What is a global network? Organization of global networks, tools and capabilities. History of the development of global networks
Having told about this, ask students to imagine that subscribers have personal computers installed instead of telephone sets; 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 a certain time - a 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. Network system tools handle routing of transmitted data. 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. Email. 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 is the high speed of correspondence delivery (minutes, rarely hours), and comparative cheapness. 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 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 various attachments to the letter. 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 be in 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 in global networks.
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 developed tools for 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. Different types of machines are used as host computers: 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). Host computers on the Internet use the Unix operating 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 that is currently running an email server program 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 information transfer speed), noise immunity, and 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
| Communication type | Speed, Mbit/s | Noise immunity |
| Twisted pair wires | 10 -100 | Low |
| Coaxial cable | To 10 | High |
| Phone line | 1 -2 | Low |
| Fiber optic cable | 10 -200 | Absolute |
Most often, dedicated telephone lines or radio communications are used for communication between host computers. If network nodes are located relatively close to each other (within a city), then communication between them can be organized via cable lines - electric or fiber optic. Recently, satellite radio communications have been actively used on the Internet.
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 and fiber optic communications. The adapter is inserted into a free socket on the motherboard and connected by 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 to a telephone signal and vice versa. 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, the actual speed depends not only on the modem, but also on the quality of the 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 communications, 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 "speaked 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 Internet application protocols, 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 a unique address within the entire network. An IP address is a sequence of four decimal integers 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 part of a 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 the WWW: Web page - the main information unit on the WWW with 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 obtain the necessary information from the Internet is to indicate 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:// - the ftp protocol is used 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 the Alta Vista search engine.
Several keywords separated by a space correspond to the logical addition operation: 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.
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.
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.
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. The World Wide Web (WWW) service was created - the 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) – unique 48-bit code of the network card (in hexadecimal system) E9-41-AC-73 IP address – digital address of the computer (network number + computer number on the network): Subnet mask determines which computers are “visible” and are 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 with a forward slash “/”, 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, the domain name of the site is white, the directory on the site is blue, and the file name is green
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.
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 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 the IP address of a computer on the network, then the serial number of the computer on the network is _____
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 _____
internet network protocol domain
The Internet is a global computer network that unites and covers all countries of the world and provides them with communication.
The World Wide Web operates on the basis of the Internet; it provides access to information and documents located on various computers connected to the Internet. In English, the World Wide Web is abbreviated WWW.
The number of users has exceeded 2 billion, which means that almost half of the world's population uses the Internet.
Through the Internet you can find any information, download programs, solve business issues, communicate via webcam and much more that the user desires.
To find all this information, there are special search engines. The most famous Google, this system is used by 83.87% of the world's population.
There are four types of computer networks:
a) Local network - connects computers located approximately at a distance of 50-100 meters within the same building.
b) Regional network - connects computers existing within a region or city.
c) Corporate network - connects computers of one company, corporation and association of companies.
d) Global network - it covers the territory of a country or several countries to use information on a global scale. This network is called the Internet.
When using the Internet, we use the services of an Internet provider. It connects clients to its network, who become part of the provider.
Each Internet user enters into an agreement with a specific provider to connect him to the network. Usually they are connected to the network through special cables, telephone lines, modems, and satellite dishes.
All Internet services are built on a client-server basis.
Server is a computer connected to a network that provides access to resources.
Client - the user's computer, or software, generates requests and processes the received data.
All information is stored on servers, they have their own addresses and are controlled by special programs. Information exchange on servers occurs using high-speed communication channels.
Individual users connect to the network through the computers of local Internet providers, which have a permanent connection. A regional provider connects to a national provider. National ones are united in networks of transnational or first-level providers. A combination of first-level networks are connected into a global network.
Protocols exist to transfer data over a network between different types of computers.
Protocol - sets of rules and agreements that describe how data is transferred over a network. Protocols are designed for computers of different types to interact with each other.
To transmit data on the Internet, a computer needs a special identified unique number.
To achieve this, a system of IP addresses was adopted, in which each address consists of a set of four numbers separated by a dot. Each number must be from the range 0-255. For example, 217.23.130.1.
Purpose and structure of global networks
Global computer network, WAN (English Wide Area Network, WAN) is a computer network covering large areas and including a large number of computers.
Global networks allow you to organize interaction between subscribers over thousands of kilometers. Data transmission in global networks is based on packet switching technology.
Each transferred file is divided into small portions, which are placed in a packet containing the addresses of both the sending and receiving computer.
Packets travel independently across the network: if one packet is lost, it can be easily resent. Since each packet is sent independently of the others and mixed with thousands of similar ones, this, among other things, ensures that data transmission over the Internet is relatively cheap. For example, the cost of sending an email is negligible compared to the cost of sending a fax message of equal length.
WANs are also called territorial computer networks, serve to provide their services to a large number of 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, the construction of 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 the constant maintenance of network equipment scattered over a large area in working order.
Typical global subscribers computer network are local enterprise networks 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.
Network operator(network operator) is the company that maintains the normal operation of the network. Service Provider, often also called provider(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.
It is much less common for a global network to be created entirely by some large corporation(such as Dow Jones or Transneft) for their internal needs. In this case, the network is called private. Very common and 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 also other types 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.
Due to the high cost of WANs, there has been a long-term trend toward a single WAN that can transmit data of any type: computer data, telephone conversations, faxes, telegrams, television images, teletex (transfer of data between two terminals), videotex (receiving data stored on the network to your terminal), etc., etc.
Although local and global computer networks are based on the same method - the method packet switching, global networks have quite a lot of differences from local networks..
Technological map of the lesson on the topic: “Internet. Organization of global networks", §10 I.G. Semakin, 11th grade
F.I. _____________________________Class_____________
Plan:
History of the development of global networks
Internet hardware
Channels of connection
Internet software
How the Internet works
Question 2: Internet Hardware
Match (connect with arrows)
Network service provider
provides network information services
a unique 32-bit (in binary) address of a computer that is connected to the Internet
Server program
organization providing data exchange services in a network environment
Symbolic address of a computer on the Internet
Domain name system
contains one or more powerful server computers
1 . Which of the following is an incorrect IP address?
1) 2.2.2.2.2 2) 111.11.1.111 3) 198.9.189.228 4) 192.167.257.127 ANSWER:_________________
2. A piece of paper with a written IP address was accidentally thrown into the trash, having previously been torn into four parts. These fragments are designated by letters A,B, IN And G. Restore IP-address. In your answer, indicate the sequence of letters denoting the fragments in the order corresponding to IP-address.
ANSWER:_____________________________________________________________________
3 .File access uk. net located on the server org. de, carried out according to the protocol ftp. Given fragments of the file address are encoded in letters from A before AND. Write down the sequence of these letters encoding the address of the specified file on the Internet.
A) org B) uk IN) . de G) . net D) :// E) ftp AND)/
ANSWER: ____________________________________________________________________
Question 3: Communication channels
Technical methods connections on the global network:
________________________________________________________________________________________________________________________________________________________________________________
Properties of communication channels: _________________________________________________________________________________
(fill in the blanks)
By parameter the most expensive are _____________________________, the cheapest _________________. By bandwidth parameter the lowest ____________________, the highest ____________________________. By noise immunity parameter the lowest____________________, the highest _______________________.
Unit of measurement of throughput - _Kbps __ or ____________.
Question 1: History of the development of global networks
What should we call a scientific and technical revolution? ______________________________________________________________________________________________________________________________________________________________
Stages of the scientific and technological revolution:
_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
1964 – _________________________________________________________________________________________________
1969 – __________________________________________________________________________________________________
1993 – _________________________________________________________________________________________________
Communication channel capacity is 512 bytes/sec. How long will it take to transfer 300 KB of information?
___________________________________________________________________________________________________________________________________________________________________________________________
Calculate the channel capacity (in Kbit/sec) if the message volume is 2,5 Mbit passes in 1/3 min
____________________________________________________________________________________________________________________________________________________________________________________________
The data transfer rate is 1024000 bps. Transferring the file over this connection took 5 seconds Determine the file size in KB.
