Computer networks General characteristics and classification of computer networks. Presentation on the topic of the concept of computer networks, their classification and characteristics Classification of computer networks presentation

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Computer networks

Classification

KR PTUZ "FPTSU" Creative work of student group 21/22 Velichkovskaya E.K. Feodosia 2009

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Computer network (computer network, data network) - a communication system between two or more computers and/or computer equipment (servers, routers and other equipment)

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Classified:

by territorial distribution

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Local area network (LAN)

A network that usually covers a relatively small area or a small group of buildings Home Office Enterprise

Typically, such networks connect computers located at distances (about 50–1000 meters) within one or more nearby buildings.

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Urban computer network

Connects computers within a city

City network - the provider's core network, points connected by high-speed channels. Distance - from 1 to 10 km.

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Regional network

connecting computers and local networks to solve common problems on a regional scale

Located within a specific territorial region

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Global network

association of computers and local networks located at a remote distance for the common use of world information resources.

Iain Foster

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by departmental affiliation

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Departmental network

Belongs to one organization and is located on its territory: ATM network Railway ticket offices Theater ticket offices, etc.

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State network

Used in government agencies

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by type of transmission medium

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wired

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Twisted pair networks

Twisted pair is a type of communication cable that consists of one or more pairs of insulated conductors, twisted together (with a small number of turns per unit length), covered with a plastic sheath.

Currently, due to its low cost and ease of installation, it is the most common solution for building local networks.

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Coaxial networks

Coaxial cable is a cable in which the inner wire is surrounded by a second shielding wire to reduce radio interference.

The main purpose of coaxial cable is signal transmission in various fields of technology

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Fiber Optic Networks

An optical fiber is a glass or plastic thread used to carry light within itself through total internal reflection.

Optical fiber can be used as a means for long-distance communication and building a computer network.

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Wireless is a technology that allows you to create computer networks that fully comply with the standards for conventional wired networks (for example, Ethernet), without the use of cable wiring.

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Radio transmission

Radio communication is used to build highways (radio relay lines), to create local networks, and to connect remote subscribers to networks and highways of various types.

A wireless network works where a cable network does not.

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In the infrared range

Has a wide frequency range. Transmission is carried out with a narrow beam in the complete absence of lateral radiation. The transmitter is a semiconductor emitting diode. A highly sensitive photodiode is used as a receiver.

High communication confidentiality.

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By transmission speed

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Information transfer rate - the speed of data transmission, expressed in the number of bits, symbols or blocks transmitted per unit of time.

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Based on the speed of information transfer, computer networks are divided into low-, medium- and high-speed. low-speed (up to 10 Mbit/s), medium-speed (up to 100 Mbit/s), high-speed (over 100 Mbit/s);

Baud A unit of signal transmission speed measured in the number of discrete transitions or events per second. If each event represents one bit, a baud is equivalent to bits/sec (this is often not the case in real communications).

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by topology (geometric diagram of connecting network nodes)

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Linear network

This is a Point-to-Point network. With this organization, the network consists of two computers directly connected to each other. The advantage of such a network organization is its simplicity and relative cheapness, but the disadvantage is that only two computers can be connected in this way.

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Common bus

The network consists of several computers, each of which is connected to a common data bus for the network. A coaxial cable can act as a bus. The main disadvantage of this organization is that if the bus breaks, all network nodes lose communication. If it is necessary to connect another node to the network, then during installation work the connection will also be lost

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Ring network

the network consists of several computers, each of which is connected to a cable closed in a ring. The signal is transmitted along the ring in one direction and passes from computer to computer. In this case, the computer, having received a signal from a neighboring machine, amplifies it and transmits it further along the ring. This happens until the signal reaches the computer to which it is addressed. The disadvantage of this method is that if at least one of the computers stops working, the entire network stops functioning, and the time it takes to transmit a signal to the required machine increases noticeably compared to other methods of connecting computers to a network.

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Star network

With this organization, the network consists of several computers, each of which is connected to the same central device. This device is called HUB. The main disadvantage of this topology is that if the HUBa fails, the remaining nodes lose communication. The main advantage of such a connection is the ability to connect new nodes to the network without interrupting the operation of other nodes. Because of this important advantage of this type of network over others, as well as because of the relatively low cost, this type of network is the most common.

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Tree network

A network that contains more than two end nodes and at least two intermediate nodes, and in which there is only one path between the two nodes. Such a network is attractive from the point of view of control and expandability, but if a fault occurs in a node, all underlying nodes are disconnected from the network.

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Mesh network

A computer network topology in which each workstation is connected to all others. This option is cumbersome and ineffective, despite its logical simplicity. An independent line must be allocated for each pair; each computer must have as many communication ports as there are computers on the network. For these reasons, the network can only have relatively small final dimensions.

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On organizing the interaction of computers

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Peer-to-peer network

All computers in a peer-to-peer network have equal rights. Any network user can access data stored on any computer.

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Advantages of peer-to-peer networks: They are the easiest to install and operate. The DOS and Windows operating systems have all the necessary functions that allow you to build a peer-to-peer network. Disadvantages: In peer-to-peer networks, it is difficult to resolve information security issues. Therefore, this method of organizing a network is used for networks with a small number of computers and where the issue of data protection is not fundamental.

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Hierarchical network

In a hierarchical network, when the network is installed, one or more computers are pre-allocated to manage data exchange over the network and resource distribution. Such a computer is called a server. Any computer that has access to the server's services is called a network client or workstation. A server in hierarchical networks is a permanent storage of shared resources. The server itself can only be a client of a server at a higher hierarchy level. Therefore, hierarchical networks are sometimes called dedicated server networks.

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Basic concepts A computer network is a method of electronic interaction between two or more computers through a data transmission medium for the purpose of receiving and transmitting information. Its purpose is to provide shared access to shared resources: hardware, software and information.

Basic Concepts A computer that has access to shared resources is called a client. A workgroup is several computers working on one project within a local network, which includes a dedicated server. Server (host computer) is a fairly powerful computer on which all shared resources and special software for managing access to the entire network are located.

1) Local networks Local network (LAN) - several computers connected to each other and concentrated in a small space (room, premises, building, group of buildings). Coaxial cables are used as the transmission medium. High transfer speed - from 1 Mbit/s to 100 Mbit/s.

3) Global networks Global networks are a network of computers remote over considerable distances (for example, the Internet). Analogue or digital wire channels, as well as satellite communication channels (usually for communication between continents), are used as the transmission medium. Limitations on transmission speed (up to 28.8 Kbit/s on analogue channels and up to 64 Kbit/s on user sections of digital channels).

Other classification characteristics of computer networks by area of ​​operation (banking networks, networks of scientific institutions, university networks); by form of operation (commercial networks and free networks, corporate and public networks); by the nature of the functions being implemented (computational, informational, mixed);

Other classification characteristics of computer networks by control method (networks with decentralized, centralized and mixed control); In terms of software compatibility, networks can be homogeneous or homogeneous (consisting of software-compatible computers) and heterogeneous or heterogeneous (computers included in the network are software incompatible).

Bus topology In a bus (line) topology, all computers are connected to one common cable, called a bus or backbone. (+) prevalence and popularity, low cost, high flexibility and data transfer speed, ease of network expansion; (–) vulnerability to physical damage to the cable, because the location of the fault is difficult to locate.

Ring topology is ring when all network nodes are connected to one closed ring channel. Information along the ring can be transmitted only in one direction and all connected computers can participate in its reception and transmission. (+) ease of device implementation, (–) low reliability

A star topology is star-shaped, when all network nodes are connected to one central node, called a host or hub. (+) high level of data protection in the central node, simplifying the search for fault localization. (–) significant cable consumption

Characteristics of a communication channel The bandwidth of a communication channel is the speed of information transfer over the network, determined by the type of network adapters and cables used. Measured in baud (bits/second). long-distance channels (satellite, fiber optic) have a capacity of 2 million baud or higher. a leased line (an ordinary copper pair of telephone wire running without switches from machine to machine) can transmit, depending on the length (no more than a few kilometers), from 64 to 256 Kbaud. dial-up (regular telephone lines) have different bandwidths, and mobile phone lines allow the modem to operate at a speed of no higher than 9600 baud.

1 - Physical layer Physical layer (Physical Layer) - level of control of the transmission medium. The medium can be twisted pair, optical fiber, coaxial cable, radio channel, analog telephone channel, etc., each such medium defines its own rules for communicating with it.

2 - Data Link Layer The Data Link Layer controls the transmission of data over the communication channel. Main functions: dividing transmitted data into portions called frames, separating data from a stream of bits transmitted at the physical level for processing at the network level, detecting transmission errors; recovery of incorrectly transferred data.

4 - Transport layer The Transport Layer provides reliable transfer (transport) of data between computer systems on the network for higher levels. Here the problems of data transfer management and related tasks are solved: error localization and processing, and data transfer itself.

7 - Application level The Application Level solves the problems of standardizing interaction with application systems. Main functions: network management; synchronization of interacting application tasks; performing system application tasks (e-mail, file sharing).

Higher-level protocols FTP - file transfer protocol The client sends requests to the server that resemble commands for working with the OS file structure (directories and files). The server executes these commands (moving from directory to directory, viewing the contents of directories, copying files from a directory on the server machine to the current directory on the client machine and back). HTTP - protocol for transferring HTML files; the protocol is implemented by the WWW (World Wide Web) service. HTML (HyperText Markup Language) stands for hypertext markup language.

Internet Internet is a union of transnational computer networks operating under various protocols, connecting all kinds of computers, physically transmitting data over all available types of lines - from twisted pair and telephone wires to optical fiber and satellite channels. We can say that the Internet is a network of networks that entangles the entire globe.

Network addressing IP address, which consists of four numbers from 0 to 255. For example, the rightmost number indicates the number of a specific computer. The remaining numbers, depending on the address class, correspond to the numbers of networks and local subnets. The first number of a computer's IP address determines whether it belongs to a network of one class or another: class A addresses - a number from 0 to 127; Class B addresses - a number from 128 to 191; Class C addresses - a number from 192 to 223.

Network addressing DNS (domain name system) - domain name system. For example, win.smtp.dol.ru The very first name on the left in the name is the name of the real computer that has an IP address, followed by the name of the group that assigned the name to this computer, then the name of a larger group, etc. The domain name system has a hierarchical structure. Top-level domains are of two types: geographical (two-letter) geographical administrative (three-, four-letter) administrative

Universal Resource Locator (URL) URL (Universal Resource Locator) - the address of a web page includes the document access protocol, the domain name or IP address of the server on which the document is located, as well as the path to the file and the file name itself: protocol: //domain name/path/filename. For example,

Internet Services A service is a pair of programs that communicate with each other according to certain rules called protocols. One of the programs in this pair is called a server, and the other is called a client. The corresponding technology is called “client-server”.

1. Electronic mail () Provides for the transmission of messages from one user with a specific computer address to another. An email address consists of two parts, separated. The mail service is based on two protocols: SMTP - correspondence is sent from a computer to a server, POP3 - received messages are received. Programs for working with e-mail – Microsoft Outlook Express, Netscape Messenger, The Bat! Mail service on Yandex, Rambler, Mail.

2. World Wide Web (WWW) The WWW service is a single information space consisting of hundreds of millions of interconnected electronic documents stored on web servers. Individual documents are called web pages. Groups of thematically linked web pages are called websites. Purposeful movement between web documents is called web navigation. Programs for viewing web pages are called browsers. The main function of a web browser is to display hypertext. Hypertext allows you to structure a document by highlighting reference words (hyperlinks) in it. Examples of browsers are Internet Explorer, Opera, Netscape Navigator, Safari, FireFox.

3. File archives The FTP service receives and transmits large files. It has its own servers on the global network on which data archives are stored. These archives may be commercial or restricted, or may be publicly available. Files become available for work (reading, execution) only after copying to your own computer. File archive servers: freeware.ru,

4. Teleconferencing (Usenet) Usenet is a worldwide discussion club. It consists of a collection of conferences whose names are organized hierarchically according to the topics discussed. Messages are sent to these conferences by users using special software. After sending, messages are sent to news servers and become available for reading by other users. To read and send messages, use news readers: Netscape News or Internet News.

5. IRC service IRC (Internet Relay Chat) is a relayed Internet chat designed for direct communication between several people in real time. This service is also called chat. The most common client programs are mIRC, Pirch, MS Chat and Virc for Windows and Homer or Ircle for Macintosh.

6. Search on the World Wide Web Internet search servers are divided into two groups: general-purpose search engines (databases containing thematically grouped information about the information resources of the World Wide Web. Such search engines allow you to find websites or web pages using keywords in the database or by searching in a hierarchical directory system); specialized search engines.

Structure of search engines Stage 1 - collecting information from the WWW using special programs called spiders, crawlers or spiders; Stage 2 - indexing words in the form of a special database; Stage 3 - processing the client's request and providing him with search results in the form of a list of hyperlinks.

Geographic domains of the 1st level AU - AUstralia (Australia) BE - BElgium (Belgium) BY - BelorussiYa (Belarus) CA - CAnada (Canada) CZ - CZech republic (Czech Republic) DE - DEutschland (Germany) EU - EUrope (European Union) FI - FInland (Finland) FR - FRance (France) IL - IsraeL (Israel) KZ - KaZakhstan (Kazakhstan) NO - NOrway (Norway) PL - PoLand (Poland) RU - RUssian Federation (Russia) SU - Soviet Union (Soviet Union) ) TV - TuValu (Tuvalu) UA - UkrainA (Ukraine) UK - United Kingdom (England) US - United States (USA) JP - JaPan (Japan)

Administrative domains of the 1st level COMCommercial (for commercial organizations) NETNetworks (Internet, telecommunication networks) ORGOrganizations (non-profit organizations or organizations that do not fall into other categories) BIZBusiness Organizations (analogous to com) INTInternational Organizations (international organizations) EDUEducational (US educational projects) MILUS Dept of Defense (US Department of Security) GOVUS Government (US Government)