Internet is a global distributed computer network. Thanks to internet, humanity has a possibility to share information, download or transfer files, communicate in various chat rooms as well as learn the latest news. Internet is the main source of information and its worldwide repository.

That it is possible to do on the Internet:

-Web-surfing;

-Remote control of computers;

-Download of different files;

-Communication;

-Search for information;

-Money transfer;

-Earnings;

-Viewing of news.

The Internet was appeared in January 1983.

Then the ARPANET network passed to TCP/IP protocol (Transmission Control Protocol / Internet Protocol), which has been successfully used so far (fig. 8.1).

Then the International Organization for Standards (ISO) has developed a model called the open system interconnection (OSI) model or the ISO/OSI model.

The ISO/OSI model divides network functions into seven levels: applied, representation level, session, transport, network, channel and physical.

Figure 8.1 - Transmission Control Protocol

The physical level. At this level, binary codes are transmitted over physical communication channels, the characteristics of electrical signals, signal transmission rates, etc. are determined.

At the physical level, the types of connectors and the purpose of each contact are standardized.

The application layer is the highest level of the ISO / OSI model. Its task is to organize interaction with user's applications.

The most common top-level protocols are:

- HTTP (the protocol of transmission of web pages);

- FTP (file transfer protocol);

- Telnet (remote control);

- SMTP, POP3 (protocol of mail exchange).

Each computer on the Internet has a unique IP Address (Internet Protocol Address), which allows you to distinguish it from other computers on the network. The IP address is a four-byte binary number and is written in decimal form (IPv4).

byte1. byte2. byte3. bytes4

For example, 192.232.0.1

This 32-bit addressing system allows you to get about 4 billion addresses.

In connection with the rapid development of the Internet, there was a problem of lack of addresses. IP-IP addressing (Internet Protocol version 6) was proposed, which uses a 128-bit addressing scheme. The new protocol can provide up to 5 • 1028 addresses.

The IPv6 protocol is already used in several thousands of networks around the world, but has not yet received as widespread on the Internet as IPv4.

Domain Name System

For Internet users, IP addressing is not very convenient, since the user must remember a lot of numbers. Therefore, a domain name system (DNS) was developed.

A domain name system is a distributed database that contains the addresses of computers connected to the Internet.

There are two types of top-level domains.

1. Top-level domains of general purpose.

com - Commercial organizations.

edu - Educational institutions.

gov - Government institutions.

For example, www.yahoo.com

2. Top-level domains of countries.

These include the domain names us, uk, kz, ru, etc.

For example, www.kstu.kz

Each resource on the Internet has a universal resource pointer (Uniform Resource Locator, URL).

Most URLs have the following form:

protocol: //host.domain/directory/file.name

where the protocol is the TCP / IP protocol that you want to use to get the resource (for example, HTTP, FTP, telnet, etc.).

Host.domain is the domain name of the host computer in which the resource is located.

Directiry is the directory name.

file.name is the name of the resource file.

For example, http://stars.ru/fact/k2.html

Ways to connect to the Internet

To connect to the Internet, there are several ways that differ from each other by connection technology, speed of use, and technical characteristics that determine the speed of information transfer and the stability of the connection itself.