. The advantages of switches are their high speed of operation, in contrast to hubs.

Using switches for video surveillance

Network video surveillance is used to organize video surveillance through the use of computer networks that allow data transmission to anywhere in the world.

Visual signal registration is carried out by means of IP cameras, which transmit digitized data over networks using the IP protocol. Switches provide additional functionality for surveillance systems. Several cameras of a video surveillance system can be connected to a switch, which distributes digital data streams between output devices: computers, video servers, monitors, etc.

The most modern video surveillance systems use controlled switches that have an interface for configuring the behavior of devices depending on the signals coming to them, transmitting information in the event of triggering alarm sensors to certain network nodes, etc.

PoE technology and video switches

Recently, the technology has become widely used to organize digital video surveillance systems.

PoE benefits:

Simplification of the electrical system: no large number of power cables extended to all devices.
Safety: PoE switches convert 220V to power the cameras, usually 12V.
Increase the range to the powered device.
The ability to turn off / reboot devices in the system remotely.
Possibility of extensive management of devices on the network.

PoE camcorders can be powered via an Ethernet cable. The switch for video surveillance, connected to the electrical network, converts the alternating current into constant power of the required power. The same function can be performed by a PoE injector connected to a switch or directly to an outlet.

PoE injector circuit

Typical POE injector: connector for power supply, connector for LAN line and signal transmission to the camera, already powered by POE

A typical injector has two ports: a device supporting the technology is connected to the POE, and a computer / switch / router to a LAN.

Scheme for connecting the injector to the system

The figure above shows that one switch, depending on the number of ports, can include several devices powered by Power over Ethernet technology. For equipment that does not support PoE, splitters can be used that convert the Ethernet signal into a digital data stream and an electrical power supply component.

What is PoE?

PoE stands for Power over Ethernet.Ethernet). But the implementation of the technology is much more complicated than using a cable with a power plug at one end and an RJ-45 connector at the other, as in the humorous picture at the beginning of the article. Such a simple implementation is simply impossible, since most electronic devices operate not on alternating, but on low voltage direct current: 12V, 24V, 48V, etc. Therefore, the network must have devices that perform, among other things, the functions of a step-down transformer and a rectifier.

In a network cable (twisted pair) with a 100BASE-T (Fast Ethernet, 100 Mbps) connection, data is transmitted over only 2 pairs, and the remaining 2 pairs remain free. One day, someone very smart came up with the idea of \u200b\u200busing these free conductors to supply power to devices. The technician receives both data and electricity over a single LAN cable. It is very convenient for those cases when the equipment needs to be installed on the roof, on a mast, in the courtyard of a private house, that is, in those places where it is problematic or expensive to bring a separate cable with power supply.

Later, another option arose - to supply current through the same veins as the information. This made it possible to apply the technology in Gigabit Ethernet networks, 10/100/1000 Mbit / s, where all 4 pairs are involved in information transmission. Power and data are transmitted at different physical levels, so they do not interfere with each other.

PoE devices

Within the framework of the technology, 3 types of devices are distinguished:

PoE Consumers (PD)

PoE Splitters

Designed to provide remote power in the network if the end device that needs to be powered does not support PoE technology. Splitters act in the opposite direction to PoE adapters: they divide the power supply and data coming to them over one cable (twisted pair) into two cables: separately electricity, separately data.

A PoE splitter can also be structurally a block or a cord.

PoE converters

During the construction of links, a situation may arise when the PoE source and consumer operate with different voltages, different standards. For these cases, there is such a group of devices as PoE converters.

How to use PoE to provide power over a twisted pair cable

Connection options using different types of devices using PoE technology are clearly illustrated by this picture with diagrams:

What is important to know for correct connection

So we bought some kind of PoE adapter, connected it to Ethernet and the mains, connected the LAN cable from it to the access point that we wanted to power. Seems simple.

2015-01-28T17: 00: 00 + 0300 2018-03-15T10: 30: 16 + 0300 Vladimir Afanasiev

Power over Ethernet (PoE) is a technology that allows a remote device to transmit electrical energy along with data through a standard twisted pair cable in an Ethernet network. For power transmission, special network switches supporting this technology are used.

About switches, in general

First, let's figure out what network switches are and what they are.

A network switch is a switch (jarg. Switch from English. Switch - switch) is a device designed to connect several nodes of a computer network within one or more network segments.

All existing switches are different

number of ports (2, 4, 8, 16, 24 and 48 ports, etc.)
data transfer rate (100Mb / s, 1Gb / s and 10Gb / s, etc.)
network layer support (network layer-layer1, layer2, layer3)
poE support and without it

Switches can also be divided into:

1 unmanaged switches - these include almost all Layer 1 switches - these are simple stand-alone devices that manage data transfer on their own and do not have manual management tools. Such switches are most widely used in "home" LANs and small businesses, the main advantage of which is the low price and autonomous operation, without the intervention of a specialist.

The disadvantages of unmanaged switches are the lack of configurability and low internal performance. Therefore, it is not reasonable to use unmanaged switches in large enterprise networks, since the administration of such a network is time-consuming, difficult to troubleshoot, and imposes a number of significant restrictions.

2.Managed switches Basically Layer 2 and Layer 3 are more advanced devices that also work in automatic mode, but in addition have built-in controls and monitoring.

The main disadvantage of managed switches is the higher cost compared to Layer 1, which depends on the capabilities of the device itself and its performance.

We will not give any special comments on the number of ports and data transfer rates. Now, in a little more detail, who are these levels Level1 (Layer1), Level2 (Layer 2) and Level3 (Layer 3).

Layer 1. This includes all devices that operate at layer 1 of the OSI network model - the physical layer. Such devices include repeaters, hubs and other devices that do not work with data at all, but work with signals. These devices transmit information from one port and relay it to all ports at once. Such devices have not been produced for a long time, and it is rather difficult to find them on the market.

Layer 2. This includes all devices that operate at layer 2 of the OSI network model - the data link layer. These devices include all unmanaged switches and some managed ones. Layer 2 switches work with data not as with a continuous flow of information (like Layer 1 switches), but as with separate pieces of information - frames. They are able to analyze received frames and work with MAC-addresses of devices of senders and receivers of a frame. Such switches "do not understand" the IP addresses of computers, for them all devices are named in the form of MAC addresses. Layer 2 switches create switch tables that map the MAC addresses of the network devices they meet to specific switch ports.

Layer 3. This includes all devices that operate at layer 3 of the OSI network model - the network layer. Which is responsible for the mutual translation of hardware and network addresses (MAC / IP) - ARP protocol, finding a path between two intermediate devices, establishing a logical connection between nodes. These devices include all routers and part of managed switches, as well as all devices that can work with various network protocols: IPv4, IPv6, IPX, IPsec, etc. It is more expedient to classify Layer 3 switches as routers, since these devices can already fully route passing traffic between different networks. Layer 3 switches fully support all functions and standards of Layer 2 switches. They can work with network devices by IP addresses. The Layer 3 switch supports the establishment of various connections: pptp, pppoe, vpn, etc.

Smart Switch Management

There may be several options.

Telnet access to the switch console port. Configuration occurs through the command line of the switch. Telnet access is not secure.

SSH

SSH access to the managed switch is carried out via the secure SSH protocol using various clients (putty, gSTP, etc.). As in the case of the configuration, it is done through the command line of the switch.

Web interface

The configuration is done via a WEB browser. In most cases, configuration via the web interface does not allow you to use all the functions of network equipment, which are fully available only in the command line mode.

Power-over-Ethernet

Now let's try to figure out why these switches are also equipped with PoE.

This technology is intended for IP telephony, wireless access points, IP cameras and other devices to which it is undesirable or impossible to run a separate electrical cable for power supply.

PoE technology does not affect the quality of data transmission. For its implementation, the properties of the Ethernet physical layer are used.

Today's 100BASE-TX Ethernet cabling has four pairs, two of which are not used. Free pairs are used to supply power. PoE provides power supply over standard twisted pair cables for remote devices such as wireless access points, IP phones, IP cameras, media converters, data readers, etc. Power is supplied over free twisted pairs 4-5 and 7-8 that are not used for data transmission.

802.3af PoE-A and PoE-B standards for 100 and 1000 Mbps networks. Pinout 8-pin connector 8P 8C (RJ45)

Power sourcing equipment (PSE) differ in the way the power is connected, while powered devices (splitters; powereddevice, abbreviated PD) are universal. Powered devices are designed to accept power in any way, including when polarity is reversed (for example, when a crossover cable is used).

It is important that the power supply only supplies power to the cable if the connected device is a powered device. Thus, equipment that does not support PoE and is accidentally connected to a power source will not be damaged. There are several steps to connecting and disconnecting power to a cable.

The first step in determining the connection is to determine if the device connected at the opposite end of the cable is powered (PD). At this stage, the Power Supply Device (PSE) supplies the cable with a voltage of 2.8 to 10 V and determines the parameters of the input resistance of the connected device. For a powered device, this resistance is 19 to 26.5 kΩ with a parallel connected capacitor of 0 to 150 nF. Only after checking the compliance of the input resistance parameters for the powered device, the power supply device proceeds to the next stage, otherwise the power supply device tries to determine the connection again, after a time interval of at least 2 ms.

After the first step of determining the connection, the power supply can additionally perform the classification step by determining the range of powers consumed by the powered device in order to then control this power. Each powered device, depending on the declared power consumption, will be assigned a class from 0 to 4. The minimum power range is class 0. Class 4 is reserved by the standard for further development. The classification is performed by introducing a voltage from 14.5 to 20.5 V into the cable by the power supply device and measuring the current in the line.

After passing through the stages of determination and classification, the power supply device supplies the cable with a voltage of 48 V with a rise front not faster than 400 ms. After supplying full voltage to the powered device, the supply device monitors its operation in two ways:

1) if the powered device consumes less than 5 mA current for 400 ms, then the powered device removes power from the cable;

2) the power supply device supplies a voltage of 1.9-5.0 V with a frequency of 500 Hz to the cable and calculates the input resistance; If this resistance is greater than 1980 kOhm for 400 ms, the power supply will remove power from the cable. In addition, the power supply continuously monitors the overload current. If the powered device draws more than 400 mA for 75 ms, the powered device will remove power from the cable. When the power supply device detects that the powered device is disconnected from the cable or an overload of the consumed current by the powered device has occurred, the voltage is removed from the cable for at least 500 ms.

There are currently two PoE standards, the IEEE 802.3af PoE standard and the IEEE 802.3at-2009 standard also known as PoE Plus. Below is a table of the two PoE standards and their classes for the type of Ethernet cable.

Standard	PoEIEEE 802.3af	PoE Plus IEEE 802.3at
Cable requirements	Category 3 (UTP CAT3) or higher	Type 1: Category 3 (UTP CAT3) or higher
Cable requirements	Category 3 (UTP CAT3) or higher	Type 2: Category 5 (UTP CAT5) or higher
Current strength	0.35 A	Type 1: 0.35 A
Current strength	0.35 A	Type 2: 0.6 A
Injector output voltage	44 - 57V	Type 1: 44 - 57V
Injector output voltage	44 - 57V	Type 2: 50 - 57V
Input voltage of the powered device	37 - 57V	Type 1: 37 - 57V
Input voltage of the powered device	37 - 57V	Type 2: 42.5 - 57V
Maximum power consumption of the powered device	PoE class 0, 3: 12.95W	Type 1: PoE class 0, 3: 12.95W
	POE class 1: 3.84 W	PoE Class 1: 3.84 W
	PoE Class 2: 6.49 W	PoE Class 2: 6.49 W
	PoE class 4: not used	Type 2: PoE Class 4:
Supported powered devices	IP cameras, IP phones, access points	All PoE Devices, Outdoor PTZ Cameras,
Supported powered devices	IP cameras, IP phones, access points	wiMAX access points, LED displays, some computers

Despite all the advantages of using 802.3af standardized PoE technology, there are disadvantages, for example:

high additional cost of devices with PoE (802.3af) function;
high power consumption of PoE switches compared to conventional switches.

Therefore, alternative solutions, called "PassivePoE", are being released in the form of an intermediate adapter kit that can only support the electrical characteristics of compliance with the 802.3af standard, (i.e. the Passive PoE injector will transmit any voltage supplied by the power supply, not necessarily 48V) but not protocol. Passive PoE is completely incompatible with the IEEE 802.3af standard.

Typically, the Passive PoE (PPoE) kit does not include a power supply. it is assumed to use the power supply supplied with the powered device The maximum cable length when using a Passive PoE injector is significantly shorter than when using a PoE injector (30-60 meters, not 100 meters). Of course, this largely depends on the parameters of the standard power supply unit, the current consumed by the device and the losses in the cable. To compensate for these losses over a long distance, it is enough to replace the standard power supply unit with a more powerful one, with a voltage of 12 to 48 volts.

The PPoE-Light passive kit consists of two adapters: Injector (INJECTOR) and Splitter (SPLITTER). Passive PoE is effective for existing network infrastructure, allowing PoE to be applied to devices that are not natively equipped. The PPoE kit does not include any power supply unit (PSU), since it is assumed that in most cases you can use the standard PSU that comes with the device. PPoE provides power supply through a standard twisted pair cable for remote devices such as wireless access points, IP phones, IP cameras, etc. Power is supplied in the same way as in classic PoE over free twisted pairs 4-5 and 7-8, which are not used for data transmission.

Let's look at a small example of how to calculate the use of PoE in a bundle of Yealink SIP-T48G phones with PoE (Power over Ethernet, 802.3af) Class 0 support with a power consumption of 2.4-10.5W and Huawei Quidway S5700-28C-PWR-EI switches with 24 ports.

The S5700 PWR switches comply with IEEE 802.3af and 802.3at (PoE +) standards. And can provide ports with a maximum load of up to 30W. In our case, the S5700-28C-PWR-EI is equipped with a power supply unit with a power of 500W and 369.6W for PoE. According to the 802.3af standard, we can power 24 ports from it with a load of 15.4 W per port, or according to the 802.3at standard, 12 ports with a load of 30 W.

Having carried out simple mathematical calculations, we get:

10 phones at 10.5 W \u003d 105 W in total, which is less than the maximum PoE output of 369.6W.

It turns out that we can connect 24 Yealink SIP-T48G phones via PoE to the Huawei Quidway S5700-28C-PWR-EI switch. Or other equipment for 12 ports according to the 802.3at (PoE +) standard with a capacity of up to 30W, for example, HP t410AiO thin clients supporting the 802.3at (PoE +) standard with a power consumption of 24W 12 pieces.

Or combine various equipment, a video camera with Grandstream GXV3674_HD_VF with PoE IEEE802.3af support, ROBIN SV 130 video intercom with PoE IEEE802.3af support, etc. There are quite a few different combinations of PoE equipment that can be created.

Conclusion

There is a lot of controversy over the feasibility of PoE. The most common argument (in terms of power supply for IP phones) is that we will put an additional Pilot for each workplace for 300 rubles. and everything will work much cheaper. So, 300 rubles. conditionally spend on each workplace (total 24) \u003d 7200r. (about 110 USD)

Now let's move this to switches and money:

Huawei S2700-26TP-EI-AC - 24 ports without PoE - 441 USD

Huawei S2700-26TP-PWR-EI - 24 ports with PoE - 563 USD

The difference is 122 USD against the savings on "pilots" - 110 USD. Doubtful, isn't it?

Saving in terms of energy consumption in our reality is most likely a questionable thing. It is more correct to position this technology as an additional convenience and a kind of solution to the aesthetic issue with a bunch of wires under the table.

When choosing a switch for the office, we chose the model with PoE.

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