Computer network is a set of computers connected by information transmission lines.

The exchange of information over a computer network is called telecommunications.

Types of computer networks

Local

networks

INTERNET global network

Regional networks

Corporate networks

The local area network is small. computer network operating within the same premises, one enterprise.

Network topologies

1. Bus topology

All computers are connected to one cable (bus). Terminators are installed at the ends of the cable. The cable used is a coaxial cable. Disabling any of the connected devices does not affect network operation.

2. Star topology

Each computer is connected by a separate wire to a separate port of the hub (Hub) or switch (Switches).

3. Ring topology

In a ring topology, computers are connected to a cable that is closed in a ring. Unlike the passive "bus" topology, here each computer amplifies the signals and passes them on to the next computer. Therefore, if one computer fails, the functioning of the network may be disrupted.

Corporate networks - formed to combine computers of certain organizations (military, banking, etc.) that are interested in protecting information from unauthorized access.

A corporate network can unite thousands and tens of thousands of computers located in different cities and countries.

An example is the Microsoft network - MicroSoft Network (MSN)

Regional networks - unite computers within the same region (city, country, continent).

The need for the formation of a single world information space led to the creation of the GLOBAL COMPUTER NETWORK INTERNET.

The need for the formation of a single global information space led to the creation

GLOBAL COMPUTER NETWORK INTERNET.

Regional computer networks, united

to the global Internet

Regional computer networks connected to the global Internet

The reliability of the network is ensured large quantity channels of information transmission with high bandwidth between local, regional and corporate networks.

Internet – it is a global computer network in which local, regional and corporate networks are interconnected by numerous high-bandwidth information transmission channels

Currently (January 2008), the backbone of the Internet is over 400 million servers.

Connection and internet

Each local, regional or corporate network has at least one computer (Internet server) that has permanent connection to the Internet.

1. Optical fiber communication lines

However, in cases where inconveniently located or remote computer networks are connected, when cable laying is difficult or impossible,

2. Wireless communication lines

If the transmitter and receiving antenna are within line of sight, then they are used

3. Radio channels

v otherwise information is exchanged through

4. satellite channel using special antennas

Hundreds of millions of user computers may periodically connect to the Internet using ISPs. Such a connection can be made both via fiber optic lines and switched telephone channels. Internet providers have high-speed connections of their servers to the Internet and therefore can provide Internet access via telephone channels to hundreds and thousands of users simultaneously.

To connect the user's computer via a telephone channel to the server of the Internet provider, modems must be connected to both computers. Modems provide transmission of digital computer data via analog telephone channels at speeds up to 56 Kbps.

An example of a regular modem

Modern ADSL technologies make it possible to use ordinary telephone channels for high-speed (1 Mbit/s and higher) Internet connection. It is important that while telephone number remains free.

Regular and ADSL modems connect to the computer's USB port and to the telephone jack.

ADSL modem example

Laptop users can connect to the Internet using a wireless WiFi technologies. Access points are installed at railway stations, airports and other public places wireless communication connected to the Internet. Within a radius of 100 meters, a laptop equipped with a wireless network card automatically accesses the Internet at speeds up to 54 Mbps.

PLC is a new telecommunications technology based on the use of power networks for high-speed information exchange (Internet from a socket). In this technology based on frequency division of a signal, a high-speed data stream is divided into several low-speed ones, each of which is transmitted on a separate frequency, and then they are combined into one signal.

At the same time, Internet devices can "see" and decode information, although conventional electrical devices - incandescent lamps, motors, etc. - do not even "guess" the presence of network traffic signals and work as usual.

Addressing in the Internet

IP address

In order for computers to find each other in the process of exchanging information, there is a unified addressing system on the Internet based on the use of IP addresses.

According to Hartley's formula N=2 I , where N is the number of possible information messages, and I- the amount of information that the received message carries,

The IP address carries the amount of information I = 32 bits, therefore the total number of possible IP addresses N is:

N=2 I = 2 32 = 4 294 967 296

So, an IP address with a length of 32 bits allows you to connect more than 4 billion computers to the Internet.

Every computer connected to the Internet has its own unique 32-bit binary IP address.

IP address example: 213.171.37.202

For readability, a binary 32-bit IP address is divided into

4 parts of 8 bits each and each part can be represented in both binary and decimal form.

In decimal notation, an IP address consists of 4 numbers separated by dots, each of which ranges from 0 to 255.

The IP addressing system takes into account the structure of the Internet, i.e. that the Internet is a network of networks, not a collection of individual computers. An IP address contains the network address and the address of a computer on that network.

Binary

Decimal

For maximum flexibility in the distribution process

IP addresses, depending on the number of computers on the network, the addresses are divided into 3 classes A, B, C. The first bits are allocated to identify the class, and the rest are divided into the network address and the computer address.

For example, a class A network address has only 7 bits for the network address and 24 bits for the computer address, i.e. can only exist N=2 I = 2 7 = 128 networks of this class, but each of which may contain N=2 I = 2 24 = 16 777 216 computers

Binary

Decimal

Class A

Class B

Network address (7bit)

Class C

Network address (14bit)

Computer address (24 bits)

Network address (21bit)

Computer address (16 bits)

Computer address (8bit)

Binary

Decimal

Class A

Class B

Class C

Network address (7bit)

Network address (14bit)

Computer address (24 bits)

Network address (21bit)

Computer address (16 bits)

Network address (8bit)

The belonging of a computer to a network of one class or another is easily determined by the first number of the computer's IP address:

• class A addresses - a number from 0 to 127;
• class B addresses - a number from 128 to 191;
• class C addresses - a number from 192 to 223;

Question: What type of network does our IP address belong to?

Domain name system

Computers can easily find each other by numerical IP address, however, it is not easy for a person to remember a numerical address, and for the convenience of Internet users, Domain Name System (DNS - Domain Name System).

Domain names and IP addresses are allocated by an international clearing house (ICANN).

DNS consists of several words separated by dots. The structure of the name reflects hierarchical structure DNS . The domains of the first (top-level) are indicated to the extreme right, to the left - the domains of the second level, etc.

Example: herba.msu.ru

this address belongs to the herba computer, which is registered in the msu (Moscow State University) level 2 domain in Russia (ru)/

The Domain Name System maps a computer's numeric IP address to a unique domain name.

Name (host) of the computer

Top-level domains are of 2 types:

• Geographic (two-letter - each country has a two-letter code);
• Administrative (three-letter)

2nd level domains are registered by 1st level domain administrators. So Microsoft registered the Microsoft 2-level domain in the administrative top-level domain com. (Microsoft's main server is named www.microsoft.com)

Administrative

Organization type

a commercial

Geographic

The country

educational

US government

International

Germany

US military

Computer network

former USSR

non-profit

England/Ireland

When at business communication representatives of two firms exchange business cards, then they (business cards) will necessarily indicate the address Email and the name of the company's corporate Web site. At the same time, you can also hear how the interlocutors exchange "Internet addresses" ("electronic addresses") of companies. In all of the above cases, one way or another, we are talking about the use of domain names.

In an e-mail address, formally, the domain name can be considered what is written after the symbol - "@". For example, in [email protected] the domain name of the mail host is corp.ru.

Attention: by the name itself, no access to the resource can be obtained.

The procedure for using the name is as follows:

1. first by name in hosts file find an IP address

2. then a connection is established with the remote information resource using the IP address.

Thanks to the domain name system, not only every computer, but also every file on the Internet has its own exact unique address - URL (Universal Resource Locator - “Universal Resource Locator”). It is built like this:

protocol:// domain name of the computer/ address in the directory tree on the computer/file name

The Internet, which is a network of networks and unites a huge number of different local, regional and corporate networks, functions and develops due to the use of a single principle of routing and data transportation.

Routing and transport of data on the Internet is based on

TCP / IP protocol, which is the basic "law" of the Internet.

The term TCP/IP includes the names of two data transfer protocols:

• TCP (Transmission Control Protocol) - transport protocol;
• IP (Internet Protocol) - routing protocol

Internet Protocol (IP) provides routing of IP packets, i.e. delivery of information from the sender's computer to the recipient's computer.

sender

Transmission Control Protocol (TCP), those. transport protocol, provides splitting of files into IP packets in the process of transmission and assembly of files in the process of receiving

sender. For example: "To: 198.78.213.185", "From: 193.124.5.33". The content of such an "envelope" with information is called Internet package (IP package) and is a set of bytes. IP packets, on the way to the recipient computer, pass through numerous intermediate Internet servers, on which the routing operation takes place (determining their further path)

DATA ROUTING

In order for the letter to reach its destination, the address of the recipient and the address of the sender are indicated on the envelope. Similarly, information is transferred between network computers. Where the IP addresses of the computers of the recipient and

sender

Routing Internet packages (IP packets ) ensures the delivery of information from the sending computer to the receiving computer.

Internet packet delivery routes can be completely different, and therefore Internet packets sent first may reach the recipient computer last.

For instance:

recipient

sender

The speed of information transfer on the Internet does not depend on the remoteness of the server

The speed of information transfer on the Internet does not depend on the remoteness of the Internet server, but on the route of the information, i.e. on the number of intermediate servers and the quality of communication lines (their bandwidth), through which information is transmitted from server to server

DATA TRANSPORT

Computers often exchange large files. If such a file is sent in its entirety, then it can “clog” this communication channel, i.e. make it unavailable for forwarding other messages.

To prevent this from happening, on the sender's computer, you need to break big file into small parts, number them and transform them into separate Internet packages to the recipient computer.

On the receiving computer, the source file must be assembled from the individual parts in the correct order, so the file can only be assembled when all Internet packets have arrived.

Data transport is done by splitting the files into Internet packets on the sending computer, routing each packet individually, and reassembling the files from the packets in their original order on the receiving computer.

For instance:

recipient

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Presentation on the topic: Global computer networks

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Computer networks A computer network is a system consisting of two or more spaced apart computers, united by communication channels, and providing distributed data processing. Computer networks are distributed systems, allowing you to combine the information resources of their computers.

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For efficient and collaborative work of several computers, they need to exchange information. Computers can exchange information using channels of various nature: cable radio channels, fiber optics, information transmission channel, information sender, information recipient.

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Types of computer networks Wide area network - combines many local, regional and corporate networks and includes hundreds of millions of computers (INTERNET) resources of computers and their peripheral devices.

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History of the global network Chronologically, the first to appear were wide area networks (WANs), that is, networks that unite geographically dispersed computers, possibly located in different cities and countries. Global computer networks have inherited a lot from other, much older and more widespread networks - telephone networks. Since laying high-quality communication lines over long distances is very expensive, the first global networks often used existing communication channels that were originally intended for completely different purposes. For example, for many years, global networks were built on the basis of telephone channels voice frequency, capable of transmitting only one conversation at a time in analog form. The progress of global computer networks was largely determined by the progress of telephone networks. Since the late 60s, digital voice transmission has become increasingly used in telephone networks, which has led to the emergence of high-speed digital channels connecting exchanges and allowing tens and hundreds of conversations to be transmitted simultaneously. A special technology of plesiochronous digital hierarchy (Plesiochrohous Digital Hierarchy, PDH) was developed, designed for the so-called primary, or core networks. Initially, PDH technology supported speeds up to 140 Mbps. But at the end of the 80s, Synchronous Digital Hierarchy (SDH) technology appeared and expanded the range of digital channel speeds up to 10 Gbps, and Dese Wave Division Multiplexing (DWDM) technology - up to hundreds of gigabits and even several terabits. per second. To date, global networks in terms of diversity and quality of services have caught up with local networks, which for a long time were leaders in this regard, although they were born much later.

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Combining computer networks Regional networks unite computers within the same region (city, country, continent). Corporate networks unite computers of one organization in different countries and cities, protecting them from unauthorized access (for example, MicroSoft Network).

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Internet (translated from English - between networks) is a giant worldwide computer network. Its purpose is to provide anyone with constant access to any information. The Internet is a global computer network covering the entire world. Today, the Internet has about 15 million subscribers in more than 150 countries around the world. The size of the network increases by 7-10% monthly. The Internet forms, as it were, the core that provides communication between various information networks belonging to various institutions around the world, one from the other.

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Types of connection to the INTERNET 1.Session connection - the user is connected to the network not permanently, but only for a certain time. Payment is charged for each hour of work in the network. Data is transmitted to the network in analog form. 2. Permanent connection - the computer is connected to the network constantly on a fast channel. Payment is charged for the amount of data received (traffic). The data is transferred to the network digital form. First of all, to connect to the INTERNET, you need a modem and phone line.

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Hardware networks To transmit and receive information on a network, each computer must have a special board - a network adapter Computers are connected to each other using cables of various types: coaxial twisted pair fiber optic depending on the type network adapter and type of cable, the speed of information transfer over a local network is usually in the range from 10 to 100 Mbps.

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Convergence of local and global networks Gradually, differences between local and global types network technologies began to smooth out. Previously isolated local networks began to unite with each other, while global networks were used as a connecting medium. The tight integration of local and global networks has led to significant interpenetration of the respective technologies. Convergence in data transmission methods occurs on the platform of digital data transmission over fiber-optic communication lines. The high quality of digital channels has changed the requirements for the protocols of global computer networks. New WAN technologies such as frame relay and ATM have emerged. In these networks, it is assumed that bit distortion occurs so rarely that it is more profitable to simply destroy the erroneous packet, and to transfer all problems associated with its loss to the software high level, which is not directly part of the frame relay and ATM networks. The dominance of the IP protocol has made a great contribution to the convergence of local and global networks. Today this protocol is used over any technologies of local and global networks - Ethernet, Token Ring, ATM, frame relay - to create a single composite network from various subnets.

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Computer global networks of the 90s, operating on the basis of high-speed digital channels, significantly expanded the range of their services and caught up with local networks in this regard. It became possible to create services whose work is related to the delivery of large amounts of information to the user in real time - images, videos, voices, in general, everything that is called multimedia information. The most striking example is the hypertext information service World Wide Web, which has become the main provider of information on the Internet. One of the manifestations of the convergence of local and global networks is the emergence of networks of the scale of a large city, occupying an intermediate position between local and global networks. City networks or networks of megacities (Metropolitan Area Networks, MAN) are designed to serve the territory of a large city. Modern networks MAN types are distinguished by a variety of services, allowing their customers to combine communication equipment various types, including office automatic telephone exchanges.

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Internet history. The Internet is the World Wide Web, a global information space. The history of the emergence and development of this world wide web is bright and unusual, because already 10 years after its appearance, it has conquered many organizations and countries that began to actively use the network for work. At first, the Internet served exclusively for groups of researchers and scientists, soon the military squeezed into this group, and after that, businessmen. After that, the popularity of the Internet grew rapidly. Users were seduced by the speed of information transfer, cheap global communication, many easy and available programs, unique database, etc. Today, at a low cost of services, each user can access information services from all countries of the world. Also, the Internet today provides opportunities for global communication around the world. Naturally, this is convenient for companies that have branches in different parts of the world, for transnational corporations, as well as for management structures.

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How and when did the Internet appear. It happened over 50 years ago. Back in 1961, on the instructions of the US Department of Defense. began work on a pilot project to create a network between computers to transmit data packets. Each node has the authority to originate, transmit, and receive messages from other computers. In this case, messages are divided into standardized elements, called "package". Each package is assigned an address, which ensures the correct and complete delivery of documents. In the first version of the theoretical development of the predecessor of the modern World Wide Web, which was released in 1964 thanks to Paul Baran, it was argued that all network nodes should have the same status. This network was called ARPANET, and it was intended to be studied various options ensuring the reliability of communication between different computers. It became the immediate predecessor of the Internet. -Paul Baran - thanks to whom in 1964 the network appeared - the progenitor of the modern Internet.

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For eight years, DARPA worked on the project, and in 1969, the Department of Defense approved ARPANET as the leading research organization in the field of computer networks. From that time, nodes began to be created new network. As early as next year, ARPANET hosts were using NCP to exchange. A year later, the network already had 15 nodes. 1972 is the year in which the addressing design teams were created to harmonize different protocols. At the same time, TCP / IP data transfer protocols were developed. In 1973, the first international connections were made. The countries that entered the ARPANET network were England and Norway. The ARPANET project turned out to be so successful that soon many organizations in the USA, England and Norway wished to join it. The history of the Internet is just beginning. In 1976, they developed the UUCP protocol, and three years later they launched USENET, which works on the basis of UUCP. The US Department of Defense in 1983 declared TCP / IP as its standard. 1984 was the year of the introduction of the DNS system, and the total number of hosts exceeded 1000. The formation of CSNET was greatly accelerated in 1986, when supercomputing centers began to be created. Already by 1987, the number of hosts had crossed over 10 thousand. And in 1988, NSFNET began using the T1 channel. -DISA - Defense Information Systems Agency - information systems defense agency.

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Internet in Russia. The network went into operation in 1995. In 1996-98, a backbone network was built for science and higher education. At the same time, networks of commercial suppliers emerged and developed. Initially, they focused on connecting organizations. In 1998, Rostelecom formed the Relcom-DS company together with Relcom. Today it is the largest provider of Internet services in Russia. To date, the Internet already has a huge database of information in Russian. According to sociologists, at the end of 1998 in Russia about 1.5 million people were Internet users, more than half of these users lived outside of Moscow. In 1999, the number of users exceeded 5 million.

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The negative impact of the Internet on humans. -Internet and vision. -Computer and bad health. -Internet is addictive.

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1.1 Internet and vision. In fact, it is not the Internet that badly affects vision, but the computer, but the Internet is definitely to blame for this. Let's look at the statistics of those whose vision deteriorates more. This means that those users who communicate on the computer are more likely to worsen their vision. Such users communicate using the Internet, which means that the Internet negatively affects our vision. Vision deteriorates due to greater fatigue, when a person sits at a computer for a very long time and continuously, vision weakens. Also, vision deteriorates when reading from the monitor screen. 1.2 Computer and bad health. Man working on a computer long time must maintain a relatively immobile position, which negatively affects the spine and blood circulation throughout the body (blood stasis). Long work on the keyboard leads to overstrain of the joints of the hand and the muscles of the forearm. Working at a computer involves processing a large amount of information and constant concentration of attention, therefore, with prolonged work at a computer, mental fatigue and impaired attention often develop. Working at a computer often absorbs all the attention of a working person, and therefore, such people often neglect normal nutrition and work from hand to mouth all day. This is directly related to the Internet, because a person at a computer will spend more time only when he is on the Internet, a person will absorb a large number of information, communication, and he will lose track of time, and health will deteriorate every minute. 1.3 The Internet is an addiction. Computer addiction is no less dangerous than drug addiction, as it leads to a significant violation of adaptation in society (inability to work, inability to start a family or simply serve oneself). Internet addiction is mental disorder, an obsessive desire to connect to the Internet and a painful inability to disconnect from the Internet in time.

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The positive impact of the Internet on people. Positive features of the influence of the Internet on a person - Earnings in the network, job search. - Ability to pay, order many services via the Internet. - Show yourself to the world. - Communicate with people, find old friends, classmates. - On the Internet, you can always get the latest news on any topic.

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We have considered some of the negative aspects of the Internet, but you can also find positive ones. We can communicate with people who are thousands of kilometers away, we can exchange information at a distance, we can make all kinds of purchases without leaving home, etc. Consider useful features Internet. 2.1Purchases over the Internet. Now it is becoming very popular to purchase through online stores, you choose the product you need, put it in the online basket and pay with a card, ATM or web wallet. It is very comfortable. 2.2Internet money. Now at this time it has become popular to have an online wallet. This is a kind of wallet, but we cannot see or touch it. it is in interactive space. It is visual, but the money that is in it is a real means of payment. With this money, we can pay for other goods from online stores. And these are just the main advantages. The needs and demands of Internet users are very different. Some want to get something new software. Others are looking for certain documents they need for their professional activities. Still others connect to the network to receive e-mail. The Internet helps everyone.

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• Besides local networks also exist:
• A corporate network is an association of local networks within a single corporation.
• A regional network is an association of computers and local networks to solve common problems regional scale.

• The need for the formation of a single global information space led to the creation of the global computer network Internet.

• The global network is an association of computers located at a remote distance for the common use of world information resources.

• Internet

• inter- "between"

• net, network- "net"

• The Internet is a global computer network that unites many local, regional and corporate networks and includes tens of millions of computers.

• Turning to the Internet, we use the services of an Internet provider. The provider connects clients to its network, which become part of the provider's network and at the same time part of all the interconnected networks that make up the Internet.

• In order for computers to find each other in the process of exchanging information, there is a unified addressing system on the Internet based on the use of an IP address.
• Every computer connected to the Internet has its own unique 32-bit (in binary system) IP address.
• The total number of IP addresses is over 4 billion:
• N=232=4294967296

• The address of a computer on a network is called an IP address.
• General form:
• XXX.XXX.XXX.XXX

• octets

• octets

• An IP address consists of four parts written as dotted decimal numbers (for example, 192.168.1.1). Each of these four parts is called an octet. An octet is eight binary digits (for example, 11000000, or 192 in decimal). Thus, each octet can take in binary form values ​​from 00000000 to 11111111, or from 0 to 255 in decimal. The following figure shows an example of an IP address where the first three octets (192.168.1) are the network number and the fourth octet (16) is the host ID.

• Host - any computer connected to the Internet, regardless of its purpose.
• 195.85.102.14

• 195th subnet of the Internet

• 85th subnet 195th subnet

• 102nd subnet 85th subnet

• 14th computer in 102 subnets

• Domain Name System (DNS)
• DNS converts the numeric IP address of a host (computer) into a set of characters.

• The Internet has a more user-friendly and user-friendly system of addresses, in which the address is indicated by an individual domain name. This is a symbolic name system.
• Each domain name consists of several words separated by dots.
• Domain names are built on a hierarchical basis. The rightmost one is the top-level domain. Further decoding of a domain name is made from right to left.

• Examples of domain names:
• microsoft.com is a commercial organization of the Microsoft Corporation
• www.gov.ru - the official website of the Russian government

• A domain is a group of computers that are grouped together in some way.

• www.qqq.microsoft.ru

• 1st level domain

• 2nd level domain

• 3rd level domain

• 1st level domains ( domain zones)

• The first level domain (top level) is 2 - 4 letters that are placed at the end of each domain name after a dot (.ru, .com, .ua, .uz, etc.), and are not used for site names by themselves.
• A second-level domain is obtained by adding the word (website name) before the first-level domain.
• A third-level domain is obtained by adding a word through a dot before the second-level domain.
• There are also fourth-level domains, they are formed according to the same principle, but are used extremely rarely. Fourth-level domain names are quite long and complex, and their names are hard to remember.

• In addition, first-level domain names can be divided into national (geographic) domains, and general use domains (ie, for sites of a certain orientation).
• Examples of geographic domain zones:
• .ru - Russian Federation
• .rf - Russian Federation
• .ua– Ukraine
• .uz – Uzbekistan (domain name registration in Uzbekistan)
• .kz - Kazakhstan
• .am - Armenia

• Examples of public domain zones:
• .info - information nodes.
• .net - providing networking
• .org - non-profit organizations
• .biz - commercial organizations
• .com - commercial
• .gov - government

• http:// - Hyper Text Transfer Protocol;
• www - World Wide Web - World Wide Web;
• myhost.mydomain - third-level domain;
• spb - second-level domain;
• Ru is the first level domain.

• Internet packet routing ensures that information is delivered from the sending computer to the receiving computer.
• Data is transported by splitting files into Internet packets on the sending computer, routing each packet individually, and reassembling the files from the packets in their original order on the receiving computer.

• To communicate with each other on the Internet, computers of different types and various operating systems use different protocols - sets of rules and agreements that describe exactly how data is transmitted over the network.

• The Internet functions and develops thanks to the use of a single data transfer protocol TCP/IP. The term TCP/IP includes the names of two protocols:
• Transmission Control Protocol (TCP)
• Internet Protocol (IP)

• The TCP/IP protocol provides for the transfer of information between computers on a network. In order for the letter to reach its destination, the information is packed into an "envelope" on which the IP addresses of the recipient's and sender's computers are "written". For example, "To: 198.78.213.165", "From: 193.124.5.33". The contents of the envelope computer language is called an IP packet and is a collection of bytes.

• IP packets on their way to the receiving computer also pass through numerous intermediate Internet servers, on which the routing operation takes place. As a result of routing, IP packets are sent from one Internet server to another, gradually approaching the recipient computer. Computers that forward, receive, and route packets must follow the same strict rules in order to act quickly and smoothly. The set of these rules for the Internet is the Internet Protocol (IP)

• On the Internet, a situation often occurs when you need to send a multi-megabyte file. In such cases, on the sending computer, it is necessary to split a large file into small parts, number them and transport them in separate IP packets to the receiving computer. On the receiving computer, you need to assemble the source file from separate parts. All these actions are performed on the basis of the Transmission Control Protocol, i.e. the transport protocol.

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The Internet is a global computer network that unites local, territorial and corporate networks WWW (World Wide Web - World Wide Web) or simply Web (Web).

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Global computer network Internet The Internet is a global computer network that unites many local, regional and corporate networks and includes tens of millions of computers. The Internet is in fact network base data. Hyperlinks link hundreds of millions of documents together into a single network database. Internet

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The word Internet (English Internet), denoting a global computer network, arose as an abbreviation for Interconnected Networks - interconnected networks or "network of networks". Unlike local networks, its "elements" are not individual computers, but networks. Information on the Internet is stored on servers connected by high-speed communication lines (fiber optic, satellite). Almost all Internet services are based on the use of "client-server" technology: the client program on the user's computer requests information, the server returns a response.

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The World Wide Web The World Wide Web or "web" (Eng. And / And / And / = World Wide Web) is a service for accessing hypertext documents (web pages) stored on servers. Now WWW is the most popular Internet service. Hypertext is text that contains active links (hyperlinks) to other documents. Hyperlinks are usually underlined and highlighted in color (blue by default). If you left-click on a hyperlink, the document that the link points to is loaded into the browser window. On modern web pages, there is not only text, but also graphics, sound, video, and each element can be a hyperlink. Such documents are called hypermedia. A site (web site) is a group of web pages that are located on the same server, united by a common idea and linked using hyperlinks. To make the site available to other computers, a special program must be running on the server - a web server. Most popular web servers:

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Apache (httpd.apache.org), a free web server for various operating systems including Windows, Linux, Mac OS; IIS (www.iis.net) - commercial web server for Windows; nginx (sysoev.ru/nginx) is a free web server and mail server for large sites (there are versions for Windows and UNIX-like systems). Browser programs are used to view web pages on the screen (Internet Explorer, Mozilla Firefox, Safari, Chrome, Opera). The browser sends a request to the web server containing the URL of the document (web page, picture, file, etc.), and the server responds with the requested data. The exchange takes place over the HTTP protocol.

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Ways to connect to a provider: The user gets access to the global network through a provider - a company whose local network is directly connected to the Internet. using a modem over a regular telephone line; the data exchange rate does not exceed 56 kbps, so this method is practically not used anymore; using an ADSL modem, which also uses a telephone line, but allows you to simultaneously talk on the phone and surf the Internet; the data transfer rate from the Internet to the user can reach 25 Mbps, however, on telephone exchange it is necessary to install additional equipment (a splitter that separates a low-frequency telephone signal from a high-frequency signal that transmits digital data); through the provider's local network (if it exists in your home); in this case, the telephone line is not used; using wireless modems (USB modems) that use networks mobile operators and work wherever mobile communication is available; the data transfer rate for 3rd generation networks (eng. 3G = 3rd generation) reaches 10 Mbps, and in 4th generation networks (4G) - up to 1 Gbps.

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New generations of mobile communication began to be developed almost every ten years since the transition from the development of the first generation of analog cellular networks in the 1970s (1G) to digital transmission networks (2G) in the 1980s. A sufficient amount of time passed from the start of development to actual implementation (for example, 1G networks were introduced in 1984, 2G networks - in 1991). In the 1990s, the 3G standard began to be developed. 4G generation networks based on the IP protocol began to be developed in 2000 and have been introduced in many countries since 2010. 4G is a generation of mobile communications with increased requirements. It is customary to refer to the fourth generation promising technologies, allowing data transmission at a speed exceeding 100 Mbit / s - mobile and 1 Gbit / s - fixed subscribers. LTE Advanced (LTE-A) and WiMAX 2 (WMAN-Advanced, IEEE 802.16m) technologies have been officially recognized wireless standards communications of the fourth generation 4G (IMT-Advanced) by the International Telecommunication Union at a conference in Geneva in 2012. Highly mobile subscribers (e.g. trains and cars) should be provided with 100 Mbps and 1 Gbps should be provided with low mobility subscribers (e.g. pedestrians and fixed subscribers)

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Working sketch diagram of the first global network ARPA NETWORK The first network consisted of 4 computers

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Short story In the 1960s, the US Department of Defense began developing computer system data transmission, which was called ARPANET (Advanced Research Projects Agency Network, advanced research agency network). This project was based on the following ideas: the network unites computers with different hardware and software;

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when connecting a new network, no alteration of the existing part is required; there is no single center (such a network is called distributed), this ensures survivability in the event of failure of any node; packet data transmission: the transmitted data is divided into small packets, one communication line is used for the simultaneous transmission of several blocks of data.

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In 1969, the first data exchange took place over a network between computers installed at the University of California and the Stanford Research Center. In 1971, an e-mail program was created, which immediately became very popular. Beginning in 1973, universities and colleges not only in the United States, but also in Europe, have been connected to the new network. In 1983, the network is divided into two parts: the military network MilNet and the public network, which is called the Internet. Story Russian Internet begins in 1990, when the Relcom postal network was organized - the first provider in the Soviet Union. In 1991, British scientist Tim Bernes-Lee developed a data exchange system in the form of hypertext - text with active links to other documents. Now it is called the World Wide Web (eng. WWW = World Wide Web) and is the most powerful service on the Internet. Many mistakenly believe that the Internet and the World Wide Web are one and the same. In fact, this is not the case, because there are other services on the Internet - e-mail, file sharing, chat rooms, forums, etc.

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Graphical depiction of links between Internet networks. Only connections between servers are shown

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The Internet functions and develops thanks to the use of a single data transfer protocol TCP/IP. Data transfer protocol TCP/IP Internet Protocol (IP) - routing protocol - provides routing of IP packets, i.e. delivery of information from the sending computer to the receiving computer. Transmission Control Protocol (TCP) - transport protocol - provides partitioning transferred files on IP packets in the process of transmission and assembly of files in the process of receiving.

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In order to account for millions of PCs on the network, unique codes are used, network protocols TCP/IP. This number consists of 4 sections, each from 0 to 255 198.168.10.65 Provider - a person or organization, an Internet service provider Each computer connected to the Internet has its own unique 32-bit IP address (Internet Protocol). Possibly 232 = 4,294,967,296 IP addresses, written as four decimal numbers from 0 to 255, separated by a dot: 123.45.67.89. Internet Addressing

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Protocols You already know that the source and destination must use the same protocol to transmit information, a set of rules and conventions that govern how data is exchanged on a network. The Internet has adopted the TCP/IP protocol, developed in 1974, as a standard. Generally speaking, this is not one protocol, but a whole family, the name of which comes from the two most important protocols - TCP (English Transfer Control Protocol - transmission control protocol) and IP (English Internet Protocol - Internet Protocol). Let's try to figure out why you need to use several protocols to work on the Internet. Suppose a browser on computer A requests a web page from a server located on computer B. The "conversation" between the browser and the server is via HTTP (HyperText Transfer Protocol). The browser and web server cannot communicate directly. To send a request to a server, the browser passes the server's address and the request text to the operating system, which invokes the TCP protocol driver.

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The task of the TCP driver is to establish a connection with remote computer and ensure data delivery. The transmitted data block is divided into packets (the packet size usually does not exceed 1.5 KB), and each packet is transmitted to the next level - the IP protocol driver, which sends it to the network at the specified address. Usually, when working on the Internet, computers A and B are not directly connected , so the task of the IP protocol is to determine the router node to which the packet needs to be sent so that it reaches computer B. When the route is determined, the packet (with added service information) is transmitted to physical layer(for example, to a network card), where it is transmitted simply as a string of bytes. Physical layer protocols can be anything, they are not defined in the standard. The IP protocol does not guarantee the delivery of packets, so the TCP driver must (using the established connection) check that the data has been received and retransmit the packet if it fails. At the other end of the connection, the TCP driver "collects" the packets into a single block of data and passes it to the application layer (the request reached the server). Routers exchange information with each other, reporting the failure or connection of some sections of the network. The routing tables are updated automatically so that packet routing takes into account the actual network structure at the time.

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Classes of IP addresses There are 5 classes of IP addresses - A, B, C, D, E. An IP address belongs to one class or another is determined by the value of the first octet (W). The correspondence between the values ​​of the first octet and the address classes is shown below. IP address class A B C D E First octet range 1-127 128-191 192-223 224-239 240-247

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Ranges: Class C to A 0.0.0.0 127.255.255.255 B 128.0.0.0 191.255.255.255 C 192.0.0.0 223.255.255.255 D 224.0.0.0 239.255.255.255 E 240.0.0.0 25

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Thus, the Internet uses a four-layer system of protocols, each of which "does its own thing": 1) the application layer - the format of requests and responses exchanged between programs; 2) transport layer (TCP) - rules for packet transmission of data blocks without regard to their content; 3) network layer (IP) - route selection rules for individual packets without a guarantee of their delivery; 4) physical layer - the rules for the transmission of individual bytes over a cable, fiber optic or other communication line.

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At the application level (which is "closest" to the user), the most commonly used protocols are: HTTP - for transferring web pages; FTP - for file transfer; SMTP - for sending e-mail messages to the server; POP3 or IMAP - to receive email messages from the server. There are other protocols (for chat rooms, newsgroups, etc.), but they all use TCP and IP, respectively, at the transport and network layers

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212.96.118.82, 256*256*256*256 Internet addresses IP addresses Any two computers on the Internet can communicate with each other. To do this, each of them must have a unique address. From the "point of view" of computers, it is more convenient to work with numerical addresses, each of which occupies the same place in memory. These addresses (called IP addresses) consist of four numbers ranging from 0 to 255, for example, 192.168.104.115

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These numbers encode the network number and computer number on the network. In order to isolate these two parts from an IP address, wildcards are used. The mask is also four numbers in the range 0-255, but it is built in a special way, according to the principle of “n ones, then zeros” in binary code. For example, the mask is 255.255.255.0 Due to the rapid development of the Internet, the addresses that can be used in such encoding will soon not be enough for everyone. Therefore, it is assumed that there will be a gradual transition to the new (sixth) version of the IP protocol, which is designated as IPv6. It has 128 bits for each address, not 32. Already, there are more than 1600 networks that use IPv6; it is supported by all modern operating systems and equipment manufacturers. Full transition to IPv6 will take several years, it will require a lot of money and the replacement of all obsolete devices. Generally speaking, an IP address is assigned not to a computer, but to an interface - a data transmission channel (network card, modem). Therefore, one computer can have several IP addresses, for example, if it has two network cards installed (or a network card and a modem).

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RU STAVROPOL ALRUS alrus.stavropol.ru Top-level domain - Country Low-level domain - City Low-level domain - Node .

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Top-level domains are of two types: geographic (two-letter - each country has a two-letter code) and administrative (two-three-letter). Domain name system Microsoft's main server www.microsoft.com microsoft Administrative Organization type com Commercial edu General education gov US government int International mil Military US net Computer network org Non-profit Country Canada Germany Japan Russia former USSR England / Ireland USA Geographic ca de jp ru su uk us com www

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Com - commercial Org - non-commercial Gov - government Edu - educational Mil - military Net - networking Biz - business; Info - information sites; Name - personal sites; Museum - museums; Primary top-level domain names

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ru - Russia au- Australia by - Belarus ca - Canada de - Germany fr - France jp - Japan In addition, each country has its own two-letter first-level domain Main top-level domain names for countries

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The distribution of IP addresses and first-level domains is handled by the international organization ICANN (Internet Corporation for Assigned Names and Numbers). Russian domain.ru was registered in 1994. A free second-level domain can be registered by anyone for a small fee. Such services are provided by special organizations - domain name registrars, for example, RU-Center (nic.ru). Third level domains can often be obtained for free. For example, the site narod.yandex.ru provides everyone with a place for a site and a third-level domain like ivanov.narod.ru.

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Previously, only Latin letters, numbers and hyphens were allowed in domain names. Now you can register domains containing other UNICODE characters, for example, letters of the Russian alphabet. Domain.rf is assigned to Russia, in which everyone can register second-level domains. Thus, two systems of addresses are currently used on the Internet: IP addresses and domain names. To establish a correspondence between them, special servers called DNS servers store tables consisting of IP address - domain name pairs. Their task is to return an IP address for a given domain name (or vice versa) at the request of a client computer.

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When registering an address, the provider provides the following data: IP address Netmask Name server Gateway Phone number of the provider's modem Instructions for logging in, etc.

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In order for the computer to be able to establish a connection with the network, in the settings network card(or modem) specifies the IP address, netmask and DNS server address. Sometimes this data is determined automatically when you connect to the provider's network. When you enter the website address (domain name) in address bar browser, first a query is sent to the DNS server, the purpose of which is to determine the IP address of the server. If successful, a request is made to obtain a web page, with the IP protocol driver using the received IP address rather than the domain name. Note that one domain name can correspond to several IP addresses. this technique is used to distribute the load on sites with a large number of visitors (for example, www.yandex.ru, www.google.com). Thus, the correspondence between domain names and IP addresses can be described as "many-to-many": several domain names can be associated with one IP address and vice versa.

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Resource address (URL) Not only does every computer on the Internet have an exact address, but so does every document. For such an address, the English abbreviation URL = Uniform Resource Locator is most often used. A typical URL consists of four parts: protocol, server name (or its IP address), directory, and document (file) name. This recording system was invented in 1990 by the creator world wide web T. Bernes-Lee. For example, the address http://example.com/doc/new/vasya-new.htm includes HTTP protocol- protocol for the exchange of hypertext documents (this is a web page); server domain name example.com; directory on the server /doc/new; the file name is vasya-new.htm.

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In other words, to access the vasya-new.htm document, which is located in the /doc/new directory on the example.com server, you need to use the HTTP protocol. Sometimes the directory and filename are not specified, such as http://example.com. This means that we are accessing the main page of the site. It may have different names, depending on the server settings (most often - index.htm, index.html, index.php). FTP is often used to download and upload files, then the document address looks something like this: ftp://files.example.com/pub/new/vasya-new.zip

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Examples of Internet addresses https://www.yandex.ru https://www.mail.ru http://www.rp5.ru/ http://ashk.rf http://support.kaspersky.ru/ Protocol transmissions Web (Internet) zone

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Basic Internet services Storage and provision of information E-mail Search engines Voice and video communication File transfer Forums and blogs Social networks Online stores Electronic payment systems, etc.

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A feature of the modern web is the involvement of users in filling sites with information and its correction. This led to the emergence of the term "Web 2.0", which is sometimes used to refer to the current stage of development of the World Wide Web. Sites using Web technologies 2.0 generally require user registration, which requires a valid email address. Anyone can create a "private zone" with their own settings and store files, photos, videos, notes there. Others may comment on these materials. Users unite in groups (communities) in order to discuss issues of interest to them together. Often participants can evaluate each other's posts, thus changing the "reputation" (or "karma") of the participants, some rivalry appears

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Social networks: VKontakte (vk.ru), Odnoklassniki (www.odnoklassniki.ru), Facebook (www.facebook.com) have become a place for many to communicate with friends and classmates. Special sites have appeared where users can blog - online diaries (www.livejournal.com, - www.blogspot.com). The influence of blogs has grown so much that they have become equated with mass media/ Actively developing wiki systems (eng. wiki) - websites, the structure and content of which users can change using the tools that are on the site itself. The most famous wiki site is the free encyclopedia Wikipedia (the Russian version is hosted on the site ru.wikipedia.org

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Domain Names Unlike computers, humans are not comfortable working with numeric addresses. They are hard to remember, it is easy to make a mistake when entering an IP address, and sometimes it is quite difficult to notice it. Therefore, in 1984, the Domain Name System (DNS = Domain Name System) was developed, which allowed the use of symbolic site names, for example, www.mail.ru. Domain (English domain - area, district) is a group of symbolic addresses on the Internet. Domains form a multi-level structure (hierarchy, tree), nested into each other, like nesting dolls. In some ways, such a system resembles a postal address, which indicates the country, city, street, house, apartment. The point at the root of the tree is the root domain. Top-level domains (they are called domain zones) can indicate a type of organization, for example

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Searching for information on the Internet The Internet now contains a huge amount of data, while finding the information you need is sometimes quite difficult. Search system is a website that is designed to search for information on the Internet. At the beginning of the development of the Internet, when there were few sites, webmasters (site creators) compiled lists of links to interesting sites. When there were a lot of links, they began to be grouped by topic. As a result of the development of this idea, catalogs appeared. A web directory is a list of links to sites broken down by topic with a brief description of them. Catalogs usually use a multi-level grouping of links (tree): each of the major topics (News, Science, Education, etc.) has sections, sections have subsections, etc. Yahoo (www.yahoo.com), founded in 1995, was the first major directory site. The largest of the Russian directories are Yandex-catalog (yaca.yandex.ru) and [email protected] (list.mail.ru). Catalogs are filled manually by human experts (catalog editors), each of whom is responsible for a specific section. In addition, webmasters can offer editors their sites for inclusion in the catalog (for free or for a fee).

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The search engine is automatic system, which stores information about all web pages known to it and issues, upon request, the addresses of those of them where the user entered keywords. A search engine robot browser (often called a "spider", eng.crawler) pumps out web pages from sites, following all the links they encounter. Keywords are a set of words and expressions that reflect the required information. The search robot uses the index to find those pages where these words occur. Each search engine has its own language, which allows you to make complex queries, for example, exclude certain keywords from the search or search for one of a given set of words. In many systems, the symbol | is used to indicate the logical operation "OR" (one of the specified words is needed), and the symbol & is used for the logical operation "AND" (both words are needed). If you need to find a phrase, it is taken in quotation marks in the query. Typically, a search robot finds thousands of pages that match a query. They are issued to the user in the order determined by the developers. Most often, citation is taken into account - the number of links from other sites to this page; the more links, the higher the "rank" of this page and the higher it is located in the search results.

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5. What family of protocols is used on the Internet? 6. Explain why there are multiple layers of protocols. Tell us about the role of protocols at different levels. 7. What is the role of router nodes? 8. How is guaranteed delivery of messages on the Internet? 9. Name the most famous application layer protocols. Where do they apply Control questions How is client-server technology used on the Internet? What is a provider? Tell me how you can access the Internet. What are the advantages and disadvantages different ways? What ideas formed the basis of the global computer network?

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How much memory space does an IP address take up? 3. Do you think two computers can have the same IP address? Justify the answer. 4. What IP addresses are used for LANs? Why does it become necessary to migrate to IPv6? What is a domain? In the form of what structure can the domain name system be represented? What domains can you register (if available)? Do you think that domains with Russian letters will be popular? Justify the answer. What is a DNS server? What functions does it perform? What is a URL? What parts does it usually consist of?