Limiting speed of information transfer. Evolution of data transfer speed in Wi-Fi networks

Text file size

Information coding in PC lies in the fact that each character is assigned a unique binary code. Thus, a person distinguishes symbols by their style, and a computer - by their codes.

KOI-8: 1 character - 1 byte = 8 bits

UNICODE: 1 character - 2 bytes = 16 bits

OBJECTIVE 1. Assuming that each character is encoded in one byte, evaluate information volume messages:

SOLUTION: We count the number of characters in the message, taking into account spaces and punctuation marks. We get N = 35. Because one character is encoded in 1 byte, then the entire message will occupy 35 bytes in the computer memory.

OBJECTIVE 2. Estimate information volume messages in Unicode: You can't get a fish out of a pond without difficulty!

SOLUTION: The number of characters in the message is 35. v Unicodeone character is encoded with 2 bytes, then the entire message will occupy 70 bytes in the computer memory.

OBJECTIVE 3. Define information volume a book (in MB) prepared on a computer, consisting of 150 pages (each page contains 40 lines, 60 characters in each line).

SOLUTION:

1) Let's count the number of characters in the book 40 * 60 * 150 = 360 000

2) The information volume of the book will be 360,000 * 1 byte = 360 bytes

3) Let's convert 360,000 bytes / 1024 = 351.5625 KB into the given units/ 1024 = 0.34332275 MB

The phrase is approximately 40 characters long. Investigatorbut, its size can be approximately estimated at 40 x 2 = 80 bytes. There is no such answer, let's try to translate the result into biyou: 80 bytes x 8 = 640 bits. The closest value from beforelaid down - 592 bits. Note that the difference between 640 and 592 is only 48/16 = 3 characters in the given encoding and itscan be considered insignificant compared to the length of the string.

Z Note: By counting the characters in the string, you can make sure that there are exactly 37 characters (including periods and spaces), so the estimate of 592 bits = 74 bytes, which corresponds to exactly 37 characters in double-byte encoding, is accurate.

AlphabetIs a set of letters, punctuation symbols, numbers, space, etc.

The total number of characters in the alphabet is called the power of the alphabet

OBJECTIVE 4. The two texts contain the same number of characters. The first text is in a 16-character alphabet. Second text in the alphabet with a capacity of 256 characters. How many times is the amount of information in the second text greater than in the first?

SOLUTION: If the first text is composed in the alphabet with a capacity (K) of 16 characters, then the amount of information that 1 character (1) carries in this text can be determined from the ratio: N = 2 ", thus, from 16 = 2" we get 1 = 4 bit. The power of the second alphabet is 256 characters, out of 256 = 2 "we get 1 = 8 bits. Since both texts contain the same number of characters, the amount of information in the second text is 2 times greater than in the first.

Information transfer rate

The data transfer rate over communication channels is limited by the channel bandwidth. The bandwidth of the communication channel changes, as does the data transfer rate in bit / s (or a multiple of this value Kbit / s, Mbit / s, byte / s, Kbyte / s, Mb / s).
To calculate the amount of information V transmitted over a communication channel with a throughput a during time t, the following formula is used:

V = a * t

OBJECTIVE 1. Via ADSL - connection, a file of 1000 Kbytes was transmitted for 32 seconds. How many seconds will it take to transfer a 625KB file.

SOLUTION:Let's find the speed of the ADSL connection: 1000 KB / 32 s. = 8000 kbps / 32 s. = 250 kbps.
Find the time to transfer a 625KB file: 625KB / 250Kbps = 5000Kbps / 250Kbps. = 20 seconds.

When solving problems on determining the speed and time of data transfer, difficulty arises with large numbers (example 3 Mb / s = 25 165 824 bit / s), therefore it is easier to work with powers of two (example 3 Mb / s = 3 * 2 10 * 2 10 * 2 3 = 3 * 2 23 bits / s).

TASK 2 . The ADSL data transfer rate is 512,000 bps. It took 1 minute to transfer the file over this connection. Determine the size of the file in kilobytes.

SOLUTION: File transfer time: 1 min = 60 s = 4 * 15 s = 2 2 * 15 s
File transfer rate: 512000 bps = 512 * 1000 bps = 2 9 * 125 * 8 bps (1 byte = 8 bits)

2 9 * 125 bytes / s = 2 9 * 125 bit / s / 2 10 = 125/2 Kb / s

To find the file size time, you need to multiply the transfer time by the transfer rate:

(2 2 * 15 s) * 125/2 Kb / s = 2 * 15 * 125 Kb = 3750 Kb

In the case of information transfer rates, these “pretty numbers” are confusing. Of course, the situation here is still different - this is a confusion between the standard (where the speed is named according to what it is at the data link level) and reality, but the meaning is very similar: the figure on the sticker does not correspond to what you see with your eyes when you turn on the computer. Let's try to sort it out with this confusion.

There are two types of connection - with a cable, and over the air, wireless.

Cable connection.

In this case, there are least problems with numbers. The connection takes place at a speed of 10, 100 or 1000 megabits (1 gigabit) per second. This is not "internet speed", not the speed of opening pages or downloading files. It is only the speed between the two points that such a cable connects. From your computer, the cable can go to the router (modem), to another computer or to the entrance to the provider's equipment, but in any case, this speed only indicates that the connection between these two points occurred at the specified speed.

Data transfer speed is limited not only by the type of cable, but also quite strongly - by the speed of your hard drive. On a gigabit connection, the file transfer speed will rest against this, and it is possible to achieve real 120 megabytes per second only in some cases.

The connection speed is selected automatically depending on how your connecting devices "agree", according to the slowest of them. If you have a gigabit network card (and most of them are in computers now), and on the other end there is 100 megabit equipment, then the connection speed will be set to 100mbit. There is no need to make any additional speed settings, if this is required, this is an indicator that there is a problem with the cable, or with the equipment you have or at the other end, and therefore the maximum speed is not automatically set.

Wireless connection.

But with this type of connection, there are much more problems and confusion. The fact is that with a wireless connection, the data transfer rate is approximately two times less than the standard figure says. How it looks in real data - see the table.

As you can see, everything is very sad and ugly, and the vaunted “N” does not even come close to showing the numbers that I would like to see. In addition, this speed is ensured under near-ideal environmental conditions: no interference, no walls with metal between the router and the computer (better line of sight), and the shorter the distance, the better. In a typical three-room apartment in a reinforced concrete building, a wireless access point installed in the back of the apartment can be almost elusive from the opposite side. The “N” standard provides the best coverage, and this advantage is more important to me personally than speed; and high-quality coverage has a good effect on speed: where the data transfer rate when using equipment with “G” is 1 megabit, only using “N” can increase it several times. However, it is not at all a fact that this will always be the case - it is in the ranges, in some cases such a switch does not give a result.

The speed is also influenced by the performance of the device that distributes the Internet (router, access point). With active use of torrents, for example, the speed of data transfer through the router can drop significantly - its processor simply cannot cope with the data stream.

The selected encryption type also affects the speed. From the very name it is clear that “encryption” is the processing of data in order to encode it. Different encryption methods can be used, and hence the performance of the device that this encryption-decryption performs is different. Therefore, it is recommended to set the WPA2 encryption type in the wireless network parameters - this is the fastest and most secure type of encryption at the moment. As a matter of fact, according to the standard, any other type of encryption will not allow "N" to turn on at "full power", but some Chinese routers spit on the standards.

One more point. In order to take full advantage of the N standard (especially for equipment supporting MIMO), the access point must be set to “N Only” mode.

If you choose “G + N Mixed” (any “mixed” mode), chances are high that your devices will not try to connect at maximum speed. This is the payment for standards interoperability. If your devices support “N”, forget about other modes - why lose the advantages offered? Using both G and N hardware on the same network will deprive you of them. However, there are routers that have two transmitters and allow you to work in two different frequency ranges at the same time, but this is rather rare, and their price is much higher (for example, Asus RT-N56U).

Other types of connection.

In addition to those described, of course, there are other types of connection. Obsolete option - connection via coaxial cable, unusual option for connection through the building's electrical network, many connection options using mobile networks - 3G, new LTE, relatively uncommon WiMAX. Any of these types of connection has speed characteristics, and any of them operates with the concept of “speed TO”. You are not deceived (well, they are not formally deceived), but it makes sense to pay attention to these numbers, understanding what they mean in reality.

Units.

There is confusion caused by incorrect use of units. Probably, this is a topic for another article (on networks and connections, which I will write shortly), but still (compressed) it will be in place.

In the computer world, a binary number system is adopted. The smallest unit of measurement is bit. Next is byte.

Ascending:

1 byte = 8 bits

1024 bits = 1 kilobits (kb)

8 kilobits = 1 kilobyte (KB)

128 kilobytes = 1 megabits (mb)

8 megabits = 1 megabyte (MB)

1024 kilobytes = 1 megabyte (MB)

128 megabytes = 1 gigabit (gb)

8 gigabits = 1 gigabyte (GB)

1024 megabytes = 1 gigabyte (GB)

Everything seems to be clear. But! Suddenly it turns out that there is confusion here too. Here's what wikipedia says:

When denoting the speed of telecommunication connections, for example, 100 Mbit / s in the 100BASE-TX standard ("copper" Fast Ethernet) corresponds to the transmission speed of exactly 100,000,000 bit / s, and 10 Gbit / s in the 10GBASE-X (Ten Gigabit Ethernet) standard - 10,000,000,000 bit / s.

Whom to believe? Decide for yourself, which is more convenient for you, read the same Wikipedia. The fact is that what is written in Wikipedia is not the ultimate truth, it is written by people (in fact, any person can write something there). But in the textbooks (in particular, in the textbook "Computer networks" from Olifer V.G., Olifer N.A.) - the calculus is normal, binary, and in 100 megabits –12.5 megabytes, and it is 12 megabytes that you will see when downloading the file on a 100-megabit LAN, in almost any program.

Different programs display the speed in different ways - some in kilobytes, some in kilobits. Formally, when we are talking about * bytes, a capital letter is put, about * bits-small (notation KB (KB, sometimes kB or KB, or KB)) - means “kilobyte”, kb (kb, or kbit) - “kilobit” , etc.), but this is not a fixed rule.

Any signal can be viewed as a function of time, or as a function of frequency. In the first case, this function shows how the signal parameters subsequently change, for example, voltage or current. If this function is continuous, then one speaks of continuous signal. If this function has a discrete form, then one speaks of discrete signal.

The frequency representation of a function is based on the fact that any function can be represented as a Fourier series

(1),
where - frequency , an, bn - amplitudes nth harmonics.

The characteristic of the channel, which determines the spectrum of frequencies that the physical medium from which the communication line that forms the channel is made passes without a significant decrease in the signal power is called bandwidth.

The maximum rate at which the channel is capable of transmitting data is called channel bandwidth or bit rate.

In 1924 Nyquist discovered the relationship between the capacity of a channel and its bandwidth.

Nyquist's theorem

where is the maximum transmission rate H - channel bandwidth expressed in Hz, M- the number of signal levels that are used for transmission. For example, this formula shows that a 3 kHz channel cannot transmit bi-level signals faster than 6000 bps.

This theorem also shows that, for example, it makes no sense to scan a line more often than double the bandwidth. Indeed, all frequencies above this are absent in the signal, and therefore all the information necessary to resume the signal will be collected during such a scan.

However, the Nyquist theorem does not take into account the noise in the channel, which is measured as the ratio of the signal power to the noise power: S / N... This value is measured in decibels: 10log10 (S / N) dB... For example, if the relation S / N equals 10, then they speak of noise at 10 dB if the ratio is 100, then - 20 dB.

In the case of a noisy channel, there is Chenon's theorem, according to which the maximum data transfer rate over a noisy channel is:
H log2 (1 + S / N) bit / sec, where S / N - signal-to-noise ratio in the channel.

The number of levels in the signal is no longer important here. This formula sets a theoretical limit that is rarely achieved in practice. For example, on a channel with a bandwidth of 3000 Hz and a noise level of 30 dB (these are the characteristics of a telephone line), data cannot be transmitted faster than at a speed of 30,000 bps.

Access methods and their classification

Access method(accessmethod) Is a set of rules that regulate the method of obtaining for use (“delight”) the transmission medium. The access method determines how the nodes get the ability to transmit data.
The following accessor classes are distinguished:

1. selective methods
2. adversarial methods (random access methods)
3. time reservation methods
4. ring methods.

All accessors, except adversarial ones, form a group of deterministic access methods. Using selective methods in order for a node to transmit data, it must obtain permission. The method is called poll(polling), if permissions are transmitted to all nodes in turn by special network equipment. The method is called passing the token(token passing), if each node passes the permission to the next after completing the transfer.

Methods random access(random access methods) are based on the "competition" of nodes for gaining access to the transmission medium. Random access can be implemented in different ways: basic asynchronous, with clock synchronization of the moments of frame transmission, with listening to the channel before transmission (“listen before you speak”), with listening to the channel during transmission (“listen while you speak”). Several of the listed methods can be used simultaneously.
Methods based on time reservation, are reduced to the allocation of time intervals (slots), which are distributed between the nodes. The node receives the channel at its disposal for the entire duration of the slots allocated to it. There are variants of methods that take into account priorities - nodes from more high priorities receive more slots.
Ring methods are used in LVM with ring topology. The ring method of register insertion consists in connecting one or more buffer registers in parallel to the ring. The data for transmission is written to the register, after which the node waits for the interframe gap. Then the contents of the register are transferred to the channel. If a frame arrives during transmission, it is written to the buffer and transmitted after its data.

Distinguish client-server and peer-to-peer methods access.

Client Server Access Methods allow for a central hub on the network that controls all others. Such methods fall into two groups: polling and non-polling.

Among polled access methods the most commonly used are “polling with stop and wait” and “continuous automatic repeat request” (ARQ). In any case, the primary node sequentially gives the nodes permission to transfer data. If a node has data to transmit, it issues it to the transmission medium; if not, it either issues a short data packet of the “no data” type, or simply does not transmit anything.

Using peer access methods all nodes are equal. Time-division multiplexing is the simplest priority-free peer-to-peer system that uses a fixed node scheduling. Each node is allocated a time interval during which the node can transmit data, and the intervals are distributed equally among all nodes.

Analog data transmission channels.

Under data transmission channel(Efficiency) is understood as a set of transmission medium (signal propagation medium) and technical means of transmission between channel interfaces. Depending on the form of information that can be transmitted by the channel, a distinction is made between analog and digital channels.

An analog channel at the input (and, accordingly, at the output) has a continuous signal, certain characteristics of which (for example, amplitude or frequency) carry the transmitted information. The digital channel receives and outputs data in digital (discrete, pulse) form.

What is internet speed and in what units is the speed of the Internet connection measured: bits or maybe bytes?

Internet speed is the maximum amount of data received by a personal computer (PC) or transmitted to the Network in a given unit of time. If you look at the change in the data transfer rate, then most often you can find: in kilobits / second (Kb / s; Kbps), or in megabits (Mb / s; Mbps). The size of any files is always indicated in bytes, KB, MB and GB.

We all know that 1 byte is 8 bits.If the speed of your Internet connection is 100 Mbps, then following from the calculations (100/8 = 12.5), we can conclude that a computer can transmit or receive no more than 12.5 in one second. MB of information. If the size of the file you want to download is 1.5 GB, then you will spend no more than two minutes on the download process.

What does the speed of the Internet connection depend on?

First of all, the speed of the Internet connection depends on your tariff plan, which your Internet provider has set for you. Also, the speed is influenced by the technology of the information transmission channel and the congestion of the Network by other users. If you limit the total bandwidth of the channel, then the more users are on the Web and the more they download files and information, the more the connection speed drops, since there is less "free space" on the Web.

Secondly, there is a dependence on the loading speed of the sites you are on. For example, if at the time of loading the server can send data to the user at a speed of at least 10 Mbps, then even if you are connected to the maximum tariff plan, you can not wait for more.

Factors that affect Internet speed:

1. When checking, the speed of the server you are accessing.

2. The speed and settings of your Wi-Fi router.

3. All programs and applications running on the computer at the time of verification.

4. Also firewalls and antiviruses running in the background.

5. Settings of your operating system (OS) and the computer itself.

How can you increase the speed of your internet connection?

1. Malicious or unwanted software, it can primarily affect the decrease in the speed of the Internet connection.

2. Viruses, worms and Trojans that accidentally get into your computer can take away some of the bandwidth. To solve this problem, you need to use anti-virus programs that will fight the infection of your PC.

3. When you use Wi-Fi that is not password protected, you also put yourself at risk, since other users usually connect to it. Therefore, a password must be set on Wi-Fi.

4. Parallel running programs also reduce the speed of the Internet connection, because they lead to an increase in the processor load, so the speed drops sharply.

Some actions are capable of increase internet speed connections, for example:

1. Increase the throughput speed of the port. This is in the event that you have a high Internet connection, and the speed has dropped sharply. Go to the "Start" menu, then "Control Panel" then to "System" and to the "Hardware" section, then click on "Device Manager". Find "Ports (COM or LPT)", then expand their contents and find "Serial port (COM 1)". After that, you need to right-click and open "Properties". After that, a window will open in which you need to go to the "Port parameters" column. After the window has opened, click on the "Speed" parameter (bits per second) and click on the number 115200 - then OK! After all these actions, the throughput speed of the port is increased. Since the default speed is 9600 bps.

2. Also, to increase the speed, you can try disabling the QoS packet scheduler. To do this, you need to run the gpedit.msc utility. In the "Start" search - gpedit.msc. Next, you need to click "Computer Configuration" after "Administrative Templates". Then go to "Network", then "QoS Packet Scheduler". Next, you need to "Limit the reserved bandwidth" then "Enable" and set 0%. Click "Apply" and restart your computer.

3. Reboot the router. Restarting your modem or router will resolve many connection problems. Unplug it, wait 30 seconds and plug it back on.

These actions, in some cases, will help you increase your speed.

Internet speed is the amount of information received and transmitted by a computer over a period of time. Now this parameter is most often measured in Megabits per second, but this is not the only value, kilobits per second can also be used. Gigabits are not yet used in everyday life.

At the same time, the size of the transferred files is usually measured in bytes, but time is not taken into account. For example: Bytes, MB, or GB.

It is very easy to calculate the time it takes to download a file from the network using a simple formula. It is known that the least amount of information is a bit. Then comes a byte, which contains 8 bits of information. Thus, a speed of 10 megabits per second (10/8 = 1.25) allows you to transfer 1.25 megabytes per second. Well, 100 Mbps - 12.5 Megabytes (100/8), respectively.

You can also calculate how much it will take to download a file of a certain size from the Internet. For example, a 2 GB movie downloaded at a speed of 100 Megabits per second can be downloaded in 3 minutes. 2 GB is 2048 Megabytes, which should be divided by 12.5. We get 163 seconds, which is about 3 minutes.
Unfortunately, not everyone is familiar with the units in which it is customary to measure information, so we will mention the main units:

1 byte is 8 bits
1 kilobyte (KB) corresponds to 1024 bytes
1 Megabyte (MB) will be equal to 1024 KB
1 Gigabyte (GB) equals 1024 MB, respectively
1 Terabyte - 1024 GB

What affects speed

The speed at which the Internet will work on the device depends primarily on:

From the tariff plan provided by the provider
From the bandwidth of the channel. Often times, the provider provides the overall speed to subscribers. That is, the channel is divided into all, and if all users are actively using the network, then the speed may also decrease.
From the location and settings of the site that the user is accessing. Some resources have limitations and do not allow you to exceed a certain threshold when loading. Also, the site may be located on another continent, which will also affect loading.

In some cases, the data transfer rate is influenced by both external and internal factors, including:

Location of the server being accessed
Setting and width of the Wi-Fi router channel, if the connection is "over the air"
Applications running on the device
Antiviruses and firewalls
OS and PC setup