home Comp. literacy Software and hardware components of the network. Software and hardware components of a computer network. Main software and hardware components of the network

Software and hardware components of the network. Software and hardware components of a computer network. Main software and hardware components of the network

Along with offline work a significant increase in the efficiency of using computers can be achieved by combining them into computer networks (network).

A computer network in the broad sense of the word is understood as any set of computers interconnected by communication channels for data transmission.

There are a number of good reasons for networking computers together. First, resource sharing allows multiple computers or other devices to share access to a single disk (file server), CD-ROM drive, tape drive, printers, plotters, scanners, and other equipment, reducing the cost per individual user.

Secondly, apart from sharing expensive peripherals, it is possible to similarly use network versions of application software. Thirdly, computer networks provide new forms of user interaction in the same team, for example, when working on a common project.

Fourthly, it becomes possible to use common means of communication between various application systems (communication services, data and video data transmission, speech, etc.). Of particular importance is the organization of distributed data processing. In the case of centralized storage of information, the processes of ensuring its integrity, as well as backup, are greatly simplified.

2. Main software and hardware components of the network

Computer network is a complex set of interconnected and coordinated software and hardware components.

Studying the network as a whole requires knowledge of the principles of operation of its individual elements:

Computers;

Communication equipment;

operating systems;

network applications.

The whole complex of software and hardware of the network can be described by a multilayer model. At the heart of any network lies the hardware layer of standardized computer platforms, i.e. the system of the end user of the network, which can be a computer or a terminal device (any input/output or information display device). Computers at the nodes of a network are sometimes referred to as host machines or simply hosts.

At present, computers of various classes are widely and successfully used in networks - from personal computers to mainframes and supercomputers. The set of computers in the network should correspond to the set of various tasks solved by the network.

The second layer is the communications equipment. Although computers are central to the processing of data in networks, communication devices have recently begun to play an equally important role.

Cabling, repeaters, bridges, switches, routers, and modular hubs have evolved from ancillary network components to being essential, along with computers and system software, both in terms of impact on network performance and cost. Today, a communications device can be a complex, dedicated multiprocessor that needs to be configured, optimized, and administered.

When designing a network, it is important to consider how easily a given operating system can interact with other operating systems on the network, how secure and secure data it is, to what extent it allows you to increase the number of users, whether it can be transferred to a different type of computer, and many other considerations.

The topmost layer of network facilities are various network applications, such as network databases, mail systems, data archiving tools, teamwork automation systems, etc.

It is important to be aware of the range of possibilities provided by applications for various areas applications, as well as how compatible they are with other network applications and operating systems.

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Computer networks

1.1.3. Main software and hardware components of the network

Even as a result of a rather superficial examination of network operation, it becomes clear that a computer network is a complex set of interconnected and coordinated software and hardware components. Studying the network as a whole requires knowledge of the principles of operation of its individual elements:

computers;
communication equipment;
operating systems;
network applications.

The whole complex of software and hardware of the network can be described by a multilayer model. At the heart of any network is the hardware layer of standardized computer platforms. At present, computers of various classes are widely and successfully used in networks - from personal computers to mainframes and supercomputers. The set of computers in the network should correspond to the set of various tasks solved by the network.

The second layer is the communications equipment. Although computers are central to the processing of data in networks, communication devices have recently begun to play an equally important role. Cabling, repeaters, bridges, switches, routers, and modular hubs have evolved from ancillary network components to being essential, along with computers and system software, both in terms of impact on network performance and cost. Today, a communications device can be a complex, dedicated multiprocessor that needs to be configured, optimized, and administered. Learning how communication equipment works requires familiarity with a large number of protocols used in both local and wide area networks.

The third layer that forms the software platform of the network is operating systems (OS). The efficiency of the entire network depends on what concepts of managing local and distributed resources are the basis of the network operating system. When designing a network, it is important to consider how easily a given operating system can interact with other operating systems on the network, how secure and secure data it is, to what extent it allows you to increase the number of users, whether it can be transferred to a different type of computer, and many other considerations.

The topmost layer of networking tools are various networking applications such as network databases, mail systems, data archiving tools, collaboration automation systems, etc. It is very important to understand the range of capabilities provided by applications for various applications, as well as to know how they are compatible with other network applications and operating systems.

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computers;

communication equipment;

operating systems;

network applications.

The simplest case of interaction between two computers

In the very simple case The interaction of computers can be implemented using the same tools that are used to interact with a computer with peripherals, for example, through a serial RS-232C interface. In contrast to the interaction of a computer with peripheral device, when the program works, as a rule, only on one side - from the side of the computer, in this case there is an interaction between two programs running on each of the computers.

A program running on one computer cannot directly access the resources of another computer - its disks, files, printer. She can only "ask" for this program running on the computer that owns these resources. These "requests" are expressed as messages transmitted over communication channels between computers. Messages can contain not only commands to perform certain actions, but also informational data itself (for example, the contents of a certain file).

Consider the case when a user working with text editor on personal computer A, you need to read part of some file located on the disk personal computer B (Fig. 4). Suppose we have connected these computers via a communication cable through COM ports, which, as you know, implement the RS-232C interface (such a connection is often called a null modem connection). Let, for definiteness, computers operate under MS-DOS, although this is of no fundamental importance in this case.

Rice. four. Interaction of two computers

The COM port driver together with the COM port controller work in much the same way as in the case of interaction between the PU and the computer described above. However, in this case, the role of the control device of the PU is performed by the controller and driver of the COM port of another computer. Together they provide the transmission of one byte of information over the cable between computers. (In "real" LANs, these line transfer functions are handled by network adapters and their drivers.)

The driver of computer B periodically polls the sign of the completion of the reception, set by the controller when the data transfer is correctly performed, and when it appears, reads the received byte from the controller buffer into RAM, thereby making it available to the programs of computer B. In some cases, the driver is called asynchronously, by interrupts from the controller.

Thus, the programs of computers A and B have a means to transfer one byte of information. But the task considered in our example is much more complicated, since it is necessary to transfer not one byte, but a certain part of the given file. Any additional problems associated with this should be solved by programs at a higher level than the COM port drivers. For definiteness, we will call such programs of computers A and B application A and application B, respectively. So, application A must generate a request message for application B. The request must specify the file name, the type of operation (in this case, reading), the offset and the size of the file area containing the required data.

To transmit this message to computer B, application A calls the COM port driver, telling it the address in RAM where the driver finds the message and then passes it byte by byte to application B. Application B, having received the request, executes it, that is, reads the required area of the file from the disk using the local OS tools to the buffer area of its random access memory, and then, using the COM port driver, transmits the read data via a communication channel to computer A, where they get to application A.

The described functions of application A could be performed by the text editor program itself, but it is not very rational to include these functions in the composition of each application - text editors, graphic editors, database management systems and other applications that need access to files. It is much more profitable to create a special software module, which will perform the functions of generating request messages and receiving results for all applications on the computer. As mentioned earlier, such a service module is called a client. On the side of computer B, another module must work - a server that is constantly waiting for requests for remote access to files located on the disk of this computer. The server, having received a request from the network, accesses the local file and performs the specified actions with it, possibly with the participation of the local OS.

The software client and server perform system functions for servicing computer A application requests for remote access to computer B files. In order for computer B applications to use computer A files, the described scheme must be symmetrically supplemented with a client for computer B and a server for computer A.

The scheme of interaction between the client and server with applications and the operating system is shown in fig. 5. Despite the fact that we have considered a very simple scheme of hardware communication of computers, the functions of programs that provide access to remote files are very similar to the functions of the modules of a network operating system operating in a network with more complex hardware communications of computers.

Rice. 5. Interaction of software components when connecting two computers

very comfortable and useful feature client program is the ability to distinguish a request from remote file from a request to a local file. If the client program knows how to do this, then applications should not care what file they work with (local or remote), client program recognizes and redirects request to a remote machine. Hence the name often used for the client part of the network OS, - redirector. Sometimes the recognition functions are separated into a separate program module, in which case not the entire client part is called the redirector, but only this module.

Definition of a computer network

Lecture 7. Local and global computer networks.

Computing (computer) network- a complex system of software and hardware components interconnected with each other. Main functions of all kinds computer networks come down to the following:

1) ensuring the sharing of hardware and software resources of the network;

2) providing shared access to data resources.

Network hardware components include:

Computers (workstations and servers);

Communication equipment (cable systems, hubs, repeaters, routers, bridges, etc.).

Workstations are user computers connected to the network. By the presence of a local disk, two types of workstations are distinguished:

1) workstation with local disk– the operating system is loaded from this disk,

2) diskless workstation - the operating system is loaded from the disk of the network server, and the boot program is stored in the network adapter chip.

There are three main ways to connect to the network:

Direct connection to the network cable system through the network adapter card (this is the most reliable and fastest method, but is used only for networks concentrated in a small area),

Connecting the station through a dedicated (non-switched) line,

Connecting the station through a switched (for example, telephone) line.

Network server – a network computer for providing certain services to network users. The following groups of servers are often distinguished by their functions:

File server - large computer disk space, which is used for storing, archiving data, coordinating data changes performed by different users, data transfer.

Database server- a network computer that performs the functions of storing, processing and managing database files with the coordination of their sharing and delimitation of user access.

Server Reserve copy data- a device for creating, storing and restoring copies of data existing on network computers.

Applications server- a powerful computer that runs application programs of users at their request.

Main elements communication equipment serve:

1) repeaters(splitters, HUB), amplifying or regenerating the signal that came to it and relaying it to the inputs of other network segments. Combining different network segments with many computers, at the same time repeaters connect only two workstations;

2) switch(swich) - a device for combining network segments, but capable, unlike a repeater, of supporting simultaneous data exchange between several pairs of workstations from different segments;

3) router(router) - a device that connects networks of the same or different types using the same data exchange protocol. By analyzing the addresses of senders and recipients, routers send data along the optimally chosen route;

4) Gateway(gateway) - a device for organizing data exchange between networks with different data exchange protocols.

To software components include:

- network operating systems designed to manage the work computer networks,

- network applications – software complexes, which extend the capabilities of network operating systems ( email programs, systems of collective work, etc.).

Combining computers into one system allows you to have access to shared resources:

equipment, for example, printers, disks, which saves money and time allocated for device maintenance;
programs and data, which provides ease of maintenance and reduces the cost of purchasing software;
information services.

Combining the resources of computers involved in the processing, transmission, storage of information allows you to increase the speed of these processes, reliability, organize the interaction of participants in joint data processing.

In this case, the user gets the opportunity to work with equipment, network services and application processes located on other computers.

An important advantage of combining computers is the transfer of information from one computer to another located at any remote distance from each other.

The network equipment operates under the control of system and application software.

Computers on a network communicate with each other using hardware and network software. The main hardware components of the network form nodes - workstations and servers. Workstations are computers installed at users' workstations and equipped with specialized software for a specific subject area. Servers, as a rule, are sufficiently powerful computers, the functions of which are to provide all the processes for managing the network.

To connect the nodes, communication systems are used, including communication lines, transmitting equipment, and various communication equipment.

7.1.2. Network hardware components

Main hardware components

The main hardware components of a computer network (Fig. 1) are:

Servers;
Workstations;
Channels (lines) of communication;
Data transmission equipment.

Rice. 1. The main hardware components of a computer network

Servers and workstations

Servers are enough powerful computers, as they must provide a high speed of data transfer and request processing. The server is a source of network resources, a computer with a large capacity of RAM, large hard drives and additional storage media. There can be many servers in the network.

The server runs under the control of a network operating system, which provides simultaneous access of network users to the data located on it. The requirements for the server are determined by the tasks that are assigned to it in a particular network. The success of the server tasks depends on the installed software. Servers can perform data storage, mail forwarding, database management, remote job processing, web page access, job printing, and a number of other functions that network users may need.

A computer that is connected to a network and has access to its resources is called workstation.

Server roles and workstation may vary across networks.

For example, a file server performs the following functions:

data storage;
data archiving;
synchronization of data changes by different users;
data transfer.

The file server receives a file access request from the workstation. The file is sent to the workstation. The user at the workstation processes the data. The file is then returned to the server.

There is another division of roles between computers on a network, such as a Client/Server network.

Client name of the workstation on which the software, which provides a solution to the problems formed in the course of the user's work.

In the process of processing data, the client forms a request to the server to perform various tasks: forwarding a message, browsing web pages, etc.

The server fulfills the request from the client. The results of the request are sent to the client. Some tasks can be performed on the client side. Communication, request processing, and data processing continue between the server and client until they complete the task. Data processing can be performed by both the server and the client.

The server provides storage of public data, organizes access to this data and transmits data to the client.

The client processes the received data and presents the processing results in a user-friendly way.

Channels of connection

Link(or communication line) - the physical medium through which the information signals of the data transmission equipment are transmitted.

The communication medium can be based on various physical principles of operation. For example, it can be a cable and connectors. The physical medium for data transmission can be the earth's atmosphere or outer space through which information signals propagate.

In telecommunications systems, data is transmitted using electric current, radio signals or light signals. All these physical processes are oscillations of the electromagnetic field of various frequencies and nature. The main characteristic of physical channels is baud rate, measured in bits (Kbps, Mbps) per second.

Depending on the physical environment, communication lines can be classified into the following groups: wired lines, cable lines, terrestrial and satellite radio channels.

wire lines- these are unshielded wires laid above the ground through the air. They mainly carry telephone or telegraph signals, but they can also be used to transmit data sent from one computer to another. The data transfer rate on such lines is measured in tens of Kbps.

cable lines- this is a set of conductors insulated with different layers. Basically, fiber-optic cables and cables based on copper wires are used: twisted pair (speed from 100 Mbps to 1 Gbps) and coaxial cable (speed - tens of Mbps). Cables are used for internal and external wiring. External cables are divided into underground, underwater and overhead cables.

The best quality cable is fiber optic cable. It consists of flexible glass fibers through which light signals propagate. It provides signal transmission with very high speed(up to 10 Gbps and above). This type of cable is reliable, as it protects data well from external interference.

Radio channels of terrestrial and satellite communications, are a channel formed between the transmitter and receiver of radio waves. Radio channels differ in the frequency ranges used and the channel range. They provide different data transfer rates. Satellite channels and radio communications are used in cases where a cable channel cannot be used, for example, in sparsely populated areas, to communicate with users of a mobile radio network.

In computer networks, all the described types of physical data transmission media are used, but fiber-optic cable seems to be the most promising. It has already begun to be widely used as backbones of territorial, city networks, and is also used in high-speed sections of local networks.

Data communication equipment

Data transmission equipment is used for direct connection of computers to the communication line. It includes data transmission devices that are responsible for transmitting information to the physical medium (communication line) and receiving data from it: a network card (adapter), modems, devices for connecting to digital channels, ISBN network terminal adapters, bridges, routers, gateways, etc.

Network card (adapter) specifies the address of the computer. A computer on the network must be correctly identified, that is, its address must be unique. Therefore, manufacturers network cards allocate a number of different addresses that do not match.

Rice. 2. Network adapter(map)

Modems- devices for converting computer digital signals into analog signals telephone line and vice versa. The common data transfer rate is 56 Kbps.

Network terminal adaptersISBN(Integrated Services Digital Network) – telephone network with service integration. The basis of such a network is digital signal processing. The subscriber is provided with two channels for voice communication and data transmission at a speed of 64 Kbps.

Digital connection devices designed to improve the quality of signals and create a permanent composite channel between two network subscribers. They are mainly used on long-distance communication lines.

Bridges- devices connecting two networks and using the same data transmission methods.

Routers or routers - devices connecting networks different type but using the same operating system.

Gateways- devices that allow organizing data exchange between two networks using different rules of interaction, for example, connecting a local area network to a global one.

Bridges, routers, gateways can operate both in the mode of full allocation of functions, and in the mode of combining them with the functions of a computer network workstation.

Data transmission equipment also includes:

Amplifiers - devices that increase the power of signals;
Regenerators that restore the shape of pulse signals distorted during transmission over long distances;
Switches - equipment for creating a long-term continuous composite channel between two subscribers of a network from segments of the physical medium with amplifiers.

A network invisible to users with intermediate equipment of the communication channel forms complex network, which is called the primary network. It does not support any services for the user, but only serves as the basis for building other networks.

7.1.3. Types of networks

Computer networks are usually classified according to different criteria. The most common is the classification by size depending on the territory occupied (Fig. 3):

local computer network - LAN (Local Area Network);
regional computer network - MAN (M e tropolitan Area Network);
global computer network - WAN (Wide Area Network).

Local computing network unites subscribers located on short distances. Typically, a local area network is used to solve the problems of individual enterprises, for example, the local area network of a clinic, store or educational institution. Local network resources are not available to users on other networks.

Regionalcomputernetworks connect nodes at considerable distances from each other. They may include local networks and other subscribers within big city, economic region, individual country. Usually, the distances between subscribers of a regional computer network are tens - hundreds of kilometers. An example of such a network is the regional network of regional libraries.

global computernetworks combine the resources of computers remote over long distances. The global computer network unites subscribers located in different countries on different continents. Interaction between subscribers of such a network can be carried out on the basis of telephone lines, radio communications and satellite communications systems.

Rice. 3. Combining computer networks of various types

Global Computing Networks Will Solve the Unification Problem information resources of all mankind and the organization of access to these resources.

Networks have a hierarchical organization (Fig. 3). They can enter one into another, uniting local networks into regional ones, and regional ones into global ones. Global Computing Networks include regional networks and can connect other global networks. An example of such a combination of networks is the Internet, where network users have a single interface for accessing the resources of global networks. Currently widespread corporate networks, which, on the one hand, solve the problems of local networks, connecting computers for the exchange of intracorporate information, on the other hand, they use global network technologies. Corporate network- a network of mixed topology, which includes several local area networks. It unites the branches of the corporation and is the property of the enterprise. A corporate network that uses unified network technologies, unified interaction methods and applications for accessing global networks and for solving internal problems is called Intranet.

7.1.4. Topologies of computer networks

The topology of networks is understood as the configuration of the physical links of the network. There are several types of topologies: fully connected, ring, star, bus, mixed.

Fully connected topology involves the interconnection of each computer (Fig. 4). A fully meshed topology is rarely used, since it requires a separate physical channel for each pair of computers.

Rice. 4. Fully connected network topology

Rice. 5. Ring network topology

Ring topology(Fig. 5) provides data transfer around the ring from one computer to another. Any pair of computers is connected in this configuration in two ways - clockwise and counterclockwise. However, in such a network, the failure of one computer breaks the communication channel between other computers.

Star topology(Fig. 6) is formed by connecting each computer to a common central device, which can be a computer, repeater or router, hub. The star topology is currently the most common.

Rice. 6. Star network topology

Bus topology(Fig. 7) ensures the dissemination of information over a common bus. If this is a wireless connection, then the radio environment plays the role of a common bus instead of a cable. Information transmitted over the bus is available simultaneously to all computers connected to it. The implementation of this topology is inexpensive and easy to scale. The disadvantage is the unreliability of the cable.

Rice. 7. Bus topology

Mixed topology– use of all topologies in one network. Typical topologies (star, ring, bus) are used in small networks. In large networks, one can distinguish separate sections, which have an arbitrarily chosen typical topology. Therefore, the topology of large networks can be called mixed. Figure 8 schematically shows a section of a network with a mixed topology.

Rice. 8. Mixed network topology

7.1.5. Types of switching in networks

Messages can be transmitted from computer to computer not directly, but in transit - through special nodes.

If the network topology is not fully connected, then data exchange between an arbitrary pair of end nodes (subscribers) should generally go through transit nodes.

The sequence of transit nodes on the way from the sender to the recipient is called route.

The connection of end nodes through a network of transit nodes is called switching.

At the same time, switching tasks are solved such as:

definition information flows for which you want to exchange data;
formation of addresses of workstations;
determination of routes for flows and selection of the optimal one;
recognition of flows and their switching at each transit node.

Information flow forms a sequence of bytes, united by a set of common features. A sign can be computer addresses.

Switch node- this is special device or a general purpose computer with a built-in software switching mechanism (softswitch). By type of switching, networks are distinguished as follows:

circuit-switched network;
packet-switched network;
message switched network.

Circuit Switched Networks originate from the first telephone networks. Circuit switching is the process of organizing the connection of a sequence of channels between a pair of subscriber systems.

Circuit switching forms a continuous network between end nodes. physical channel from intermediate channel sections connected in series by switches with equal data rates. A connection is established between the end nodes and data transfer begins. At the end of the transmission, the channel is terminated. Switches are used for network switching.

Figure 9 shows a circuit switched network. Switching nodes (UK1–UK5) serve the workstations connected to them. (PC1–PC5). For example, to transfer data from workstation 1 (PC1) to workstation 2 (PC2), a channel must be established between nodes 1 (UC1) and 4 (UC4). This channel can be established along the routes UK1-UK3-UK2-UK4 or UK1-UK5-UK4. To organize data transfer, RS1 sends a request to establish a connection to the switching node (UC1) indicating the destination address (RS2). The switching node (ST1) must choose the route for the formation of a composite channel, and then transfer the request to the next node, for example, ST3, and that one to the next one, until the request is transmitted from the node ST4 to RS2. If the request is accepted by the destination computer, then a response is sent source computer through an already established channel, for example, UK1-UK2-UK4. It is considered that the channel between PC1 and PC2 is established. After that, data can be sent through it. At the end of the data transfer, the channel is terminated.

Rice. 9. Switching network

Packet networks appeared as a result of experiments in global computer networks. Packet switching is a technology for delivering messages that are divided into portions (individual packets) for data transmission, which can be sent from source to destination by different routes. The specific route is chosen by the sending and receiving computers based on the availability of the connection and the amount of traffic.

Message-switched networks. This type of switching establishes a logical channel for transmitting a message from one computer to another through switching nodes. Each intermediate device on the path of this route receives the message, stores it locally until the next section of the link becomes free, and sends it to the next device as soon as the link becomes free.

7.1.6. Reference Model for Open Systems Interconnection

The emergence of networks in which different types of computers functioned led to the need to develop standards for the exchange of information. The functioning of computers in networks is possible due to the rules of interaction, called protocols. When information is transmitted, they interact at different levels.

Communications and processes in open networks occur according to the ISO OSI standard model, which describes the rules for the interaction of systems with an open architecture from various manufacturers.

ISO - International Standard Organization - International Organization of Standards.

OSI is an abbreviation that stands for two variants:

Open System Interconnection - Interaction of Open Systems - VOS;
Optimum Scale Integration - Information system with an optimal degree of integration.

The interaction is based on a set of structures, rules, and programs that ensure the processing of events in networks. These sets are called in the OSI model levels. Each layer is described by protocols (a set of transmission rules). In the OSI model, seven levels of interaction are distinguished to perform a certain set of exchange functions on each of them.

Level 1- physical. Describes the transfer binary information on the communication line: voltages, frequencies, the nature of the transmission medium. Protocols of this layer provide communication, reception and transmission of the bit stream.

Level 2- channel. Provides access to the medium, communication channel control, data transmission in blocks (frames). At this level, blocks are formed, the beginning and end of the frame in the bit stream is determined, the correctness of their transmission is checked, the presence and correction of errors.

Level 3- network. Provides a connection between any two points in the network. Routing takes place at this level, i.e. determination of the path along which data is transmitted through different communication lines, address processing.

At this level, the information is converted into packets for transmission to the destination. Data transfer occurs after the establishment of a virtual communication channel. After the data is transmitted, the channel is closed. Packets are transmitted over different physical routes, i.e. the channel is determined dynamically. The address is determined during connection establishment. Data can also be transmitted not only by packets, but also by other methods.

Widespread network layer protocol IP (Internet Protocol).

Level 4- transport. The task of the transport layer is to transfer information from one point of the network to another and ensure the quality of transportation. This level controls the data flow, the correctness of the transmission of blocks, the correctness of delivery to the destination, the sequence order, collects information from the blocks in its previous form. Can confirm receipt and correct delivery when transmitted by other methods.

The common transport protocol is TCP (Transmission Control Protocol). Often, network and transport layer protocols are collectively referred to as TCP / IP, meaning by this a whole family of protocols, because they implement internetworking technology.

TCP divides the transmitted information into several parts and numbers each part to restore their order when received. The TCP packet is placed inside the IP packet. Upon receipt, the IP packet is decompressed first, and then the TCP packet. The data is then collected according to the packet numbers.

Other standard protocols also operate at this level.

Level 5- session. Establishes, maintains, terminates connections. Coordinates interactions during a communication session: starts a session, ends it, restores crashed sessions. At this level, domain network names are converted to numbers and vice versa.

Level 6– representative (representation of data). Responsible for the syntax and semantics of the transmitted information, encryption, encoding and data compression. For example, at this stage, textual information, images are recoded, compressed, and decompressed.

Level 7- applied. Provides information transfer between programs. This layer connects the user to the network, enabling various services such as file transfer, electronic messages, browsing Internet information. The following protocols are used at this level: FTP (file transfer), HTTP (HyperText Transfer Protocol) – hypertext transfer protocol.

Each layer provides a service to the upper layer adjacent to it, receives a service from the lower layer adjacent to it, exchanges blocks of data to perform its tasks.

Interactions are carried out sequentially level by level. The transmitted information coming from the user must be processed first by the application (seventh) level of rules, then must be processed at the representative, then session, transport level. Then, sequentially, the information is processed by the network, link level and is transmitted to the physical environment of the network. After processing at the physical layer and transferring it to another computer, the information is processed in reverse order from the lower layers to the next, and finally, after the application layer of processing, it is received by the user.

The task of each level when transmitting information is to prepare data in accordance with the standard and transfer it to the next lower level. Upon receipt of information - to the next top.

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Just about the complex. Programs. Iron. Internet. Windows