Basic information about the Internet. General information about the global Internet network Basic Internet services

Any person who conducts creative work has his own information. Sooner or later, there is a need to exchange the results of your work with colleagues, discuss certain issues, and get advice. Today, the most promising solution to this problem is the use of computer communications.

computer communications- integration of computers into a single system.

Computer network- a group of computers connected to each other or to a central server so that they can communicate with each other and share various resources.

Main types of networks:

- the local network- unites computers within a limited territorial space - rooms, departments, buildings;

- 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, obtaining 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 is a number 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.

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

The client computer must be equipped with the appropriate hardware and software tools. 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 implement work with various Internet services. Consider the most popular Internet services.

Email - Email. It is the first and still one of the most popular services on the Internet. It is a typical lazy read service. The recipient receives your message on his computer after some, perhaps quite a long period of time, and reads the message when it suits him. E-mail is very similar to regular paper mail. However, email has one major and obvious advantage over regular mail. This is speed. For example, a message to another continent will not take 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 at your convenience. 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 email address. Mailbox where the email message is sent. The following form of address is accepted on the Internet: user_name@domain_name. For example, [email protected]. The domain name indicates on which server the mailbox is located. The username is called the login. You can send by e-mail both text messages and attached files (Attachment).

Work with e-mail is carried out off-line using special email 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 principle of distribution, unlike e-mail, is from one addressee to many. A message sent by one person gets to the computers of all nodes connected to this echo conference. There are many 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 is a hypertext system. The most popular Internet service. More than half of the data flow on the network falls on it. Actually, this service made the development of the Internet very fast. This information tool has taken over the web so much that many people don't use any other service when browsing the Internet. The basis of the WWW is a hypermedia document, i.e. 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 with a single entity. Links to informational resources The Internet (eg http://www.belmednet.com/healthcare/article.htm) is 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 where the document you are looking for is located. The other part (/healthcare/article.htm) specifies the name or location of the resource on this server. Essentially, it is a path in the server's disk file system to a Web document, which is a regular file.

To work with the WWW, special programs are used - browsers. The most widespread Internet Explorer included in the standard Microsoft supply 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 one and vice versa.

IRC(Internet Relay Chat) - real time chat. Users join one of the topic group channels and participate in a conversation that is conducted by typing. Synchronization of 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 similar service on WWW servers. These are chat rooms.

ICQ- lnternet paging. The principle of the system is this. 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 in on-line enable mode. Key concept " contact list” (Contact List) is a list that contains the numbers of your interlocutors. It is on your computer. Having connected to the server, ICQ announces your presence on the Internet and immediately finds out which of your recipients is currently 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.

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

Architecture and principles of the Internet

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

Global networks (Wide Area Network, WAN)- these are networks designed to combine 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 for public information the data that he would like to communicate to the whole world.

In fact, the Internet is not just a network - it is a structure that connects conventional networks. The Internet is a "network of networks".

To describe today's Internet, it is useful to use a strict definition.

In his book « TheMatrix :computerNetworksandConferencingSystemsworld wide » John Quaterman describes the Internet as "a metanet consisting of many networks that operate according to the protocols of the TCP / IP family, are united through gateways and use a single address space and namespace".

On the Internet, there is no single point of subscription or registration, instead you contact a service provider who gives you access to the network through your local computer. The implications of such decentralization in terms of the availability of network resources are also significant. The data transmission medium on the Internet cannot be considered only as a network of wires or fiber optic lines. The digitized data is sent via routers , that connect networks and use complex algorithms to select the best routes for information flows(Fig. 1).

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

The communication subnetwork consists of information transmission channels and communication nodes that are designed to transmit data over the network, select the optimal route for information transmission, packet switching and implement a number of other functions using a computer (one or more) and the corresponding software available in the communication node. Computers used by client users 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 Scheme of interaction on the Internet

Internet is a global information system that:

· is logically interconnected by the space of globally unique addresses based on the Internet protocol (IP);

• 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 communication and other related infrastructure described here.

Internet infrastructure(fig.2):

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

2. the level of networks and access points (large telecommunications networks) connected to the backbone.

3. the level of regional and other networks.

4.ISP - Internet Service Providers.

5.users.

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

Fig.2 Internet infrastructure

The network architecture is based on multilevel message passing principle . The message is generated onthe top level of the model ISO/OSI .. Then (on transmission) it is afterconsistently passes all levels of the system to the lowest, where it is transmitted over the communication channel to the addressee. As you go through eachfrom the levels of the system, the message is transformed, divided into relatively short parts, which are supplied with additionalheadings providing similar levels of informationnor on the destination node. At this node, the message passes from the lower level to the upper one, stripping off the headers. As a result, the recipient receives the message in its original form.

In territorial networks data exchange management implementis controlled by the top-level protocols of the model ISO/OSI . Regardless internal design of each specific top protocollevel, they are characterized by the presence of common functions: initialization of communication, transmission and reception of data, completion of the exchange. Every protocount has the means to identify any workstation networksby name, network address, or both. Activizainformation exchange between interacting nodesis determined after the destination node is identified by the node initiatingdata exchange. The originating station sets one of the methods for organizing data exchange: datagram method or method communication sessions. The protocol provides the means to receive/transmitchi messages by addressee and source. In this case, usually overlayThere are restrictions on the length of messages.

TCP/IP- internetworking technology

The most common exchange control protocoldata is the TCP/IP protocol. The main difference between the network Internet from other networks lies precisely in its TCP / IP protocols, covercontaining a whole family of protocols for interaction between computersnetworks. TCP/IP is a technology of interconnection, Internet technology. Therefore r a global network that unites manynetworking with technologyTCP/IP, is called Internet.

TCP/IP protocol is a family of softwarehigher level protocols that do not work with hardware prejerks. Technically, the TCP / IP protocol consists of two parts - IP and TCP.

Protocol IP ( Internet Protocol - internet protocol) is the main protocol of the family, it implements the distribution of formations in IP -network and is performed at the third (network) level of the mod whether ISO/OSI. IP protocol provides datagram packet deliveryComrade, 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 stream. Networks that use the protocol IP are called IP -networks. They work mainly on analog channels (i.e., to connect a computer to a network, you need IP mo dem) and are packet-switched networks. The package is called hereetsya datagram.

High level protocol TCP ( transmission control protocol- transmission control protocol) works at the transport layer andpartially - at the session level. This is a protocol with the establishment of lological connection between sender and receiver. He obesmaintains session communication between two nodes with a guaranteed delivery of information, monitors the integrity of the transmission received information, preserves the order of the packet stream.

For computers, the TCP / IP protocol is the same as the rules of timespeech for people. It is accepted as the official standard on the web. Internet , i.e. network technology TCP/IP has de facto become a technologey of the World Wide Web.

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

INTERNET ADDRESSING

Basic protocols of the Internet

The operation of the Internet is based on the use of families communication protocols TCP/IP (transmissioncontrolProtocol/ InternetProtocol). TCP/IP is used to transmit data both on the global Internet and in many local networks.

The name TCP/IP defines a family of network communication protocols. Protocol is a set of rules that all companies must adhere to in order to ensure the compatibility of their hardware and software. These rules guarantee the compatibility of manufactured hardware and software. In addition, TCP / IP is a guarantee that your Personal Computer will be able to 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 software or hardware manufacturer is for the operation of the entire system. The ideology of open systems involves the use of standard hardware and software. TCP/IP is an open protocol and all specific 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 tasks they perform. We will only mention the main protocols, since their total number is more than a dozen:

· transport protocols- manage data transfer between two machines :

· TCP/ IP(Transmission Control Protocol),

· UDP(User Datagram Protocol);

· routing protocols- handle the addressing of the data, ensure the actual transmission of the data, and determine best ways package movement :

· IP(Internet Protocol)

· ICMP(Internet Control Message Protocol),

· RIP(Routing Information Protocol)

· and others;

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

· DNS(Domain Name System),

· ARP(Address Resolution Protocol)

· and others;

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

· FTP(File Transfer Protocol),

· TELNET,

· HTTP(HyperText Transfer Protocol)

· NNTP(Net News Transfer Protocol)

·and others

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

· gateway protocols help transmit routing messages and network status information over 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 send e-mail messages, when working with directories and files on 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 session connection with an ISP over a telephone line) has a unique address called IP-address.

An IP address is 32 bits long and consists of four parts of 8 bits, named according to network terminology. octets (octets) . This means that each part of the IP address can take on a value between 0 and 255. The four parts are combined into a record in which each eight-bit value is separated by a dot. When we are talking about about the network address, it usually means the 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 combinations of bits are reserved for special purposes, which reduces the number of potential addresses. In addition, 8-bit quads are grouped in special ways depending on the network type, so that the actual number of addresses is even smaller.

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

Any IP- the address consists of two parts: network addresses(network ID, Network ID ) and host addresses(host ID, Host ID ) in this network. Due to this structure, the IP addresses of computers in different networks may have the same number. But since the network addresses 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's a small organization, then it probably has few computers (and therefore IP addresses) on its network. On the contrary, a large corporation may have thousands (or even more) of computers, united in many interconnected local area networks. For maximum flexibility IPAddresses are divided into classes: A, B and C. There are more 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 legal total size of an IP address, the classes break 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 value of the first octet, which is in the range 1-126, is reserved for giant multinational corporations and the largest providers. Thus, in the world there can be only 126 large companies in class A, each of which can contain almost 17 million computers.

ClassBuses The first 2 octets as the network address, the value of the first octet can be between 128-191. Each class B network can have about 65,000 computers, and the largest universities and other large organizations have such networks.

Respectively, in classC the first three octets are already allocated for the network address, and the value of the first octet can be in the range of 192-223. These are the most common networks, their number can exceed more than two million, and the number of computers (hosts) in each network can be up to 254. a few bits are reserved at the beginning of the IP address to identify the class.

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

Whenever a message is sent to any host computer on the Internet, the IP address is used to indicate the address of the sender and recipient. Of course, users do not have to remember all the IP addresses themselves, since there is a special service TCP/IP called Domain Name System

Table 1. Structure of IP addresses in networks of various classes

Network class	First octet value (W)	Network number octets	Host number octets	Number of possible networks	The number of hosts in 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)

The concept of a subnet mask

To separate the network ID from the host ID, a special 32-bit number called the subnet mask is used. Outwardly, the subnet mask is exactly the same set of four octets separated by dots, like any IP address. Table 2 shows the default subnet mask values for class A , B , C networks.

Table 2. Subnet mask value (default)

Network class	Mask value in bits (binary representation)	Mask value in decimal form
	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 Siberian Federal University, which has a class B network, has 10 faculties and each of them has 200 computers (hosts). 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 are not the only possible ones. For example, the system administrator of a particular IP network might use a different subnet mask value to highlight just some of the bits in the host ID octet.

How to registerIPyour organization's network?

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

To obtain one of these unique identifiers, called a domain name, a company or ISP sends a request to the authority that controls Internet connectivity, the InterNIC. If InterNIC (or the body authorized by it for such registration in a given country) approves the company name, 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 you can find out about the work of InterNIC by visiting the Internet page http://rs.internic.ru.

DOMAIN NAME SYSTEM

Domain names

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

IN this case concept domain means a collection of Internet hosts grouped together in some way (for example, by territorial, when it comes to the domain of the state).

Of course, the use of the host's domain name was only introduced to make it easier for users to remember the names of the computers they need. The computers themselves, for obvious reasons, do not need such a service and completely manage 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 compiling domain names, then there are no such strict restrictions on the number of component parts of the name and their meanings, as in the case of IP addresses. For example, if there is a host with the name khti, included in the domain of the Republic of Khakassia Khakassia, which, in turn, is part of the Russian domain en, then the domain name of such a computer will be khti. Khakassia. en. 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. en .

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 domain name or the name of one of seven special domains that indicate the host belongs to an organization of a certain 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 in the main international domain of commercial organizations.

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

Table1. International Top Level Domains

domain name	Domain Host Ownership
ARPA	Great-great... grandmother Internet, ARPANet (decaying)
COM	Commercial organizations (firms, companies, banks, etc.)
GOV	Government agencies and organizations
EDU	Educational institutions
MIL	Military establishments
NET	"Network" organizations that operate or operate the Internet
ORG	Organizations that do not fit into any of the above categories

Historically, these seven default top-level domains indicate the fact of the geographic location of (belonging to) a host in the United States. Therefore, the International Committee InterNIC, along with the above top-level domains, allows the use of domains (special character combinations) to identify other countries in which the organization that owns 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: . en- for Russia (so far, the domain . su, uniting hosts on the territory of the republics of the former USSR), .ca- for Canada, . UK- for the UK, etc. They are usually 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 (Deutschland) ) - Germany, etc.

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

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

HowworkserversDNS

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

Doing it DomainNameSystem(DNS, Domain name system) a service provided by TCP/IP that assists in addressing messages. Thanks to DNS work instead of remembering the IP address, you can use a much simpler domain address. The DNS system translates a computer's symbolic domain name into an IP address by finding an entry in a distributed database (stored on thousands of computers) that matches that domain name. It is also worth noting that DNS servers in the Russian-language computer literature are often referred to as "name servers".

Root zone name servers

Although there are thousands of name servers in the world, there are nine name servers at the head of the entire DNS system, named root zone servers ( root zone servers ) . Root Zone Servers Named a. root_ server. net, b. root_ server. net and so on until i. root_ server. net. The first one is a. root_ server. net- acts as the primary Internet name server, managed from the InterNIC information center, which registers all domains that are included in several top-level domains. The rest of the name servers are secondary to it, but they all keep copies of the same files. Thanks to this, any of the servers in the root zone can replace and insure the others.

These computers host information about nameserver hosts serving seven top-level domains: .com , .edu , .mil , .gov , .net , .org , and the special .arpa (Figure 1). Any one of these nine servers carries the same top level file as .uk (UK), .de (Germany), .jp (Japan) and so on.

Rice. 1. Hierarchical structure of Internet domain names

The root zone files contain all host computer names and IP -addresses of name servers for each subdomain included 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 and IP - the address of at least one name server serving each of the secondary domains included in any top-level domain. For foreign country domains, the database stores information on name servers for each country. For example, in a certain domaincompany. comthe root zone files for a domain contain nameserver data for any address ending incompany. com.

In addition to the root zone name servers, there are local name servers set in lower-level domains. The local name server caches a list of hosts it has recently looked up. This eliminates the need to constantly access the system DNS with queries about frequently used host computers. In addition, local nameservers are iterative, and 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.

Root servers Internet at the top of the structure DNS , on the contrary, only issue pointers to the next level domains. Get to the end of the chain and get the required IP -address - local nameserver task. To solve it, he must go down the hierarchical structure, successively asking local servers names are pointers to its lower levels.

Internet is a World Wide Web in which information is stored on servers. Servers have their own addresses and are controlled by specialized programs. They allow you to send mail and files, search databases, etc. Information is exchanged between network servers via high-speed communication channels. Access of individual users to Internet information resources is usually carried out by telephone network through an ISP or corporate network. Some organization that has a modem pool for connecting with clients and accessing the World Wide Web acts as a provider. Note that corporate networks built on the principles of the Internet are called Intranet Internet architecture Consider a simplified scheme for building the Internet. Figure 1 shows the network architecture. Leased telephone lines, fiber optic and satellite communication channels are used as a high-speed data transmission line. Any organization to connect to lnternet uses a special computer called a gateway (gateway). It installs software that processes all messages passing through the gateway. Each gateway has its own IP address. If a message arrives addressed to local network to which the gateway is connected, it is transmitted to this local network. If the message is destined for another network, then it is passed on to the next gateway. Each gateway has information about all other gateways and networks. When a message is sent from a local network through a gateway to the Internet, then

Fig.1. Internet architecture

this selects the "fastest" path. Gateways exchange information about routing and network status with each other using a special gateway protocol. Some companies may act as a provider. Provider has its own gateway to the Internet and allows other companies and individuals to connect to the Web through this gateway. In addition to information about message routing, the gateway needs information about the parameters of the subnets connected to the larger network in order to correct message routes in case of failures in certain parts of the network. There are two types of gateways: internal and external. internal refers to gateways that are located on a small subnet and provide connectivity to a larger corporate network. These gateways communicate with each other using the Internal Gateway Protocol (IGP). External gateways are used in large networks like the Internet, their settings are constantly changing due to changes in small subnets. Communication between external gateways is carried out through the external gateway protocol EGP (Exterior Gateway Protocol).

User connection to the Internet can be carried out in different ways, differing in cost, convenience and scope of services provided. These methods are:

e-mail (E-mail);

teleconferences (UseNet);

remote terminal emulation system (TelNet);

search and transfer of binary files (FTP);

search and transfer of text files using the menu system (Gopher);

search and transmission of documents using hypertext links (WWW, or the World Wide Web).

The creation and development of these methods is connected historically. Each of them is characterized by its capabilities and differences in the organization of information exchange protocols. In the general case, a protocol is a set of instructions that regulate the operation of interconnected systems or objects in a network. E-mail (E-mail)- the simplest and affordable way access on the Internet. It allows you to send any type of files (including texts, images, sound inserts) to email addresses anywhere in the world in a short period of time at any time of the day. To send a message, you only need to know the recipient's email address. E-mail is based on the serial transmission of information over a network from one mail server to another until the message reaches its destination. The advantages of e-mail include high efficiency and low cost. The disadvantage of e-mail is the limited volume of files sent. usenet designed as a text information exchange system. It allows all Internet users to participate in group discussions, called teleconferences, in which all sorts of problems are discussed. Now in the world there are more than 10 thousand teleconferences. The information sent in the teleconference becomes available to any network client who has applied to this newsgroup. Currently, teleconferencing allows you to transfer files of any type, including text, image and audio files. To work with teleconferences, the most commonly used tools are programs for viewing and editing Web documents. telnet is a protocol that allows you to use the resources of a remote computer. In other words, it is a protocol for remote terminal access on a network. In this case, we are talking about sending commands from a local computer to a remote computer on the network. FTP is a network protocol for working with any type of files: text and binary, which is an example of a system with a client-server architecture. An FTP server is installed on a remote computer in order to allow users to view file system and copy the required files. To implement communication via the FTP protocol, a program - an FTP server - must function on a remote computer system. The advantage of this protocol is the ability to transfer files of any type - texts, images, executable programs. The disadvantage of the FTP protocol is the need to know the location of the information being searched. Protocol gopher and the software that implements it provide users with the opportunity to work with information resources without knowing their location in advance. To get started using this protocol, it is enough to know the address of one Gopher server. In the future, the work is to select commands, presented in the form of simple and understandable menus. At the same time, the menu items of one server may contain links to the menus of other servers, which makes it easier to find the required information on the Internet. While working with the Gopher system, the client program does not maintain a permanent connection with the Gopher server, so network resources are used more economically.WWW(World Web - The World Wide Web) is the most advanced tool for organizing network resources. It is based on the hypertext representation of information. Hypertext- this is a text containing links to other parts of this document, to other documents, to objects of a non-textual nature (sound, image, video), as well as a system that allows you to read such text, track links, display pictures and play audio and video inserts. Hypertext with non-text components (sound, video) is called hypermedia. The ultimate goal of the WWW is to combine all network resources (files, texts, databases, server programs) into a single worldwide hypertext. The operation of the Internet is based on the use of a family of communication protocols - Data Transfer Control Protocol / Internet Protocol (Transmission Control Protocol / Internet Protocol - TCP/IP), which is used to transfer data over the WAN and many local area networks. TCP/IP is a family of protocols. It consists of protocols that can be divided by purpose into the following groups:

transport protocols that control the transfer of data between two computers;

routing protocols that handle data addressing and determine the shortest available paths to the destination;

network address support protocols designed to identify a computer by its unique number or name;

application protocols that provide access to all kinds of network services;

gateway protocols that help transmit routing messages and network status information over the network, as well as process data for local area networks;

other protocols that do not belong to the specified categories, but provide the client with the convenience of working on the network.

The TCP/IP architecture is based on reference model, however, in it the first three levels of the OSI model are combined into one (Fig. 2).

ModelOSI
Application layer	Application layer
Presentation Layer
User network interface layer
transport layer	transport layer
network layer	Internet
Link layer	network interface
Physical layer	Physical layer

Fig.2. Reference Model Layers and TCP/IP Protocols

Any document or message is sent to the network from an application program (application layer). Then, through the modem and the telephone line (transport layer), the message gets to the Internet node and then with the help of network programs(network interface) is transmitted to the communication line of global network nodes (physical layer). Programs of each level process the message or transmitted document in their own way, without knowing anything about its content. Network addresses On the Internet, each computer is assigned its own unique network address - an IP address, which is 32 bits long and consists of 4 parts of 8 bits. Each part can take values from 0 to 255 and is separated from other parts by a dot. For example, 194.105.195.17 and 147.115.3.27 represent two IP addresses. A network address has two parts: a network address and a host address on that network. Under host refers to a computer connected to a network and providing various network services. This structure of the IP address allows computers on different networks to have the same addresses. For maximum flexibility, IP addresses are classified into classes A, B, C and allocated depending on the number of local networks and computers in them. These three classes of IP addresses determine the size of an organization's local area network. Depending on the class, a complete 32-bit address is broken down into 8-bit components in different ways. In this case, the first one to three bits at the beginning of the IP address identify the corresponding class. The structure of IP addresses is shown in Figure 3.

Fig.3. Structure of IP addresses

By the first number of the IP address, you can determine the type of class to which the organization belongs: Class A addresses - numbers from 0 to 127. Class B addresses - numbers from 128 to 191. Class C addresses - numbers from 192 to 223. Class A network address allows you to identify more than 16 million computers in the local network of the organization, but there can be no more than 128 local networks of this class. A class B network address allows for more local networks, but with fewer computers on the network itself. Finally, class C networks can have a maximum of 254 computers, but there can be over 2 million such networks. When a message is sent to the Internet, an IP address is used to indicate the sender and recipient. The client does not need to remember network addresses because the network uses domain names that are translated by the domain name system into IP addresses. Domain addressing Internet addresses are built according to the domain addressing system (domain name system, DNS). This means that the user's address consists of two parts: the user ID and the domain name, separated by the @ symbol

<идентификатор пользователя>@<название домена>

The user ID and domain name may consist of segments separated by a dot. It is allowed to use Latin letters, numbers and some other symbols in the address. For example:

Ivan. [email protected]

In the example, the user ID has two segments and the domain name has four. Typically, domain segments or subdomains form a hierarchical structure: the first subdomain on the left is usually the name of the computer that is assigned that address, the next one is the name of the organization where that computer is located, and the rightmost (top-level subdomain) is the abbreviation for the country. The address given means that it belongs to Ivan Kirillov, an employee of the law faculty of St. Petersburg University in Russia, who has a computer named mycomputer. User identifiers can be anything: full name and surname, initials, surname with initials, nicknames, as well as the names of organizations or departments. At the same time, one computer can have an arbitrary (limited by the allowed number of IP addresses) number of registered users with their addresses, or a user can have several addresses on the domain (one, for example, for personal correspondence, and the other for official). Moreover, it is possible to have several addresses on different computers. The top-level subdomain, denoting the country, usually consists of two letters: en-Russia, su- the territory of the republics of the former Soviet Union, ca- Canada, UK- Great Britain, ua- Ukraine, de- Germany, etc. In the USA, a different system is traditionally used. The top-level subdomain consists of three letters and indicates that the owner of the address belongs to one of the following classes: com - commercial organizations; edu - educational and scientific organizations; gov - government agencies; mil - military organizations; net - network administration; org - other organizations. In Russia, a second-level subdomain usually denotes the city or geographical region where this address is located, for example: msk - Moscow; spb - St. Petersburg; nsk - Novosibirsk; altai - Altai Territory. Note that in the UK, address subdomains arranged in reverse order.

Web document viewers

To work in the WWW on a computer, you must have special program - browser(browser). A browser is an application program that interacts with the WWW and allows you to receive various documents from the network, view and edit their contents. Browsers provide the ability to work with documents containing textual and multimedia information. In addition, they support all the previously discussed methods and protocols for accessing the Internet. WWW documents usually contain hypertext (text with hyperlinks). Unlike plain text, documents on the Web contain commands that define their structure, including links to other documents. This allows the browser to format the document for display on the screen in accordance with the capabilities of a particular computer. Since the Internet uses heterogeneous hardware and software tools, a universal hypertext markup language - HTML (HyperText Markup Language) was adopted to develop Web pages. HTML includes a set of commands used to describe the structure of a document. With HTML, a document is broken down into the appropriate logical components: paragraphs, headings, lists, and so on. The specific formatting attributes of a document (body text and highlighted components) when viewing it are determined by the browser used. The most common browsers are:

Mosaic for Windows

cello program;

Linx program;

Microsoft Internet Explorer (MSIE);
Netscape Communicator.

Let us briefly consider their purpose and main features. The main focus will be on MSIE as one of the most popular browsers. His latest version 4.0 is distributed on the Internet by Microsoft for free and is included with Windows 98. Mosaic For Windows- one of the first viewers. It has a very simple graphical user interface and allows you to display formatted Web documents on the screen. Its disadvantage is the need to install additional software for working with graphic files, audio and video images, which is not included as standard with the browser. The program cello was developed as an alternative to Mosaic. Directly provides access to HTTP, Gopher, FTP servers, UseNet teleconferences, and also supports Telnet when using external client programs. The program has a very simple interface, which allows you to quickly learn how to work with it. The inconvenience of working with the browser is the small number of buttons on the control panel, so you constantly have to work with drop-down menus. The program Linx refers to the number of browsers with a text interface. Hypertext links are highlighted on the screen with a different color or inverted background and text colors. The advantage of this browser is the ability to quickly find textual information on the WWW using hypertext links. Viewed pages can be marked with bookmarks that can be created while working with the browser. Browser EINet WinWeb differs for the better in a small amount of main memory occupied during operation, good support for interactive forms, stable and reliable operation. The navigation mechanism is simple and user-friendly. There is a built-in tool for searching documents by keywords. Browser settings allow you to select the fonts and colors used when displaying documents and highlighting hyperlinks. Browser Internet Works allows you to work not only with WWW, but also with FTP and Gopher servers. The documents that the user works with can be presented at three levels. At the same time, the transition from page to page can occur both within the same level and between them, using the toolbar buttons and the ability to work in multi-window mode. Viewing a text document can occur while downloading media files in the background. It is possible to customize the interface by the user. The generally recognized leaders among programs for viewing and editing Web-documents - browsers Netscape Communicator and MicroSoft lnternet Explorer are the most convenient and multifunctional. They allow you to display on the screen any documents created in any operating environment and on any computer with a configuration that provides network operation.

Microsoft Internet Explorer 4.0

According to various experts, this browser is almost superior in terms of ease of use and its functionality to Netscape Communicator. It consists of the following components:

MSIE browser;

desktop update component;
Outlook Express;
Microsoft NetMeeting;
Front Page Express;
task Manager.

MSIE Browser allows you to browse the Web from the Windows Explorer window, from the My Computer window, and even from the control panel. In this case, the page may be located on the Internet, in corporate network or on your computer's hard drive. The Windows Explorer panel takes the form of a Web page, which greatly simplifies the work and speeds up the process of finding the right sites. The browser allows you to set various levels of protection, such as preventing the display of unwanted information, for example, related to violence. You can protect your computer from potentially dangerous files and programs by setting different protection levels for different Internet zones. When shopping online, you can secure your credit card and shipping address with Microsoft Wallet, which is part of the Explorer. The most interesting information from the web can be sent directly to your desktop. To do this, you only need to subscribe to the desired channels. The channel is displayed as a shortcut on the desktop and is updated regularly by the content provider. For example, every morning you can receive the latest sports news. The user himself can create any channel.Desktop can be designed as a Web page with direct display of information that will be updated automatically. For example, you can place a news ticker from the Internet on your desktop. To open folders with files and launch programs, one click of the left mouse button is enough. To select an element, simply point to it with the mouse. Outlook Express is an Internet Explorer mail and news program that exchanges e-mail messages, reads and sends group news messages, and works with newsgroups. You can easily switch between mail folders, news servers and newsgroups. News is usually downloaded to a computer for later viewing offline, without wasting time connecting to the Internet. Microsoft NetMeeting allows you to hold conferences on the Web or local area network. This can use a network or a modem. During the conference, you can talk to your interlocutor via the Internet, and with a video image (if you have a video camera connected to your computer), as well as work in a common application. Microsoft Chat used to negotiate online in a special chat room. This uses comic book graphic format or plain text format. The user is given the opportunity to select a cartoon character that will represent him during negotiations with several people at once. With some of them you can talk secretly from the rest. FrontPage Express is used to create, edit and publish your own Web pages. It includes a set of templates with which you can create Web pages of any complexity with any number of links to other information sources.Task Manager serves for planning and execution of some standard procedures. It starts with Windows and runs in the background, executing given programs at specific times.

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