They have the greatest information transmission capacity. Channel capacity

There are many factors that can distort or damage a signal. The most common of these is interference or noise, which is any unwanted signal that mixes with and distorts the signal intended to be transmitted or received. For digital data, the question arises: to what extent do these distortions limit the possible data transfer rate? The maximum possible speed under certain conditions at which information can be transmitted along a specific communication path, or channel, is called pass ability channel.

There are four concepts that we will try to tie together.

Data transfer rate - the speed in bits per second (bit/s) at which you can

transmit data;

Bandwidth - the bandwidth of the transmitted signal, limited by transmission to ohms and the nature of the transmitting medium.

It is expressed in periods in seconds, or hertz (Hz).

Noise. Average noise level in the communication channel.

Error level – frequency of occurrence of errors and side effects.

An error is considered to be the reception of 1 and the transmission of 0 and vice versa.

1. The problem is this: communications are not cheap and, in general, the wider their bandwidth, the more expensive they are. Moreover, all transmission channels of practical interest have limited bandwidth. Limitations are caused by the physical properties of the transmission medium or by deliberate bandwidth limitations in the transmitter itself, made to prevent interference with other sources.

One of the main problems in building wireless systems is solving the problem of access of many users to a limited resource of the transmission medium. There are several basic access methods (also called multiplexing or multiplexing methods), based on the division of parameters such as space, time, frequency and code between stations. The purpose of multiplexing is to allocate space, time, frequency and/or code to each communication channel with a minimum of mutual interference and maximum use of the characteristics of the transmission medium.

Sealwith spatialdivision

Based on the separation of signals in space when the transmitter sends a signal using a code With, time t and frequency f in area s i. That is, each wireless device can transmit data only within the boundaries of one specific territory, in which any other device is prohibited from transmitting its messages.

For example, if a radio station broadcasts on a strictly defined frequency in its assigned territory, and some other station in the same area also starts broadcasting on the same frequency, then radio listeners will not be able to receive a “clean” signal from any of these stations . It’s another matter if radio stations operate on the same frequency in different cities. There will be no distortion of the signals of each radio station due to the limited range of propagation of the signals of these stations, which eliminates their overlap with each other. A typical example is cellular telephone systems.

Sealwith frequency sectionltion(Frequency Division Multiplexing, FDM)

Each device operates at a strictly defined frequency, thanks to which several devices can transmit data in one territory (Figure 3.2.6). This is one of the most well-known methods, one way or another used in the most modern wireless communication systems.

Figure 3.2.6 – Principle of frequency division of channels

A clear illustration of a frequency multiplexing scheme is the operation of several radio stations operating at different frequencies in one city. To reliably detune from each other, their operating frequencies must be separated by a protective frequency interval to prevent mutual interference.

This scheme, although it allows the use of multiple devices in a given area, itself leads to unnecessary waste of usually scarce frequency resources, since it requires the allocation of a separate frequency for each wireless device.

Sealwith temporary sectionelaziness(Time Division Multiplexing, TDM)

In this scheme, the distribution of channels occurs in time, i.e. each transmitter broadcasts a signal at the same frequency f in area s, but at different periods of time t i (usually cyclically repeating) with strict requirements for synchronization of the transmission process (Figure 3.2.7).

Figure 3.2.7 – Principle of time division of channels

This scheme is quite convenient, since time intervals can be dynamically redistributed between network devices. Devices with more traffic are assigned longer intervals than devices with less traffic.

The main disadvantage of time multiplex systems is the instant loss of information when synchronization in the channel is lost, for example, due to strong interference, accidental or intentional. However, successful experience in operating such famous TDM systems as cellular telephone networks GSM standard, indicates sufficient reliability of the temporary compaction mechanism.

Sealcode-separated(Code Division Multiplexing, CDM)

In this scheme, all transmitters transmit signals at the same frequency f , in area s and during t, but with different codes c i.

The name of the CDM-based channel separation mechanism (CDMA, CDM Access)

the cellular telephone standard IS-95a was even named, as well as a number of standards for the third generation of cellular communication systems (cdma2000, WCDMA, etc.).

In the CDM scheme, each transmitter replaces each bit of the original data stream with a CDM symbol - a code sequence of length 11, 16, 32, 64, etc. bits (they are called chips). The code sequence is unique for each transmitter. As a rule, if a certain CDM code is used to replace “1” in the original data stream, then to replace “0” the same code is used, but inverted.

The receiver knows the CDM code of the transmitter whose signals it must receive. It constantly receives all signals and digitizes them. Then, in a special device (correlator), it performs the operation of convolution (multiplication with accumulation) of the input digitized signal with the CDM code known to it and its inversion. In a somewhat simplified form, this looks like the operation of the scalar product of the input signal vector and the vector with the CDM code.

If the signal at the correlator output exceeds a certain set threshold level, the receiver considers that it has received a 1 or 0. To increase the probability of reception, the transmitter can repeat sending each bit several times. In this case, the receiver perceives signals from other transmitters with other CDM codes as additive noise.

Moreover, due to high redundancy (each bit is replaced by dozens of chips), the received signal power can be comparable to the integrated noise power. The similarity of CDM signals to random (Gaussian) noise is achieved using CDM codes generated by a pseudorandom sequence generator. Therefore, this method is also called the method of spreading the signal spectrum using direct sequence (DSSS - Direct Sequence Spread Spectrum), spectrum spreading will be discussed below.

The strongest aspect of this seal lies in the increased security and secrecy of data transmission: without knowing the code, it is impossible to receive a signal, and in some cases, to detect its presence. In addition, the code space is incomparably larger compared to the frequency multiplexing scheme, which makes it possible to assign each transmitter its own individual code without any problems.

Until recently, the main problem of code multiplexing was the complexity of the technical implementation of receivers and the need to ensure accurate synchronization of the transmitter and receiver to ensure guaranteed receipt of the packet.

Multiplexing mechanism via orthogonal carrier frequencies (OrthogonalFrequencyDivisionMultiplexing, OFDM)

The entire available frequency range is divided into quite a few subcarriers (from several hundred to thousands). One communication channel (receiver and transmitter) is assigned for transmission several such carriers, selected from the entire set according to a certain law. Transmission is carried out simultaneously on all subcarriers, i.e. in each transmitter the outgoing data stream is divided into N substreams, where N– the number of subcarriers assigned to this transmitter.

The distribution of subcarriers can change dynamically during operation, which makes this mechanism no less flexible than the time multiplexing method.

The OFDM scheme has several advantages. First, only some subchannels will be subject to selective fading, not the entire signal. If the data stream is protected by forward error correction code, then this fading is easy to combat. But more importantly, OFDM allows intersymbol interference to be suppressed. Intersymbol interference has a significant impact at high data rates because the distance between bits (or symbols) is small.

In the OFDM scheme, the data transmission rate is reduced by N times, which allows you to increase the symbol transmission time by N once. Thus, if the symbol transmission time for the source stream is T s , then the period of the OFDM signal will be equal to NT s. This allows you to significantly reduce the impact of intersymbol interference. When designing a system N is chosen so that the value NT s significantly exceeded the root-mean-square spread of channel delays.

49. What determines the throughput of a communication channel?

A communication system is understood as a set of devices and environments that ensure the transmission of messages from the sender to the recipient. IN general case the generalized communication system is represented by a block diagram.

Bandwidth is the maximum possible speed of information transfer. Bandwidth is equal to the telegraph speed, measured by the number of telegraph calls transmitted per unit of time. The maximum throughput depends on the channel bandwidth, and in the general case on the ratio Pc / Pп (signal power to interference power) and is determined by the formula. This is Shannon's formula, which is valid for any communication system in the presence of fluctuation interference.

50. What is the essence of frequency multiplexing/channel division in multi-channel information transmission systems.

Compaction - combining subscriber signals into a single signal.

Separation is the separation of individual subscriber signals from a single group signal.

The essence of frequency multiplexing is that all subscribers operate on the same frequency band, but each in their own band.

With frequency multiplexing, interchannel interference occurs due to the imperfection of the filtering systems and the infinity of the signal spectrum.

The main advantage of multichannel communication systems with frequency multiplexing is the economical use of the frequency spectrum; significant disadvantages are the accumulation of interference that occurs at intermediate amplification points, and, as a result, relatively low noise immunity.

51. What is the essence of time multiplexing/separation of channels in multi-channel information transmission systems?

With time multiplexing, all subscribers work in the same frequency band, but they work cyclically, each at their own time, and the cycle time is determined by T. Kotelnikova (With time multiplexing, which is a logical development of pulse communication systems, a communication line or group communication path through electronic switches is provided alternately to transmit signals of each channel.)

When transmitting speech T=125 μs

Communication systems with frequency and time multiplexing are used on trunk cable lines, radio relay lines etc.

52. What are the principles of organizing aeronautical radio communications and terrestrial telecommunications.

The organization of communication is understood as a scheme for connecting subscribers with channels and distributing resources allocated for communication, ensuring high efficiency of information exchange between links.

Basic element of aviation air communication - radio network. A radio network is a set of RS installed at the locations of interacting correspondents (in the control center and on board the aircraft) and united by common radio channels, those operating on the same radio frequencies. As a rule, radio networks are organized along a radial basis. The radio network allows for the exchange of information between the dispatcher and the crew of each aircraft, as well as the circular transmission of data to all aircraft simultaneously. Radio networks are created depending on the number of ATC sectors.

The most important element ensuring continuity is the regulated procedure for changing radio networks. In aeronautical networks, one frequency is usually assigned for transmission and reception, and communication is carried out in simplex mode when transmission and reception alternate with each other.

The elements of terrestrial communication networks are: subscriber units, channels and communication nodes. CS communication nodes serve to distribute information along communication lines and channels leading to different geographical locations. The principle of constructing wired telegraph communication is radial-nodal, that is, main GUS nodes are provided, uniting groups of regional nodes, and communication channels connecting nodes with main nodes and with each other. This principle ensures the achievement of high efficiency and reliability of communication, since workarounds can be used. When creating terrestrial communication networks, channels of national communication networks are widely used. Ground telecommunications in civil aviation serve for communication between airfields, administrative and operational control bodies. A landline telephone network is also being organized.

In any communication system, information is transmitted through a channel. The information transfer rate was defined in § 2.9. This speed depends not only on the channel itself, but also on the properties of the signal supplied to its input and therefore cannot characterize the channel as a means of transmitting information. Let's try to find a way to assess the ability of a channel to transmit information. Let us first consider a discrete channel through which symbols from the alphabet of volume are transmitted per unit time. When transmitting each symbol, on average, the following amount of information passes through the channel [see. (2.135) and (2.140)]:

Where random symbols at the entrance and exit of the channel. Of the four entropies appearing here, the own information of the transmitted symbol is determined by the source discrete signal and does not depend on the properties of the channel. The remaining three entropies generally depend on both the signal source and the channel.

Let's imagine that symbols from different sources, characterized by different probability distributions (but, of course, with the same values. For each such source, the amount of information transmitted over the channel takes on its own value. Maximum amount transmitted information, taken from all possible

input signal sources, characterizes the channel itself and is called the channel capacity. Per character

where maximization is performed over all multidimensional probability distributions. You can also determine the channel capacity C per unit of time (second):

The last equality follows from the additivity of entropy. In the future, wherever this is not specifically stated, we will understand throughput as throughput per second.

As an example, let us calculate the capacity of a symmetric channel without memory, for which the transition probabilities are given by formula (3.36). According to (3.52) and (3.53)

Value in in this case is easily calculated, since the conditional transition probability takes only two values: if if The first of these values ​​occurs with probability and the second with probability. In addition, since a channel without memory is considered, the results of receiving individual symbols are independent of each other. That's why

Consequently, it does not depend on the probability distribution B, but is determined only by the transition probabilities of the channel. This property is preserved for all channel models with additive noise.

Substituting (3.56) into (3.55), we obtain

Since on the right side only the term depends on the probability distribution, it is necessary to maximize it. The maximum value according to (2.123) is equal to and it is realized when all received symbols are equally probable and independent of each other. It is easy to verify that this condition is satisfied if the input symbols are equally probable and independent, since

At the same time

Hence the throughput per second

For a binary symmetric channel, the throughput in binary units per second

The dependence on according to (3.59) is shown in Fig. 3.9.

With the throughput of a binary channel, since with such a probability of error, a sequence of output binary symbols can be obtained without transmitting signals over the channel at all, but by choosing them at random (for example, based on the results of tossing a coin), i.e., when the sequences at the output and input of the channel are independent. The event is called a channel break. The fact that the throughput at in a binary channel is the same as at (noise-free channel) is explained by the fact that at it is enough to invert all the output symbols (i.e., replace 0 with 1 and 1 with 0) in order to correctly restore the input signal .

Rice. 3.9. Dependence of the capacity of a binary symmetric channel without memory on the probability of erroneous reception of a symbol

Bandwidth continuous channel is calculated similarly. Let, for example, a channel have a limited bandwidth of width. Then the signals at the input and output of the channel, according to Kotelnikov’s theorem, are determined by their samples taken at intervals and therefore the information passing through the channel over some time is equal to the sum of the amounts of information transmitted for each such sample. Channel capacity per such sample

Here the random variables are cross sections of processes at the input and output of the channel and the maximum is taken over all acceptable input signals, i.e. for all distributions.

The throughput C is defined as the sum of the Count values ​​taken over all samples per second. In this case, of course, the differential entropies in (3.60) must be calculated taking into account the probabilistic connections between the samples.

Let us calculate, for example, the capacity of a continuous channel without memory with additive white Gaussian noise, which has a bandwidth of width if the average signal power (variance) does not exceed a given value. We denote the power (dispersion) of noise in the band. The samples of the input and output signals, as well as noise, are related by the equality

n since it has a normal distribution with zero mathematical expectation, then the conditional probability density for fixed and will also be normal - with mathematical expectation and dispersion. Let's find the capacity per one sample:

According to (2.152), the differential entropy of the normal distribution does not depend on the mathematical expectation and is equal. Therefore, to find it, we need to find such a distribution density that maximizes From (3.61), taking into account that independent random variables, we have

Thus, the variance is fixed, as given. According to (2.153), for a fixed dispersion, the maximum differential entropy is ensured normal distribution. From (3.61) it is clear that with a normal one-dimensional distribution the distribution will also be normal and, therefore,

Turning to the throughput C per second, we note that the information transmitted over several samples is maximum when the signal samples are independent. This can be achieved if the signal is chosen so that its spectral density is uniform in the band. As was shown in samples separated by intervals that are multiples of them are mutually uncorrelated, and for Gaussian quantities uncorrelated means independence.

Therefore, the throughput C (per second) can be found by adding the throughputs (3.63) for independent samples:

It is realized if the Gaussian process has a uniform spectral density in the frequency band (quasi-white noise).

From formula (3.64) it is clear that if the signal power were not limited, then the throughput would be infinite. Bandwidth is zero if the signal-to-noise ratio of the channel is zero. As this ratio increases, the throughput increases indefinitely, but slowly, due to a logarithmic dependence.

Relation (3.64) is often called Shannon's formula. This formula is important in information theory, since it determines the dependence of the capacity of the continuous channel under consideration on such technical characteristics, such as bandwidth and signal-to-noise ratio. Shannon's formula indicates the possibility of trading bandwidth for signal power and vice versa. However, since C depends linearly on and on logarithmically, it is usually impractical to compensate for a possible reduction in bandwidth by increasing the signal power. More efficient is the reverse exchange of signal power for bandwidth.

Greetings dear reader! Today we will cover a topic such as Internet speed and how to check it. The fact is that inexperienced users Such questions are often asked, many begin to ask, they say, I need to connect to a new provider, what speed should I choose in the tariff, or which provider is better for the speed to be good.

Today we will look at:

What is Internet speed?

You don't have to be a technician to understand what it is. Let's just try to give an analogy. The point is that in Everyday life we often encounter speed. For example, we move by measuring the speed of walking or driving a car. Rotational speed washing machine We set depending on the washing mode. We are trying to determine how quickly the snow will melt (it’s just spring outside, I want the snow to melt quickly)))). And so on and everything is measured relative to time.

In electronics, computer technology, the Internet, the volume of information transmitted per unit of time is measured. The time taken is seconds. For volume - Kilobits (kb) or Kilobytes (Kb), and also Megabytes (Mb). Bits are minimum unit information and the computer works with groups of bits called Bytes. 1 Byte = 8 Bits. And here everything is simple, the more Bits can pass (download) per second, the better. In other words, you can quickly download music or movies, whatever.

Nowadays there are many providers, and each of them guarantees high speed. If you want to find out the Internet speed of your provider, you can safely call hotline and they will tell you everything that interests you. But will this speed be real? Is not a fact. About alternative ways I’ll tell you to check your Internet speed later.

I would like to note that the maximum speed available and available to all users is 100 Mb/s. This is the maximum that a network card can give you. computer. In fact, the Internet speed throughout the world is the same - 100 Mb/s. Or let’s give an example, let’s say a common one music file, weighs approximately 4-5 MB. In this case, we convert 1 MB into bytes and get that the download speed of 1 MB will be equal to 125 kbps, which means 4 MB will be downloaded in 40 seconds. This is the maximum possible.

Bandwidth

Household users often confuse concepts such as Internet speed And throughput. The last concept is exactly what your provider can provide you with. Many, including myself, wondered why providers different speeds they cost differently. From the above, we understood that the Internet speed is the same.

The concepts are very similar, but their meanings are different, although they are measured in the same way. Internet speed— the speed of information transmission (volume of information) per unit of time, that is, how quickly information comes from the source to the recipient.

Bandwidth- measured in the same way as Internet speed in KB/s or MB/s, the maximum possible data transfer speed from source to recipient via a specific communication channel. That is, this speed shows exactly how much information can be transmitted over a specific communication channel per unit of time.

In data transmission networks, a lot of information can be transmitted over a specific channel from one source to several recipients, and depending on many factors, the speed will be different for each recipient, but the speed of the channel itself is usually constant.

So it turns out that the sum of all data transmission rates over a specific channel cannot exceed the speed throughput channel! So it turns out that the provider cannot guarantee at a predetermined data transfer rate from any source. To the client they can provide only maximum throughput. That's why you connected, for example, 25 Mb/s, and your measured speed is approximately 15 Mb/s.

Bandwidth and provider.

For some reason, the contracts say specifically the speed of the Internet, but in essence they provide exactly the bandwidth. Also, the fact that you will have 15 Mb/s today does not mean anything. Tomorrow or in an hour it will be 20 Mb/s. or maybe 5 Mb/s. It changes constantly and depends on many factors, including the number of recipients themselves (as they say, how many in this moment people are sitting on this communication channel).

In turn, the Provider itself can guarantee the throughput of its own communication channels. This could be a channel from a client to a direct exit to global connectivity Internet, and from the client to the central hub of the provider, where informational resources, and from one client connection point to another. The provider is also responsible for the trunk channel to another Provider. Therefore, what is next is not answered by the provider. And if the throughput capacity is lower there, it won’t get any higher.

Popular mistakes when analyzing Internet speed.

Why do we always end up with a situation where the speed is exactly lower than we want (what we connected to). There are a lot of factors. The most common is the person himself who is trying to determine the speed. He just doesn't understand what he sees correctly.

I have many friends and colleagues trying to find out what and how and why and give them all advice in order to get maximum opportunities in less than a day. It's all about where you are, what you want to do, and so on. For myself personally, I connected fiber-optic Internet from Rostelecom at 25 Mb/s. I was satisfied with the price, I was satisfied with the quality of service, and the speed itself. I have enough to watch online films, play online, download data. If I need to download something big, I put it on at night and go to bed. This may not suit you, everything is individual. But this is my opinion, attitude and questions about what Internet speed I have do not arise. Simply because it is difficult to accurately determine, everything is approximately, everything is relative.

But for some reason I went astray. And so, I have identified the two most common mistakes:

1. When downloading data, it turns out that the data from the downloader itself is incorrect and the user is not attentive. The downloader itself shows an approximate download speed and is not accurate. Speed ​​always varies and depends on many factors. Plus, there have been cases when the bootloader shows a speed of 782 Kbps, and the user immediately says that it is 10 times less than stated: 8192 Kbps. You need to take a closer look at the speed values. In the first case, Kilobytes, in the second, kilobits. What happens: 782*8=6256 kB/s. This is the speed at which the file was downloaded. Given that the data is approximate and close to the declared speed, this is normal.
2. Many people look at the icon at the bottom right in the form of two monitors and see the inscription “connection speed 100 MB” (on Windows version 7 and higher there is no such thing, although they told me it was written there, but I couldn’t find where), but they have, for example, 512 kbit/s connected, and they begin to think that this value is greater, which means the Provider is deceiving us and they start calling him. It's a matter of inattention again. Down there, the connection speed between the modem and the computer is shown and has no connection with the Internet speed.

What determines the data transfer speed?

From many things, but I have identified three of the most common. To begin with, if you tried, say, to download data in Mariinsk from a server in Novosibirsk, then divided the amount of data by the download time and got the speed, then you will not get reliable information. Your resulting Internet speed will be lower and your Provider is not to blame for anything.

That's why:

1. Overload of some communication channel between Novosibirsk and Mariinsk, and there are many of them, the chain is long. There may even be foreign providers. Simply put, your signal does not go directly from Mariinsk to Novosibirsk in a straight line, there are many branches and many other providers who have their own communication channels with different capacities. And your speed cannot be greater than the slowest communication channel. So it turns out that if somewhere there is a channel with the lowest bandwidth, then your speed will be exactly that low.
2. Heavy load on the server itself or restrictions on the release of information by the server owner himself.
3. Poor performance of your network equipment, or heavy load on your computer during measurements.
4. In general, the downloaded data itself does not go in one stream in one direction, it is divided into packets. Your computer sends requests, packets arrive, broken or not received packets are resent. In general, two-way communication is ongoing, which is another plus for wasting time.
5. You can also note computing power servers, because the higher the declared speed, the more computing resources are needed. This complex processes, requiring serious hardware.

How to correctly determine speed.

For some reason, many people think that Providers always want to deceive them. I already wrote above why I chose Rostelecom and I sit calmly and don’t worry. All major providers, on the contrary, are interested in providing you with exactly the speed, or rather the bandwidth, that you pay for. And it's not that anyone can check the speed and complain.

But how do you measure speed?

Today there are many ways to do this. Simply enter the query “measure Internet speed” into a search engine and select, for example, speedtest.net.

First, select the region, the provider you have.

Click check, in a few seconds, maybe minutes, you will find out your Internet speed. BUT, this will just show you the speed of information exchange between you and the site and will not show the bandwidth of your provider in any way. Which is what I talked about above.

But to check the throughput, we do the following:

1. Download and install any program that can read and show the volume of received and sent data. For example TMeter, DUMeter, etc.
2. And now we are trying to load our channel by any means, downloading as much as possible more information At the same time, the files must be large, and in turn, the files must be downloaded from different sites. By the way, the Torrent program can help you a lot. There we install as many downloads as possible and analyze the data received.
3. Now you can determine your Internet speed, or rather the bandwidth to your provider. After all, more than what your provider allows you will not get through to you))).

And in conclusion, I want to say, thank you for reading my articles, leaving comments, correcting me if something is wrong, I am always for adequate criticism. Read the following tips. Share information on social networks, Bye everyone!

What is Internet speed? updated: September 11, 2017 by: Subbotin Pavel

With technological progress, the capabilities of the Internet have also expanded. However, in order for the user to take full advantage of them, a stable and high speed connection. First of all, it depends on the throughput of communication channels. Therefore, it is necessary to find out how to measure data transfer speed and what factors influence it.

What is communication channel capacity?

In order to familiarize yourself and understand new term, you need to know what a communication channel is. If we talk in simple language, communication channels are devices and means through which transmission occurs over a distance. For example, communication between computers is carried out using fiber optics and cable networks. In addition, a common method of communication is via a radio channel (a computer connected to a modem or a Wi-Fi network).

Bandwidth is called maximum speed transmission of information in one specific unit of time.

Typically, the following units are used to indicate throughput:

Bandwidth Measurement

Measuring throughput is a fairly important operation. It is carried out in order to find out the exact speed of your Internet connection. The measurement can be done using the following steps:

• The simplest is to download a large file and send it to the other end. The disadvantage is that it is impossible to determine the accuracy of the measurement.
• In addition, you can use the resource speedtest.net. The service allows you to measure the width of the Internet channel “leading” to the server. However, this method is also not suitable for holistic measurement; the service provides data about the entire line to the server, and not about specific channel communications. In addition, the object being measured does not have access to global network Internet.
• The optimal solution for measurement is the client-server utility Iperf. It allows you to measure time and the amount of data transferred. After the operation is completed, the program provides the user with a report.

Thanks to the above methods, you can special problems measure real speed Internet connections. If the readings do not meet your current needs, then you may need to think about changing providers.

Bandwidth Calculation

In order to find and calculate the capacity of a communication line, it is necessary to use the Shannon-Hartley theorem. It says: you can find the throughput of a communication channel (line) by calculating the mutual relationship between the potential throughput, as well as the bandwidth of the communication line. The formula for calculating throughput is as follows:

I=Glog 2 (1+A s /A n).

In this formula, each element has its own meaning:

• I- denotes the maximum throughput parameter.
• G- parameter of the bandwidth intended for signal transmission.
• A s/ A n- ratio of noise and signal.

The Shannon-Hartley theorem suggests that to reduce external noise or increase signal strength, it is best to use a wide cable for data transmission.

Signal transmission methods

Today, there are three main ways to transmit signals between computers:

• Transmission over radio networks.
• Data transmission via cable.
• Data transmission via fiber optic connections.

Each of these methods has individual characteristics of communication channels, which will be discussed below.

The advantages of transmitting information via radio channels include: versatility of use, ease of installation and configuration of such equipment. As a rule, a radio transmitter is used for receiving and method. It can be a modem for a computer or a Wi-Fi adapter.

The disadvantages of this transmission method include unstable and relatively low speed, greater dependence on the presence of radio towers, as well as the high cost of use ( Mobile Internet almost twice as expensive as a “stationary” one).

The advantages of data transmission via cable are: reliability, ease of operation and maintenance. Information is transmitted via electric current. Relatively speaking, a current at a certain voltage moves from point A to point B. A is later converted into information. The wires can withstand temperature changes, bending and mechanical stress very well. The disadvantages include unstable speed, as well as deterioration of the connection due to rain or thunderstorms.

Perhaps the most advanced data transmission technology at the moment is the use of fiber optic cable. Millions of tiny glass tubes are used in the design of the communication channels of the communication channel network. And the signal transmitted through them is a light pulse. Since the speed of light is several times higher than the speed of current, this technology allowed to speed up the Internet connection several hundred times.

The disadvantages include the fragility of fiber optic cables. First of all, they can't stand it mechanical damage: broken tubes cannot transmit a light signal through themselves, and sudden temperature changes also lead to their cracking. Well, the increased background radiation makes the tubes cloudy - because of this, the signal may deteriorate. In addition, the fiber optic cable is difficult to repair if it breaks, so it has to be completely replaced.

The above suggests that over time, communication channels and networks of communication channels are improved, which leads to an increase in data transfer rates.

Average capacity of communication lines

From the above, we can conclude that communication channels differ in their properties, which affect the speed of information transfer. As mentioned earlier, communication channels can be wired, wireless or based on the use of fiber optic cables. The last type of creating data networks is the most effective. And its average communication channel capacity is 100 Mbit/s.

What is a beat? How is bit rate measured?

Bit rate is a measurement of connection speed. Calculated in bits, the smallest units of information storage, per 1 second. It was inherent in communication channels in the era of “ early development» Internet: at that time in global web Mostly text files were transferred.

Currently, the basic unit of measurement is 1 byte. It, in turn, is equal to 8 bits. Beginner users very often make a grave mistake: they confuse kilobits and kilobytes. This is where the confusion arises when a channel with a bandwidth of 512 kbps does not live up to expectations and produces a speed of only 64 KB/s. To avoid confusion, you need to remember that if bits are used to indicate speed, then the entry will be made without abbreviations: bit/s, kbit/s, kbit/s or kbps.

Factors affecting Internet speed

As you know, the final speed of the Internet depends on the bandwidth of the communication channel. The speed of information transfer is also affected by:

• Connection methods.

Radio waves, cables and fiber optic cables. The properties, advantages and disadvantages of these connection methods were discussed above.

• Server load.

The busier the server is, the slower it receives or transmits files and signals.

• External interference.

Interference has the greatest impact on connections created using radio waves. This is caused cell phones, radio receivers and other radio signal receivers and transmitters.

• Status of network equipment.

Of course, connection methods, the state of servers and the presence of interference play an important role in ensuring high-speed Internet. However, even if the above indicators are normal, and the Internet speed is low, the problem is hidden in the computer’s network equipment. Modern network cards capable of maintaining an Internet connection at speeds of up to 100 Mbit per second. Previously, cards could provide maximum throughput of 30 and 50 Mbps, respectively.

How to increase Internet speed?

As mentioned earlier, the throughput of a communication channel depends on many factors: the connection method, the performance of the server, the presence of noise and interference, as well as the condition of the network equipment. To increase connection speed at home, you can replace network equipment with more advanced ones, as well as switch to another connection method (from radio waves to cable or fiber optic).

Finally

To summarize, it is worth saying that communication channel bandwidth and Internet speed are not the same thing. To calculate the first quantity, it is necessary to use the Shannon-Hartley law. According to him, noise can be reduced and signal strength increased by replacing the transmission channel with a wider one.

Increasing the speed of your Internet connection is also possible. But it is carried out by changing the provider, replacing the connection method, improving network equipment, and also protecting devices for transmitting and receiving information from sources that cause interference.