Specify the main purpose of a computer network. Software and hardware components of computer networks Software hardware components of computer networks

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, which reduces the cost per individual user.

Secondly, apart from sharing expensive peripheral devices, it is possible to similarly use network versions of the 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.

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 network operating systems, 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 network tools are different 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.

Appointment and a brief description of main components of computer networks.

Computing network called a set of interconnected and distributed computers over a certain territory.

Computing network- a computer complex, including a geographically distributed system of computers and their terminals, combined into a single system.

According to the degree of geographical distribution, computer networks are divided into local, urban, corporate, global, etc.

The computer network consists of three components:

Data transmission network, including data transmission channels and switching facilities;

Computers connected by a data network;

Network software.

Computing network is a complex complex interconnected software and hardware components:

computers(host computers, network computers, workstations, servers) located in network nodes;

network operating system and application software managing computers;

communication equipment– equipment and data transmission channels with their accompanying peripheral devices; interface cards and devices (network cards, modems); routers and switching devices.

Software and hardware components of a computer network

computer network, network- a spatially distributed system of software and hardware components connected by computer communication lines.

Among the hardware computers and communication equipment can be distinguished. Software components consist of operating systems and network applications.

Currently, the network uses computers of various types and classes with different characteristics. It is the basis of any computer network. Computers and their characteristics determine the capabilities of a computer network. But recently, communication equipment (cable systems, repeaters, bridges, routers, etc.) has begun to play an equally important role. Some of these devices, given their complexity, cost, and other characteristics, can be called computers that solve highly specific tasks to ensure network performance.

For effective work networks are used special network OS(network OS), which, unlike personal operating systems, are designed to solve special tasks for managing work computer networks. Network operating systems are installed on dedicated computers.

Network Applications- it is applied software complexes, which expand the capabilities of network operating systems. Among them are email programs, systems of collective work, network databases, etc.

As the network operating system evolves, some functions of network applications become regular functions of the operating system.

All devices connected to the network can be divided into three functional groups:

1) workstations;

2) network servers;

3) communication nodes.

1) Workstation, workstation is a personal computer connected to a network on which a network user performs his work. Each work station handles its local files and uses its own operating system. But at the same time, network resources are available to the user.

There are three types of workstations:

Workstation with local disk,

diskless workstation,

Remote workstation.

On a workstation with a disk (hard or floppy), the operating system boots from this local disk. For a diskless station, the operating system is loaded from the disk of the file server. This possibility is provided by a special chip installed on the network adapter of the diskless station.

A remote workstation is a station that connects to a local network through telecommunication channels (for example, using a telephone network).

2) Network server, network server is a computer connected to a network and providing certain services to network users, such as storing public data, printing jobs, processing a query to a DBMS, remote processing of jobs, etc.

According to the functions performed, the following groups of servers can be distinguished.

File server, file server - a computer that stores the data of network users and provides users with access to this data. Typically, this computer has a large amount of disk space. The file server provides simultaneous user access to shared data.

The file server performs the following functions:

Data storage;

Data archiving;

Data transfer.

Database server, database server - a computer that performs the functions of storing, processing and managing database files (DB).

The database server performs the following functions:

Storage of databases, support of their integrity, completeness, relevance;

Receiving and processing queries to databases, as well as sending processing results to a workstation;

Coordination of data changes performed by different users;

Support for distributed databases, interaction with other database servers located elsewhere.

Application server, application server - a computer that is used to run user applications.

A communications server is a device or computer that provides users of a local network with transparent access to their serial ports input/output.

With the media server, you can create a shared modem by connecting it to one of the server's ports. The user, having connected to the communication server, can work with such a modem in the same way as if the modem was connected directly to the workstation.

An access server is a dedicated computer that allows you to perform remote job processing. Programs initiated from a remote workstation run on that server.

From the remote workstation, commands entered by the user from the keyboard are received, and the results of the task are returned.

Fax server, fax server - a device or computer that sends and receives fax messages for local network users.

Server Reserve copy data, backup server - a device or computer that solves the problem of creating, storing and restoring copies of data located on file servers and workstations. One of the network file servers can be used as such a server.

It should be noted that all the listed types of servers can operate on one computer dedicated for these purposes.

3) Communication nodes of the network include the following devices:

Repeaters;

Switches (bridges);

Routers;

The length of the network, the distance between stations are primarily determined by the physical characteristics of the transmission medium (coaxial cable, twisted pair, etc.). When transmitting data in any environment, signal attenuation occurs, which leads to a limitation of the distance. To overcome this limitation and expand the network, special devices are installed - repeaters, bridges and switches. The part of the network that does not include the expander is called the network segment.

Repeater, repeater - a device that amplifies or regenerates the signal that came to it. The repeater, having received a packet from one segment, transmits it to all the others. In this case, the repeater does not decouple the segments attached to it. At any moment in all segments connected by the repeater, data exchange is supported only between two stations.

Switch, switch, bridge, bridge is a device that, like a repeater, allows you to combine multiple segments. Unlike a repeater, a bridge decouples the segments attached to it, that is, it simultaneously supports several data exchange processes for each pair of stations of different segments.

router- a device that connects the networks of one or different types one communication protocol. The router analyzes the destination address and sends the data along the optimal route.

gateway- This is a device that allows you to organize the exchange of data between different network objects using different data exchange protocols.

The main hardware components of the network are as follows:

1. Subscriber systems: computers (workstations or clients and servers); printers; scanners, etc.

2. Network hardware: network adapters; concentrators (hubs); bridges; routers, etc.

3. Communication channels: cables; connectors; devices for transmitting and receiving data in wireless technologies.

The main software components of the network are as follows:

1. Network operating systems, where the most famous of them are: MS Windows; LANtastic; NetWare; Unix; Linux, etc.

2. Network software (Network Services): network client; LAN card; protocol; remote access service.

LAN (Local computer network) is a collection of computers, communication channels, network adapters running a network operating system and network software.

On a LAN, each PC is called a workstation, with the exception of one or more computers that are designed to act as servers. Each workstation and server has network cards (adapters) that are interconnected through physical channels. In addition to the local operating system, network software is activated on each workstation, allowing the station to communicate with the file server.

Computers included in the client LAN - server architecture, are divided into two types: workstations, or clients, intended for users, and servers, which are usually inaccessible to ordinary users and are designed to manage network resources.

Workstations

A workstation is a subscriber system specialized for solving certain tasks and using network resources. The workstation networking software includes the following services:

Client for networks;

File and Printer Access Service;

Network protocols for of this type networks;

network board;

Remote access controller.

The workstation is different from the usual standalone personal computer as follows:

The presence network card (network adapter) and communication channel;

Additional messages appear on the screen while the OS is loading, informing you that the network operating system is loading;

Before you begin, you must provide the network software with a username and password. This is called the network logon procedure;

After connecting to the LAN, additional network drives appear;

it becomes possible to use network equipment which may be located far from the workplace.

Network adapters

To connect a PC to a network, an interface device is required, which is called a network adapter, interface, module, or card. It is inserted into the slot motherboard. Network adapter cards are installed on each workstation and on the file server. The workstation sends a request through the network adapter to the file server and receives a response through the network adapter when the file server is ready.

Network adapters, together with network software, are able to recognize and handle errors that may occur due to electrical interference, collisions, or poor performance of the equipment.

Various types network adapters differ not only in methods of accessing the communication channel and protocols, but also in the following parameters:

Transmission speed;

Packet buffer size;

Tire type;

Bus speed;

Compatible with various microprocessors;

Using direct memory access (DMA);

Addressing I / O ports and interrupt requests;

connector design.

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) a workstation with a 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 – network computer to provide certain services network users. The following groups of servers are often distinguished by their functions:

File Server- a computer with a large amount of disk space, 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.

Data backup server- a device for creating, storing and restoring copies of data existing on network computers.

Applications server – powerful computer, on which application programs 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 operation of a network of computers,

- network applications- software packages that expand the capabilities of network operating systems (mail programs, teamwork systems, etc.).

The above components can be combined into a network different ways and means. According to the composition of their components, the methods of their connection, the scope of use and other features, networks can be divided into classes in such a way that the belonging of the described network to one or another class could quite fully characterize the properties and qualitative parameters of the network.

However, this kind of classification of networks is rather conditional. The most widespread today is the division of computer networks on the basis of territorial location. On this basis, networks are divided into three main classes:

LAN - local networks (Local Area Networks); ·
MAN - city networks (Metropolitan Area Networks). ·
WAN - global networks (Wide Area Networks);

Local area network (LAN) is communication system, which supports, within a building or some other limited area, one or more high-speed digital information transmission channels provided to connected devices for short-term exclusive use. The territories covered by the LA can vary significantly.
The length of communication lines for some networks can be no more than 1000 m, while other LANs are able to serve the whole city. Served territories can be both factories, ships, aircraft, and institutions, universities, colleges. Coaxial cables are typically used as the transmission medium, although twisted-pair and fiber optic networks are becoming more common, and wireless technology has also rapidly developed in recent years. local networks, which use one of three types of radiation: broadband radio signals, low-power microwave radiation (MW radiation), and infrared rays.
short distances between network nodes, the transmission medium used and the associated low probability of errors in the transmitted data make it possible to maintain high speeds exchange - from 1 Mbit / s to 100 Mbit / s (at present, there are already industrial designs of LANs with speeds of the order of 1 Gbit / s).

City networks typically cover a group of buildings and are implemented on fiber optic or broadband cables. According to their characteristics, they are intermediate between local and global networks. Recently, in connection with the laying of high-speed and reliable fiber-optic cables in urban and intercity areas, and new promising network protocols, for example, ATM (Asynchronous Transfer Mode - asynchronous transfer mode), which in the future can be used both in local and global networks.

Global networks, unlike local ones, as a rule, cover much larger territories and even most regions of the globe (an example is Internet). Currently, analog or digital wired channels are used as a transmission medium in global networks, as well as satellite channels communications (usually for communications between continents). Transfer rate limits (up to 28.8 Kbps on analog channels and up to 64 Kbps on user sites digital channels) and the relatively low reliability of analog channels, which requires the use of error detection and correction tools at the lower levels of the protocols, significantly reduce the speed of data exchange in global networks compared to local ones.
There are other classification features of computer networks. For example:

According to the sphere of operation, the networks can be divided into banking networks, networks of scientific institutions, university networks;

According to the form of functioning, commercial networks and free networks, corporate and public networks can be distinguished;

According to the nature of the implemented functions, the networks are subdivided into computational networks designed to solve control problems based on the computational processing of the initial information; informational, designed to obtain reference data at the request of users; mixed, in which computing and information functions are implemented;

According to the method of control, computer networks are divided into networks with decentralized, centralized and mixed control. In the first case, each computer that is part of the network includes a complete set software tools to coordinate network operations. Networks of this type are complex and quite expensive, since the operating systems of individual computers are developed with a focus on collective access to the common memory field of the network. In the conditions of mixed networks under centralized control, tasks with the highest priority and, as a rule, are associated with the processing of large amounts of information;

According to software compatibility, networks are homogeneous or homogeneous (consisting of software-compatible computers) and heterogeneous or heterogeneous (if the computers included in the network are programmatically incompatible).

Even as a result of a rather superficial consideration 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 network operating systems, 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 network 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.

The simplest case of interaction between two computers

In the simplest case, the interaction of computers can be implemented using the same means 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 a peripheral device, when the program usually works only on one side - from the side of the computer, in this case there is an interaction of 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 a part of some file located on the disk of 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. 4. 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 is transferred correctly, 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 specified file. All related to this additional problems must be solved by higher level programs than 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 as part 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.