Telecommunications abstract. Computer networks and telecommunications. Below are the domain names of some countries

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://allbest.ru

NATIONAL TECHNICAL UNIVERSITY OF UKRAINE

"Kyiv Polytechnic Institute"

Department of Mathematical Modeling of Economic Systems

Lecture notes for studying the academic discipline

« Computer networks and telecommunications"

for the knowledge sector: 0306 "Management and Administration"

areas of training: 6.030601 “Management”

Ph.D. physics and mathematics sciences,

Associate Professor, Department of MMES

Ristsov I.K.

Lecture 1. Fundamentals of computer networks

1.1 General information

Computer network--This is a collection of computers connected by data transmission channels.

The general diagram of a computer network is shown in Fig. 1.

Rice. 1.1 General diagram of a computer network

A computer network solves two main technical tasks:

· provides fast data exchange between computers;

· provides collective access to network resources (printers, programs, data).

The socio-economic significance of computer networks lies in the fact that a computer network creates the prerequisites for collective information work.

Computer networks are conventionally divided by territorial basis into local, regional and global networks.

Local networks connect subscribers of one or several neighboring buildings. Computers in a local network are connected by a common high-speed communication channel. Typically, the distance between local network subscribers is no more than 1 km, but can reach 10 km. when using radio channels.

Regional networks unite subscribers of one region or country. Often regional networks are created by individual departments (tax office, customs, banks). The distances between subscribers here can reach several thousand km.

Global network connects users around the world. The global network uses all types of physical media for communication, from telephone lines to satellite channels.

Posted on http://allbest.ru

Rice. 1.2 Network classification

Note that networks at different levels can be closely interconnected, since higher-level networks are built from lower-level networks. For example, a local network can act as a node in a regional or global network. All devices connected to the network can be divided into the following functional groups.

Posted on http://allbest.ru

Rice. 1.3 Computer network hardware

Work station This is a personal computer connected to a network using specialized network devices, which use adapters and modems. Server-- this is, as a rule, a powerful computer on a network that provides users with certain services.

Data channels or communication lines are currently being built based on cableher (wires) or based on radiochannels(see Fig. 1.4).

Posted on http://allbest.ru

Rice. 1.4 Types of data channels

twisted pair cable consists of two conductors enclosed in a plastic sheath. To reduce the influence of interference, a shielded shell is also inserted into it, and then the twisted pair is called shielded. A Level 3 twisted pair cable can provide data transfer rates of up to 10 Megabits per second, and Level 5 up to 100 Megabits per second. The advantage of twisted pair is the relative cheapness and manufacturability of installation, and the disadvantage is low noise immunity and insufficient high speed data transmission.

In fiber optic cable Light pulses are used to transmit data. This cable is not susceptible to electromagnetic interference and can provide transmission speeds of up to 10 Gbit per second. Thus, the advantage of an optical cable is its high noise immunity and high data transfer speed, and its disadvantage is its relatively high cost.

Radio channels terrestrial and satellite communications are formed using a transmitter and receiver of radio waves and belong to the technology wireless transmission data. Satellite communications are used mainly on the Internet for communication between stations located at very long distances, and to serve subscribers in the most inaccessible places in the world. The throughput of satellite channels is quite high and amounts to several tens of Mbit/s.

The current wireless communication standard for local networks is WiFi (Wireless Fidelity-- “wireless precision”). This technology allows you to connect several computers to one access point (wireless router). The data exchange speed can reach up to 50 Mbit/s.

Radio channels Bluetooth(literally translated blue Tooth) is a technology for transmitting data over short distances (no more than 10 m) and can be used to create home computer networks. Currently Bluetooth time ensures the exchange of information between devices such as pocket and regular personal computers, Cell phones, laptops, printers, digital cameras, mice, keyboards, joysticks, headphones, headsets. This uses reliable, inexpensive, widely available short-range radio frequency. The data transfer speed here does not exceed 1 Mbit/s.

TO network devices include: adapters, modems, hubs, switches, routers.

Adapters and modems are used to connect a computer with data transmission channels. Adapters connect the computer with cable systems and radio channels (radio adapters). Modems (modulator, demodulator) are used to connect a computer to traditional communication networks, such as telephone or television networks.

Hub This is a network device designed to connect several computers into a common network segment. The hub, having received a packet from one line, simply transmits it to all other lines connected to it. Therefore, at any given time, data exchange is supported only between two stations. Currently, hubs are almost never produced - they have been replaced by switches, which are superior to hubs in the functions they perform, and their cost is not much more

Switch-- a device designed to connect several nodes of a computer network. Unlike a hub, which distributes traffic from one connected device to all others, a switch transmits data only directly to the recipient, but can also transmit broadcast packets to all nodes on the network. Direct transmission of packets to the destination improves network performance and security by eliminating the need (and ability) for other network segments to process data that was not intended for them.

Router is a network device that forwards data packets between different network nodes. Typically, a router uses the destination address specified in the data packets and determines from the routing table the path along which the data should be sent. In addition, routers often play the role of hardware network gateways, which are used to connect networks of different levels. IN Lately Radio routers (routers) are widely used at home to connect several computers to the global network.

Lecture 2. Local computer networks

2.1 Protocols and reference model

For coordinated work different devices In a local network, there must be an agreement, which is usually formalized in the form of an industry standard (protocol). The interaction of devices in a computer network is a complex process that requires solving many problems. The engineers decided to divide them into separate subtasks (levels), the solution of each of which is a relatively simple problem (the “divide and conquer” principle).

Rules or conventions are established to describe the relationships across a network, called protocol.

A protocol is a set of rules that defines the format of network messages and the set of network services that are provided at each layer.

The international organization for standardization ISO has developed a model of interaction between open systems OSI (Open System Interconnection), the diagram of which is shown in Fig. 2.1. The following layers and protocols can be distinguished in the OSI model:

1. Physical layer. On physical level the characteristics of electrical signals transmitting bits of information through communication channels are determined. The physical layer functions on a computer are performed by the network adapter.

2. Data Link Layer. At this level, the availability of the communication channel is determined, since only one computer can transfer data at a time. In addition, errors are detected and corrected here. Data exchange is carried out in certain portions, which are called personnel. Link layer protocols are implemented by network adapters and their drivers.

3. Network layer. At this level issues of delivering a separate data packet to the addressee are resolved. Each packet is provided with an address for both the recipient and the sender. A packet can pass through several network nodes, so the problem of choosing the best route arises here.

4. Transport layer. Here the message is broken down into parts called in packages. At this level issues of the order of delivery of packets related to one message are monitored, and transmission errors (distortion or loss of packets) are corrected. Protocols at the transport level and higher are implemented in software.

5. Application layer. At this level, user access (interface) to network services is provided. These include email, hypertext, and other collaboration services. The unit of information at this level is messages.

A set of protocols sufficient to organize interaction on a network is called stack of communication protocols.

Rice. 2.1. Protocols in the OSI model.

2.2 Network topology and access methods

Local computer networks are built mainly on physical and data link layer protocols. In turn, link layer protocols may differ connection topology And access methods.

Topology -- it is a geometric configuration of connections between computers in a network using communication lines. Historically, various connection topologies have been used: (common bus, ring, star).

Rice. 2.2. Star topology.

Currently, the star topology is mainly used (Fig. 2.2). Based on basic topologies using network equipment More complex network configurations are being created. In particular, tree structures are created using the “star”.

For the correct use of the common data transmission medium, special shared access methods to the environment (Media Access Control). Typically, the access method allows only one pair of computers to use the communication channel at a time. In practice, situations are possible when two computers simultaneously try to transfer their portions of data, that is, the so-called collision. One of the main tasks of the access method is to resolve and eliminate the consequences of such collisions.

An access method is a set of rules that determine the order of use of a common shared data transmission medium and eliminate the consequences of collisions.

2 . 3 Family Standards Ethernet

Most widespread in local networks received network standard Ethernet, which regulates work at the physical and data link levels. Subsequently, on its basis, the international standard IEEE 802.3 was developed, which currently describes three subfamilies: Ethernet; Fast Ethernet; Gigabit Ethernet.

The Ethernet standard itself currently has only historical significance, since it was focused on data transfer rates of up to 10 Mbit/s.

The Fast Ethernet standard (IEEE 802.3u) provides data transfer rates of up to 100 Mbit/s, and is based on a star topology: The Gigabit Ethernet standard (IEEE 802.3z) provides data transfer rates of up to 1 Gbit/s, and is designed for twisted pair cables category or fiber optic cable. Already appeared new standard for 10 Gigabit Ethernet, which should be included in the next version of the IEEE 802.3 standard.

All Ethernet protocols are used as access method multiple access method with carrier sensing and collision detection(carrier-sense-multiply-access with collision detection), or CSMA/CD method . This method is used in networks where all computers have direct access to a common data transmission medium and can immediately receive data sent by any computer.

2 . 4 Corporate networks

A corporate network connects computers within one large enterprise or corporation. In English-language literature this type of network is called " enterprise- wide networks" (enterprise-scale networks). The number of computers in such a network can be measured in hundreds, and the number of servers in dozens.

The corporate network is built by levels (hierarchically). At the first level there are local networks working groups, which unites employees of the same profile (accounting, human resources department, etc.). Workgroups usually unite up to 10 computers, in which all computers are considered equal. The advantage of this architecture is its reliability, but the disadvantage is that it is difficult to manage such a network. As a rule, a file server and a network printer are also included in the workgroup for ease of work. Hubs and switches are most often used as network equipment at this level.

At the next level, which is called department level, workgroups of one department or division are combined into one segment using a switch. Network services that need to be provided to all department employees are usually implemented on a specially dedicated server. In this case, a network operating system is installed on the server, which allows you to keep track of all users using accounts and manage network resources. Thus, here the server also acts as central device, providing information resources, and as a dedicated computer, which usually has more memory, more powerful communications, etc.

At the next level of the hierarchy, which is called level campuses, small local networks are combined into one large network. This network can cover all buildings in which the enterprise is located and transmit data over distances of up to several kilometers. Sometimes these networks have a so-called backbone, or main network, to which other subnets are connected. Switches and routers are used as network equipment. A fragment of an enterprise-scale corporate network is shown in the following figure.

Rice. 3.1. Corporate network

Note that in corporate networks the territorial attribute may not have any meaning. Such networks can be scattered across the globe. In this case, modern communication means are used to connect remote local networks ( satellite channels). Large corporations have their own dedicated communication lines that are not accessible from the Internet.

Centralized management of a local network allows you to increase the number of computers in it to hundreds and even thousands of units. But centralization and concentration of distributed resources also has an obvious drawback, since an unreliable (bottleneck) place appears in the network. The failure of the central server can lead to the shutdown of the entire enterprise, since it is the collective work that is paralyzed. Therefore, servers are made an order of magnitude more reliable than workstations, and in especially important cases they are duplicated and form the so-called clusters.

The appearance of a dedicated server on the network leads to the emergence of “shared memory”, which can be used to store the results of collective work. Historically, the first to appear were the so-called file servers, on which the results of the work were stored in the form of files. However, it soon became clear that it was quite difficult to find the necessary information among the huge number of files.

The next significant step towards the socialization of data in computer networks was client-server architecture. This architecture assumes the presence general databases, which are usually stored on specially allocated for this purpose database servers. When accessing a database server, the client may not be aware of the location of the data he is interested in, since the request is formulated in a special structured language (SQL). The benefit compared to file servers is achieved by reducing the network load on the client side.

Another achievement of the client-server architecture was the transition to working with general programs. In this case, a program for managing a certain business process can only run on the server, and only a small module of this program will run on the client. Thus, the concept appears application server, that is, a server on which common application programs run. Note that the same hardware server can act as both a database server and an application server.

Using the example of corporate networks, we can trace the process of mutual penetration of local and global networks, which led to the emergence intranet-technologies. An intranet network is a corporate network that operates using standard protocols used on the Internet. At the same time, access from the global network to the corporate network is usually protected or completely blocked.

Lecture 3. Global computer network Internet

The Internet is a global computer network that connects tens of millions of subscribers in more than 150 countries around the world. The Internet literally means internet, that is network of networks, which generally reflects its essence.

Internet can also be considered as global information space, which is growing monthly by 7-10% percent and as a new type of media, distinctive feature which is interactivity. Thus, the Internet is both a mechanism for disseminating information and a medium for interaction between users, regardless of their geographical location. Currently, the influence of the Internet extends to virtually all of humanity as a whole.

3 .1 History of the Internet

First research into the connection remote computers were carried out in the early 60s. In 1965, a computer located at MIT was connected to a computer in California via telephone line. In 1969, a network project called ARPANET began and four remote computers were included.

At first, technology was used to connect computers circuit switching, characteristic of telephone technologies. Its essence is that during the exchange of information between subscribers there must be a physical communication channel. As a result of the experiment, it turned out that circuit switching is not suitable for creating computer networks, and this required the use of new data transmission technology - packet switching.

When using this technology, all messages transmitted on the network are divided into small parts, which are called packages. Each packet is provided with a header that indicates the destination address of the packet. Routers use the address to forward packets to each other until it reaches its destination.

In 1971-72, the basic principles for building a new unified network (Internet) were formulated:

· to add a new subnet to the Internet, no additional changes should be made to the network itself;

· packets on the Internet are transmitted based on the principle of packet switching, with non-guaranteed delivery of individual packets. If the packet does not reach its destination, it must be transmitted again after a short time;

· to connect subnets, special devices are used - routers, which should simplify the passage of the packet flow as much as possible;

· The interconnected network should not have centralized management.

The key to connecting subnets was a new protocol that supported internetworking, which appeared in 1973, called TCP (Transmission Control Protocol).

TCP worked well for most networking problems, but in some cases packet loss occurred. This fact led to the division of TCP into two protocols: IP for addressing and transmitting individual packets, and TCP for separating messages into packets, ensuring integrity and recovery lost packets. The combined protocol is commonly called TCP/IP.

3 .2 Structure and principles of operation of the Internet

Currently, the Internet is based on high-speed backbone networks. Independent networks connect to backbone network through network access points NAP (Network Access Point). Independent networks are considered as autonomous systems, that is, each has its own administration and its own routing protocols.

Rice. 4.1. Internet structure

Typically, large, independent, national networks act as autonomous systems. Examples of such networks are the EUNet network, covering the countries of central Europe, and the RUNet network, which unites subnetworks in Russia. Autonomous networks can form companies specializing in providing Internet access services, -- providers. Such providers in Ukraine, for example, are Volya, Adamant, Lucky Net, etc.

An important parameter that determines the quality of network work is network access speed, which is classified depending on the capacity of physical communication channels as follows:

· for a modem connection, which is used by most Internet users, the channel capacity is low - from 20 to 60 Kbps;

· for dedicated telephone lines and those used to connect small local computer networks to the Internet - from 64 Kbit/s to 2 Mbit/s;

· for satellite and fiber optic communication channels, which are mainly used to create autonomous networks - from 2 Mbit/s. and higher.

The Internet uses the TCP/IP family of protocols (Fig. 4.2).

Rice. 4.2.

At the link and physical layers, TCP/IP supports many of the existing standards that define the data transmission medium. This could be, for example, Ethernet and Token Ring technologies for local computer networks or X.25 and ISDN for organizing large territorial networks.

One of the main protocols of this family is inter network protocol IP. The data flow at this level is broken down into specific parts called IP-packages(datagrams). The IP protocol treats each packet as an independent unit, unconnected to other packets, and routes it individually. The IP protocol is a type of connectionless protocol, that is, no control information other than what is contained in the IP packet itself is transmitted over the network. In addition, the IP protocol does not guarantee reliable packet delivery.

The TCP protocol operates at the transport layer and determines the packet size, transmission parameters, and message integrity control. Since the IP protocol does not guarantee reliable delivery of messages, this problem is solved by TCP protocol. Unlike the IP protocol, the TCP protocol establishes a logical connection between communicating processes. Before data transmission, a request is sent to start the transmission session, and a confirmation is sent by the recipient. The reliability of the TCP protocol lies in the fact that the data source repeats sending it if it does not receive confirmation of its successful receipt from the recipient within a certain period of time.

The application layer brings together all the services that the Internet provides to users. The most important application protocols include the Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP), and the email protocols SMTP, POP, IMAP, and MIME.

3.3 IP -addresses

Each computer connected to the Internet has a unique IP-address, which consists of four bytes and is written as four decimal numbers separated by dots, for example:

194.85.120.66

An IP address consists of two logical parts: the network number and the host number on the network. The network number is issued by a special division of the Internet - InterNIC (Internet Network Information Center) or its representatives. The node number is determined by the network administrator. Depending on how many bytes in the IP address are allocated for the network number and host number, several classes of IP addresses are distinguished.

Rice. 3.3. IP address structure

If the network number occupies one byte, and the node number takes three bytes, then this address refers to class A. The number of nodes in the network in this class can reach 2 24 , or 16777216. The network number in this class varies from 1.0.0.0 to 126.0.0.0.

If two bytes are allocated for the network number and node number, then the address belongs to class B. The number of possible nodes in a class B network is 2 16, or 65,536 nodes. The Class B network number varies from 128.0.0.0 to 191.255.0.0.

If three bytes are allocated for the network number, then the address belongs to class C. The number of nodes in a class C network is limited to 2 8, or 256. The network number varies from 192.0.1.0 to 223.255.255.0.

For example, in the IP address 194.85.120.66, 66 is the host number on the network, and 194.85.120.0 is the class C network number.

3.4 Domain names

It is extremely inconvenient for a person to use numeric IP addresses, so it seems logical to use symbolic names instead of IP addresses. On the Internet, the domain name system (DNS Domain Name System), which has a hierarchical structure, is used for this purpose. The minor part of the domain name corresponds to the end node of the network. The component parts are separated from each other by a dot.

For example, mail. econ. pu. ru. One node can have several names, but only one IP address.

A set of names in which several of the higher parts of the domain name coincide is called domain. For example, names mail. econ. pu. ru And www. econ. pu. ru belong to the domain econ. pu. ru.

The most important thing is the root domain. This is followed by domains of the first, second and third levels.

The root domain is managed by InterNIC. First-level domains are assigned for each country, and it is customary to use three-letter and two-letter abbreviations.

So, for example, for Russia the first level domain is ru, for the USA it is us.

In addition, several top-level domain names are assigned to different types of organizations:

· com -- commercial organizations (for example, ibm. com);

edu - educational organizations (for example, spb. edu)

· gov -- government organizations (for example, loc. gov);

org -- non-profit organizations (for example, w3. org);

net - organizations that support networks (for example, ukr. net);

Below are the domain names of some countries:

	ch -- Switzerland	au -- Australia
fr -- France	se -- Sweden	hu -- Hungary
sa -- Canada	jp -- Japan	ru -- Russia
	hk -- Hong Kong	ua -- Ukraine
de -- N1mechina	mx -- Mexico	fi -- F1nland1ya

Each domain name has its own DNS-server, which stores a database of correspondence between IP addresses and domain names located in a given domain, and also contains links to DNS servers of lower-level domains.

Thus, in order to obtain a computer's address by its domain name, the application only needs to contact the DNS server of the root domain, which, in turn, will forward the request to the DNS server of the lower-level domain. Thanks to this organization of the domain name system, the name resolution load is evenly distributed among the DNS servers.

computer information software

Lecture 4. Basic services on the Internet

The main information services on the Internet include the following services:

· World Wide Web hypertext service.

· Email;

· FTP archives;

All services on the Internet operate according to a client-server scheme. On the server side, all services are combined into one program called Internet server, and on the client side, each service is represented by a separate client program. But recently there has been a unification of client programs and one program - a browser, can now provide all types of information services (mail, file transfer, chats, etc.).

4 .1 Email

System Email(e-mail) allows you to deliver a message to any computer connected to the Internet. The message can contain text, and a file of any format (graphics, music, etc.) can be attached to the message.

All email users have unique addresses. The Internet has adopted an address system that is based on the domain address of the machine connected to the network.

The user's address consists of two parts, separated by the "@" symbol:<имя>@<доменное_имя>. For example, Jones@ Registry. org, where Jones is the username and Registry.org is the domain name of the mail server.

Windows OS provides two programs as an email client: MS Outlook Express and MS Outlook. The first of them is a pure email client, and the second combines the functions of a personal information organizer.

Recently, the so-called Web-based mail has appeared, when work with the mail server is carried out through a browser. But it’s too early to equate “real” mail with Web-based mail, since the latter imposes quite strict restrictions on both the amount of information stored and the storage time. In addition, from a confidentiality point of view, it is better to store personal correspondence on your computer rather than on a server.

In addition, the so-called instant mail (Internet pager) and voice mail (Skype) appeared, when messages are exchanged in real time.

Instant mail clients include Microsoft MSN Messenger, the popular Israeli ISQ program and others. Recently popular social networks (Facebook) can be considered as a type of instant mail, when communication takes place among a whole group of interlocutors.

4 . 2 Hypertext service World Wide Web

The World Wide Web service is currently the most popular service on the Internet. It is also abbreviated as WWW, W3 or simply Web. The idea behind the WWW service was to apply the hypertext model to information resources located on the Internet. A hypertext document can contain text, graphics, sound, video, as well as hyperlinks that directly access network information resources.

The WWW service has the following three main components:

· HTML (Hyper Text Markup Language) markup language for hypertext documents;

· a universal way to address resources on the URL network (Universal Resource Locator);

· HTTP (HyperText Transfer Protocol) hypertext information exchange protocol.

Later two more components were added to them:

· universal gateway interface CGI (Common Gateway Interface) for server-side programming;

· JavaScript programming language for client-side programming, which allows you to enter program code inside HTML documents.

The client-side program for the WWW service is a browser (browser), which provides access to almost all information resources on the network using HTML interpretation.

The most common browsers include Microsoft Internet Explorer, Opera, Mozilla and others. Let's take a brief look at the main components of the WWW service.

4.3 Hypertext Markup Language HTML

Most documents on the WWW service are stored in HTML format. HTML is a set of commands that tell the browser to display the contents of a document, but the HTML commands themselves are not displayed. IN HTML language a mechanism of hypertext links has been implemented, which ensures the connection of one document with others. These documents may be located on the same server as the page from which they are linked, or they may be hosted on a different server.

Commands in the text of an HTML document are called tags (descriptors). An HTML tag can contain a list of attributes. The tag text is enclosed in angle brackets (< и >).

4.3 Universal Resource URL

In order to obtain information from the Internet, you need to know the address where it is located. A universal resource address (URL) is an address on the WWW system that uniquely identifies any document.

In general, the uniform resource address has the following format:

protocol://computer/path.

In other words, the universal resource address can be described by the following formula:

URL= external path (domain name) + internal path.

The main protocol on the World Wide Web is HTTP, the hypertext transfer protocol, so most addresses start like this: http://

But other data transfer protocols can also be used, for example the file transfer protocol - FTP. Then the first place in the universal resource address is the name of the protocol used, for example, ftp://

Computer-- this is the address of the server with which you want to connect. Either the IP address or the server name in the domain name system can be used. For example: http://www.econ.pu.ru or ftp://194.85.120.66. Most server addresses on the World Wide Web begin with the prefix www. This prefix is simply used as a convenience to indicate that a Web server is running on a given computer.

Path is an exact indication of the location of the document on the Web server. This can be the name of a directory and a file, as in the following example:

http://www.econ.pu.ru/info/history/jubilee.htm.

If you enter this address in the “address” line of the browser, the browser will establish a connection with the computer www.econ.pu.ru via HTTP and request from it a document called jubilee.htm from the /info/history directory.

The last part of the URA may include additional information that is typically used to convey to the Web server the parameters of the user's request in interactive pages, as well as the path and name of the program on the server that will process the request. For example:

http://www.econ.pu.ru/sf/cgi-bin/main.bat?object=teachers&id=1

Upon receiving such a request, the Web server will try to find the main.bat program in the /sf/cgi-bin directory, run it and pass it the object and id parameters with the appropriate values.

IN modern versions browsers do not need to specify the protocol name at the beginning of each resource address. If the protocol name is not specified, the browser will try to determine which protocol to use. If the file name is not specified, but only the directory in which it should be located, then The user will be sent the file that the Web server administrator has designated as the default file. Typically this is a file called index.htm (index.html) or default.htm (default.html). If there is no default file in the directory, an error message will be displayed.

4.4 Hypertext Transfer Protocol(HTTP) is a standard protocol for transferring documents between servers and browsers in the WWW service. The HTTP protocol allows a connection to be established between a client and a server, and the connection is maintained only while the server processes client requests.

The client's request and the server's response form a so-called transaction. Data exchange via the HTTP protocol occurs as follows.

The client establishes a connection to the server using the specified port number. If the client is a browser, the port number is specified in the URL request. If no number is specified, the default is port 80. The client then sends a request for the document, specifying the HTTP command, the document address, and the HTTP version number.

For example:

GET / index. html HTTP/1.0

Posted on Allbest.ru

...

THEMATIC PLANNING

Grade 10

Topic name

Textbook section

Number of hours

Practice

Introduction. Structure of computer science

Preface, §1.1

Working in MS Windows: working with windows, folders, files, objects

Theoretical computer science

Working with MS Word. Entering, editing and formatting texts

Information means and information technologies

Working with MS Word. Fonts, text design

Informational resources. National information resources of Russia

Working with MS Word. Inserting objects. Working with tables

Final work with the word processor MS Word

History and development of computer telecommunications. Technical and software resources Internet

Preparation of a summary on the topic “ Computer telecommunications» using MS Word

How the Network works. Information services Internet

Work with by email and teleconferences

Basic concepts of the World Wide Web. Working with the WWW browser

Working with a browser, viewing Web pages

Internet search service. Searching for information on WWW

Working with search engines

Website creation

Saving downloaded Web pages

Final creative task for working with the Internet

Computer information modeling. Basic concepts of systemology

Introduction to the PowerPoint Presentation Suite

Making a presentation on the topic “Models and systems”

About communication types and control systems

Drawing Tools in MS Word

Graphs and networks. Hierarchical structures and trees

Building system models on graphs

Description of hierarchical systems

Tabular organization of data

Construction of tabular information models using MS Word

Social informatics. Concept information society. (Give a topic for an essay)

§6.1, §6.2, §6.3

Information security issues and legal acts in the information sphere

Defense of abstracts on social informatics issues

Grade 11

Topic name

Textbook section

Number of hours

Practice

Information Systems. Local computer networks

Basic concepts of databases. DBMS

Design information system

Creating a database structure and filling it in

Using the database. Requests.

The report as the final document of the information system operation

Geographic information systems

Planning and management tasks. Table processor as a tool for solving them

Business graphics and its implementation in a spreadsheet processor

Representation of dependencies between quantities. Regression models and forecasting

Correlation dependencies

Optimal planning

by discipline "Computer networks and telecommunications"

INTRODUCTION... 65

2 CABLES AND INTERFACES... 10

3 DATA EXCHANGE ON THE NETWORK.. 15

6 INTERNET SERVICES 40

8 WEB VIEWERS 54

INTRODUCTION 6

1 NETWORK CONCEPTS AND TERMS... 7

1.1 Basic concepts. 7

1.2 Classification of networks by scale. 7

1.3 Classification of networks based on the presence of a server. 7

1.3.1 Peer-to-peer networks. 7

1.3.2 Networks with a dedicated server. 8

1.4 Network selection. 9

2 CABLES AND INTERFACES... 10

2.1 Cable types. 10

2.1.1 Twisted pair cable – twisted pair 10

2.1.2 Coaxial cable. eleven

2.1.3 Fiber optic cable. 12

2.2 Wireless technologies. 12

2.2.1 Radio communication. 13

2.2.2 Microwave communications. 13

2.2.3 Infrared communication. 13

2.3 Cable parameters. 13

3 DATA EXCHANGE ON THE NETWORK.. 15

3.1 General concepts. Protocol. Protocol stack. 15

3.2 ISO/OSI 16 model

3.3 Functions of ISO/OSI 18 model layers

3.4 Application interaction protocols and transport subsystem protocols. 21

3.5 Functional compliance of types of communication equipment with levels of the OSI 22 model

3.6 IEEE 802.24 Specification

3.7 According to the protocol stack. 25

4 NETWORK EQUIPMENT AND TOPOLOGIES.. 27

4.1 Network components. 27

4.1.1 Network cards. 27

4.1.2 Repeaters and amplifiers. 28

4.1.3 Concentrators. 29

4.1.4 Bridges. 29

4.1.5 Routers. thirty

4.1.6 Gateways. thirty

4.2 Types of network topology. 31

4.2.1 Tire. 31

4.2.2 Ring. 32

4.2.3 Star. 32

4.2.5 Mixed topologies. 33

5 GLOBAL INTERNET NETWORK.. 36

5.1 Theoretical basis Internet. 36

5.2 Working with Internet services. 37

6 INTERNET SERVICES 40

6.1 Terminal mode. 40

6.2 Electronic mail (E-Mail) 40

6.4 Teleconferencing service (Usenet) 41

6.5 World Wide Web (WWW) Service 43

6.6 Domain Name Service (DNS) 45

6.7 File Transfer Service (FTP) 48

6.8 Internet Relay Chat Service 49

6.9 ICQ service.. 49

7 CONNECTING TO THE INTERNET.. 51

7.1 Basic concepts. 51

7.2 Installing the modem. 52

7.3 Connecting to an Internet service provider's computer. 53

8 WEB VIEWERS 54

8.1 The concept of browsers and their functions. 54

8.2 Working with the program Internet Explorer 54

8.2.1 Opening and viewing Web pages. 56

8.2.3 Browser control techniques. 57

8.2.4 Working with multiple windows. 58

8.2.5 Setting browser properties. 58

8.3 Searching for information on the World Wide Web. 60

8.4 Receiving files from the Internet. 62

9 WORKING WITH ELECTRONIC MESSAGES... 64

9.1 Sending and receiving messages. 64

9.2 Working with the program Outlook Express. 65

9.2.1 Creation account. 65

9.2.2 Creating an email message. 66

9.2.3 Preparing responses to messages. 66

9.2.4 Reading teleconference messages. 67

9.3 Working with the address book. 67

INTRODUCTION

The material discussed in this lecture notes is not about a specific operating system and not even about a specific type of operating system. It examines operating systems (OS) from a very general perspective, and the described fundamental concepts and design principles are valid for most operating systems.

1 NETWORK CONCEPTS AND TERMS

1.1 Basic concepts

A network is a connection between two or more computers, allowing them to share resources.

1.2 Classification of networks by scale

The local network(Local Area Network) is a collection of networked computers located within a small physical region, such as a single building.

This is a set of computers and other connected devices that fit within the coverage area of one physical network. Local networks are the basic building blocks for building internetworks and global networks.

Global networks(Wide Area Network) can connect networks around the world; third-party communications tools are typically used for internetworking.

WAN connections can be very expensive as communication costs increase with bandwidth. Thus, only a small number of WAN connections support the same bandwidth as regular LANs.

Regional networks(Metropolitan Area Network) use wide area network technologies to connect local networks in a specific geographic region, such as a city.

1.3 Classification of networks based on the presence of a server

1.3.1 Peer-to-peer networks

Computers in peer-to-peer networks can act as both clients and servers. Since all computers in this type of network have equal rights, peer-to-peer networks do not have centralized control over resource sharing. Any computer on this network can share its resources with any computer on the same network. Peer-to-peer relationships also mean that no one computer has higher access priority or greater responsibility for sharing resources.

Advantages of peer-to-peer networks:

– they are easy to install and configure;

– individual machines do not depend on a dedicated server;

– users are able to control their own resources;

– inexpensive type of networks to purchase and operate;

– no additional hardware or software is needed other than the operating system;

– there is no need to hire a network administrator;

– works well with a number of users not exceeding 10.

Disadvantages of peer-to-peer networks:

– applying network security to only one resource at a time;

– users must remember as many passwords as there are shared resources;

- must be produced backup separately on each computer to protect all shared data;

– when gaining access to a resource, a drop in performance is felt on the computer on which this resource is located;

– There is no centralized organizational scheme for searching and managing access to data.

1.3.2 Dedicated server networks

Microsoft prefers the term Server-based. A server is a machine (computer) whose main task is to respond to client requests. Servers are rarely managed by anyone directly - only to be installed, configured or maintained.

Advantages of networks with a dedicated server:

– they provide centralized management of user accounts, security and access, which simplifies network administration;

– more powerful equipment means more efficient access to network resources;

– users only need to remember one password to log into the network, which allows them to access all resources they are entitled to;

– such networks scale (grow) better with the increase in the number of clients.

Disadvantages of dedicated server networks:

– a server malfunction can make the network inoperable, at best – loss of network resources;

– such networks require qualified personnel to maintain complex specialized software;

– the cost of the network increases due to the need for specialized equipment and software.

1.4 Network selection

The choice of network depends on a number of circumstances:

– number of computers in the network (up to 10 – peer-to-peer networks);

– financial reasons;

– presence of centralized management, security;

– access to specialized servers;

– access to the global network.

2 CABLES AND INTERFACES

At the lowest level of network communications is the medium over which data is transmitted. In relation to data transmission, the term media (media, data transmission medium) can include both cable and wireless technologies.

2.1 Cable types

There are several different types of cables used in modern networks. Different network situations may require various types cables

2.1.1 Twisted pair cable

It is a network media used in many network topologies, including Ethernet, ARCNet, IBM Token Ring.

There are two types of twisted pair.

1. Unshielded twisted pair.

There are five categories of unshielded twisted pair cable. They are numbered in order of increasing quality from CAT1 to CAT5. Higher grade cables typically contain more pairs of conductors, and these conductors have more turns per unit length.

CAT1 – telephone cable, does not support digital transmission data.

CAT2 is a rarely used older type of unshielded twisted pair cable. It supports data transfer rates up to 4 Mbps.

CAT3 is the minimum level of unshielded twisted pair cable required for today's digital networks, has a throughput of 10 Mbit/s.

CAT4 is an intermediate cable specification that supports data rates up to 16 Mbps.

CAT5 is the most efficient type of unshielded twisted pair cable, supporting data transfer rates up to 100 Mbps.

UTP cables connect each computer's network card to a network panel or network hub using an RJ-45 connector at each connection point.

An example of such a configuration is the 10Base-T Ethernet network standard, which is characterized by unshielded twisted pair cable (CAT3 to CAT5) and the use of an RJ-45 connector.

Flaws:

– sensitivity to interference from external electromagnetic sources;

– mutual signal overlap between adjacent wires;

– unshielded twisted pair is vulnerable to signal interception;

– large signal attenuation along the way (limited to 100 m).

2. Shielded twisted pair.

It has a similar design as the previous one and is subject to the same 100-meter limit. Typically contains four or more pairs of stranded copper insulated wires in the middle, along with electrically grounded braided copper mesh or aluminum foil, creating a shield from external electromagnetic influences.

Flaws:

– the cable is less flexible;

– requires electrical grounding.

2.1.2 Coaxial cable

This type of cable consists of a central copper conductor that is thicker than the wires in a twisted pair cable. The center conductor is covered with a layer of foamy plastic insulating material, which in turn is surrounded by a second conductor, usually woven copper mesh or aluminum foil. The external conductor is not used for data transmission, but acts as grounding.

Coaxial cable can transmit data at speeds up to 10 Mbps over a maximum distance of 185 m to 500 m.

The two main types of coaxial cable used in LANs are Thicknet and Thinnet.

Also known as RG-58 cable, it is the most used. It is the most flexible of all coaxial cable types and is approximately 6mm thick. It can be used to connect each computer to other computers on the local network using a T connector, British Naval Connector (BNC) connector and 50 Ohm terminator terminations. Mainly used for 10Base-2 Ethernet networks.

This configuration supports data transfer rates of up to 10 Mbps over a maximum distance of 185 m between repeaters.

Is a thicker and more expensive coaxial cable. It is similar in design to the previous one, but less flexible. Used as the basis for 10Base-5 Ethernet networks. This cable is marked RG-8 or RG-11, approximately 12 mm in diameter. It is used as a linear bus. To connect to each network card a special external transceiver AUI (Attachment unit interface) and a “vampire” (branch) piercing the cable sheath are used to gain access to the wire.

It has a thick center conductor that provides reliable data transmission over distances of up to 500 m per cable segment. Often used to create connecting highways. Data transfer speed up to 10 Mbit/s.

2.1.3 Fiber optic cable

Provide excellent speed of information transfer over long distances. They are immune to electromagnetic noise and eavesdropping.

It consists of a central glass or plastic conductor surrounded by another layer of glass or plastic coating, and an outer protective sheath. Data is transmitted over the cable using a laser or LED transmitter that sends unidirectional light pulses through a central glass fiber. The glass coating helps keep the light focused in the inner conductor. At the other end of the conductor, the signal is received by a photodiode receiver, which converts the light signals into an electrical signal.

The data transfer speed for fiber optic cable reaches from 100 Mbit/s to 2 Gbit/s. Data can be reliably transmitted over distances of up to 2 km without a repeater.

Light pulses travel in only one direction, so you need to have two conductors: an incoming cable and an outgoing cable.

This cable is difficult to install and is the most expensive type of cable.

2.2 Wireless technologies

Wireless data transmission methods are a more convenient form. Wireless technologies vary in signal types, frequency, and transmission distance.

The three main types of wireless data transmission are: radio communications, microwave communications, and infrared communications.

2.2.1 Radio communications

Radio communication technologies send data at radio frequencies and have virtually no range limitations. Used to connect local networks over large geographical distances.

Flaws:

– radio transmission is expensive,

– subject to government regulation,

– extremely sensitive to electronic or atmospheric influences,

– is susceptible to interception and therefore requires encryption.

2.2.2 Microwave communications

Supports data transmission in the microwave range, uses high frequencies and is used both over short distances and in global communications.

Limitation: The transmitter and receiver must be within line of sight of each other.

Widely used in global information transmission using satellites and terrestrial satellite antennas.

2.2.3 Infrared communication

Operates at high frequencies approaching the frequencies of visible light. Can be used to establish two-way or broadcast data transmission over short distances. Typically LEDs are used to transmit infrared waves to the receiver.

These waves can be physically blocked and experience interference with bright light, so transmission is limited to short distances.

2.3 Cable parameters

When planning a network or expanding an existing network, several cabling issues need to be clearly considered: cost, distance, data speed, ease of installation, number of nodes supported.

A comparison of cable types by data transfer speed, cable cost, installation complexity, and maximum data transfer distance is presented in Table 2.1.

The number of nodes per segment and nodes in the network when building networks with different cable usage is presented in Table 2.2.

Table 2.1 – Comparative characteristics of cables

Table 2.2 – Number of nodes depending on network type

3 DATA EXCHANGE ON THE NETWORK

3.1 General concepts. Protocol. Protocol stack.

The main goal that is pursued when connecting computers into a network is the ability to use the resources of each computer by all network users. In order to realize this feature, computers connected to the network must have the necessary means of interaction with other computers on the network.

The task of sharing network resources includes solving many problems - choosing a method for addressing computers and coordinating electrical signals when establishing electrical communication, ensuring reliable data transmission and processing error messages, generating sent and interpreting received messages, as well as many other equally important tasks.

The usual approach to solving a complex problem is to break it down into several subproblems. A certain module is assigned to solve each subtask. At the same time, the functions of each module and the rules for their interaction are clearly defined.

A special case of task decomposition is a multi-level representation, in which the entire set of modules that solve subtasks is divided into hierarchically ordered groups - levels. For each level, a set of query functions is defined, with which modules at a given level can be accessed by modules at a higher level to solve their problems.

This set of functions performed by a given layer for a higher layer, as well as the message formats exchanged between two neighboring layers during their interaction, is called an interface.

The rules for interaction between two machines can be described as a set of procedures for each level. Such formalized rules that determine the sequence and format of messages exchanged between network components lying at the same level, but in different nodes, are called protocols.

An agreed upon set of protocols at different levels, sufficient to organize internetworking, is called protocol stack.

When organizing interaction, two main types of protocols can be used. IN connection-oriented protocols(connection-oriented network service, CONS) before exchanging data, the sender and recipient must first establish a logical connection, that is, agree on the parameters of the exchange procedure that will be valid only within the framework of this connection. After completing the dialogue, they must terminate this connection. When a new connection is established, the negotiation procedure is carried out again.

The second group of protocols is connectionless protocols(connectionless network service, CLNS). Such protocols are also called datagram protocols. The sender simply transmits the message when it is ready.

3.2 ISO/OSI model

Just because a protocol is an agreement between two interacting entities, in this case two computers working on a network, does not mean that it is necessarily a standard. But in practice, when implementing networks, they tend to use standard protocols. These may be proprietary, national or international standards.

The International Standards Organization (ISO) has developed a model that clearly defines the different levels of interaction between systems, gives them standard names, and specifies what work each level should do. This model is called the interaction model open systems(Open System Interconnection, OSI) or ISO/OSI model.

In the OSI model, communication is divided into seven layers or layers (Fig. 1). Each level deals with one specific aspect of interaction. Thus, the interaction problem is decomposed into 7 particular problems, each of which can be solved independently of the others. Each layer maintains interfaces with the layers above and below.

The OSI model describes only system communications, not end-user applications. Applications implement their own communication protocols by accessing system facilities. It should be borne in mind that the application can take over the functions of some of the upper layers of the OSI model, in which case, if necessary, internetworking it accesses directly the system tools that perform the functions of the remaining lower layers of the OSI model.

An end-user application can use system interaction tools not only to organize a dialogue with another application running on another machine, but also simply to receive the services of a particular network service.

So, let's say an application makes a request to an application layer, such as a file service. Based on this request, the application level software generates a standard format message, which contains service information (header) and, possibly, transmitted data. This message is then forwarded to the representative level.

The presentation layer adds its header to the message and passes the result down to the session layer, which in turn adds its header, and so on.

Finally, the message reaches the lowest, physical layer, which actually transmits it along the communication lines.

When a message arrives on another machine over the network, it moves up sequentially from level to level. Each level analyzes, processes and deletes the header of its level, performs the corresponding this level function and passes the message to the higher level.

In addition to the term "message", there are other names used by network specialists to designate a unit of data exchange. ISO standards for protocols of any level use the term “protocol data unit” - Protocol Data Unit (PDU). In addition, the names frame, packet, and datagram are often used.

3.3 Functions of ISO/OSI model layers

Physical level. This layer deals with the transmission of bits over physical channels, such as coaxial cable, twisted pair cable, or fiber optic cable. This level is related to the characteristics of physical data transmission media, such as bandwidth, noise immunity, characteristic impedance and others. At the same level, the characteristics of electrical signals are determined, such as requirements for pulse edges, voltage or current levels of the transmitted signal, type of coding, signal transmission speed. In addition, the types of connectors and the purpose of each contact are standardized here.

Physical layer functions are implemented in all devices connected to the network. On the computer side, the physical layer functions are performed by the network adapter or serial port.

Data link level. One of the tasks of the link layer is to check the availability of the transmission medium. Another task of the link layer is to implement error detection and correction mechanisms. To do this, at the data link layer, bits are grouped into sets called frames. The link layer ensures that each frame is transmitted correctly by placing a special sequence of bits at the beginning and end of each frame to mark it, and also calculates a checksum by summing all the bytes of the frame in a certain way and adding the checksum to the frame. When the frame arrives, the receiver again calculates the checksum of the received data and compares the result with the checksum from the frame. If they match, the frame is considered correct and accepted. If the checksums do not match, an error is recorded.

The link layer protocols used in local networks contain a certain structure of connections between computers and methods for addressing them. Although the data link layer provides frame delivery between any two nodes on a local network, it does this only in a network with a very specific connection topology, precisely the topology for which it was designed. Typical topologies supported by LAN link layer protocols include shared bus, ring, and star. Examples of link layer protocols are Ethernet, Token Ring, FDDI, 100VG-AnyLAN.

Network layer. This level serves to form a unified transport system that unites several networks with different principles for transmitting information between end nodes.

Network layer messages are usually called packets. When organizing packet delivery at the network level, the concept of “network number” is used. In this case, the recipient's address consists of the network number and the computer number on this network.

In order to transmit a message from a sender located on one network to a recipient located on another network, you need to make a number of transit transfers (hops) between networks, each time choosing the appropriate route. Thus, a route is a sequence of routers through which a packet passes.

The problem of choosing the best path is called routing and its solution is the main task of the network layer. This problem is complicated by the fact that the shortest path is not always the best. Often the criterion for choosing a route is the time of data transmission along this route; it depends on the capacity of communication channels and traffic intensity, which can change over time.

At the network level, two types of protocols are defined. The first type refers to the definition of rules for transmitting end node data packets from the node to the router and between routers. These are the protocols that are usually meant when people talk about network layer protocols. The network layer also includes another type of protocol, called routing information exchange protocols. Using these protocols, routers collect information about the topology of internetwork connections. Network layer protocols are implemented by operating system software modules, as well as router software and hardware.

Examples of network layer protocols are the TCP/IP stack IP Internetwork Protocol and the Novell IPX stack Internetwork Protocol.

Transport layer. On the way from the sender to the recipient, packets may be corrupted or lost. While some applications have their own error handling, there are others that prefer to deal with a reliable connection right away. The job of the transport layer is to ensure that applications or the upper layers of the stack - application and session - transfer data with the degree of reliability that they require. The OSI model defines five classes of service provided by the transport layer.

As a rule, all protocols, starting from the transport layer and above, are implemented software end nodes of the network - components of their network operating systems. Examples of transport protocols include the TCP and UDP protocols of the TCP/IP stack and the SPX protocol of the Novell stack.

Session level. The session layer provides conversation management to record which party is currently active and also provides synchronization facilities. The latter allow you to insert checkpoints into long transfers so that in case of failure you can go back to the last checkpoint, instead of starting all over again. In practice, few applications use the session layer, and it is rarely implemented.

Presentation level. This layer provides assurance that information conveyed by the application layer will be understood by the application layer in another system. If necessary, the presentation layer converts data formats into some common presentation format, and at the reception, accordingly, performs the reverse conversion. In this way, application layers can overcome, for example, syntactic differences in data representation. At this level, encryption and decryption of data can be performed, thanks to which the secrecy of data exchange is ensured for all application services at once. An example of a protocol that operates at the presentation layer is the Secure Socket Layer (SSL) protocol, which provides secure messaging for the application layer protocols of the TCP/IP stack.

Application layer. The application layer is really just a set of various protocols that enable network users to access shared resources such as files, printers, or hypertext Web pages, and to collaborate, for example, using the email protocol. The unit of data that the application layer operates on is usually called a message.

There is a very wide variety of application layer protocols. Let us give as examples at least a few of the most common implementations of file services: NCP in the Novell NetWare operating system, SMB in Microsoft Windows NT, NFS, FTP and TFTP, which are part of the TCP/IP stack.

3.4 Application interaction protocols and transport subsystem protocols

Functions at all layers of the OSI model can be classified into one of two groups: either functions that depend on a specific technical implementation of the network, or functions that are oriented to work with applications.

The three lower levels - physical, channel and network - are network-dependent, that is, the protocols of these levels are closely related to the technical implementation of the network and the communication equipment used.

The top three layers - session, presentation and application - are application-oriented and have little dependence on technical features building a network. The protocols at these layers are not affected by any changes in network topology, hardware replacement, or migration to another network technology.

The transport layer is the intermediate layer, it hides all the details of the functioning of the lower layers from the upper layers. This allows you to develop applications that are independent of the technical means directly involved in transporting messages.

Figure 2 shows the layers of the OSI model at which the various network elements operate.

A computer with a network OS installed on it interacts with another computer using protocols of all seven levels. Computers carry out this interaction through various communication devices: hubs, modems, bridges, switches, routers, multiplexers. Depending on the type, the communication device can either operate only on physical level(repeater), either on the physical and link (bridge and switch), or on the physical, link and network, sometimes also capturing the transport layer (router).

3.5 Functional correspondence of types of communication equipment to the levels of the OSI model

The best way The key to understanding the differences between network adapters, repeaters, bridges/switches, and routers is to look at how they work in terms of the OSI model. The relationship between the functions of these devices and the layers of the OSI model is shown in Figure 3.

A repeater, which regenerates signals, thereby allowing you to increase the length of the network, operates at the physical level.

The network adapter operates at the physical and data link layers. The physical layer includes that part of the functions of the network adapter that is associated with the reception and transmission of signals over the communication line, and gaining access to the shared transmission medium and recognizing the MAC address of the computer is already a function of the link layer.

Bridges do most of their work at the data link layer. For them, the network is represented by a set of MAC addresses of devices. They extract these addresses from headers added to packets at the data link layer and use them during packet processing to decide which port to send a particular packet to. Bridges do not have access to higher-level network address information. Therefore, they are limited in making decisions about possible paths or routes for packets to travel through the network.

Routers operate at the network layer of the OSI model. For routers, a network is a set of device network addresses and a set of network paths. Routers analyze everything possible ways between any two network nodes and select the shortest one. When choosing, other factors may be taken into account, for example, the state of intermediate nodes and communication lines, line capacity or the cost of data transmission.

In order for a router to perform the functions assigned to it, it must have access to more detailed information about the network than that available to the bridge. In addition to the network address, the network layer packet header contains data, for example, about the criteria that should be used when choosing a route, about the lifetime of the packet in the network, and about which upper-level protocol the packet belongs to.

Thanks to the use additional information, a router can perform more packet operations than a bridge/switch. Therefore, the software required to operate the router is more complex.

Figure 3 shows another type of communication device - a gateway, which can operate at any level of the OSI model. A gateway is a device that performs protocol translation. A gateway is placed between communicating networks and serves as an intermediary, translating messages coming from one network into the format of another network. The gateway can be implemented either purely by software installed on a regular computer, or on the basis of a specialized computer. Translating one protocol stack into another is a complex intellectual task that requires maximum complete information about the network, so the gateway uses the headers of all broadcast protocols.

3.6 IEEE 802 Specification

Around the same time that the OSI model was introduced, the IEEE 802 specification was published, which effectively extends the OSI networking model. This expansion occurs at the data link and physical layers, which determine how more than one computer can access a network without conflicting with other computers on the network.

This standard details these layers by breaking the data link layer into 2 sublayers:

– Logical Link Control (LLC) – logical link control sublevel. Manages connections between data channels and defines the use of logical interface points, called Services Access Points, which other computers can use to pass information to higher layers of the OSI model;

– Media Access Control (MAC) – device access control sublayer. Provides parallel access for several network adapters at the physical level, has direct interaction with the computer's network card and is responsible for ensuring error-free data transfer between computers on the network.

3.7 By protocol stack

A protocol suite (or protocol stack) is a combination of protocols that work together to provide network communication. These protocol suites are usually divided into three groups, corresponding to the OSI network model:

– network;

– transport;

– applied.

Network protocols provide the following services:

– addressing and routing of information;

– checking for errors;

– retransmission request;

– establishing rules of interaction in a specific network environment.

Popular network protocols:

– DDP (Delivery Datagram Protocol). The Apple data transfer protocol used in AppleTalk.

– IP (Internet Protocol). Part of the TCP/IP protocol suite that provides addressing and routing information.

– IPX (Internetwork Packet eXchange) and NWLink. A Novell NetWare networking protocol (and Microsoft's implementation of this protocol) used for routing and forwarding packets.

– NetBEUI. Developed jointly by IBM and Microsoft, this protocol provides transport services for NetBIOS.

Transport protocols are responsible for ensuring reliable transport of data between computers.

Popular transport protocols:

– ATP (AppleTalk Transaction Protocol) and NBP (Name Binding Protocol). AppleTalk session and transport protocols.

– NetBIOS/NetBEUI. The first one establishes a connection between computers, and the second one provides data transfer services for this connection.

– SPX (Sequenced Packet exchange) and NWLink. Novell's connection-oriented protocol used to provide data delivery (and Microsoft's implementation of this protocol).

– TCP (Transmission Control Protocol). Part of the TCP/IP protocol suite responsible for reliable data delivery.

Application protocols responsible for the interaction of applications.

Popular application protocols:

– AFP (AppleTalk File Protocol). Macintosh Remote File Management Protocol.

– FTP (File Transfer Protocol). Another member of the TCP/IP protocol suite, used to provide file transfer services.

– NCP (NetWare Core Protocol – NetWare Basic Protocol). Novell client shell and redirectors.

– SMTP (Simple Mail Transport Protocol). A member of the TCP/IP protocol suite responsible for transmitting electronic mail.

– SNMP (Simple Network Management Protocol). TCP/IP protocol used to manage and monitor network devices.

4 NETWORK EQUIPMENT AND TOPOLOGIES

4.1 Network components

There are many network devices that can be used to create, segment, and enhance a network.

4.1.1 Network cards

Network adapter(Network Interface Card, NIC) - This peripheral device A computer that directly interacts with a data transmission medium that connects it directly or through other communications equipment with other computers. This device solves the problem of reliable exchange of binary data, represented by corresponding electromagnetic signals, over external communication lines. Like any computer controller, the network adapter operates under the control of the operating system driver.

Most modern standards for local networks assume that a special communication device (hub, bridge, switch or router) is installed between the network adapters of interacting computers, which takes on some functions for controlling the data flow.

A network adapter typically performs the following functions:

– Formatting of transmitted information in the form of a frame of a certain format. The frame includes several service fields, including the address of the destination computer and the frame checksum.

– Gaining access to the data transmission medium. Local networks mainly use communication channels shared between a group of computers (common bus, ring), access to which is provided using a special algorithm (the most often used is the random access method or the method of passing an access token along the ring).

– Encoding a sequence of frame bits using a sequence of electrical signals when transmitting data and decoding when receiving them. Coding must ensure the transmission of original information over communication lines with a certain bandwidth and a certain level of interference so that the receiving side can recognize the sent information with a high degree of probability.

– Converting information from parallel to serial form and vice versa. This operation is due to the fact that in computer networks information is transmitted in serial form, bit by bit, and not byte by byte, as inside a computer.

– Synchronization of bits, bytes and frames. For stable reception of transmitted information, it is necessary to maintain constant synchronization of the receiver and transmitter of information.

Network adapters differ in the type and capacity of the internal data bus used in the computer - ISA, EISA, PCI, MCA.

Network adapters also differ in the type of network technology adopted on the network - Ethernet, Token Ring, FDDI, etc. Usually, specific model The network adapter operates on a specific network technology (for example, Ethernet).

Due to the fact that each technology now has the ability to use different transmission media, a network adapter can support both one and several media at the same time. In the case when the network adapter supports only one data transmission medium, but it is necessary to use another, transceivers and converters are used.

Transceiver(transceiver, transmitter+receiver) is part of the network adapter, its terminal device that connects to the cable. In Ethernet variants, it turned out to be convenient to produce network adapters with an AUI port, to which a transceiver for the required environment can be connected.

Instead of selecting a suitable transceiver, you can use converter, which can match the output of a transceiver designed for one medium to another (for example, a twisted-pair output is converted to a coaxial cable output).

4.1.2 Repeaters and amplifiers

As mentioned earlier, the signal weakens as it moves across the network. To prevent this attenuation, repeaters and/or amplifiers can be used to amplify the signal passing through them.

Repeaters are used in digital signal networks to combat signal attenuation (weakening). When the repeater receives a weakened signal, it cleans the signal, amplifies it, and sends it to the next segment.

Amplifiers, although they have a similar purpose, are used to increase the transmission range in networks using an analog signal. This is called broadband transmission. The carrier is divided into several channels so that different frequencies can be transmitted in parallel.

Typically, the network architecture determines the maximum number of repeaters that can be installed on a single network. The reason for this is a phenomenon known as propagation delay. The period required for each repeater to clean up and amplify the signal, multiplied by the number of repeaters, can result in noticeable delays in the transmission of data across the network.

4.1.3 Hubs

A hub (HUB) is a network device that operates at the physical layer of the OSI network model, serving as the central connection point and link in a star network configuration.

There are three main types of hubs:

– passive (passive);

– active (active);

– intellectual (intelligent).

Passive hubs require no power and act as a physical connection point without adding anything to the signal passing through).

Active ones require energy, which is used to restore and strengthen the signal.

Smart hubs can provide services such as packet switching and traffic routing.

4.1.4 Bridges

A bridge is a device used to connect network segments. Bridges can be considered an improvement on repeaters because they reduce network load: bridges read the address network card(MAC address) of the receiving computer from each incoming data packet and look at special tables to determine what to do with the packet.

The bridge operates at the data link layer of the OSI network model.

A bridge functions as a repeater, it receives data from any segment, but it is more discriminating than a repeater. If the recipient is on the same physical segment as the bridge, then the bridge knows that the packet is no longer needed. If the recipient is on a different segment, the bridge knows to forward the packet.

This processing reduces network load because the segment will not receive messages that do not belong to it.

Bridges can connect segments that use different types of media (10BaseT, 10Base2), as well as with different media access schemes (Ethernet, Token Ring).

4.1.5 Routers

A router is a network communication device that operates at the network layer of the network model and can connect two or more network segments (or subnets).

It functions like a bridge, but to filter traffic it uses not the address of the computer's network card, but rather the network address information carried in the network layer portion of the packet.

After receiving this information, the router uses the routing table to determine where to route the packet.

There are two types of routing devices: static and dynamic. The former use a static routing table, which must be created and updated by the network administrator. The second ones create and update their tables themselves.

Routers can reduce network congestion, increase throughput, and improve the reliability of data delivery.

The router can be either a special electronic device, and a specialized computer connected to several network segments using several network cards.

It can connect several small subnets using various protocols, if the protocols used support routing. Routed protocols have the ability to redirect data packets to other network segments (TCP/IP, IPX/SPX). Non-routable protocol – NetBEUI. It cannot operate outside of its own subnet.

4.1.6 Gateways

A gateway is a method of communicating between two or more network segments. Allows disparate systems to communicate on the network (Intel and Macintosh).

Another function of gateways is protocol conversion. The gateway can receive IPX/SPX directed to a TCP/IP client on the remote segment. The gateway converts the source protocol to the desired destination protocol.

The gateway operates at the transport layer of the network model.

4.2 Types of network topology

Network topology refers to a description of its physical location, that is, how computers are connected to each other on the network and through which devices they are included in the physical topology.

There are four main topologies:

– Bus (bus);

– Ring (ring);

– Star (star);

– Mesh (cell).

The physical bus topology, also called a linear bus, consists of a single cable to which all computers in the segment are connected (Fig. 4.1).

Messages are sent over the line to all connected stations, regardless of who the recipient is. Each computer examines every packet on the wire to determine the recipient of the packet. If the packet is intended for another station, the computer rejects it. If the packet is intended for a given computer, then it will receive and process it.

Figure 4.1 – Bus topology

The main bus cable, known as the backbone, has terminations (terminators) at both ends to prevent signal reflections. Typically, bus topology networks use two types of media: thick and thin Ethernet.

Flaws:

– it is difficult to isolate problems with a station or other network component;

– faults in the backbone cable can lead to failure of the entire network.

4.2.2 Ring

Ring topology is used primarily in Token Ring and FDDI (fiber optic) networks.

In a physical ring topology, the data lines actually form a logical ring to which all computers on the network are connected (Figure 4.2).

Figure 4.2 – Ring topology

Access to the media in the ring is carried out through tokens, which are sent in a circle from station to station, giving them the opportunity to forward the packet if necessary. A computer can only send data when it owns the token.

Since each computer in this topology is part of a ring, it has the ability to forward any data packets it receives that are addressed to another station.

Flaws:

– problems at one station can lead to a failure of the entire network;

– when reconfiguring any part of the network, it is necessary to temporarily disconnect the entire network.

4.2.3 Star

In a Star topology, all computers on the network are connected to each other using a central hub (Fig. 4.3).

All data that the station sends is sent directly to the hub, which forwards the packet towards the recipient.

In this topology, only one computer can send data at a time. If two or more computers try to send data at the same time, they will all fail and be forced to wait a random amount of time to try again.

These networks scale better than other networks. Problems at one station do not bring down the entire network. Having a central hub makes it easy to add a new computer.

Flaws:

– requires more cable than other topologies;

– failure of the hub will disable the entire network segment.

Figure 4.3 – Star topology

The Mesh (cell) topology connects all computers in pairs (Fig. 4.4).

Figure 4.4 – Cell topology

Mesh networks are used significantly large quantity cable than other topologies. These networks are much more difficult to install. But these networks are fault-tolerant (able to operate in the presence of damage).

4.2.5 Mixed topologies

In practice, there are many combinations of major network topologies. Let's look at the main ones.

Star Bus

The mixed Star Bus topology (star on a bus) combines the Bus and Star topologies (Fig. 4.5).

The Star Ring topology is also known as a Star-wired Ring because the hub itself is designed as a ring.

This network is identical to a star topology, but the hub is actually wired together as a logical ring.

Just like a physical ring, this network sends tokens to determine the order in which computers transmit data.

Figure 4.5 – Star-on-bus topology

Hybrid Mesh

Since implementing a true mesh topology on large networks can be expensive, a Hybrid Mesh topology network can provide some of the significant benefits of a true mesh network.

Mainly used to connect servers storing critical data (Fig. 4.6).

Figure 4.6 – “Hybrid cell” topology

5 GLOBAL INTERNET

5.1 Theoretical foundations of the Internet

Early experiments on transmitting and receiving information using computers began in the 50s and were of a laboratory nature. Only in the late 60s, with funds from the Advanced Development Agency of the US Department of Defense, was it created national network. She got the name ARPANET. This network connected several major scientific, research and educational centers. Its main task was to coordinate groups of teams working on common scientific and technical projects, and its main purpose was the exchange of files with scientific and design documentation by e-mail.

The ARPANET went live in 1969. The few nodes included in it at that time were connected by dedicated lines. Reception and transmission of information was provided by programs running on host computers. The network gradually expanded by connecting new nodes, and by the early 80s, based on the largest nodes, their own regional networks were created, recreating the general ARPANET architecture at a lower level (on a regional or local scale).

For real the birth of the Internet It is generally accepted that the year is 1983. This year has seen revolutionary changes in computer communications software. The birthday of the Internet in the modern sense of the word was the date of standardization of the TCP/IP communication protocol, which underlies the World Wide Web to this day.

TCP/IP is not one network protocol, but several protocols lying at different levels of the OSI network model (this is the so-called protocol stack). Of these, TCP is a transport layer protocol. It controls how information is transferred. IP address protocol. It belongs to the network layer and determines where transmission occurs.

Lesson notes

in the discipline "Computer networks and telecommunications"

Lesson topic:“Methods of searching for information on the Internet. Internet search servers"

Group: D3T1

The purpose of the lesson: consolidate, generalize and systematize the knowledge and skills of students on the topic “Methods of searching for information on the Internet. Internet search servers”, using non-standard and creative tasks.

Lesson objectives: educational:

Study methods of searching for information on the Internet;

Continued development of skills in using Internet services;

Strengthening interdisciplinary connections (developing students’ mathematical horizons, increasing their readiness for subsequent perception of ideas for organizing work in computer networks;

stimulating interest in the topic being studied through solving non-standard problems;

To identify the quality and level of mastery of knowledge and skills on the topic “Methods of searching for information on the Internet. Internet search servers";

developing :

development of cognitive interest, logical thinking and attention of students;

development of individual practical skills and the ability to work in a team;

development of communication competence in students, skills to evaluate the results of actions performed, and apply acquired knowledge when solving problems;

educational :

increasing student motivation through the use of non-standard tasks;

formation of a creative approach to problem solving, clarity and organization, the ability to evaluate one’s own activities and the activities of one’s comrades;

fostering a spirit of healthy competition and friendly attitude towards each other;

cultivating a sense of collectivism, the ability to work in a group, respect for the opinions of others, worthy of accepting criticism addressed to oneself;

create conditions for real self-esteem of students;

developing skills of self-organization and initiative;

cultivating a sense of purpose and perseverance to achieve goals.

Type of lesson: combined lesson (multimedia lecture with elements practical work).

Type of lesson: obtaining and forming knowledge, skills, systematization and consolidation of the studied material.

Interdisciplinary connections: " Computer Science", "Information Technologies", "Applied Electronics", "Discrete Mathematics".

Forms and methods of teaching: verbal, visual, practical, interactive; individual work of students, problem solving; group work (team work), creative problem solving.

Place of the lesson in the work program: the lesson is held after studying theoretical material on the topic “Basic services of telecommunication technologies.”

Student knowledge requirements:

Students must have an idea:

About Internet services

Students must noble b:

- basic logical functions, methods of specifying logical functions with a truth table;

Basic Internet services;

Basic principles of the functioning of large networks;

mechanisms of functioning of telecommunication networks.

Students mustbe able to :

use standard communication packages to organize network interaction,

Use mailers for working with Internet e-mail and Internet browsers for searching for information.

Total time classes: 90 minutes.

Lesson equipment: Microsoft PowerPoint presentation program, computers with Microsoft program PowerPoint computer presentation “Methods of searching for information on the Internet. Internet search servers", multimedia projector, screen, speakers, didactic handouts, control sheets.

Topic: “Methods of searching for information on the Internet. Internet search servers" carries a large cognitive load. Teaching methods of working in computer networks is impossible without developing students’ logical thinking and the ability to operate with concepts and symbols of mathematical logic.

The following questions should be addressed during the lesson:

methods of searching for information on the Internet;

Internet search servers;

composing queries for search engines using logical expressions;

Recommendations for the lesson:

The frontal question is made in the form of oral answers based on the materials of the previous lesson on questions that are demonstrated on the presentation slides.

During the lesson, as the material is explained, students make notes in notes and give their own examples.

The theoretical part of the lesson is based on a slide lecture.

The practical part of the lesson is built on the basis of individual work and the completion of practical tasks assigned by the teacher.

Lesson Plan

Organizational moment – 1 min.

Introductory word – 2 min.

Theoretical part: multimedia lecture “Methods of searching for information on the Internet. Internet search servers” – 30 min.

Student presentations on topics: Yandex search engine, Rambler, Google – 15 min

Problem solving workshop: student work under the guidance of a teacher on the Internet – 35 min.

Reflection –3 min.

Conclusion – 2 min.

Homework assignment – 2 min.

During the classes

Organizing time. Greeting students, conversation with the duty officer . Marking students absent from class.

Introductory word. Setting lesson goals and motivation . Today we have a lesson on the topic “Methods of searching for information on the Internet. Internet search servers" using non-standard and creative tasks.

(Slide 1 is shown. Title). We will get acquainted with one topic from the section “Internet Information Resources and Application Level Protocols”, repeat, generalize and integrate the studied material on given topic. Your task is to demonstrate theoretical knowledge of the basic concepts and methods of using Internet resources. Today in class you will also have to evaluate your knowledge, how complete and sufficient it is. Prepare to study further topics. Now you see the plan in accordance with which we have to work today. (Demonstrated slide 2)

Theoretical part: multimedia lecture “ Methods for searching information on the Internet. Internet search servers»

Interactive lecture (projector + screen) in dialogue with students using an electronic presentation.

When organizing the lesson, a group form of organizing students’ independent work was used: students are divided into groups. Each group is responsible for a specific search engine. The first group is the Yandex search engine, the second group is the Rambler search engine, the third group is the Google search engine.

general information

According to the analytical service Netcraft, as of October 2013, more than 360 million sites were registered on the Internet and more than 2 million sites appeared on the Internet every month. (Demonstrated slide 3)

What are the signs of a site's reliability?

3. Sources of information.

4. Accuracy in providing information (literacy).

5. The purpose of creating the site.

6. Relevance of data (updating).

If the answer to all six questions is yes, we will consider this site "absolutely reliable."

If the answer to the last two is ambiguously positive, it will be "quite a reliable site."

If not all three first signs are observed, but the first or second are detected, then we will call the site "raising suspicion."

In the absence of the main (first three) signs, this will be "not trustworthy" source. (Demonstrated slide 4)

If we consider the diagram of information flows on the Internet, we can see that all services and resources of the network fall under the control of search engines. (Demonstrated slide 5).

The paradox of the Internet is that the more useful information accumulates, the more difficult it is to find anything you need. (Demonstrated slide 6).

Various search engines are used to find the necessary information:

1.Search engines. These search tools respond to a request with

a list of pages that meet the specified criteria. For example:

Yandex ( http://www.yandex.ru);

2. Catalogs, in which sites are organized by categories of a specially developed rubricator tree. For example: Yahoo (http:// www. yahoo. com);

3. Thematic collections of links. Sometimes they contain a rubricator and can be considered as a special case of a catalog limited to a certain topic. For example: , website alledu.ru;

4. Portals. Sometimes they contain a rubricator and can be considered as a special case of a catalog limited to a certain topic. For example , http:// www.5 ballov. ru

5. Search mechanisms operating within Web -site.

(Demonstrated slide 7)

Question: List the names of Russian-language portals that provide search tools? (The most popular: Yandex, Rambler, Google)

Question: What are the characteristics of search engines?

You named the main characteristics of search engines. Everyone prepared answers to specific questions at home using their own search engine.

II. First presentation on the Yandex search engine. (Students of the first group speak)

III. Second presentation on the Rambler search engine.(Students of the second group speak)

IV. Third presentation on the Google search engine. (Students of the third group speak)

(Demonstrated slides 8,9,10)

. Generalization. Each group filled out a table on the search engine (characteristics of search engines, as well as a table of the query language). We can conclude: each search node is different from the others, and in order to extract useful information from the Internet, you need to know where and how to search.

Continuation of the lecture:

How to formulate a request to find the necessary information?

1. Regardless of the form in which you used the word in the query, the search takes into account all its forms according to the rules of the Russian language.

For example,
if the query “go” is specified, then the search result will find links to documents containing the words “go”, “goes”, “walked”, “went”, etc.

2. If you typed a word with a capital letter in the query, only words with a capital letter will be found, otherwise both words with a capital and a small letter will be found.

For example,
the query 'swifts' will find both birds and the flight group. The query 'Swifts' - the flight group and those cases where a bird is mentioned when it is written with a capital letter.

3. Although the default search takes into account all forms of a given word, it is possible to search by exact word form. In this case, the request is preceded by Exclamation point "!".

For example,
the request!college will find links containing the word colleges

(Demonstrated slide 11)

If you want the words from the query to be found, then put a “+” in front of each of them. If you want to exclude any words from the search result, put a “-” in front of each of them.

Attention! The "-" sign is a minus sign. It must be written separated by a space from the previous one and together with the following word.

For example, ‘ jet printer ".
If you write ‘jet printer " or 'jet printer ", the "-" sign will be ignored.

For example, request "private advertisements for sale of computers ", will return many links to sites with a variety of private advertisements. And the request "private advertisements for sale + computers " will show advertisements for the sale of computers.

If you need a description of Crimea, and not offers from numerous travel agencies, it makes sense to ask such a request "guide to Crimea - agency - tour " (Demonstrated slide 12).

Several words typed in a query, separated by spaces, mean that they all must be included in one sentence of the document being searched. Using the "&" character will have the same effect.

For example,
when asked ‘laser printer" or "laser & printer" , or "+laser +printer" The search result will be a list of documents that contain both the word “laser” and the word ‘printer’ in the same sentence

The tilde sign "~" allows you to find documents with sentences that do not contain a word preceded by a tilde sign.

For example,
upon request ‘sport ~ football "all documents containing the word 'sport' will be found, next to which (within the sentence) there is no word 'football'." (Demonstrated slide 13)

Single & and ~ characters search within a single sentence, while double && and ~~ search within a document.

For example,
on request "recipes && processed & cheese " documents will be found that contain both the word "recipes" and the words "melted" and “cheese”, and “processed” and “cheese” should be in the same sentence.

You can place a "|" between words to find documents that contain any of the specified words. (Convenient when searching for synonyms).

For example,
Request like "photo | photography | photograph | snapshot | photographic image " specifies a search for documents containing at least one of the listed words.

(Demonstrated slide 14)

Instead of one word in a query, you can substitute an entire expression. To do this, it must be put in brackets.

For example,
request "(Visual C manual) " will return all documents with the words "Visual C manual".

(Demonstrated slide 15)

Problem solving workshop: student work under the guidance of a teacher on the Internet

Writing queries for search engines using logical expressions.

Examples of tasks and solutions

Example 1

The table shows queries to the search server. Arrange the query numbers in ascending order of the number of pages that the search engine will find for each query. To indicate the logical operation "OR" in a query, the symbol is used|, and for the logical operation “AND” – &.

1) printers & scanners & sale

2) printers & scanners

3) printers | scanners

4) printers | scanners | sale

Solution (via diagrams):

we will write down all the answers via logical operations

,
,
,

Let's show the areas defined by these expressions in a three-area diagram

Comparing the diagrams, we find a sequence of areas in increasing order: (1,2,3,4), and each subsequent area in this series covers the entire previous one (as suggested in the task, this is important!)

therefore, the correct answer is 1234.

Example 2

Request	Number of pages (thousands)
cakes & pastries
cake

How many pages (in thousands) will be found upon request

cake | bakery

Solution (solving a system of equations):

this task is a simplified version of the previous one, since only two areas are used here (instead of three): “cake” (we denote it by P) and “baking” (B)

Let's draw these areas in the form of a diagram (Eulerian circles); when they intersected, three subregions were formed, designated by the numbers 1, 2 and 3;

number of sites satisfying the request in the area i, we will denote by N i

We compose equations that determine the queries specified in the condition:

cakes & pastriesN 2 = 3200

cakeN 1 + N 2 = 8700

bakeryN 2 + N 3 = 7500

substituting the value N 2 from the first equation to the others, we get

N 1 = 8700 - N 2 = 8700 – 3200 = 5500

N 3 = 7500 - N 2 = 7500 – 3200 = 4300

number of sites on request cake | bakery equals

N 1 + N 2 + N 3 = 5500 + 3200 + 4300 = 13000

so the answer is 13,000.

Example 3

The table shows the queries and the number of pages that the search engine found for these queries in a certain segment of the Internet:

Request	Number of pages (thousands)
Dynamo & Rubin
Spartak & Rubin
(Dynamo \| Spartak) & Rubin

How many pages (in thousands) will be found upon request

Rubin & Dynamo & Spartak

R solution (Eulerian circles):

In this problem, the data is incomplete, since it does not allow us to determine the sizes of all areas; however, they are enough to answer the question posed

let's denote the areas that correspond to each request

Request	Regions	Number of pages (thousands)
Dynamo & Rubin
Spartak & Rubin
(Dynamo \| Spartak) & Rubin
Ruby& Dynamo & Spartak

It follows from the table that the total result of the first two queries includes area 2 twice (1 + 2 + 2 + 3), therefore, comparing this result with the third query (1 + 2 + 3), we immediately find the result of the fourth:

N 2 = (320 + 280) – 430 = 170

so the answer is 170.

(Demonstrated slides 16-22).

Independent group work of students using cards

When organizing the lesson, a group form of organizing students’ independent work was used: students, divided into three groups, solve the received logical problems for information requests.

After solving the problem and receiving the required answer, students sit down at their computers and ask their search programs the same queries,

Each group is responsible for a specific search engine. The first group is the Yandex search engine, the second group is the Rambler search engine, the third group is the Google search engine.

Search engines provide information about the number of sites found that satisfy queries. Compare the results obtained with the calculated data and analyze the work search engine.

(Demonstrated slide 23)

Generalization.(Demonstrated slide 24)

The results of the work of three groups working with different search engines are analyzed by discussion. An assessment of the work of each group and each search program is given.

1. Write down the best way to find this information (choice of search engine, type of query).

2. Use the capabilities of several search engines and determine the most effective search engines.

3. Analyze the results obtained from the point of view of the efficiency of search engines and the efficiency of queries using logical expressions. Present the results of the work in the table:

	Type of request
		Relevance level	Relevance level	Relevance level

Explanation: Relevance(Latin relevo - lift, facilitate) in information retrieval - semantic correspondence between the search query and the search image of the document, i.e. semantic correspondence between the information request and the received message.. By degree relevance SERPs judge the effectiveness of the search engine.

Reflection (Demonstrated slide 25)

Questions for reflection:

What are your results?

Which tasks did you like the most?

What tasks caused difficulties, how did you cope?

What else needs to be worked on?

Are you ready for the test?

Determine the percentage of your readiness for the test.

Through my work in class I:

not entirely satisfied;
I'm not happy because...

Conclusion. (Demonstrated slide 26)

Teaching assistants in each group announce the amount of points scored by each team and each student during the assignments.

The total points are made up of presentations, answers to questions, active participation in calculations and experiments on organizing queries, and analysis of the results obtained in groups. For each element of participation, the student is assigned 1 point. The maximum number of points is 10.

All points received for the individual work of each student are added and their work in class is assessed based on them.

The teacher has the right to add 2 points to those students who actively participated in general discussions and analysis of overall results.

Thus, the maximum number of points can reach 12.

Grade "5" is set if during the lesson the student gains a total 11-12 points;

grade “4” - 9-10 points;

grade “3” - 6-8 points;

grade “2” - less than 6 points.

We were able to look at the global computer network Internet from various angles. Both its positive and negative qualities and the capabilities of its resources have been identified. Summarizing all of the above, we can conclude that the Internet is a very important source of information, which undoubtedly needs to be used, but we should not forget about the problems that a computer network brings with it.

You worked well today, coped with the task assigned to you, and also showed good knowledge on the topic “Methods of searching for information on the Internet. Internet search servers." For your work in class you receive the following grades (each student’s grades for work in class are announced).

Thanks everyone for Good work. Well done!

Homework assignment (Demonstrated slide 27)

1. Review the rules for transforming logical expressions and the laws of algebra of logic – Chapter 2, § 2.1.- 5.6; pp. 36-76, V. Lysakova, E. Rakitina. Logic in computer science. Moscow. Laboratory basic knowledge, 2002

2. Repeat methods for composing queries for search engines using logical expressions -

2.Using logical expressions, make a query for the search engine and determine the number of sites found

- the table shows the queries;

Determine the number of pages that a search engine found for these queries in a certain segment of the Internet

Request	Number of pages (thousands)
cruiser\| battleship
cruiser
battleship

Analyze the results obtained

Literature:(Demonstrated slide 28)

Olifer V.G., Olifer N.A. Computer networks. Principles, technologies, protocols: Textbook for universities. 3rd ed. - SPb.: PETER, 2006. - 958 p.: ill. (electronic textbook)

Fundamentals of computer networks: Textbook. – M.: BINOM. Laboratory of Knowledge, 2006. – 167 pp.: ill.

Methodological manual “Methods of searching for information on the Internet”, Zhigulevsk, GBOU SPO ZhGK, 2013-16

V. Lysakova, E. Rakitina. Logic in computer science. Moscow. Basic Knowledge Laboratory, 2002

Computer telecommunications are used in various spheres of life in modern society: business, finance, banking, and the media.

Telecommunications- in the broad sense of the word, these are means of remote transmission of information, such as radio, television, telephone, telegraph, teletype, telex, telefax, as well as computer telecommunications that appeared relatively recently.

Computer telecommunications, or telecommunications in the narrow sense, are means of remotely transmitting information between computers using various communication channels.

Computer telecommunications are based on three main elements: a computer, a modem, and a telephone network.

It is impossible to transmit data directly from one computer to another via telephone lines, since the computer uses digital signals, and telephone lines use analog. Conversion digital signals in analog is called modulation, and the reverse process is called demodulation. Flight such a transformation modem.

Modems are available in two types: built into the computer and external. The most famous companies producing high-quality modems: Hayes Microcomputer Products, US Robotics, Multech, Paradyne.

Modem characteristics:

1. Baud rate reflects the number of bits transferred per second. The most common modem speeds are 1200, 2400 and 9600 bps. The maximum speed is approximately 3800 bps. Obviously, the higher the speed, the greater the amount of information per unit of time that can be transmitted. On the other hand, not all high-speed modems can withstand the outdated telephone equipment in our country. And besides, the higher the data transfer rate, the greater the likelihood of errors in the data. Therefore, the modem must support the standard MNP error correction protocol. There are currently 10 protocol classes. Starting from class 5, the protocol not only allows error correction, but also data compression. MNP protocols are built into the modem and run automatically.

2. The modem must be Hayes-compatible, i.e. execute a specific standard set of commands developed by Hayes Microcomputer Products. Most of the commands for such modems begin with the letters AT.

Modems operate in full-duplex or half-duplex data transmission mode. In duplex mode, data is transmitted through the modem in both directions. In half-duplex mode, data is transmitted in one direction at a time. This scheme is convenient when one-way data transfer is needed (faxes, file transfers), but is not suitable for interactive access (such as in a BBS).

In addition to its main purpose, the modem performs many other functions. For example, it can automatically dial a subscriber, answer a phone call, or report the current state of the telephone line. The modem performs all these functions under computer control.

When several communication systems are combined, a telecommunication computer network. Most of the computers included in the network perform the functions of subscriber points.

Subscriber point- this is the workplace of a user who, having a computer, peripheral equipment, modem, telephone, can connect to any network and receive or transmit information.

In order for computer systems to form a single whole, and information to be transmitted over the network around the clock, there are computer communication nodes in the network, which are called host computers(Host) Host computers with modems are constantly connected to the telephone network and all subscribers communicate through them.

Most of existing networks- These are small computer networks that have only one host computer.

The next type of networks are wide area networks that connect large node computers. Data transfer between such computers is carried out via satellites or dedicated channels. The most famous global Internet network. Domestic networks - Relcom, Glasnet, Rico.

After connecting to the network, the registered user is provided with a variety of services, the main ones being:

computer-based interpersonal telecommunications (messaging, electronic news bulletins, teleconferencing, etc.);

access to remote databases.

The entire set of computer communications systems and information flows of various natures circulating in global networks is called cyberspace.

Created on a computer screen using computer technology images real objects and processes of various nature - people, musical instruments, instruments, machines, works of art, etc. called virtual reality Of course, these are not “photographs” of objects (even moving ones, like in a movie) with which you have no contact, but quite tangible objects. You can work with them as if they were a real thing (for example, tuning and playing a piano), and conduct research and testing.

Thus, cyberspace and virtual reality, which are gradually entering our lives, introduce us to the information resources of all humanity, expand our horizons and change the very way of life.