Global networks. History of the development of global networks

Wide Area Networks (WAN), also called territorial computer networks, serve to provide their services a large number end subscribers scattered over a large area - within a region, region, country, continent or the entire globe.

Due to the large length of communication channels, building a global network requires very large costs, which include the cost of cables and work on their installation, the cost of switching equipment and intermediate amplification equipment that provides the necessary channel bandwidth, as well as operating costs for constantly maintaining a scattered network in working order. over a large area of ​​network equipment.

Typical subscribers of a global computer network are local networks of enterprises located in different cities and countries that need to exchange data with each other. Individual computers also use the services of global networks. Large mainframe computers typically provide access to corporate data, while personal computers are used to access corporate data and public Internet data.

WANs are usually created by large telecommunications companies to provide paid services to subscribers. Such networks are called public or public. There are also such concepts as network operator and network service provider. The network operator is the company that supports normal work networks. A service provider, often also called a service provider, is a company that provides paid services to network subscribers. The owner, operator, and service provider may be one company, or they may represent different companies.

Much less often, a global network is created entirely by some large corporation (such as Dow Jones or Transneft) for its internal needs. In this case, the network is called private. Very often there is an intermediate option - a corporate network uses the services or equipment of a public wide area network, but supplements these services or equipment with its own. The most typical example here is the rental of communication channels, on the basis of which their own territorial networks are created.

In addition to global computing networks, there are other types of territorial information transmission networks. First of all, these are telephone and telegraph networks that have been operating for many decades, as well as the telex network.

Global Internet

The concept of a global network - a system of connected computers located at large distances from each other - appeared in the process of the development of computer networks. In 1964, it was created in the USA computer system early warning of approaching enemy missiles. The first global network for non-military purposes was the ARPANET network in the United States, introduced in 1969. It had a scientific purpose and combined computers from several universities in the country.

In the 80s-90s of the last century in different countries Many industry and regional national computer networks are being created. Their integration into an international network took place on the basis of the Internet internetworking environment.

An important year in the history of the Internet was 1993, when the service was created World Wide Web (WWW) - Worldwide Information Network (World Wide Web). With the advent of WWW, interest in the Internet sharply increased, and the process of its rapid development and spread began. Many people, when talking about the Internet, mean WWW, although this is only one of its services.

Internet hardware

The main components of any global network are computer nodes and communication channels.

Here we can draw an analogy with the telephone network: the nodes of the telephone network are automatic telephone exchanges - automatic telephone exchanges, which are interconnected by communication lines and form a city telephone network. Each subscriber's phone is connected to a specific PBX.

Users' personal computers are connected to computer network nodes in the same way that subscriber phones are connected to telephone exchanges. Moreover, the role of a computer network subscriber can be either an individual person through his PC, or an entire organization through his local network. In the latter case, a local network server is connected to the node.

An organization that provides data exchange services with a network environment is called a network service provider. The English word “provider” means “supplier”, “supplier”. The user enters into an agreement with the provider to connect to his node and subsequently pays him for the services provided (similar to how we pay for telephone network services).

A node contains one or more powerful computers that are constantly connected to the network. Information services are provided by the operation of server programs installed on host computers.

Each host computer has its own permanent Internet address; it's called an IP address.

Along with digital IP addresses, the Internet operates a system of symbolic addresses, which is more convenient and understandable for users. It is called the Domain Name System (DNS).

The domain name system is built on a hierarchical principle. The first domain on the right (also called a suffix) is the top-level domain, the next one is the second-level domain, etc. The last one (first on the left) is the computer name. Top-level domains can be geographical (two-letter) or administrative (three-letter). For example, the Russian Internet zone belongs to geographic domain ru. More examples: uk - domain of England; ca - domain of Canada; de - German domain; jp - Japanese domain. Administrative top-level domains most often belong to the American zone of the Internet: gov - US government network; mil - military network; edu - educational network; com - commercial network.

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History of the development of global networks 1964 USA. A computer system for early warning of approaching enemy missiles has been created. The first global network for non-military purposes ARPANET was created. It had a scientific purpose and united the computers of several universities. Created World service Wide Web (WWW) – Worldwide Information Network.

Each computer connected to the Internet must have its own address, which is called an IP address (IP = Internet Protocol). An IP address consists of four numbers separated by dots; each of these numbers is in the range 0...255, for example:

How the Internet Works The Internet uses packet transmission of information. The TCP/IP protocol, the transmission control protocol, is responsible for its operation. According to the TCP protocol, the transmitted message is broken up on the sending server and restored to its original form on the receiving server. The purpose of the IP protocol is to deliver each individual packet to its destination.

Network addresses Physical address (MAC address) - a unique 48-bit code network card(in hexadecimal system) E9-41-AC-73 IP address – digital address of the computer (network number + computer number on the network): The subnet mask determines which computers are “visible” and are located on the same subnet; when superimposed on an IP address (logical AND operation) gives the network number FF.FF.FF.0 network number, computer number 48

Network addresses Gateway - the address of the computer through which packets go to other networks (the Internet): DNS server - the address of the computer where requests for converting a domain address to an IP address go: WINS server - the address of the computer where requests for conversion go computer network name to IP address.

The address of a document on the Internet (URL = Uniform Resource Locator) consists of the following parts: a protocol, most often http (for Web pages) or ftp (for file archives) a protocol, most often http (for Web pages) or ftp (for file archives) archives) signs: //, separating the protocol from the rest of the address signs: //, separating the protocol from the rest of the address domain name(or IP address) of the site domain name (or IP address) of the site directory on the server where the file is located directory on the server where the file is located file name file name It is customary to separate directories not with a backslash “\” (as in Windows), but straight “/”, as in the UNIX system and its “relatives”, for example, in Linux, an example address (URL) here the protocol is highlighted with a yellow marker, white – the domain name of the site, blue – the directory on the site and green – the file name

Task IP address Subnet mask Determine the computer number on the network

Solution IP address Subnet mask A bitwise conjunction is used - the logical operation “AND”; Output: computer number on the network is 48.

The Subnet Mask task is a 32-bit binary number, which determines which part of the computer's IP address is the network address, and which part of the IP address defines the computer's subnet address. In a subnet mask, the most significant bits allocated in the computer's IP address for the network address have the value 1; the low-order bits allocated in the computer's IP address for the computer's subnet address have the value 0. For example, the subnet mask can look like: () This means that the 19 most significant bits in the IP address contain the network address, the remaining 13 low-order bits contain the address of the computer on the network. If the subnet mask and IP address computer on the network, then serial number computer on the network equals_____

Solution Let's perform the bitwise conjunction above; the zero bits of the mask and the corresponding bits of the IP address, which determine the computer number on the network, are highlighted in white: = 12 Answer: 12.

Problem A subnet mask is a 32-bit binary number that determines which part of a computer's IP address is the network address, and which part of the IP address defines the computer's subnet address. In a subnet mask, the most significant bits allocated in the computer's IP address for the network address have the value 1; the low-order bits allocated in the computer's IP address for the computer's subnet address have the value 0. For example, the subnet mask could look like: () This means that the 19 most significant bits in the IP address contain the network address, the remaining 13 low-order bits contain the address of the computer on the network. If the subnet mask and the IP address of a computer on the network, then the serial number of the computer on the network is _____

Having told about this, ask students to imagine what subscribers have instead of telephone sets personal computers installed; instead of switches there are powerful computer nodes and a wide variety of information circulates through such a network: from text to video and sound. This is the modern world system of global computer networks.

The first global computer network began operating in 1969 in the USA, it was called ARPANET and united only 4 remote computers. An example of a modern network for scientific and educational purposes is BITNET. It covers 35 countries in Europe, Asia and America, uniting more than 800 universities, colleges, and research centers. The largest Russian network is RELCOM, created in 1990, RELCOM is part of the European association of networks EUNET, which, in turn, is a member of the giant global INTERNET community. This hierarchy is typical for the organization of global networks.

In Fig. Figure 12.3 shows the typical architecture of a global network. The network consists of nodes host computers (U1, U2,...), PCs of network subscribers (All, All, ...), communication lines. Typically, a network node contains not one, but many computers. The functions of servers for different network services can be performed by different computers.

Host computers are always on, always ready to receive and transmit information. In this case they say that they operate in the mode on-line. Subscribers' computers connect to the network (in on-line) only for certain time- communication session. Having forwarded and received the necessary information, the subscriber can disconnect from the network and then work with the received information autonomously - in the off-line. The route for transmitting information to the user is usually unknown. He can only be sure that the information passes through the connection node and reaches its destination. Routing of transmitted data is carried out system tools networks. In different sessions, communication with the same correspondent can take different routes.

A gateway is a computer that organizes the connection of a given network with other global networks.

^ Information services of global networks. E-mail. g history of global networks, electronic mail (e-mail) appeared as the very first information service. This service remains the main and most important in computer telecommunications. We can say that there is a process of replacing traditional paper mail with e-mail. The advantages of the latter are obvious: first of all, it high speed correspondence delivery (minutes, rarely hours), comparatively cheap. Already, huge volumes of business and personal correspondence are sent via e-mail. E-mail, combined with fax, provides the vast majority of needs for the transmission of letters and documents.

In order for a subscriber to use e-mail services, he must:

• 
  have a hardware connection of your own personal computer to the mail server of a computer network node;
• 
  have your own mailbox and password on this server to access it;
• 
  have a personal email address;
• 
  Have an email client program (mailer) on your computer.

The preparation of an email is carried out by the user in the mode off-line- disconnection from the network. Using an email client program, he generates the text of the letter, indicates the recipient's address, and attaches it to the letter various applications. Then the User goes into mode on-line, those. connects to the mail server and issues the “deliver mail” command. Prepared correspondence is transferred to the server, and correspondence received at the User’s address is transferred from the server to his PC. In this case, midday letters are deleted from the mailbox, and sent ones are added to it. The mail server periodically scans subscribers' mailboxes and, having found outgoing correspondence there, organizes its poisoning.

The example of email illustrates the point well. client-server technologies, accepted in modern networks. This technology is based on the division of software functions that serve each information service between the client computer and the server. The corresponding software is called a client program and a server program (often said in short: client And server). Popular email client programs are: MAIL for MS-DOS and Outlook Express for Windows.

In the initial period of e-mail development, transmitted correspondence could only have text format. Data of a different format (binary files) was recoded into text format using a special transcoder program UUDECOD. The Internet now uses the MIME standard, which allows a wide variety of information to be transmitted in the body of an email message without such recoding. According to this standard, the sending machine places in the header of the email message descriptions of the types of information units that make up the letter. Based on these descriptions, the receiving machine correctly interprets the received information. Now in an email, in addition to text, you can place graphic images (type image), audio information (audio), videos (video), and any applications (application).

Along with e-mail, there are other types of information services for users.

Telnet. This service allows the user to work in terminal mode of a remote computer, i.e. use programs installed on it in the same way as programs on their own computer.

FTP. This is the name of the network protocol and programs that work with directories and files on a remote machine. The FTP client has the ability to browse the directories of FTP servers and copy files of interest.

Archie. This is the name of special servers that act as search programs in the FTP server system. They help you quickly find the files you need.

Gopher. A system for searching and retrieving information from the network with advanced tools multi-level menus, reference books, index links, etc.

^ WAIS. Network information retrieval system based on distributed databases and libraries.

Usenet. Teleconference system. Another name is newsgroups. Serves subscribers of certain thematic conferences, sending them materials by e-mail.

^ Network hardware. Host computers (servers). The host computer has its own unique address on the network and acts as a host machine serving subscribers. Used as host computers different types machines: from powerful PCs to minicomputers and even mainframes (large computers). The main requirements are a high-speed processor and a large amount of disk memory (tens and hundreds of GB). On host computers in Internet networks operating room used Unix system. All server programs that serve applications run under Unix.

From what has already been mentioned above, it follows that the concept of “server” has a software and hardware meaning. For example, a host computer on which at the moment The email server program is running and acts as a mail server. If the WWW server program starts running on the same machine, then it becomes a Web server. Often the functions of servers for various services are divided on a network node between different computers.

^ Communication lines. The main types of communication lines between computers on a network are telephone lines, electrical cables, fiber optic cable and radio communications. The main parameters of communication lines are throughput ( maximum speed information transmission), noise immunity, cost. In terms of cost, the most expensive are fiber optic lines, the cheapest are telephone lines. However, as the price decreases, the quality of the line also decreases. In table 12.1 provides comparative characteristics of lines in terms of speed and noise immunity.

Table 12.1

Characteristics of communication lines

Typically, subscribers (clients) connect to their provider's node through a telephone line. Radio communications are increasingly being used for these purposes.

To transmit information over communication channels, it is necessary to convert it from the form in which it exists in the computer into signals transmitted over communication lines. Such transformations are carried out by special devices called network adapters. There are adapters for cable, for fiber optic communications. The adapter is inserted into an empty socket motherboard and connects with a cable to the adapter of another computer. This is usually done on local networks.

In global networks connected via telephone lines, modems. The purpose of a modem is to convert information from binary computer code into a telephone signal and back. In addition, the modem performs a number of other functions. For example, a network client modem must dial up to the node to which it connects.

The main characteristic of the modem is the maximum data transfer speed. Currently it ranges from 1200 bps to 112,000 bps. However real speed depends not only on the modem, but also on the quality telephone lines. In Russian urban networks, the acceptable transmission speed is low and amounts to 2400-14400 bps. In the future, when there is a complete transition of telephone lines to digital communication, the need to use modems will disappear.

Internet. To the question of what the Internet is, you can read different answers in the literature. Most often this question is answered this way: the Internet is a supernetwork covering the whole world, which is a collection of many (more than 2000) networks that support a single TCP/IP protocol (Transmission Control Protocol/Internet Protocol).

Protocol - is a standard for representing, transforming and transferring information on a computer network. Figuratively, we can say this: a protocol is a specific network language. While the various global networks operated autonomously, they "spoke in different languages" To unite them, it was necessary to come up with a common language (a kind of network Esperanto), which became the TCP/IP protocol. This protocol is supported by both software and hardware of the network. It comes down to standardizing the following procedures:

• 
  splitting the transmitted data into packets (parts);

• 
  addressing packets and transmitting them along specific routes to their destination;

• 
  assembling packages into raw data form.

Others have been implemented based on the TCP/IP protocol application protocols Internet, forming the basis of the service on the network.

The basis of the Internet is a system of so-called IP addresses. Each host computer connected to the Internet receives an address that is unique within the entire network. An IP address is a sequence of four integers decimal numbers, separated by dots. For example: 195.205.31.47. Since the Internet is a network of networks, the first number determines the network to which the computer belongs, the following numbers specify the coordinates of the computer in this network.

Digital addressing is an “internal matter” of the system. It is inconvenient for users. Therefore, the alphabetic form of writing addresses is used for users - domain addresses. Domains are symbolic names separated by dots. Example of a domain address: www.psu.ru. The address is read from right to left. The first domain on the right is called a suffix. Most often, it identifies the country in which the computer is located (thus, the computer is an element national network). For example, ru - Russia, uk - Great Britain, fr - France. US host computer addresses usually have a suffix indicating their affiliation with corporate networks: edu - scientific and educational organizations, gov - government organizations, mil - military, etc.

The following domains (there may be more than one) define the host computer in this network (PSU - Internet center of Perm State University). The last domain is the name of the server (Web server). Using a special server program, a connection is established between numeric and domain addresses.

All of the above characteristics of the Internet are most often unknown to the user. From the user's point of view, the Internet is a certain set of information services that he can receive from the network. Services include: e-mail, teleconferences (mailing lists), file archives, directories and databases, World Wide Web - WWW, etc. The Internet is unlimited information resources. The impact that the Internet will have on the development of human society is not yet fully realized.

^ Information services Internet. Along with the information services listed by Gillie (e-mail, teleconferences, etc.) provided to users of global networks, there are services, the emergence and development of which is associated inclusively with the development of the global Internet. The most prominent among them is the WWW.

WWW- World Wide Web - World Wide Web. This is a hypertext information system on the Internet. Recently, WWW and its software have become a universal means of information services on the Internet. They provide users with access to almost all of the resources listed above (FTP, e-mail, WAIS, Gopher, etc.). Basic concepts related to WWW: Web page - basic information item on WWW having its own address;

Web server - a computer that stores Web pages and the corresponding software for working with them;

Web browser - a client program that allows you to retrieve and view Web pages;

A website is a section of data on a Web server owned by an organization or person. In this section, its owner places his information in the form of many interconnected Web pages. Typically, a site has a title - a home page, from which you can move through the pages of the site using hyperlinks or back-and-forth signs.

The most popular Web browsers are Internet Explorer and Netscape Navigator. The main task of the browser is to contact the Web server for the desired page and display the page on the screen. The simplest way to get necessary information from the Internet - indicating the address of the resource you are looking for.

To store and search information on the Internet, universal addressing is used, which is called URL - Uniform Resource Locator. A URL contains information not only about where the resource is located, but also what protocol it should be accessed through. The URL consists of two parts: the first (left) indicates the protocol used, and the second (right) indicates where exactly the resource is located on the network (the name of the corresponding server). These parts are separated by a colon, for example:

Http://servername/path/file

Ftp:// - used ftp protocol when accessing ftp servers;

Gopher:// - connection to Gopher servers;

Http:// - use of the hypertext protocol (Hyper Text Transfer Protocol), which underlies the WWW. This type of connection must be specified when accessing any WWW server.

Here is an example of the address of a file containing a distance learning course in German:

Http://www.scholar.urc.ac.ru/Teaher/German/main.html

In addition to direct addressing, searching for information on the Internet can be carried out using hyperlinks.

There are a number of special search programs available to help users on the Internet. They are also called search servers, search engines, search engines. Such a system is constantly in operation. Using special robot programs, it periodically crawls all Web servers on the network and collects summary information about their content. Based on the results of such views, directories and index lists are organized indicating documents where keyword definitions are found. User requests for information search are then served using these lists. The search engine provides the user with a list of document addresses that contain the keywords specified by the user.

Below are the addresses of the most popular Russian search servers:

Http://yandex.ru/ http://www.altavista.telia.com/

http://www.list.ru/

Searching for information using keywords requires certain skills from the user. Online search algorithms, like searching for information in databases, are based on logic. Let's consider this issue using the example of organizing a search using several keywords, adopted in search engine Alta Vista.

1. 
   Some keywords, separated by a space, correspond to the logical addition operation: OR (OR). For example, by specifying the key: , we will get a list of all documents in which the word “School” or the word “computer science” appears. Obviously, there will be too many such documents and most of them are not needed by the user.
2. 
   Several words enclosed in quotation marks are perceived as a single whole. By specifying “School computer science” in the request, we will receive documents containing such a string.
3. 
   The “+” sign between words is equivalent to the logical Multiplication operation: AND (AND). By specifying the key in the request, we will receive all documents that contain these two words at the same time, but they can be arranged in any order and randomly.

In addition to WWW, among the relatively new Internet services there are the following:

^IRC. Internet Relay Chat- “chat” in real time. Allows you to conduct a written dialogue with remote interlocutors on-line;

Internet telephony. A service that supports online voice communication among network clients.

If it is possible to access the Internet, students’ practical work can be organized in the following areas:

• 
  preparing, sending and receiving email;
• 
  working with a Web browser, viewing Web pages;
• 
  contacting FTP servers, retrieving files;

• 
  searching for information on the WWW using search programs.

Tasks for students to perform practical work on the Internet are contained in the manual.