Any person who conducts creative work has his own information. Sooner or later, it becomes necessary to exchange the results of one's work with colleagues, to discuss certain issues, to get advice. Today, the most promising solution to this problem is the use of computer communications.

Computer communications - combining computers into a single system.

Computer network - a group of computers connected to each other or to a central server so that they can transfer information among themselves and share various resources.

The main types of networks:

- the local network - unites computers within a limited territorial space - a room, department, building;

- regional network - unites computers within the administrative territory;

- global network - covers countries, continents.

The most famous global network is the Internet

It is important to note that at present the Internet serves not only (and not so much) for solving professional and educational problems, but also for communication, receiving information of an entertaining and educational nature, and commercial activities.

The global computer network Internet is (in a simplified form) a set of computers interconnected by communication channels. Each computer (node) on the Internet has a unique address of the form: xxx.xxx.xxx.xxx, where xxx are numbers from 0 to 255. This address is called an IP address (Internet Protocol Address). An IP address corresponds to a "verbal" address - a domain name. The domain addressing system has a number of obvious advantages: addresses are easier to remember, carry a certain semantic load, one computer can be assigned several different names.

At the key nodes of the network there are router programs that direct the client's request to the desired address, where a special server program processes the request and sends back the necessary information.

The client's computer must be equipped with the appropriate hardware and software. The former are most often represented by a modem or network card (if the computer is part of a local network). The range of the latter is very wide and allows you to work with various Internet services. Let's consider the most popular Internet services.

Email - Email. It is the first and still one of the most popular Internet services. It is a typical deferred read service. The addressee receives your message on his computer after some, perhaps quite a long period of time, and reads the message when it is convenient for him. Email is very similar to regular paper mail. However, email has one major and clear advantage over regular mail. This is speed. For example, a message to another mainland will take not several days or weeks, but only a few minutes or even seconds, depending on the quality of the connection. Email has advantages over telephone connection... You send your message when it's convenient. And the addressee answers when it is convenient for him. The exchange of information does not require simultaneous connection of computers to the Internet.

An email address is a name that uniquely identifies an electronic mailboxwhere the email is sent. The following form of address is accepted on the Internet: username @ domainname. For example, [email protected] The domain name tells which server the mailbox is located on. Username is usually called login. You can send by e-mail as text messagesand attached files (Attachment).

Work with the by email it is carried out off-line using special mail programs, for example, Microsoft Outlook. However, it is possible to use mail using a browser in on-line mode.

Usenet- network news. It is a global teleconferencing system (or bulletin board), sorted by topic, through which millions of people around the world exchange information. The distribution principle, unlike e-mail, is from one addressee to many. A message sent by one person reaches the computers of all nodes connected to this echo conference. There are a lot of thematic conferences. Each echo conference has a person - a moderator who monitors the implementation of the rules of work.

WWW (World Wide Web - the world wide web) - hypertext system. The most popular Internet service. More than half of the data traffic on the network falls on it. Actually, this service made the development of the Internet very fast. This means of working with information has conquered the network so much that many people do not use any other services when working on the Internet. The basis of the WWW is a hypermedia document, that is, a document in which each element can be a link to another document or part of it. Links are organized in such a way that any information resource on the Internet is addressed unambiguously. Moreover, the user works with all information resources of the Internet, as a whole. Links to information internet resources (for example, http://www.belmednet.com/healthcare/article.htm) are organized as follows. The first part of the address (http: //) is a resource identifier and indicates the protocol used. The next part of the address indicates the location of the resource. This part can be divided into two. The first part is the domain name of the computer (in this example, -www.belmednet.com). This is the unique name of the computer on which the searched document is located. The other part (/healthcare/article.htm) indicates the name or location of the resource on this server. Essentially, this is the way to file system server disk to a Web document that is a regular file.

To work with WWW special programs are used - browsers. The most widespread is Internet Explorer, which is included in the standard delivery of Microsoft Windows.

FTP is a File Transfer Protocol and at the same time it is a service that allows you to organize access to file archives. The program for working with them is called an FTP client and allows you to copy files from a remote computer to a local computer and vice versa.

IRC(Internet Relay Chat) - real time chat. Users join one of the thematic group channels and participate in a conversation that is conducted by typing. Synchronizing IRC nodes allows, by connecting to one of them, to participate in the entire IRC network. Such a service allows several people to discuss a problem and resembles a telephone conference call. Now there is a practical implementation of such a service on WWW-servers. These are chat rooms.

ICQ- lnternet paging. The principle of the system is as follows. Each registered user has an ICQ client program. When connected to the Internet, this program connects to a special server and reports that the user is on-line. The key concept "Contact List" is a list that contains the numbers of your interlocutors. It is on your computer. Connecting to the server, ICQ informs about your presence on the Internet and immediately finds out which of your addressees is in the moment is online. The status of the interlocutor is immediately displayed in the program. If the user is on the Internet, you can exchange messages with him, which are transmitted almost instantly.

Purpose: get acquainted with the structure and basic principles of the World Wide Web, with the basic Internet protocols and the addressing system.

Architecture and principles of the Internet

Global networks, reaching millions of people, have completely changed the process of information dissemination and perception.

Wide Area Networks (WAN) - These are networks designed to unite individual computers and local networks located at a considerable distance (hundreds and thousands of kilometers) from each other. Global networks unite users located all over the world, using a wide variety of communication channels.

Modern Internet - a very complex and high-tech system that allows the user to communicate with people located anywhere in the world, quickly and comfortably find any necessary information, publish data for general information that he would like to communicate to the whole world.

In reality, the Internet is not just a network; it is a structure that connects ordinary networks. The Internet is a "network of networks".

To describe the Internet today, it is helpful to use a strict definition.

In his book « TheMatrix:ComputerNetworksandConferencingSystemsWorldwide " John Quarterman describes the Internet as "A meta-network, consisting of many networks that operate according to the protocols of the TCP / IP family, are connected through gateways and use a single address and namespace".

There is no single point of subscription or registration on the Internet; instead, you contact a service provider who gives you access to the network through your local computer. The consequences of such decentralization in terms of the availability of network resources are also quite significant. The data transmission medium on the Internet should not be considered only as a web of wires or fiber-optic lines. The digitized data is sent through routers , which connect networks and, using complex algorithms, choose the best routes for information flows (Fig. 1).

Unlike local networks, which have their own high-speed information transfer channels, global (as well as regional and, as a rule, corporate ) the network includes a communication subnetwork (otherwise: a territorial communication network, information transmission system), to which local networks, individual components and terminals (means of input and display of information) are connected (Fig. 2).

A communication subnetwork consists of information transmission channels and communication nodes, which are designed to transmit data over the network, select the optimal route for transmitting information, switch packets and implement a number of other functions using a computer (one or more) and the corresponding softwareavailable in the communication node. The computers that the client users run are called workstations , and computers that are sources of network resources provided to users are called servers ... This network structure is called nodal .

Fig. 1 The scheme of interaction on the Internet

the Internet Is a global information system that:

· Logically interconnected by the space of globally unique addresses based on the Internet Protocol (IP);

· Is capable of supporting communications using the transmission control protocol family - TCP / IP or its subsequent extensions / successors and / or other IP-compatible protocols;

· Provides, uses or makes available, on a public or private basis, high-level services built on top of the communications and other related infrastructure described herein.

Internet infrastructure(fig. 2):

1. backbone level (a system of interconnected high-speed telecommunication servers).

2. layer of networks and access points (large telecommunication networks) connected to the backbone.

3.level of regional and other networks.

4.ISP - Internet Service Providers.

5. users.

To technical resources of the Internet includes computer nodes, routers, gateways, communication channels, etc.

Fig. 2 Internet infrastructure

The network architecture is based on multilevel message transmission principle ... The message is generated onthe topmost level of the modelISO / OSI .. Then (during transmission) it afterconsequently, it goes through all levels of the system to the lowest level, where it is transmitted via the communication channel to the addressee. As you progress through eachfrom the levels of the system, the message is transformed, split into relatively short parts, which are supplied with additionalheaders providing information similar to thosenor on the destination node. At this node, the message travels from the bottom to the top, stripping off the headers. As a result, the addressee receives the message in its original form.

In territorial networks data exchange control carry outis handled by the top-level protocols of the modelISO / OSI ... Regardless internal design of each specific protocol upperlevel, they are characterized by the presence of common functions: initialization of communication, transmission and reception of data, completion of exchange. Each protostake has means to identify any workstation on the networkby name, network address, or both. Activizationthe exchange of information between interacting nodes beginningis called after identification of the destination node by the node initiatingdata exchange. The originating station sets up one of themethods of organizing data exchange: datagram method or method communication sessions. The protocol provides the means for receiving / transmittingchi messages by addressee and source. In this case, usually superimposingthere are restrictions on the length of messages.

T CP / IP- interworking technology

The most common exchange control protocoldata is TCP / IP. The main difference between the network Internet from other networks lies precisely in its TCP / IP protocolscoveringa whole family of protocols for interaction between computersnetwork operators. TCP / IP is an internetworking technology,internet technology. Therefore r a global network that connects meset of networks with technology TCP / IPis called Internet.

TCP / IP protocol is a family of software implementedhigher-level protocols that do not work with hardwarejerking. Technically, TCP / IP protocol has two parts -IP and TCP.

Protocol IP ( Internet Protocol - internet protocol) is an the main protocol of the family, it implements the distribution offormations in IP -network and is performed at the third (network) level modewhether ISO / OSI. IP protocol provides datagram packet deliverycom, its main task is packet routing. He is not responsible for the reliability of information delivery, for its integrity, for the preservationthe order of the packet flow. Networks that use the protocolIP are called IP -networks. They work mainly on analog channels (i.e., to connect a computer to the network, you needIP -mo dem) and are packet-switched networks. The package is called hereis datagram.

High-level protocol TCP ( Transmission Control Protocol - transmission control protocol) works at the transport level andpartially - at the session level. This is a protocol with the establishment of loa logical connection between sender and receiver. He obesmaintains a session connection between two nodes with guaranteed delivery of information, monitors the integrity of the transmissioninformation, preserves the order of the packet flow.

For computers, TCP / IP is the same as rules fordialect for people. It is accepted as the official standard on the webInternet , i.e. network technology TCP / IP has become a de facto technologygia of the world wide Internet.

The key part of the protocol is the packet routing scheme based on unique network addresses.Internet. Each work tea station, which is part of a local or global network, havinghas a unique address that includes two parts that definenetwork address and station address within the network. This scheme allows re send messages both within this network and to external networks.

ADDRESSING ON THE INTERNET

Basic Internet Protocols

Job internet networks based on the use of communication protocol families TCP / IP (TransmissionControlProtocol/ InternetProtocol). TCP / IP is used for data transmission both in the global Internet network and in many local networks.

The name TCP / IP defines a family of protocols for transmitting network data. Protocol is a set of rules that all companies must adhere to in order to ensure the compatibility of manufactured hardware and software. These rules guarantee the compatibility of the manufactured hardware and software. In addition, TCP / IP is a guarantee that your personal computer can communicate over the Internet with any computer in the world that also works with TCP / IP. As long as certain standards are met, it does not matter who the manufacturer of the software or hardware is for the entire system to function. The open systems ideology assumes the use of standard hardware and software. TCP / IP is an open protocol and all special information is published and can be freely used.

The various services included in TCP / IP and the functions of this protocol family can be classified according to the type of task they perform. We will mention only the main protocols, since their total number is more than a dozen:

· transport protocols- manage the transfer of data between two machines :

· TCP/ IP (Transmission Control Protocol),

· UDP (User Datagram Protocol);

· routing protocols- handle data addressing, provide actual data transfer, and determine the best path for the packet to travel :

· IP (Internet Protocol),

· ICMP (Internet Control Message Protocol),

· RIP (Routing Information Protocol)

· other;

· network address support protocols- handle data addressing, provide machine identification with a unique number and name :

· DNS (Domain Name System),

· ARP (Address Resolution Protocol)

· other;

· application service protocolsare programs that a user (or computer) uses to access various services :

· FTP (File Transfer Protocol),

· TELNET,

· HTTP (HyperText Transfer Protocol)

· NNTP(NetNewsTransfer Protocol)

·other

This includes transfer of files between computers, remote terminal access to the system, transfer of hypermedia information, etc .;

· gateway protocols help to transmit over the network messages about routing and information about the state of the network, as well as process data for local networks :

· EGP (Exterior Gateway Protocol),

· GGP (Gateway-to-Gateway Protocol),

· IGP (Interior Gateway Protocol);

· other protocols - used to transfer e-mail messages, when working with directories and files of a remote computer, and so on :

· SMTP (Simple Mail Transfer Protocol),

· NFS (Network File System).

IP-addressing

Now let's take a closer look at the concept of an IP address.

Every computer on the Internet (including any PC when it establishes a dial-up connection to an ISP) has a unique address called IP-address.

An IP address is 32 bits long and consists of four 8-bit parts, named according to network terminology octets (octets) ... This means that each part of the IP address can have a value between 0 and 255. The four parts are combined into a record in which each 8-bit value is separated by a period. When referring to a network address, it is usually an IP address.

If all 32 bits of an IP address were used, there would be over four billion possible addresses — more than enough for the future expansion of the Internet. However, some bit combinations are reserved for special purposes, which reduces the number of potential addresses. In addition, 8-bit quadruples are grouped in special ways depending on the type of network, so that the actual number of addresses is even smaller.

With the concept IP addresses are closely related concept host (host) ... Some simply equate the concept of a host with a computer connected to the Internet. In principle, this is so, but in general under the host means any device that uses the TCP / IP protocol to communicate with other equipment. That is, in addition to computers, it can be special network devices - routers, hubs (habs) and others. These devices also have their own unique IP addresses, just like the computers of the users' network nodes.

Any IP-address consists of two parts: network addresses (Network ID) and host addresses (host ID, Host ID) in this network... Thanks to this structure, the IP addresses of computers on different networks can have the same numbers. But since the addresses of the networks are different, these computers are uniquely identified and cannot be confused with each other.

IP addresses are allocated depending on the size of the organization and the type of its activities. If it is a small organization, then most likely there are few computers (and therefore IP addresses) on its network. In contrast, a large corporation may have thousands (or even more) computers connected into many interconnected local networks. For maximum flexibility IP-addresses are divided into classes: A, B and C. There are still classes D and E, but they are used for specific service purposes.

So, three classes of IP-addresses allow you to distribute them depending on the size of the organization's network. Since 32 bits is the allowed full size of an IP address, the classes split the four 8-bit parts of the address into a network address and a host address depending on the class.

Class network addressA determined by the first octet of the IP address (counted from left to right). The first octet, in the range 1-126, is reserved for giant multinationals and major providers. Thus, in class A in the world there can be only 126 large companies, each of which can contain almost 17 million computers.

ClassB uses The first 2 octets as the network address, the value of the first octet can be in the range 128-191. Each class B network may have about 65,000 computers, and such networks are owned by the largest universities and other large organizations.

Respectively, in the classC the first three octets are already allocated for the network address, and the value of the first octet can be in the range 192-223. These are the most widespread networks, their number can exceed more than two million, and the number of computers (hosts) in each network - up to 254. It should be noted that "gaps" in the valid values \u200b\u200bof the first octet between classes of networks appear due to the fact that one or several bits are reserved at the beginning of the IP address to identify the class.

If any If an IP address is symbolically designated as a set of octets w .x .y .z, then the structure for networks of different classes can be presented in Table 1.

Whenever a message is sent to any host on the Internet, the IP address is used to indicate the source and destination addresses. Of course, users do not have to remember all the IP addresses themselves, as there is a special TCP / IP service called the Domain Name System for this.

Table 1. The structure of IP-addresses in networks of different classes

Network class	First octet value (W)	Network number octets	Host number octets	Number of possible networks	The number of hosts on such networks
	1-126		x.y.z	128(2 7)	16777214(2 24)
	128-191	w.x	y.z	16384(2 14)	65536(2 16)
	192-223	w.x.y		2097151(2 21)	254(2 8)

Subnet mask concept

In order to separate the network ID from the host ID, a special 32-bit number called the subnet mask is used. Superficially, the subnet mask is exactly the same set of four octets, separated by dots, like any IP address. Table 2 lists the default subnet mask values \u200b\u200bfor Class A, B, C networks.

Table 2. Subnet mask value (default)

Network class	Mask value in bits (binary representation)	Decimal mask value
	11111111 00000000 00000000 00000000	255.0.0.0
	11111111 11111111 00000000 00000000	255.255.0,0
	11111111 11111111 1111111100000000	255,255.255.0

The mask is also used to logically divide large IP networks into a number of smaller subnets. Imagine, for example, that the Siberian Federal University, which has a class B network, has 10 faculties, and each of them has 200 computers (hosts) installed. Using a subnet mask of 255.255.0.0, this network can be divided into 254 separate subnets with up to 254 hosts each.

The default subnet mask values \u200b\u200bare not the only ones available. For example, the system administrator for a particular IP network might use a different subnet mask value to highlight only a few bits in the host ID octet.

How to registerIP-the network of your organization?

In fact, end users are not involved in this task, which falls on the shoulders of the system administrator of the organization. In turn, he is assisted in this by Internet providers, usually taking over all registration procedures in an appropriate international organization called InterNIC (NetworkInformationCenter). For example, the Siberian Federal University wishes to receive an Internet e-mail address containing the string sfu -kras .ru. This identifier, including the company name, allows the sender of the e-mail to identify the recipient's company.

To obtain one of these unique identifiers, called a domain name, a company or provider sends a request to the authority that controls Internet connectivity - InterNIC. If InterNIC (or the body authorized by it for such registration in a given country) approves the name of the company, then it is added to the Internet database. Domain names must be unique to prevent errors. The concept of a domain and its role in addressing messages sent over the Internet will be discussed below. Additional information on the work of InterNIC can be found by visiting the Internet page http://rs.internic.ru.

DOMAIN NAME SYSTEM

Domain names

In addition to IP addresses, the so-called domain host name ... Just like the IP address, this is the name is unique for each computer (host) connected to the Internet - only here words are used instead of the numeric values \u200b\u200bof the address.

In this case, the concept domain means a collection of Internet hosts that are grouped together according to some attribute (for example, by territorial, when it comes to the state domain).

Of course, the use of a domain host name was introduced only to make it easier for users to remember the names of the computers they wanted. The computers themselves, for obvious reasons, do not need such a service and are completely dispensed with IP addresses. But just imagine that instead of such sonorous names as, www. microsoft. com or www. ibm. com you would have to memorize sets of numbers - 207.46.19.190 or 129.42.60.216 respectively.

If we talk about the rules for composing domain names, then there are no such strict restrictions on the number of constituent parts of the name and their meanings, as in the case of IP addresses. For example, if there is a host with the name khtiincluded in the domain of the Republic of Khakassia khakassia, and that, in turn, is included in the Russian domain ru, then the domain name of such a computer will be khti. khakassia. ru... In general, the number of components of a domain name can be different and contain from one or more parts, for example, rage. mp3. apple. sda. org or www. ru .

Most often, a company's domain name consists of three components, the first part is the host name, the second is the company's domain name, and the last is the country's domain name or the name of one of seven special domains that indicate the ownership of the host, the organization of a specific activity profile (see Table 1 ). So, if your company is called "KomLinc", then most often the company's Web server will be called www .komlinc .ru (if it is a Russian company), or, for example, www .komlinc .com, if you asked the provider to register you mainly international domain of commercial organizations.

The last part of the domain name is called the top-level domain identifier (for example, . ru or . com). There are seven top-level domains established by InterNIC.

Table1. International top level domains

domain name	Domain host ownership
ARPA	Great-great ... grandma Internet, ARPANet (obsolete)
COM	Commercial organizations (firms, companies, banks, etc.)
GOV	Government agencies and organizations
EDU	Educational institutions
MIL	Military institutions
NET	"Networking" organizations that control or are part of the Internet
ORG	Organizations that do not fit into any of the listed categories

Historically, these seven default top-level domains denote the geographic location (belonging to them) of a host in the United States. Therefore, the international committee InterNIC, along with the above-mentioned top-level domains, allows the use of domains (special combinations of characters) to identify other countries in which the organization-owner of this host is located.

So, top-level domains are subdivided into organizational(see Table 1) and territorial. There are two-letter designations for all countries of the world: . ru - for Russia (so far, the domain . suuniting hosts on the territory of the republics of the former USSR), .ca - for Canada, . uk - for the UK, etc. They are commonly used in place of one of the seven identifiers listed in Table 1 above.

Territorial top-level domains:

... ru (Russia) - Russia;

Su (Soviet Union ) - countries of the former USSR, now a number of CIS states;

Uk (United Kingdom ) - Great Britain;

Ua (Ukraine) - Ukraine;

Bg (Bulgaria) - Bulgaria;

Hu (Hungary) - Hungary;

De (Deutchland ) - Germany, etc.

C complete list all domain names of states can be found on various servers on the Internet.

Not all companies outside the United States have country identifiers. To some extent, the use of a country identifier or one of the seven U.S. identifiers depends on when the company domain name was registered. For example, companies that have long been connected to the Internet (when the number of registered organizations was relatively small) were given a three-letter identifier. Some corporations operating outside of the United States but registering a domain name through a US company are free to choose whether to use the host country ID. Today in Russia you can get a domain identifier . com, for which you should discuss this issue with your Internet provider.

howworkservers DNS

Now let's talk about how domain names are converted to computer-readable IP addresses.

Is doing this DomainNameSystem(DNS, Domain Name System) a service provided by TCP / IP that assists in addressing messages. It is thanks to the work of DNS that you can not remember the IP address, but use a much simpler domain address. The DNS system translates the symbolic domain name of a computer into an IP address by finding an entry in a distributed database (stored on thousands of computers) that corresponds to that domain name. It is also worth noting that DNS servers in Russian-language computer literature are often called "Name servers".

Root Zone Name Servers

Although there are thousands of name servers in the world, there are nine servers at the head of the entire DNS system, named root zone servers ( root zone servers ) . Root zone servers got names a. root_ server. net, b. root_ server. net and so on up to i. root_ server. net... The first one is a. root_ server. net - Acts as the primary Internet name server, managed from the InterNIC clearinghouse, which registers all domains in multiple top-level domains. The rest of the name servers are secondary to it, but they all keep copies of the same files. This allows any of the root zone servers to replace and back up the rest.

These computers host information about the host computers of the name servers that serve the seven top-level domains: .com, .edu, .mil, .gov, .net, .org, and custom.arpa (Figure 1). Any of these nine servers carry the same top-level file as .uk (UK), .de (Germany), .jp (Japan), and so on.

Figure: 1. Hierarchical structure of Internet domain names

The root zone files contain all host names andIP -addresses of name servers for each subdomain in the top-level domain. In other words, each root server has information about all top-level domains, and also knows the name of the host computer andIP -address of at least one name server serving each of the secondary domains included in any top-level domain. For domains of foreign countries, the database stores information on name servers for each country. For example, in a certain domaincompany. com the root zone files for the domain contain the name server information for any address ending incompany. com.

In addition to root zone name servers, there are local name servers installed in lower-level domains. The local name server caches a list of hosts it has recently searched for. This eliminates the need to constantly contact the systemDNS with queries about frequently used host computers. Also, local name servers are iterativeand the root zone servers are recursive... This means that the local name server will repeat the process of requesting information about other name servers until it receives a response.

The root serversInternet at the top of the structureDNS on the contrary, they only provide pointers to domains of the next level. Reach the end of the chain and get the requiredIP -address is the task of the local name server. To solve it, it must go down the hierarchical structure, sequentially asking local name servers for pointers to its lower levels.

Literally translated into Russian, the Internet is an inter-network, i.e. it is a pooling of networks. Now the Internet is the world's COP.

The Internet is a unique collection of LAN, MAN, WAN that are connected together.

The basis of the Internet is the ARPANET network, developed in 1969 with funds from the Defense Advanced Research Projects Agency (DAPRA). The ARPANET is the result of research to create a COP that is robust enough to function in wartime. Despite the fact that the ARPANET was created with military money, it was developed mainly in universities. Some parts of it were classified, but most of it was open because maximum opportunity and ease of use of the network d. make it more stable, more reliable, more stable, more accessible, more useful.

One of the earliest standardized services was email, followed by a standard for file transfers, and then a standard for newsgroups. None of these services were developed for commercial or private use. All of this was done by people interested in creating open standards that anyone could use.

The main group that oversees the development of the Internet is the Internet Society ISOC. ISOC oversees many volunteer groups: the Architect Group, Engineering Force, Research Force, Digital Access Control Group, Disaster Relief Committee, Internet Action Forum, and more. But there is no single authoritarian figure on the Internet, senior officials may be ... from networks connected to the Internet. Nobody pays for the Internet in general. Everyone pays for their share.

Host (Host) - a host PC that performs centralized functions of supporting this network, makes programs and data files available to other PCs on the Internet.

Protocol is a set of semantic and syntactic rules and procedures that determine the operation of functional devices in the communication process.

A dedicated channel is a communication channel to which terminal data processing devices are permanently connected, does not require switching.

Dial-up channel is a communication channel of subscribers, to which connection is made through general-purpose telephone channels by dialing the subscriber's number on the telephone dialer. This creates a temporary connection.

The real birthday of the Internet is 1983, when there was a revolutionary change in computer communications software. In 1983, the TCP / IP communication protocol was standardized.

TCP / IP (Transmission Control Protocol over Internet Protocol) is a transmission control protocol over the Internet protocol. It is a common protocol for all PCs Internet, It is software that allows separate parts of the Internet to work together, forming single network... TCP / IP is independent of the hardware and cabling of the networks.

TCP / IP is a union of two standards (stack): TCP and IP, which play different roles in the process of communication over the Internet. IP defines a low-level method of moving information from one PC to another, TCP provides a high-level method of determining if information is present and validating it (I-book, IP pages, and TCP is a language).

TCP Tasks:

1) Ensuring guaranteed passage of information through the Internet without data loss;

2) Prevention of accidental or unauthorized intentional distortion, changes in information during the passage;

3) Retransmission if it is received in an incorrect form;

4) Providing methods for splitting long messages into smaller sections of their transmission and then combining them into a single whole;

5) Providing the possibility of extended communication between two subscribers simultaneously with other subscribers.

IP includes:

1) Methods for uniquely identifying each PC on the Internet so that users can always determine where this or that information came from;

2) Methods for determining the availability of received information;

3) A system that divides information into small portions that could move without interference through any Internet switches.

Each host computer has two addresses:

1) PC friendly digital IP address;

2) User-friendly DNS (Domain name system) address.

The IP address consists of 4 numbers separated by dots. Each number is 1 byte long, i.e. takes a value from 1 to 255.

123 refers to the top-level network, 89 directly to the corresponding host PC. The first two numbers are the address of the network and the last two are the address of the host PCs within that network.

The domain name system assigns PCs alphabetic names, domain names, which are the symbolic form of the address of a networked PC. For example, to find out the conditions for connecting to NTV + satellite television, you can try to contact the www / ntv / ru server (ru at the end of the name indicates that the company's server belongs to the Russian Internet sector).

Translating domain names into related ones IP addresses DNS domain name servers are running.

The domain name system is a method of naming by assigning responsibility to different groups of users for subsets of names. Each level in this system is called a domain. Domains are separated from one another by dots. In the name of m. any number of domains, but five are rare. Each subsequent domain (as viewed from left to right) is larger than the previous one.

Initially, there were six organizational top-level domains: commercial organizations - edu, educational institutions - gov, military institutions - mil, other organizations - org, network resources - net.

In order for foreign countries to control the names of the systems located in them, a two-letter domain was created.

Laboratory work No. 4

Lesson topic:Global computer network Internet. Power Point Presentation Software

Lesson objectives:

1. Master the skills of browsing Web-pages and Web-sites, searching for the necessary information on the Internet.

1. To master the skills of working with the program-browser MS Internet Explorer.

2. Master the skills of receiving and sending messages by e-mail.

3. Become familiar with the Power Point interface.

4. Learn to create, edit, format, customize and show slide multimedia presentations in Power Point.

5. Learn to independently study the material in preparation for laboratory work.

6. Develop technical thinking.

Time: 180 minutes ... A place: computer class

Equipment:

1. Personal computers

2. Assignment for laboratory work (handout)

1. Informatics. Basic course. Textbook for universities. Ed. S.V. Simonovich. 2nd ed. - SPb .: Peter, 2009.

2. V.G. Olifer, N.A. Olifer. Basics of data transmission networks. Lecture course. Tutorial. 2nd ed. Moscow: Internet University of Information Technologies (www.intuit.ru), 2005.

3. Laboratory workshop in informatics. Textbook for universities. 2nd ed. Ed. V.A. Ostreykovsky. M: Higher School, 2008.

General information about the Internet.

Global computer network INTERNET can be viewed from two points of view: physical and logical.

From a physical point of view, the INTERNET is a huge collection of individual computers and computer networks that unite hundreds of millions of computers around the world.

From a logical point of view, INTERNET is a global world information system - huge information spacecovering the entire globe.

Since its inception (1960s), the global computer network INTERNET has been steadily expanding both quantitatively and qualitatively.

At present, the global computer network INTERNET provides users with the following basic services:

Search and selection of information for its further use (service WWW-World Wide Web);

Work with e-mail (E-Mail service);

Working with an electronic newspaper - the so-called. conference (Usenet service);

Real-time communication (IRC service).

In general, the INTERNET exchanges information between any two computers connected to the network. For this, the INTERNET uses two basic concepts - concepts addresses and protocol.

Each computer connected to the network has its own unique address. This address consists of four parts, each of which is one byte, i.e. eight binary digits. This means that each of the four parts of the address written in the decimal system can take a value from 0 to 255. These parts are combined into a record, where each part is separated from the other by a point. For example, record 129.102.83.94 can be a unique address of a computer connected to the INTERNET, i.e. an address that is no longer repeated.

Such addresses on the INTERNET are called IP addresses (IP- Internet Protocol). Each computer that has its own unique digital address on the INTERNET is called a "host" (from the English word Host).

However, the use of the system of digital IP-addresses is not always convenient, therefore there is another on the INTERNET - the domain-based address system or abbreviated system DNS (DOMAIN NAME SYSTEM - domain name system).

Domain address of the computer Is a unique name, usually meaningful and much easier to remember than a digital IP address. For example.

The basis for the organization of the Internet was the computer network of the US Department of Defense ARPA - Advanced Research Project Agency), created in the early 70s

years for communication of computers of scientific organizations, military institutions and enterprises of the defense industry. The network was built, with the participation of the Pentagon, as a closed infrastructure resistant to external influences, capable of surviving a nuclear attack, ,.ᴇ. great attention was paid to its reliability.

Over time, the network lost its strategic importance, its main customers were individuals and non-state computer networks. The very name of the Internet (“between networks”) shows its purpose: combining separate local and global networks into a single information space. The Internet provides information exchange between all computers that are part of the networks connected to it. Computer type and operating system doesn't matter.

The creation of the Relcom computer network on the basis of the Kurchatov Institute of Atomic Energy began in early 1990 on the Russian Internet. By the end of 1990, more than 30 local networks of different organizations were integrated into the network, which made it possible to carry out its official registration and connection to the world network.

Today the Internet is ϶ᴛᴏ a global, intercontinental network. It unites tens of millions of computers and local networks, and, according to various estimates, hundreds of millions of people use its services. The exact figure is unknown, since the network does not have a single control center and is not owned by anyone.

The Internet is based on high-speed telecommunications backbone networks... To the backbone via NAP network access points

(Network Access Point) connect autonomous systems, each of which already has its own administrative control, its own internal routing protocols.

The main cells of the Internet are local area networks. There are local computersindependently connected to the Internet.

Networked or local computers directly connected to the Internet are called host computers.

If some local network is connected to the Internet, then each workstation of this network also has an Internet connection through the host computer of the network.

Each computer connected to the Internet has its own address, where a subscriber can find it from anywhere in the world.

An important parameter is the speed of Internet access. It is determined by the bandwidth of communication channels between autonomous systems, inside

Autonomous systems and subscriber access channels to autonomous systems. For modem access via telephone lines, which is used by most individual users of personal computers, this speed is low - from 19 to 50 Kbps for access via dedicated telephone lines, typical for small LANs, this speed is ranging from

64 kbps up to 2 Mbps, and only for networks organizing interaction through fiber-optic and satellite communication channels, throughput exceeds 2 Mbps.

The structure of the Internet is a typical client-server, that is, there are computers that mainly receive information from the network, "clients", and there are computers that supply clients with information - "servers" (of course, servers also receive information, or rather accumulate it, but all the same their main function is to give information).