Transmitted from the given network. Physical transmission of data over communication lines. Without his consent

If you want to understand how the Internet works, you need to understand what it is. The Internet is just a data network. It is not for nothing that its second name is the phrase “global network”. It is a set of software and hardware equipment that is connected by communication channels.

Hardware includes client, server, and network equipment. Their purpose is to transmit data, which can be absolutely any information from plain text to long video.

A client means a personal computer, laptop, phone or any other device that is capable of sending requests for information from the network, receiving responses to them and displaying them in an accessible form. The server refers to the place where information is stored. These are databases that respond to client requests and convey to him what he is interested in. Network equipment is a channel that connects the server and the client.

How information is transferred

If we consider the essence of the global network schematically, it will look like this. The client sends a request for information to the server. This request is transmitted for processing through the network equipment to the server. Upon receipt, the server will generate an answer to the question and send it back via the network equipment to the client. This creates a diagram of interaction between the client and the server. In order for this scheme to work smoothly, the server must be in working order around the clock, otherwise the information stored in its possession will be inaccessible.

How network equipment works

In order for the client and server to interact with each other, network equipment is used: modems, routers, switches and communication channels.

The modem works by processing information from digital form into analog signals and vice versa, after which it transmits it via optical communication channels.

Routers work by storing a "routing table" that contains packets to transmit data and their corresponding addresses.

The switch transmits information between devices that are directly connected to it over a short distance using a special cable. As a rule, switches are used to create local networks, so modems and routers are used to work on the Internet.

I talked about digital signals. Why are these digital signals so good? As strange as it may sound, digital signals are analog in nature, since they are transmitted by changing the value of voltage or current, but they transmit signals with previously agreed levels. At their core, they are discrete signals. What does the word “discrete” mean? Discrete means consisting of separate parts, separate, discontinuous. Digital signals are classified as discrete signals, since they have only TWO STATES: “active” and “not active” - “there is voltage/current” and “no voltage/current”.

The main advantage of digital signals is that they are easier to transmit and process. Voltage is most often used for transmission. Therefore, two states are accepted: the voltage is close to zero (less than 10% of the voltage value) and the voltage is close to the supply voltage (more than 65% of the value). For example, with a circuit supply voltage of 5 Volts, we receive a signal with a voltage of 0.5 Volts - “zero”, but if 4.1 Volts - “one”.

Serial method of information transmission

There are simply two wires, an electrical signal source and an electrical signal receiver, that attach to these wires.

This is the PHYSICAL LEVEL.

As we have already said, we can transmit only two signals through these two wires: “there is voltage/current” and “there is no voltage/current”. What methods of information transfer can we implement?

The simplest way is that there is a signal (the light is on) - this is ONE, there is no signal (the light is not on) - this is ZERO

If you think about it, you can come up with several more different combinations. For example, take a wide impulse as one, and a narrow impulse as zero:

Or even even take the front and tail of the pulse as one and zero. Below is a picture, in case you have forgotten what the front and tail of a pulse are.

And here is the practical implementation:

Yes, you can come up with any number of different combinations, if the “recipient” and “sender” agree on reception and transmission. Here I have presented simply the most popular methods of transmitting a digital signal. That is, all these methods are PROTOCOLS. And, as I already said, you can come up with a lot of them.

Communication speed

Imagine the scene... Students, there is a lecture... The teacher dictates the lecture, and the students write it down

But if the teacher very quickly dictates a lecture, and in addition this lecture is on physics or mathematical analysis, then the result is:

Why did this happen?

From the point of view of digital data transmission, we can say that the speed of data exchange between the “Sender” and the “Recipient” is different. Therefore, there may be a real situation where the “Receiver” (student) is unable to receive data from the “Sender” (teacher) due to a mismatch in the data transfer rate: the transfer rate may be higher or lower than that to which the receiver (student) is configured. .

This problem is solved differently in different serial data transmission standards:

preliminary agreement on the data transfer speed (agree with the teacher to dictate the lecture slower or a little faster);
Before transmitting information, the “Sender” transmits some service information, using which the “Recipient” adapts to the “Sender” (Teacher: “Whoever does not record this lecture in full will not receive credit”)

Most often, the first method is used: the required data exchange speed is pre-set in communication devices. For this, a clock generator is used, which generates pulses to synchronize all nodes of the device, as well as to synchronize the communication process between devices.

Flow control

It is also possible that the “Recipient” (student) is not ready to accept the data transmitted by the “Sender” (teacher) for any reason: busy, malfunction, etc.

This problem is solved using various methods:

1) At the protocol level. For example, the exchange protocol stipulates: after the “Sender” transmits the “start of data transmission” service signal within a certain time, the “Recipient” is obliged to confirm the acceptance of this signal by transmitting a special “ready to receive” service signal. This method is called “software flow control” - “Soft”

2) At the physical level- additional communication channels are used, through which the “Sender”, BEFORE transmitting information, asks the “Recipient” about his readiness to receive). This method is called “hardware flow control” - “Hard”;

Both methods are very common. Sometimes they are used simultaneously: both at the physical level and at the exchange protocol level.

When transmitting information it is important synchronize the operation of the transmitter and receiver. The method of setting the communication mode between devices is called “synchronization”. Only in this case can the “Recipient” correctly (reliably) receive the message transmitted by the “Sender”.

Communication Modes

Simplex communication.

In this case, the Recipient can only receive signals from the sender and cannot influence him in any way. This is mainly television or radio. We can only either watch or listen to them.

Half duplex communication.

In this mode, both the sender and the receiver can transmit signals to each other alternately if the channel is free. An excellent example of half-duplex communication is walkie-talkies. If both subscribers chatter into their radios at the same time, then no one will hear anyone.

- First, first. I'm second. How can you hear?

– I can hear you normally, lights out!

The signal can only be sent by the sender, in which case the receiver receives it. Or the signal can be sent by the receiver, in which case the sender receives it. That is, both the sender and the recipient have equal rights to access the channel (communication line). If they both transmit a signal to the line at once, then, as I already said, nothing will come of it.

Duplex communication.

In this mode, both signal reception and transmission can be carried out in two directions at once simultaneously. A striking example of this is a conversation on a mobile or home phone, or a conversation on Skype.

, optical fiber, wireless communication channels or storage device.

Data transmission can be analog or digital (that is, a stream of binary signals), and can be modulated either through analog modulation or through digital encoding.

While analog communication is the transmission of a constantly changing digital signal, digital communication is the continuous transmission of messages. The messages are either a train of pulses meaning a linear code (in passband) or are limited to a set of continuously varying waveforms using a digital modulation technique. This modulation method and the corresponding demodulation are carried out by modem equipment.

The transmitted data may be digital messages coming from a data source, such as a computer or keyboard. It can be an analog signal - a telephone call or a video signal - digitized into a bitstream using pulse-coded modulation (PCM) or more advanced source coding schemes (analog-to-digital conversion and data compression). Source encoding and decoding is done by the codec or encoding equipment.

Serial and parallel transmission

In telecommunications, parallel transmission is the simultaneous transmission of signal elements of one symbol or another data object. In digital communications, parallel transmission is the simultaneous transmission of corresponding signal elements along two or more paths. By using multiple electrical wires, multiple bits can be transmitted simultaneously, allowing for higher transmission rates than serial transmission. This technique is used internally in the computer, such as on internal data buses, and sometimes in external devices such as printers. The main problem with this is "skew" because the wires in parallel transmission have slightly different properties (not on purpose), so some bits may arrive before others, which can corrupt the message. The parity bit can help reduce errors. However, an electrical wire for parallel data transmission is less reliable over long distances because transmission is much more likely to be disrupted.

Types of communication channels

Simplex
Multipoint:

Links

Wikimedia Foundation.

2010.
Novikov transfer

Signal Transduction (Biology)

See what “Data transfer” is in other dictionaries: Data transfer - in a broad sense, the process of transmitting data over a communication channel from a source to a receiver. There are synchronous and asynchronous data transfer. In English: Data communications See also: Data transmission Information interactions Data Financial... ...

Financial Dictionary DATA TRANSFER

Financial Dictionary Modern encyclopedia - (telecode communication) the field of telecommunications, covering issues of transmitting information presented in a formalized form (for example, by signs) and intended for processing by an electronic computer or already processed by them. Transfer... ...

See what “Data transfer” is in other dictionaries: Big Encyclopedic Dictionary - DATA TRANSMISSION, sending encoded information (data) over wired, optical or radio communication lines between several interacting electronic computers or between electronic computers and... ...

Illustrated Encyclopedic Dictionary data transfer - Sending data using communications from one place to receive it in another place. [GOST 24402 88] Topics: teleprocessing and computer networks EN data broadcastingdata communicationdata communicationsdata transfersdata... ...

Illustrated Encyclopedic Dictionary- 02/01/16 data transmission: Transfer of data from one point to one or more points using telecommunications. Source … Dictionary-reference book of terms of normative and technical documentation

See what “Data transfer” is in other dictionaries:- (sometimes telecode communication) an area of telecommunications (See Telecommunications), with the purpose of transmitting information presented on the basis of pre-established rules in formalized form by signs or continuous functions and intended for ... ... Great Soviet Encyclopedia

Illustrated Encyclopedic Dictionary- transfer of discrete information (data), presented in a formalized form (for example, by signs), from their source to the consumer between two or more computers, between computers and users in automatic and automated control systems, in... ... encyclopedic Dictionary

Illustrated Encyclopedic Dictionary- duomenų perdavimas statusas T sritis automatika atitikmenys: engl. data transmission vok. Datenübertragung, f rus. data transmission, f pranc. transmission de données, f; transmission des données, f … Automatikos terminų žodynas

Financial Dictionary- transfer of discrete information (data) presented in formalizations. form (for example, signs), from their source to the consumer between two or more computers, between computers and users in automatic and automated control systems, information, computing... Natural science. encyclopedic Dictionary

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Programmable data transmission in computer networks, Tikhomirov Dmitry Leonidovich. The means that provide programmable data transmission (PD) in computer networks are considered. The lower level interfaces (channel interfaces) have been optimized and synthesized. Architecture developed...

Communication line generally consists of a physical medium through which electrical information signals, data transmission equipment and intermediate equipment are transmitted. Synonymous with the term communication line(line) is the term link(channel).

The physical medium of data transmission can be a cable, that is, a set of wires, insulating and protective sheaths and connecting connectors, as well as the earth's atmosphere or outer space through which electromagnetic waves propagate.

Depending on the data transmission medium, communication lines are divided into the following:

§ wired (aerial);

§ cable (copper and fiber optic);

§ radio channels for terrestrial and satellite communications.

Wired (overhead) communication lines are wires without any insulating or shielding braiding, laid between poles and hanging in the air. Such communication lines traditionally carry telephone or telegraph signals, but in the absence of other options, these lines are also used to transmit computer data. The speed and noise immunity of these lines leave much to be desired. Today, wired communication lines are quickly being replaced by cable lines.

Cable lines are quite complex structures. The cable consists of conductors enclosed in several layers of insulation: electrical, electromagnetic, mechanical, and also, possibly, climatic. In addition, the cable can be equipped with connectors that allow you to quickly connect various equipment to it. There are three main types of cable used in computer networks: twisted pair copper cables, copper coaxial cables, and fiber optic cables.

A twisted pair of wires is called twisted pair Twisted pair exists in a shielded version , when a pair of copper wires is wrapped in an insulating shield, and unshielded , when the insulating wrap is missing. Twisting the wires reduces the effect of external interference on the useful signals transmitted along the cable.

Coaxial cable has an asymmetrical design and consists of an internal copper core and braid, separated from the core by a layer of insulation. There are several types of coaxial cable, differing in characteristics and areas of application - for local networks, for wide area networks, for cable television, etc.

Fiber Optic Cable consists of thin fibers through which light signals travel. This is the highest quality type of cable - it provides data transmission at very high speeds (up to 10 Gbit/s and higher) and better than other types of transmission media protects data from external interference.

Terrestrial and satellite radio channels are formed using a transmitter and receiver of radio waves. There are a large number of different types of radio channels, differing both in the frequency range used and in the channel range. The short, medium and long wave bands (KB, MW and LW), also called amplitude modulation (AM) bands based on the type of signal modulation method used in them, provide long-distance communication, but at a low data transfer rate. The fastest channels are those operating on ultrashort wave (VHF) bands, which are characterized by frequency modulation, as well as ultra-high frequency bands (microwaves).

In the microwave range (above 4 GHz), signals are no longer reflected by the Earth’s ionosphere and stable communication requires direct visibility between the transmitter and receiver. Therefore, such frequencies are used either by satellite channels or radio relay channels, where this condition is met.

In computer networks today, almost all described types of physical data transmission media are used, but the most promising are fiber optic ones. Today, both backbones of large territorial networks and high-speed communication lines of local networks are built on them.

Twisted pair is also a popular medium, characterized by an excellent quality-to-cost ratio and ease of installation. Using twisted pair cables, end users of networks are usually connected at distances of up to 100 meters from the hub. Satellite channels and radio communications are used most often in cases where cable communications cannot be used - for example, when a channel passes through a sparsely populated area or to communicate with a mobile network user.

Even when considering the simplest network, consisting of just two machines, one can see many of the problems inherent in any computer network, including problems associated with the physical transmission of signals over communication lines , without the solution of which any type of communication is impossible.

In computing, it is used to represent data. binary code . Inside the computer, data ones and zeros correspond to discrete electrical signals. Representing data as electrical or optical signals is called encoding . There are various ways to encode the binary digits 1 and 0, for example, potential a method in which one corresponds to one voltage level and zero to another, or pulse a method when pulses of different or the same polarity are used to represent numbers.

Similar approaches can be used to encode data and transfer it between two computers over communication lines. However, these communication lines differ in their electrical characteristics from those that exist inside the computer. The main difference between external communication lines and internal ones is their much longer , and also because they pass outside a shielded enclosure through spaces often subject to strong electromagnetic interference. All this leads to significantly greater distortion of rectangular pulses (for example, “rolling over” of the fronts) than inside the computer. Therefore, to reliably recognize pulses at the receiving end of a communication line when transmitting data inside and outside the computer, it is not always possible to use the same speeds and coding methods. For example, the slow rise of the pulse edge due to the high capacitive load of the line requires the transmission of pulses at a lower speed (so that the leading and trailing edges of adjacent pulses do not overlap and the pulse has time to grow to the required level).

Used in computer networks both potential and pulse coding of discrete data , as well as a specific way of representing data that is never used inside a computer - modulation(Fig. 3). During modulation, discrete information is represented by a sinusoidal signal of the frequency that is well transmitted by the existing communication line.

Potential or pulse coding is used on high quality channels, and modulation based on sine waves is preferable when the channel introduces severe distortion into the transmitted signals. Modulation is typically used in wide area networks to transmit data over analog telephone links, which were designed to carry voice in analog form and are therefore not well suited for direct pulse transmission.

To convert data from one type to another, use modems. Term "modem" - short for modulator/demodulator. A binary zero is converted, for example, into a low-frequency signal, and a one into a high-frequency signal. In other words, by converting data, the modem modulates the frequency of the analog signal (Fig. 4).

The method of signal transmission is also affected by the number of wires in the communication lines between computers.

Data transfer can occur in parallel (Fig. 5) or sequentially (Fig. 6).

To reduce the cost of communication lines in networks, they usually strive to reduce the number of wires and because of this they do not use parallel transmission of all the bits of one byte or even several bytes, as is done inside a computer, but sequential, bit-by-bit transmission, requiring only one pair of wires.

There are also three different methods used to connect computers and devices, referred to by three different terms. The connection happens: simplex, half duplex and full duplex(Fig. 7 ).

A simplex connection is said to occur when data moves in only one direction. A half-duplex connection allows data to travel in both directions, but at different times, and finally, a full-duplex connection is where data travels in both directions at the same time.

Rice. 7. Examples of data flows.

Another important concept is connection switching.

Any communication networks support some method of switching their subscribers among themselves. These subscribers can be remote computers, local networks, fax machines, or simply interlocutors communicating using telephones. It is practically impossible to provide each pair of interacting subscribers with their own non-switched (i.e., permanent connection) physical communication line, which they could exclusively “own” for a long time. Therefore, any network always uses some method of switching subscribers, which ensures the availability of existing physical channels simultaneously for several communication sessions between network subscribers.

Connection switching allows network hardware to share the same physical communication channel between many devices. The two main ways to switch connections are - circuit switching and packet switching.

Circuit switching creates a single, continuous connection between two network devices. While these devices communicate, no other device can use this connection to transmit its own information - it is forced to wait until the connection becomes free.

A simple example of a circuit switch is an A-B switch, which is used to connect two computers to one printer. To allow one of the computers to print, you turn a toggle switch, establishing a continuous connection between the computer and the printer. A point-to-point connection is formed . As shown in the picture, only one computer can print at the same time.

Rice. 6Switching circuits

Most modern networks, including the Internet, use packet switching. Data transfer programs on such networks divide the data into pieces called packets. In a packet switching network, data can travel simultaneously in one packet, or in several. The data will arrive at the same destination, even though the paths it took may be completely different.

To compare two types of network connections, let's assume that we interrupted the channel in each of them. For example, by disconnecting the printer from the manager in Fig. 6 (by moving the toggle switch to position B), you have deprived it of the ability to print. A circuit switching connection requires a continuous communication channel.

Rice. 7. Packet switching

On the contrary, data in a packet switching network can travel in different ways. This can be seen in Fig. 7. Data does not necessarily follow one path on the way between office and home computers; breaking one of the channels will not lead to loss of connection - the data will simply take a different route. Packet switching networks have many alternative routes for packets.

Packet switching is a subscriber switching technique that was specifically designed for the efficient transmission of computer traffic.

The crux of the problem is pulsating nature of traffic , which is generated by typical network applications. For example, when accessing a remote file server, the user first views the contents of that server's directory, which results in the transfer of a small amount of data. He then opens the desired file in a text editor, an operation that can create quite a lot of data exchange, especially if the file contains large graphics. After displaying a few pages of a file, the user works with them locally for a while, which requires no network transfer at all, and then returns modified copies of the pages to the server - again creating intensive network transfer.

The traffic ripple factor of an individual network user, equal to the ratio of the average intensity of data exchange to the maximum possible, can be 1:50 or 1:100. If for the described session we organize channel switching between the user’s computer and the server, then most of the time the channel will be idle. At the same time, the network's switching capabilities will be used and will not be available to other network users.

When packet switching occurs, all messages transmitted by a network user are broken up at the source node into relatively small parts called packets. A message is a logically completed piece of data - a request to transfer a file, a response to this request containing the entire file, etc.

Messages can be of any length, from a few bytes to many megabytes. On the contrary, packets can usually also have a variable length, but within narrow limits, for example from 46 to 1500 bytes. Each packet is provided with a header that specifies the address information needed to deliver the packet to the destination node, as well as the packet number that will be used by the destination node to assemble the message.

Packets are transported in the network as independent information blocks. Network switches receive packets from end nodes and, based on address information, transmit them to each other, and ultimately to the destination node.

Packet network switches differ from circuit switches in that they have internal buffer memory to temporarily store packets if the switch's output port is busy transmitting another packet when a packet is received. In this case, the packet remains for some time in the queue of packets in the buffer memory of the output port, and when its turn reaches it, it is transferred to the next switch. This data transmission scheme allows you to smooth out traffic ripples on the backbone links between switches and thereby use them in the most effective way to increase the throughput of the network as a whole.

Indeed, for a pair of subscribers, the most effective would be to provide them with sole use of a switched communication channel, as is provided in circuit-switched networks. With this method, the interaction time between a pair of subscribers would be minimal, since data would be transmitted from one subscriber to another without delay.

A packet switched network slows down the process of communication between a particular pair of subscribers. However, the total amount of computer data transmitted by the network per unit time using the packet switching technique will be higher than using the circuit switching technique.

Typically, given the same access speed, a packet-switched network turns out to be 2-3 times cheaper than a circuit-switched network, that is, a public telephone network.

Each of these schemes ( circuit switching (circuit switching) or packet switching (packet switching)) has its advantages and disadvantages, but according to the long-term forecasts of many experts, the future belongs to packet switching technology, as it is more flexible and universal.

Circuit-switched networks are well suited to switch data at a constant rate, where the unit of switching is not a single byte or packet of data, but a long-term synchronous data stream between two subscribers.

Both packet-switched networks and circuit-switched networks can be divided into two classes on another basis - networks with dynamic switching and networks with constant switching.

In the first case, the network allows a connection to be established at the initiative of the network user. Switching is performed for the duration of the communication session, and then (again at the initiative of one of the interacting users) the connection is broken. In general, any network user can connect to any other network user. Typically, the connection period between a pair of users during dynamic switching ranges from several seconds to several hours and ends when a certain job is performed - transferring a file, viewing a page of text or image, etc.

In the second case, the network does not provide the user with the opportunity to perform dynamic switching with another arbitrary network user. Instead, the network allows a pair of users to request a connection for an extended period of time. The connection is established not by users, but by the personnel maintaining the network. The time for which permanent switching is established is usually measured in several months. The permanent switching mode in circuit-switched networks is often called service dedicated or leased channels.

Examples of networks that support dynamic switching mode are public telephone networks, local networks, and the Internet.

Some network types support both modes of operation.

Another problem that needs to be solved when transmitting signals is the problem mutual synchronization of the transmitter of one computer with the receiver of another . When organizing the interaction of modules inside a computer, this problem is solved very simply, since in this case all modules are synchronized from a common clock generator. The problem of synchronization when communicating between computers can be solved in different ways, both by exchanging special clock pulses over a separate line, and by periodic synchronization with predetermined codes or pulses of a characteristic shape that differs from the shape of data pulses.

Asynchronous and synchronous transmission. When exchanging data at the physical layer, the unit of information is a bit, so the physical layer always maintains bit synchronization between the receiver and transmitter.

However, when the quality of the communication line is poor (usually this applies to telephone dial-up channels), additional synchronization means are introduced at the byte level to reduce the cost of equipment and increase the reliability of data transmission.

This mode of operation is called asynchronous or start-stop. Another reason for using this mode of operation is the presence of devices that generate bytes of data at random times. This is how the keyboard of a display or other terminal device works, from which a person enters data for processing by a computer.

In asynchronous mode, each byte of data is accompanied by special start and stop signals. The purpose of these signals is, firstly, to notify the receiver of the arrival of data and, secondly, to give the receiver enough time to perform some synchronization-related functions before the next byte arrives.

The described mode is called asynchronous because each byte can be slightly shifted in time relative to the bit clocks of the previous byte

The task of reliable exchange of binary signals represented by corresponding electromagnetic signals in computer networks is solved by a certain class of equipment. In local networks, these are network adapters, and in global networks, these are data transmission equipment, which includes, for example, the modems discussed above. This equipment encodes and decodes each information bit, synchronizes the transmission of electromagnetic signals over communication lines, verifies the correctness of transmission using a checksum, and can perform some other operations.

Control questions:

3. What communication lines are used in computer networks?

4. Which lines of communication are the most promising?

5. How are binary signals transmitted in a network? What is modulation?

6. What is the modem used for?

7. What is serial and parallel data transmission?

8. What is simplex, half duplex and full duplex connection?

9. What is connection switching?

10. What are the two main methods of switching a connection?

11. What is packet switching and what are its advantages?

12. When is it appropriate to use circuit switching?

13. Explain the concepts of asynchronous and synchronous data transfer?

Thanks to progress, we have received many devices and instruments that make our lives easier, which operate through the invention of new technologies. A breakthrough in the field of communications was not only the transmission of information via a wireless channel, but also the synchronization of various types of devices in the absence of a wired connection.

What is wireless data transmission?

The answer to this question is simple: BPD is the transfer of information from one device to another, which are located at a certain distance, without the participation of a wired connection.

The technology of transmitting voice information over a radio channel began to be used at the end of the 19th century. Since then, a large number of radio communication systems have appeared, which are used in the production of equipment for home, office or enterprise.

There are several ways to synchronize devices to transfer data. Each of them is used in a specific area and has individual properties. Wireless data networks differ in their characteristics, so the minimum and maximum distance between devices, depending on the type of information transmission technology, will be different.

To synchronize devices over a radio channel, special adapters are installed that are capable of sending and receiving information. Here we can talk about either a small module that is built into a smartphone or an orbital satellite. The receiver and transmitter can be different types of devices. Transmission is carried out through channels of different frequencies and ranges. Let us dwell in more detail on the specifics of implementing different types of wireless synchronization.

Classification of wireless channels

Depending on the nature of the transmission medium, four types of wireless data transmission are distinguished.

Cellular radio channels

Data transmission is carried out wirelessly from the transmitter to the receiver. The transmitter generates a radio pulse of a certain frequency and amplitude, the vibration is emitted into space. The receiver filters and processes the signal, after which the necessary information is extracted. Radio waves are partially absorbed by the atmosphere, so this connection can be distorted by high humidity or rain. Mobile communications operate precisely on the basis of radio wave standards; wireless data transmission channels differ in the speed of information transfer and the range of operating frequencies. The radio frequency category of data transmission includes Bluetooth - a technology for wireless data exchange between devices. The following protocols are used in Russia:

GSM. This is a global cellular communications system. Frequency - 900/1800 MHz, maximum data transfer rate - 270 Kbps.
CDMA. This standard provides the best communication quality. Operating frequency - 450 MHz.
UMTS. It has two operating frequency bands: 1885-2012 MHz and 2110-2200 MHz.

Satellite channels

This method of transmitting information involves using a satellite on which an antenna with special equipment is installed. The signal arrives from the subscriber to the nearest ground station, then the signal is redirected to the satellite. From there, the information is sent to the receiver, another ground station. Satellite communications are used to provide television and radio broadcasting. You can use a satellite phone at any point remote from cellular stations.

Infrared channels

Communication is established between the receiver and the transmitter, which are located at a close distance from each other. This channel for wireless data transmission operates using LED radiation. Communication can be two-way or broadcast.

Laser channels

The principle of operation is the same as in the previous version, only a laser beam is used instead of LEDs. Objects must be in close proximity to each other.

Wireless data transmission media differ in their specificity. The main distinguishing features are range and area of application.

Technologies and standards for wireless data transmission

Information technology is currently developing at a rapid pace. Information can now be transmitted using radio waves, infrared or laser radiation. This method of exchanging information is much more convenient than the wired type of synchronization. The range of action will differ depending on the technology.

Here are some examples:

Personal Area Networks (WPAN). Peripheral equipment is connected using these standards. Using wireless computer mice and keyboards is much more convenient than their wired counterparts. The wireless data transfer speed is quite high. Personal networks allow you to equip smart home systems and synchronize wireless accessories with gadgets. Examples of technologies that work using personal area networks are Bluetooth and ZigBee.
Local area networks (WLANs) are based on 802.11 standards products. The term Wi-Fi is now known to everyone. This name was originally given to products of the 802.11 standard series, and now this term refers to products of any standard from this family. WLAN networks are able to create a larger operating radius compared to WPAN, and the level of protection has also increased.
Urban Area Networks (WMAN). Such networks work on the same principle as Wi-Fi. A distinctive feature of this wireless data transmission system is its wider coverage of territories; a larger number of receivers can connect to this network. WMAN is the same as Wi Max, a technology that provides broadband connection.
Global networks (WWAN) - GPRS, EDGE, HSPA, LTE. Networks of this type can operate on the basis of packet data transmission or through circuit switching.

Differences in the technical characteristics of networks determine the scope of their application. If we consider the general properties of wireless networks, then we can distinguish the following categories:

corporate networks - used to connect objects within one company;
operator networks - created by telecom operators to provide services.

If we consider wireless data transfer protocols, then we can distinguish the following categories:

IEEE 802.11a, b, n, g, y. These protocols are usually combined under the common marketing name Wi-Fi. Protocols differ in communication range, operating frequency range and data transfer speed.
IEEE 802.15.1. Within the framework of the standard, data is transmitted using Bluetooth technology.
IEEE 802.15.4. Standard for wireless synchronization using ZigBee technology.
IEEE 802.16. A telecommunications standard that has a wide range. WiMax is functionally similar to LTE technology.

Currently, the most popular of all wireless data transfer protocols are 802.11 and 802.15.1. Wi-Fi and Bluetooth technologies operate on the basis of these protocols.

Bluetooth

An access point, as in the case of Wi-Fi, can be any device equipped with a special controller that forms a piconet around itself. This piconet may include several devices; if desired, they can be combined into bridges for data transmission.

Some computers and laptops already have a built-in Bluetooth controller; if this function is missing, then USB adapters are used that connect to the device and provide it with the ability to wirelessly transfer data.

Bluetooth uses a frequency of 2.4 GHz, while energy consumption is as low as possible. It was this indicator that allowed the technology to occupy its niche in the field of information technology. Low energy consumption is due to low transmitter power, short range and low data transfer rate. Despite this, these characteristics turned out to be sufficient for connecting and operating various types of peripheral equipment. Bluetooth technology has provided us with a wide variety of wireless accessories: headphones, speakers, computer mice, keyboards and much more.

1st class. The range of wireless synchronization can reach 100 m. Devices of this type are usually used on an industrial scale.
2nd grade. The range is 10 m. Devices of this class are the most common. Most wireless accessories fall into this category.
3rd grade. Range - 1 meter. Such receivers are installed in game consoles or in some headsets when there is no point in moving the transmitter and receiver away from each other.

The wireless data transmission system based on Bluetooth technology is very convenient for connecting devices. The cost of chips is quite low, so equipping equipment with a wireless connection function does not greatly affect the increase in its price.

WiFi

Along with Bluetooth, Wi-Fi technology has become equally ubiquitous in the field of wireless communications technology. However, popularity did not come to her immediately. Development of Wi-Fi technology began in the 80s, but the final version was presented only in 1997. Apple has decided to use a new option on its laptops. This is how the first network cards appeared in the iBook.

The operating principle of Wi-Fi technology is as follows: a chip is built into the device, which can provide reliable wireless synchronization with another similar chip. If there are more than two devices, then you need to use an access point.

A Wi-Fi access point is a wireless analogue of a stationary router. Unlike the latter, the connection is made without wires, via radio waves. This makes it possible to connect several devices at once. Do not forget that when using a large number of devices, the data transfer speed will be significantly reduced. To protect data, Wi-Fi networks are protected by encryption. Without entering a password, you will not be able to connect to such a data source.

The first Wi-Fi technology standard was adopted in 1997, but it never became widespread because the data transfer speed was too low. Later, the 802.11a and 802.11b standards appeared. The first gave a transfer speed of 54 Mb/s, but worked at a frequency of 5 GHz, which is not allowed everywhere. The second option allowed networks to transmit data at a maximum speed of 11 Mb/s, which was not enough. Then the 802.11g standard appeared. It combines the advantages of previous options, providing fairly high speed at an operating frequency of 2.4 GHz. The 802.11y standard is analogous to 802.11g and has a longer network range (up to 5 km in open space).

LTE

This standard is currently the most promising along with other global networks. Mobile broadband provides the fastest wireless packet data transfer speeds. Regarding the operating frequency band, everything is ambiguous. The LTE standard is very flexible; networks can be based in the frequency range from 1.4 to 20 MHz.

The range of networks depends on the altitude of the base station and can reach 100 km. The ability to connect to networks is provided to a large number of gadgets: smartphones, tablets, laptops, game consoles and other devices that support this standard. The devices must have a built-in LTE module that works in conjunction with the existing GSM and 3G standards. If the LTE connection is lost, the device will switch to the existing access to 3G or GSM networks without interrupting the connection.

Regarding the data transfer speed, the following can be noted: compared to 3G networks, it has increased several times and reached 20 Mbit/s. The introduction of a large number of gadgets equipped with LTE modules ensures the demand for this technology. New base stations are being installed, which provide services even to settlements remote from megacities.

Let's consider the principle of operation of fourth generation networks. Wireless packet data transmission technology is carried out using the IP protocol. For fast and stable synchronization, both frequency and time duplex are formed between the base station and the mobile station. Due to the large number of combinations of paired frequency ranges, broadband connection of subscribers is possible.

The spread of LTE networks has reduced tariffs for using mobile communications. The wide range of the network allows operators to save on expensive equipment.

Data communication devices

In our daily lives, we are surrounded by devices that operate on the basis of wireless data transmission technologies. Moreover, each device has several activity modules of various standards. Example: a classic smartphone uses GSM, 3G, LTE networks to transmit packet and voice data, Wi-Fi to access the Internet via an access point, Bluetooth to synchronize the device with accessories.

Let's look at the most popular wireless data transmission devices that have become widespread:

Wi-Fi router. This device is capable of providing Internet access to several devices. The device itself is synchronized with the Internet source either wired or using a SIM card from a cellular network operator.
Smartphone. A universal communication tool that makes it possible to transmit voice information, send short text messages, access the Internet and synchronize with wireless or wired accessories.
Tablet PC. Functionally it can be identical to a smartphone. A distinctive feature is the large screen, which makes using the gadget more comfortable for certain types of work.
Personal Computer. A full-fledged stationary device with a built-in operating system that allows you to work on Internet networks, including wireless ones. Wireless data transfer to a computer from an access point is usually carried out via a Wi-Fi adapter, which is connected via a USB connector.
Laptop. A smaller version of a personal computer. Most laptops have a built-in Bluetooth adapter and Wi-Fi module, which allows you to synchronize to access the Internet, as well as connect wireless accessories without additional USB adapters.
Wireless accessories and peripherals. This category includes wireless speakers, headphones, headsets, mice, keyboards and other popular accessories that connect to devices or computers.
TV or Smart-TV. A TV with an operating system is functionally similar to a computer, so having built-in wireless modules is a necessity.
Game console. To install software, this gadget has a wireless Internet connection. Game consoles are synchronized with the device using Bluetooth technology.
Wireless equipment "Smart Home". A very complex and multifaceted system that is controlled wirelessly. All sensors and equipment elements are equipped with special modules for signal transmission.

With the improvement of wireless technologies, old devices are constantly being replaced by new devices that are functionally more efficient and practical. Wireless data transmission equipment is rapidly changing and modifying.

Prospects for the use of wireless networks

The current trend is to replace wired equipment with newer wireless options. This is much more convenient not only because of the mobility of the devices, but also from the point of view of ease of use.

The production of wireless equipment will make it possible not only to introduce the latest systems into the world of communication devices, but also to equip the housing of the standard average resident of any locality with the latest technology. Currently, only high-income people living in megacities can afford this.

In the field of wireless radio communications, constant research is being carried out, the result of which is innovative technologies that differ from their predecessors in their greater productivity, reduced energy consumption and practicality of use. The result of such research is the emergence of new equipment. Manufacturers are always interested in producing products that will comply with innovative technologies.

More productive access points and powerful base stations will enable the ubiquity of new technologies in large enterprises. The equipment can be controlled remotely. In the field of education, wireless technologies can facilitate the learning and control process. Some schools are already beginning to implement the process of mobile education. It consists of distance learning via video communication over the Internet. The listed examples are only the initial step in the transition of the development of society to a new stage, which will be built on the basis of wireless technologies.

Benefits of wireless synchronization

If you compare wired and wireless data transmission, you can identify many advantages of the latter:

wires do not interfere;
high data transfer speed;
practicality and speed of connection;
mobility of equipment use;
wear or breakage of connections is excluded;
it is possible to use several wireless connection options in one device;
the ability to connect several devices to an Internet access point at once.

Along with this, there are some disadvantages:

radiation from a large number of devices can adversely affect human health;
When various wireless equipment is located close together, there is a possibility of interference and communication failures.

The reasons for the widespread use of wireless networks are obvious. Every average member of modern society needs to stay connected at all times.

Finally

Wireless technologies have provided the opportunity for the widespread introduction of telecommunications equipment, which is widely used in all countries of the world. Constant improvements and new discoveries in the field of wireless communications give us an increasing level of comfort, and home improvement with the help of innovative devices is becoming more accessible to most people.