What types of information can be transmitted over the Internet. Transfer of information

Hello! Today there will be a rather graphic article explaining how data will be transferred in local networks using protocols of various levels.

initial situation

So, first we have some application that needs to send data to another application. Let the source Node 1 want to send something to Node 2. The IP addresses are 192.168.1.1 and 2, respectively. According to the chart...

Packet hopping

1. Node 1. (Application layer) “I need to send data to 192.168.1.2 per port 2099 , delivery reliability is not required!”.
2. Node 1. (Transport Layer) UDP protocol, give me your details here.”
3. Node 1. (Application layer) “Here, hold on! ” - arbitrary hexadecimal data. (Further <данные> )
4. Node 1. (Transport layer) “Excellent. I'll attach a UDP header to them so as not to lose the packet. Let's fix some data and port numbers in the header. What's free? UDP:42133! Fine. A port of destination UDP:2099. Let's attach this title. We lower the packet further, to the network layer. (Package: [ <заголовок транспортного уровня> <данные> ]
5. Node 1. (Network layer) “Received your packet, where to send it? On IP:192.168.1.2? I will also attach network layer information to this header. Well, your reverse IP: 192.168.1.1 and some more information from yourself ... Hey, link layer! Here's a package for you!" [ <заголовок сетевого уровня> <заголовок транспортного уровня> <данные> ]
6. Node 1. (Link layer) “Op-pa. Package. Where to deliver? We look at the title ... Taxi, at 192.168.1.2. Hmmm.. I don't remember the MAC address associated with this IP, I'll look in the switching table apr… Hmm. I don't have that address yet. We will ask the environment. We will postpone the package for now.”
7. (parking package)
8. Node 1. (Link layer) “Hey Wednesday! Is there someone online at 192.168.1.2? Reply to my MAC: 0001.43B7.623C! I have a package for you! Physical layer pass it plz!”
9. Node 1. (Physical layer) The above broadcast packet is sent to all stations (to address FFFF.FFFF.FFFF)
   Each station in the broadcast domain will receive this packet and ignore it if its IP is different from the IP in this packet. The station, whose IP address matches the specified one, will respond with an oncoming packet.
10. Switch. “I received a frame from port 1. I am analyzing the destination. O! broadcast frame. I will send it to all other ports except where it came from. Just in case, I'll remember that on the first port I have ”.
11. Node 3. (Physical) “I received a broadcast frame. Channel, I transmit.
12. Node 3. (Channel) “Received. Hey network! they ask IP 192.168.1.2, and we have 192.168.1.3. Ignore.”
13. Node 2. (Physical) “I received a broadcast frame. Channel! I pass it on to you."
14. Node 2. (Link layer) “Got it! O! This is for me! Physical, wire back the following: Listen, 0001.43B7.623C! It's me! My IP address is 192.168.1.2! Remember my MAC 0004.9A41.0966 in your switching table. And don't forget the package!
15. Switch. “I received a frame from port 2. for MAC: 0001.43B7.623C. Judging by the table, I have it on the side of port 1. I will send a frame to this port. And along the way, I will save the address 0004.9A41.0966 as an address on the side of port 2, it will come in handy.
16. Node 1. (Link layer) “The owner of the address 192.168.1.2 was found. Now I will attach the destination address to the packet, as well as my reverse MAC and give it to the physical layer for transmission. Physical! Keep the package! [ <заголовок канального уровня> <заголовок сетевого уровня> <заголовок транспортного уровня> <данные> ]
17. Node 1. (Physical layer) “OK.”
18. Switch. “Oops, got a frame for MAC: 0004.9A41.0966. I have it from the side of port 2. I send the frame there.”
19. Node 2. (Physical layer) “Received a frame. I transmit to the channel level. [ <заголовок канального уровня> <заголовок сетевого уровня> <заголовок транспортного уровня> <данные> ]
20. Node 2. (Channel) “So, a packet arrived from 0001.43B7.623C. Really for me. And it contains some IP protocol data. This is not my topic, I will remove the title of my level and give it higher, to the network.”[ <заголовок сетевого уровня> <заголовок транспортного уровня> <данные> ]
21. Node 2. (Network) “Some packet from IP 192.168.1.1, and in it some transport layer data. Packet for IP: 192.168.1.2, I'll send it to the appropriate interface, let the transporters sort it out there.”[ <заголовок транспортного уровня> <данные> ]
22. Node 2. (Transport) “A packet came from the network, there is data for port 2099, some service is hanging, waiting for the packet. Pass it on!” [ <данные> ]
23. Node 2. (Applied) “Hurrah! Data for me!. Thank you for your attention ^_^”

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Receipt accounts users in local network

That is, in a narrow sense, it is a global community of small and large networks. In a broader sense, it is global informational space, which stores a huge amount of information on millions of computers that exchange data.

In 1969, when the Internet was created, this network connected only four host computers, and today their number is measured in tens of millions. Every computer connected to the Internet is part of the Net.

In order to start with the most familiar scheme for everyone, let's look at how a home computer connects to the Internet, and trace the channels through which information travels, transmitted and received by us from the Web. If you access the Internet from your home computer, then most likely you are using a modem connection (Fig. 1).

In principle, the connection with the provider can go through various channels: over a telephone line, over a leased line, based on wireless or satellite communications, over a network cable television or even along lines of force - all these alternatives are shown in fig. one .

Most often this is the so-called temporary (session) connection over a telephone line. You dial one of the phone numbers provided by your ISP and dial one of their modems. On fig. 1 shows a set of provider modems, the so-called modem pool. Once you have connected with your ISP (Internet Service Provider) provider, you become part of that ISP's network. The provider provides its users with various services, e-mail, Usenet, etc.

Each provider has its own backbone network, or backbone. On fig. 1, we have conventionally depicted the backbone network of a certain ISP-A provider. Its backbone network is shown in green.

Typically, ISP providers are large companies that in a number of regions have so-called points of presence (POP, Point of Presence), where local users connect.

Usually a large provider has a point of presence (POP) in several major cities. Each city has similar modem pools that are called by local clients of that ISP in that city. The provider can lease fiber optic lines from telephone company to connect all of its Points of Presence (POPs), or it can run its own fiber optic lines. The largest communication companies have their own high bandwidth channels. On fig. 1 we have shown the core networks of two ISPs. Obviously, all clients of the ISP-A provider can interact with each other over their own network, and all clients of the ISP-B company - on their own, but if there is no connection between the ISP-A and ISP-B networks, the clients of the company "A" and the clients of the company " B" cannot communicate with each other. To implement this service, companies "A" and "B" agree to connect to the so-called access points (NAP - Network Access Points) in different cities, and traffic between the two companies flows over the networks through the NAP. On fig. 1 shows the backbone networks of only two ISPs. Similarly, a connection to other backbone networks is organized, as a result of which a combination of many networks is formed. high level.

There are hundreds of large ISPs on the Internet, their backbone networks are connected through NAPs in various cities, and billions of bytes of data flow through different networks through NAP nodes.

If you use the Internet at the office, then most likely you are connected to a local area network (LAN - Local Area Network). In this case, the scheme we have considered is somewhat modified (Fig. 2). The organization's network is usually separate from outside world a certain information security service, which is conditionally shown in our diagram as a brick wall. Connection options to the provider may be different, although most often it is a leased line.

Since it is not possible to represent the entire set Internet networks, it is often depicted as a blurry cloud, highlighting only the main elements in it: routers, points of presence (POP) and access points (NAP).

The speed of information transfer in different parts of the Network varies significantly. Trunk lines, or backbones, connect all regions of the world (Fig. 5) - these are high-speed channels built on the basis of fiber-optic cables. Cables are designated OC (optical carrier), such as OC-3, OC-12 or OC-48. So, the OC-3 line can transmit 155 Mbps, and the OC-48 - 2488 Mbps (2.488 Gbps). At the same time, receiving information on a home computer with a 56K modem connection occurs at a speed of only 56,000 bps.

How information is transmitted on the Internet

Routers

How is the transmission of information through all these multiple channels? How can a message be delivered from one computer to another across the world, traversing several different networks in a fraction of a second? In order to explain this process, it is necessary to introduce a few concepts and, first of all, to talk about the operation of routers. Delivery of information to the desired address is impossible without routers that determine which route to transmit information. A router is a device that works with several channels, sending the next block of data to the selected channel. The channel is selected at the address specified in the header of the received message.

Thus, the router performs two distinct but related functions. First, it sends information to free channels, preventing "blockage" of bottlenecks in the Network; secondly, it checks that the information is going in the right direction. When two networks are combined, the router joins both networks, passing information from one to the other, and in some cases transfers data from one protocol to another, while protecting networks from excess traffic. This function of routers can be compared to the work of a patrol service, which monitors traffic in the city from a helicopter, monitors the general situation with breakdowns and traffic jams, and reports on the busiest sections of the route so that drivers choose the best route and avoid traffic jams.

Internet Protocols

Let's now turn to the consideration of ways to transmit information on the Internet. For this, it is necessary to introduce such a concept as a protocol. In a broad sense, a protocol is a predetermined rule (standard) according to which one who wants to use a certain service interacts with the latter. In relation to the Internet, a protocol is a rule for the transmission of information on the Web.

Two types of protocols should be distinguished: basic and application. The underlying protocols are responsible for the physical transfer of messages between computers on the Internet. These are IP and TCP protocols. Application protocols are called higher-level protocols, they are responsible for the functioning of specialized services. For example, the http protocol is used to transfer hypertext messages, the ftp protocol is used to transfer files, SMTP is used to transfer Email etc.

A set of protocols of different layers working simultaneously is called a protocol stack. Each lower level of the protocol stack has its own system of rules and provides a service for the higher ones.

This interaction can be compared to the forwarding scheme of a regular letter. For example, the director of firm "A" writes a letter and gives it to the secretary. The secretary places the letter in an envelope, writes the address and takes the envelope to the post office. The post office delivers the letter to the post office. The post office delivers the letter to the recipient - the secretary of the director of the company "B". The secretary opens the envelope and sends the letter to the director of the company "B". Information (letter) is transmitted from the upper level to the lower one, acquiring additional information at each stage. official information(package, address on the envelope, postal code, container with correspondence, etc.), which is not related to the text of the letter.

The bottom level is the level of the postal transport that transports the letter to its destination. At the destination, the reverse process occurs: the correspondence is retrieved, the address is read, the postman carries the envelope to the secretary of firm B, who takes out the letter, determines its urgency, importance, and, depending on this, passes the information above. The directors of firms "A" and "B", passing information to each other, do not care about the problems of sending this information, just like a secretary does not care how mail is delivered.

Likewise, each protocol in the protocol stack performs its own function without concern for the functions of the protocol at another layer.

At the lower level, that is, at the TCP / IP level, two main protocols are used: IP (Internet Protocol - Internet protocol) and TCP (Transmission Control Protocol - transmission control protocol).

The architecture of the TCP/IP protocols is designed for the internetwork. The Internet consists of heterogeneous subnets connected to each other by gateways. Subnets can be different local networks (Token Ring, Ethernet, etc.), different national, regional and global networks. Machines can connect to these networks different types. Each of the subnets works in accordance with its principles and type of connection. In this case, each subnet can receive a packet of information and deliver it to the specified address. Thus, each subnet is required to have some sort of end-to-end protocol for passing messages between two external networks.

The diagram in fig. 6. Suppose there is a certain message sent by e-mail. Mail is transmitted using the SMTP application protocol, which relies on the TCP/IP protocols. According to the TCP protocol, the sent data is broken into small packets of a fixed structure and length, marked so that when received, the data can be collected in the correct sequence.

Typically, the length of one packet does not exceed 1500 bytes. Therefore, one e-mail can consist of several hundred such packets. The small packet length does not block communication lines and does not allow individual users to take over the communication channel for a long time.

For each TCP packet received, the IP protocol adds information that can be used to determine the sender and destination addresses. On fig. 6 this is represented as putting the address on the envelope. For each incoming packet, the router through which a packet passes, using the IP address, determines which of the nearest neighbors needs to forward this packet so that it reaches the recipient faster - that is, it decides on the optimal path for the next packet. At the same time, the geographically shortest path is not always optimal (a fast channel to another continent may be better than a slow one to a neighboring city). Obviously, the speed and paths of different packets can be different.

Thus, the IP protocol carries out the movement of data on the network, and the TCP protocol provides reliable data delivery using a system of error-correcting codes. Moreover, two network servers can simultaneously transmit many TCP packets from different clients in both directions along one line.

Some novice users think that Internet communication is similar to telephone communication. I would like to emphasize once again the main difference between the transmission of information over the telephone network and over the Internet: when you call someone on the phone in another region of the country or even on another continent, the telephone system establishes a channel between your phone and the one you are calling to. A channel can consist of dozens of sections: copper wires, fiber optic lines, wireless sections, satellite connection etc. These sections are unchanged throughout the entire communication session. This means that the line between you and the person you are calling is constant throughout the conversation, so damage to any part of that line, such as a broken wire during a storm, can interrupt your conversation.

At the same time, if the connection is normal, then the part of the network allocated to you is no longer available to others. This is a circuit-switched network. The Internet is a packet-switched network, which is a different story. The process of sending email is fundamentally different.

As already noted, Internet data in any form (be it an email message, a Web page, or a downloadable file) travels as a group of packets. Each packet is sent to its destination along the best path available. Therefore, even if some section of the Network is broken, this will not affect the delivery of the packet, which will be sent along an alternative path. Thus, during data delivery, there is no need for a fixed link between two users. The principle of packet switching provides the main advantage of the Internet - reliability. The network can distribute the load over different areas in thousandths of a second. If a piece of network equipment is damaged, the packet can bypass that place and take a different path, ensuring the delivery of the entire message.

Internet Addressing

We have already mentioned the IP address, now let's talk about it in more detail. Every computer connected to the Internet is assigned an identification number called an IP address.

But if you make a session connection (that is, you connect for the duration of the Internet access session), then the IP address is allocated to you only for the duration of this session. Assigning an address for the duration of a communication session is called dynamic IP address allocation. This is handy for the ISP because, while you are not connected to the Internet, the IP address you received may be allocated to another user. This IP address is only unique for the duration of your session - the next time you access the Internet through your ISP, the IP address may be different. Thus, an ISP must have one IP address for every modem it serves, not for every client, which can be many more.

An IP address has the format xxx.xxx.xxx.xxx, where xxx is a number between 0 and 255. Consider a typical IP address: 193.27.61.137.

To make it easier to remember, an IP address is usually expressed as a series of decimal numbers separated by dots. But computers store it in binary form. For example, the same IP address in binary would look like this:

11000001.00011011.00111101.10001001.

The four numbers in an IP address are called octets because each of them has eight bits in binary representation: 4×8=32. Since each of the eight positions can have two different states: 1 or 0, the total number of possible combinations is 28, or 256, that is, each octet can take values ​​​​from 0 to 255. The combination of four octets gives 232 values, that is, approximately 4, 3 billion combinations, excluding some reserved addresses.

Octets serve not only to separate numbers, but also perform other functions. Octets can be divided into two sections: Net and Host. The net section is used to determine the network to which the computer belongs. Host, sometimes called a host, identifies a particular computer on a network.

This system is similar to the system used in regular mail, where one part of the address specifies a street and the other part specifies a specific house on that street.

At an early stage of its development, the Internet consisted of a small number of computers connected by modems and telephone lines. Users could then establish a connection to a computer by typing a numeric address such as 163.25.51.132. This was convenient as long as the network consisted of several computers. As their number increased, given the fact that a textual name is always more convenient to remember than a digital one, digital names gradually began to be replaced by textual ones.

The problem of automating this process arose, and in 1983, the so-called DNS (Domain Name System) system was created at the University of Wisconsin, USA, which automatically established a correspondence between text names and IP addresses. Instead of numbers, a notation like http://www.myhobby.narod.ru/, which has become familiar to us today, was proposed.

This is how regular mail is sorted. People are used to being guided by geographical addresses, for example: “Moscow, st. Ryleeva, 3, apt. 10", while the machine at the post office quickly sorts the mail by index.

Thus, when sending information, computers use digital addresses, people use letter addresses, and the DNS server serves as a kind of translator.

Before proceeding to the description of the operation of DNS servers, a few words should be said about the structure of domain names.

Domain names

When you access the Web or send e-mail, you are using a domain name. For example, http://www.microsoft.com/ contains the domain name microsoft.com. Similarly, email address [email protected] contains the domain name aha.ru.

AT domain system names, the principle of assigning names is implemented with the definition of responsibility for their subset of the corresponding network groups.

And if every group sticks to it simple rule and always confirms that the names it assigns are unique among its many immediate subordinates, then no two systems, anywhere on the Internet, can get the same name.

The addresses indicated on envelopes when delivering letters by regular mail are also unique. Thus, an address based on geographic and administrative names uniquely identifies a destination.

Domains also have a similar hierarchy. In the names, the domains are separated from each other by dots: companya.msk.ru, companyb.spb.ru. The name can have a different number of domains, but usually there are no more than five. As you move through the domains in a name from left to right, the number of names included in the corresponding group increases.

Every time you use a domain name, you are also using DNS servers to translate the literal domain name into a machine language IP address.

As an example, let's consider the address http://www.pc.dpt1.company.msk.ru/ .

The first name in the name is the name of the working machine - a real computer with an IP address. This name is created and maintained by the dpt1 group. The group is part of a larger company division, followed by the msk domain - it defines the names of the Moscow part of the network, and ru - the Russian one.

Each country has its own domain. So au - corresponds to Australia, be - to Belgium, etc. These are geographic top-level domains.

In addition to the geographical feature, a thematic one is used, according to which there are the following domain names first level:

• com - denotes commercial enterprises;
• (edu) - educational;

How DNS Server Works

The NS server receives a request to convert a domain name to an IP address. In this case, the DNS server performs the following actions:

• responds to the request with an IP address because it already knows the IP address of the requested domain.
• contacts another DNS server to find the IP address of the requested name. This request can be chained multiple times.
• gives a message: "I do not know the IP address of the domain you are requesting, but here is the IP address of the DNS server that knows more than me";
• reports that such a domain does not exist.

Let's imagine that you typed the address http://www.pc.dpt1.company.com/ in your browser, which has an address in the COM top-level domain (Figure 9). In its simplest form, your browser contacts a DNS server to obtain the IP address of the computer you are looking for, and the DNS server returns the IP address you are looking for (Figure 10).

In practice, on a network of millions of computers, finding a DNS server that knows the information you need is a whole problem. In other words, if you are looking for a computer on the Web, then first of all you need to find the DNS server that stores the information you need. In this case, a whole chain of servers can be involved in the search for information. The operation of DNS servers can be explained using the example shown in Fig. eleven .

Let's assume that the DNS server you've accessed (indicated as DNS1 in Figure 11) doesn't have necessary information. DNS1 will start looking up the IP address by contacting one of the root DNS servers. Root DNS servers know the IP addresses of all DNS servers responsible for top-level domain names (COM, EDU, GOV, INT, MIL, NET, ORG, etc.).

For example, your DNS1 server might query the root DNS server for an address. If the root server doesn't know this address, it might respond with "I don't know the IP address for http://www.pc.dpt1.company.com/ , but I can provide the DNS server's COM IP address."

Your DNS then sends a query to the COM DNS asking for the IP address it is looking up. This happens until a DNS server is found that will provide the necessary information.

One of the reasons a system works reliably is because of its redundancy. There are many DNS servers at every level, so if one of them can't provide an answer, there's probably another that has the information you need. Another technology that makes searching faster is the caching system. Once the DNS server makes a request, it caches the resulting IP address. Once having made a request to the root DNS (root DNS) and received DNS server address serving COM domains, next time it will no longer have to re-access similar request. This caching happens with each request, which gradually optimizes the speed of the system. Even though the operation of the DNS server is not visible to users, these servers perform billions of requests every day, supporting the work of millions of users.

ComputerPress 5 "2002

Data transfer methods over communication networks.

Currently, there are a large number of ways to transfer data. But in all methods, data transmission occurs on the principle of electrical signals. electrical signals is, translating into computer language, bits , which are digital or analog signals that turn into electrical impulses.

The totality of all types of data transmission is called data link. It includes such means of data transmission as: Internet networks, fixed lines, points of data reception and transmission. Data transmission channels are divided into two types: analog and discrete.
The main difference is that analog type is a continuous signal, and discrete, in turn, is a discontinuous data stream.

To provide best performance all devices work with devices in a discrete form. In discrete form, apply digital codes which are converted into electrical signals. And for the transfer of discrete data using an analog signal, it is required modulation discrete signal.

When information is used on the device, inverse transformation signal. The inverse signal transformation is called demodulation. Thus, there are two signal conversion processes: modulation and demodulation. In the process of modulation, information is a sinusoidal signal with a certain frequency.

The following are used to transform the data. modulation methods:
1. Data amplitude modulation;
2. Frequency modulation data;
3. Phase modulation of data.

To transmit discrete type data over a digital channel, a system is used coding. Basically, there are two types of coding.
1. Potential coding;
2. Pulse coding.

It is worth noting that the coding methods presented above are used on high-quality channels of information transmission. And it is wiser to resort to modulation only when signal distortion occurs during data transmission.

In most cases, modulation is used in working with large information networks. Since most of the information is transmitted via analog line. This is due to the fact that these lines were developed long before the advent of digital signals.

Also each kind of channel has its own way data synchronization. There are two main types of data synchronization: asynchronous and synchronous . Synchronization is used to accurately transfer data from source to destination.

Synchronization requires additional hardware. For example, to perform the synchronization process, an additional line is needed to transmit clock pulses to the communication channel. With the help of synchronization, uninterrupted and clear data transfer is carried out. The data transfer process begins with the appearance of clock pulses.

The main feature of asynchronous data transfer is that an additional communication channel is not required. AT this type when transmitting, bytes are used that accompany the transmitted byte of information.

Three main methods are used to exchange data between computer networks. information transfer method:

1. Simplex (unidirectional);
2. Half duplex;
3. Duplex (bidirectional).

Before submitting information to computer network, the sender divides the information into small blocks, which are most often called data packets. At the final destination, all packets are assembled into a single sequential list. Then there is a process of converting all parts into a single source material.

To work correctly, the data packet must contain information such as:

Additional operations to increase the efficiency of the communication channel.
There are three types computer system switching:
1. Channel switching;
2. Packet switching;
3. Message switching.
Circuit switching serves to create a continuous channel from series-connected lines. After this channel formed, all information and files can be transferred to high speed.
Message switching serves to work with mail files and servers. This operation includes a number of possibilities such as: transmission, reception, storage. A large number of messages are usually transmitted in blocks. When sending a group of messages, the block passes from one communication node to another and eventually reaches the addressee. If a block transmission error occurs (communication failure, technical problems, etc.), then the entire block of messages will begin to be transmitted again. Until the entire block of messages reaches the recipient, it will be impossible to make a new transmission.

Digital data communication is a physical process in which data is transferred as signals between points. Data is transmitted over certain channels in the form of telecommunications.

Such channels can be: FOCL, copper wires, as well as wireless channels. Data transmission on the Internet can be digital and analog.

If analog communication is the transmission of a constantly changing signal, then digital communication is a continuous transmission of messages (a sequence of pulses, a set of waves). Such modulation is carried out using modem equipment.

Data transfer to the Internet

Today it is simply impossible to imagine any modern office without the Internet. But what can he be? Available anywhere or fixed? Or maybe both of these options? In each of these cases, the Internet must have high speed and traffic, be available, and work without failures.

The transmitted information can be in the form of a digital message that comes from the source itself (keyboard, computer).

Also, data transmission over a local network can be carried out in the form of an analog signal. In its role is the video signal, phone call. All of them are digitized into a special bit stream. For this, a special pulse-coding modulator or an analog-to-digital converter is used.

Encoding and decoding of the same source is performed using a codec or specially designed encoding equipment.

Types of data transfer

There are two types of information transfer in telecommunications:

• Sequential. In this case, the transmission of information in the form of characters and other data objects occurs in serial mode. These digital data networks send bits over a single wire, optical path, or frequency. Concerning this process requires less time to process the signal itself, and the transmission rate itself is greater. There is also less chance of error. A serial network can also be used over longer distances. This is due to the easy transmission of the parity bit and digit.


• Parallel. This is the simultaneous transmission of information (signal elements of one character). Application a large number wires in digital communications helps to transmit several bits at the same time. All this allows to achieve a high speed of information transfer. This method used inside the computer itself (in internal data buses, for example). The only drawback here is the "skew". It is due to the fact that the wires may differ from each other in their characteristics. That is why one bit can come a little earlier than the other. And this, in turn, negatively affects the integrity of the message itself, damaging it.

According to the principle of switching networks can be:

• Packet switched. All information in this case is transmitted in small parcels. They are also called packets, the switching of which occurs independently. Most of the computer networks at the present time. But to work here you need more sophisticated equipment.


• With circuit switching. A special channel (logical or physical) is allocated for transmission between devices. Information is transmitted continuously over it.

Data transmission over the electrical network

The use of a 220 volt network for transmitting information has long been of interest to many developers. Even some 15 years ago, such an idea caused only a smile. But today, data transmission over a 220 volt network is not surprising. It has high chances and prospects for great commercial success.

The most important advantage of this method of information transfer is the absence of the need for laying cables and performing installation work. After all, there is electricity in absolutely every home.

For developers, the most promising areas for using such communications are systems for remote collection of information, for example, meter readings, security systems and smart House and much more.

Unfortunately, even low-speed data transfer over a 220v network alternating current could not be widely used in our country. This is due to the rather low quality of power communications, as well as the low popularity of modems for such transmission in the modern market.

Such devices are implemented on the basis of microcontrollers. This makes it possible at the software level to resolve any issues that arise regarding the information transfer protocol, equipment addressing, checking the quality of communication, and much more.

But in practice, a rather primitive task may arise - this is the inclusion and disconnection of one load without breaking the supply line itself. A special transmitter can solve it.

At present, there are already many adapters that allow you to organize a local network through a regular 220-volt home outlet. It is quite easy and simple to do this. You just need to plug in such an adapter, which can become a point WiFi access, or work through the RJ-45 connector. The information transfer rate in this case can reach up to 95 Mbps.

When using one phase, it is possible to transfer data not only within one room, but also to a neighboring apartment or office space. And most importantly - you will not need to lay an Internet cable.

Increasing the performance of data networks

At the present time, the market offers just a huge range of equipment with which you can effectively upgrade these networks.

Realizing the fact that the current levels of the data transmission network no longer suit many companies, the developers of various technological solutions offer users to use several inexpensive and original solutions. They can significantly increase throughput information transmission networks.

What applies here? One of these innovations is the use of duplex data transmission mode in the local Ethernet networks. Replacing just network adapter, it is possible to double the performance of the selected segments of the network itself.

During full duplex operation, each network hardware capable of simultaneously receiving and transmitting information over a twisted pair cable.

The only limitation here is the fact that you can only connect one network device to each of the hub ports. All this narrows the scope of this equipment. You can only create high-performance sections of the network itself between the server and the switch, for example.

The peculiarities of this innovation include the fact that there is no need to track collisions. This is just one way to modernize the information transmission network.

Data transmission technologies at the exhibition

Many other innovations and Hi-tech in this industry, you can find out at the international exhibition "Communication". It takes place in the large exhibition complex of our country, Expocentre Fairgrounds. Expocentre is located almost in the center of Moscow, near the Vystavochnaya metro station.

Exhibition "Communication" be able to tell potential target audience about novelties in the world of communication. It is here that leading experts in this industry from all over the world gather in one place. The conferences, congresses, symposiums, round tables and master classes held here set the vector for the development of this field of activity for the coming year.

The exhibition will definitely showcase modern technologies data transmission.

Information is a set of ones and zeros, so the task is to accurately transmit a certain sequence of these ones and zeros from point A to point B, from the receiver to the transmitter.

This happens either along the wire along which it goes electrical signal, (or a light signal in a fiber optic cable), or in the wireless case, the same signal is transmitted using radio waves.

To transmit a sequence of ones and zeros, you just need to agree on which signal will mean one and which zero.

There can be as many kinds of such modulations as there are properties of radio waves.

• Waves have amplitude. Great, we can use the change in the amplitude of the carrier wave to encode our zeros and ones - this is amplitude modulation, in which case the signal amplitude for transmitting a zero can be (for example) half as much as for a one.
• Waves have a frequency. Changing the frequency can also be used - this will already be frequency modulation, such modulation similarly represents a logical unit with an interval with a higher frequency than zero.
• Coding using changes in the phase of the carrier wave - phase modulation.
  So, you are talking on the phone, the sound enters the microphone, then the converter and the transmitter, the transmitter emits radio waves modulated, that is, changed so that they carry a certain signal, in the case of a telephone, an audio signal.

In the receiver antenna, which stands on the nearest house / tower, under the influence of radio waves, electrical oscillations of the same frequency arise as that of the radio wave, the receiver receives the signal, and then a bunch of receiver transmitter converters and wires between them come into play ...

The principle is the same as that of the radio, it is practically the same thing. To transmit information, electromagnetic waves of radio frequencies (that is, with a very long wavelength) are used. Some characteristic (amplitude or frequency) is selected for the wave. Then there is the so-called modulation. Roughly speaking (very simplified) in the case mobile communications the characteristic of the original wave that carries the signal is matched with the characteristic of the acoustic wave, that is, in fact, using the information contained in the original wave, your phone creates sound waves that your ears can perceive.

Let the variable parameter of the carrier signal wave be the frequency, for example. On the fingers: here the frequency is n Hz, here m Hz, then these frequencies correspond to the frequencies of the sound wave, and the vibrator in the phone already creates the most sound waves.

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AT electronic devices there are ADCs. And CAP. The first converts the analog signal (sound) to digital, and the second vice versa. The moment of working with digital is modulation. There is also the Kotelnikov theorem, which says that any signal can be represented as the sum of an array of numbers from special function sinc. Basically, it is already sharpened in the software. To smooth the signal or suppress flickering interference, the Fourier transform is used, and the search for the maximum signal / (noise + interference) ratio is used. There is also the criterion of maximum and minimum (the meaning is simply in relation to what we consider). Smoothing - iterative join i-th values digits (digital signal values, that is, the usual function, such as sine) with a certain step h. Less than h, more than i - smoothing is better. But slower work algorithm.

Everyone writes about telephone conversations, half of all write in semi-professional "slang" ... They asked - how for absolute zeros in this ... Eh ... Although my answer will be at the very bottom, and no one will reach it, I consider it my sacred duty to tell :D

We have already talked about telephony here, but not about bluetooth and Wi-Fi. And it's pretty interesting there. The technology is the same here and there: radio waves of a certain range are used (everything is strictly regulated). Device A takes the information, dances over it with a tambourine, converts it to 1010001, for example, and sends it by radio waves, and device B converts the radio waves into 1010001, dances back with a tambourine and receives the original information. And now some details in a fun and understandable language:

Alice went to Bob's cafe (your phone ended up with you in a cafe with Wi-Fi or at a friend's house). She turned off the music, took off her headphones (you turned on the Wi-Fi on the phone), and immediately heard Bob from the counter yelling at the whole cafe so that you could hear on the street:

My name is Bob wifi network"Bob"), I'm around (Signal strength: excellent), after coffee I'm still pinned (Baud rate: 24.3 Mbps), I use protection (Security: WPA2 PSK) and don't let strangers (Password protected).

"Some kind of preoccupied moron ... Well, anything is better than nobody," Alice thought and said hello (connecting to Wi-Fi, your phone first of all appears).

Bob looked at her, squinted suspiciously and asked (enter password): "We haven't met before, what's wrong?"

“It’s somehow too rude for a seller in a cafe ...”, Alice noted to herself, but did not become rude in response, but simply said in an offended tone that she had come in to buy coffee with a donut.

Oh, please forgive me! I've had so few BUYER visitors lately, mostly only school kids come to gawk. Yes, and the day as a whole is bad, so it fell off by accident ... For God's sake, don't take it to heart, sit down, I'll do everything right now. By the way, here is our discount card for you!

(After checking the password, if everything is correct, the router gives your phone an ID (like hanging a sticker on your forehead - it will recognize you at a glance), and then it says the encryption key of the transmitted information)

Many people think of the transmission of information by radio waves as "From point A to point B. In a straight line." In fact, the router sends a signal in all directions. Your phone, being "in the affected area" catches it and also answers in all directions. The router picks up a signal, etc. In this regard (there are no several direct connections, but just a huge cloud of mixed radio waves), all devices that send information each time introduce themselves, name the addressee, and only then say the information.

That is, both Alice and Bob will always yell at the top of their voices (even if next to each other) something like "Alice to Bobu [lyrashubvloubtslo (encrypted information)]", "Bob to Alice [ftallk]", "Bob Everyone [My name is Bob (and hereinafter)]", "Bob Sare [aoyoaroaoa]".

Bluetooth and telephony work in the same way, the protocols are just different (the rules by which the parties introduce themselves, agree and interact in general).

Briefly for non-professionals:
1) Signal transmission through the air (without wires) is possible due to the presence of such a physical phenomenon as electromagnetic waves, or, in short, radio waves. (Actually, even life is impossible without them - this is one of the foundations of nature). Mankind more than 100 years ago learned to use radio waves to transmit information.
2) It is very difficult and long to explain how it happens in detail, although some have tried here. Well, I'll try it too. Digital signals (zeros and ones) are encoded, encrypted and converted in a special way. Redundant information is removed from a set of numbers (for example, there is no point in transmitting many zeros or ones in a row, you can only transmit information about how many there are), then they are mixed in a special way and a little redundant information is added - this is to be able to recover lost data (transmission errors inevitable), then they are modulated. In the modulator, a certain set of units and numbers is assigned a certain state of the radio wave (most often this is the state of phase and amplitude). The smaller the sequence of numbers we encode, the greater the noise immunity, but the smaller amount of information can be transmitted per unit of time (that is, the information transfer rate will be lower). Then the signal is transferred to the desired frequency and sent to the air. At the receiver, the reverse conversion takes place. In reality, for different information transfer protocols, their own additional troubles are added: encryption, protective coding, often the modulated signal is remodulated again (hierarchical modulations). And all in order to increase the speed and quality of information transfer. The more problems, the higher the price of devices, but when some kind of information transfer protocol becomes massive and standard, the price of chips begins to fall, and devices become cheaper. So Wi-max was not really launched - the engineers of various companies could not agree on standardization, and LTE quickly went to the masses.
The difference between the transmission of digital signals from analog ones is also that digital ones are transmitted in packets. This allows the receiver and transmitter to work on the same frequency in turn, as well as distribute the signal among several users at the same time so that they usually do not notice it. Some protocols allow several different transmitters to work on the same frequency, and modulation methods "cope" with high noise and multipath reception problems (this is when several re-reflected copies of one radio wave hit the receiver, which is especially typical for cities).
Analogue signals (picture and sound) before transmission over digital channels connections are preliminarily digitized, that is, they are translated into a sequence of zeros and ones, which, by the way, are also "mocked": they remove unnecessary information, encode from errors, etc.
Digital Methods transmission of information allows us to more efficiently and economically use a limited natural resource - the radio frequency spectrum (the totality of all possible radio waves), but, you know (let's cry), if aliens ever detect our digital signals, they are unlikely to decode and understand them - very much everything "twisted". For the same reason, we most likely will not analyze their signals.

They talked about the basic principles of transmission here (DAC, ADC, coding, radio waves, modulation and other bells and whistles of radio physics and radio engineering), but why is transmission possible?
If in general it is clear how information is transmitted over a conventional wire (let's say an electrical signal through a SWB cable), then the propagation of radio waves is a process that largely depends on many parameters of the medium and the configuration of the wave itself (frequency / wavelength).
For example, the transmission of information in fiber optic networks is possible due to the phenomenon of total internal reflection of light (light, as we know, is partly a wave).

Some waves propagate (roughly speaking) directly from the source to the receiver. This is the so-called line of sight. Here we will add television and the mobile communications mentioned in the question. Well, everyone's favorite Wi-Fi. The radio waves used in them belong to the VHF range (ultra-short waves), and therefore to the microwave (extra high frequencies).
What determines the possibility of extending this range? Again, from the presence of obstacles. Various obstacles (walls, ceilings, furniture, metal doors, etc.) located between Wi-Fi and devices may partially or significantly reflect/absorb radio signals, resulting in partial or complete signal loss.

In cities with high-rise buildings, buildings are the main obstacle to the radio signal. The presence of solid walls (concrete + reinforcement), sheet metal, plaster on the walls, steel frames, etc. affects the quality of the radio signal and can significantly degrade the performance of Wi-Fi devices.

Why is this happening? We open a school physics textbook and find the phenomenon of diffraction, the main condition of which is the commensurability of the wavelength with the size of the obstacles. For the same 4g, the wavelength is 1 cm to 10 cm (and now let's estimate the height and length of the walls of a five-story building). Therefore, they try to place mobile communication towers above city buildings so that the waves not only go around obstacles (diffraction), but literally fall on our heads.

But don't forget about signal strength! A low-power signal is more likely to fall into oblivion than a powerful one.