A system of interconnected local networks. General principles of organizing local networks. Basic Internet services

Topic 1.3: Open systems and the OSI model

Topic 1.4: Basics of local networks

Topic 1.5: Basic technologies of local networks

Topic 1.6: Basic software and hardware components of a LAN

Local networks

1.4. LAN Basics

1.4.1. Basic concepts of LAN

LAN classification

Computer network is a collection of computers connected by data transmission channels. Depending on the distance between computers, the following computer networks are distinguished:

• local area networks - LAN;
• territorial computer networks, which include regional MAN and global WAN networks;
• corporate networks.

A local area network is a LAN in which the PC and communication equipment are located a short distance from each other. A LAN is usually designed to collect, store, transmit, process and provide distributed information to users within a department or company. In addition, the LAN usually has access to the Internet.

Local networks can be classified by:

• management level;
• purpose;
• homogeneity;
• administrative relations between computers;
• topology;
• architecture.

Let's take a closer look at the classification of LAN

The following LANs are distinguished by management level:

• Workgroup LANs, which consist of several PCs running the same operating system. In such a LAN, as a rule, there are several dedicated servers: a file server, a print server;
• LAN of structural units (departments). The LAN data contains several dozen PCs and servers such as: file server, print server, database server;
• LAN of enterprises (firms). These LANs can contain over 100 computers and servers such as: file server, print server, database server, mail server and other servers.

According to their purpose, networks are divided into:

• computer networks intended for computational work;
• information and computer networks, which are intended both for conducting settlement work and for providing information resources;
• information-advisers, who, based on data processing, generate information to support decision-making;
• information-control networks, which are designed to manage objects based on information processing.

The types of computers used can be distinguished:

• homogeneous networks that contain the same type of computers and system software;
• heterogeneous networks that contain different types of computers and system software.

According to the administrative relationships between computers, we can distinguish:

• LAN with centralized management (with dedicated servers);
• LANs without centralized control (decentralized) or peer-to-peer (single-level) networks.

According to topology (main topologies), LANs are divided into:

• bus topology;
• star topology;
• ring topology.

According to architecture (main types of architectures), LANs are divided into:

1. Ethernet.
2. Arcnet.
3. Token ring.
4. FDDI.

A local network can be considered a connection between two or more devices using a cable, radio waves or optical signals, in which data exchange between them becomes possible. Devices located in the same room or building and connected to each other are called a local computer network (LAN - Local Area Network). The number of devices connected to such a network is limited by the capabilities of the cable system and network equipment used.

The connection between devices can be direct or using additional communication nodes.

Networks are backbone information structures consisting of logical and physical levels or components, the main purpose of which is the exchange of information.

The physical layer is represented by network components that provide a physical connection between computers. Such components are typically: network interface (network card or network adapter card, standard or extended communications or parallel port or multiport card), network media (coaxial cable, two-wire so-called twisted pair or fiber optic) and node elements (routers, hubs, repeaters (repeaters, hubs), switches) and end elements (terminators, connectors, sockets, plugs).

Currently, there is a clear structuring of networks into local and global, the process of integrating the former into the latter, where networks with several hundred computers are still considered local, and global networks number tens of thousands of connected computer systems. The information exchange speed reaches 200 Mbit/s, and 10 Mbit/s is considered the basic initial and low-cost configuration. Now computer networks make it possible not only to transmit or receive information in the literal sense of the concept, but also provide many service opportunities, the list of which is constantly expanding. This includes remote administration, distributed file systems, remote program execution, e-mail, remote printing, distributed databases, remote access systems and distributed control systems, search engines, teleconferencing and much more.

Devices used both as control centers in the network and as information storage devices are called servers. If devices are located relatively close to each other and connected using high-speed network adapters, then such networks are called local networks. When using a local network, devices are usually located within the same room, building, or in several nearby houses. A local computer network, as a rule, unites no more than a hundred computer systems belonging to any one structure, and is of a corporate nature, both in its operation and in the nature of the system software.

The principles of organization and software protocols of local and global computer systems can be either different or absolutely the same. Therefore, it is impossible to classify a network as local or global only on the basis of the type of network interaction and basic software.

2.List 3 basic network topologies:

Write down the answer: __________________________________________

3. Select the transmission speed of the medium-speed network.

1) up to 100Mbit/s

2) up to 100MB/s

3) up to 1000Mbit/s

4. Global network is.

1. system of interconnected local networks

2. a system of interconnected computers

3. system of interconnected local telecommunications networks

4. a system of interconnected local networks and computers of individual users

5. To connect two computers via telephone lines you must have:

1. Modem

2. two modems

3. telephone, modem and special software

4. via modem on each computer and special software

6. Which of the following computer connection diagrams is a closed chain?

1. Tire

2. Ring

3. Star

4. There is no right answer

7. Which cable provides data transfer speeds of up to 10 Mbit/s?

1. Coaxial

2. twisted pair

3. fiber optic

4. there is no right answer

8.The largest network size (up to 20 km) has a topology:

Star

Ring

Tire

9.The smallest network size (up to 200 m) has a topology:

Star

Ring

Tire

10. The topology of a computer network in which all computers on the network are connected to a central node is called

1. Tire

2. Ring

3. Star

4. There is no right answer

11. Protocol is

1. the ability of a computer to send files through communication channels

2. device for local network operation

3. standard for data transmission via a computer network

4. standard for sending messages via email

12. Highest level of security

Star

Ring

Tire

13.For general access of network users, the following is used:

1) workstation

2) server

3) client

14. Multiport devices to connect PC using network cable?

Write down the answer: __________________________________________

15. Communication channel providing high-speed transmission?

Write down the answer: __________________________________________

16. A computer that uses server resources is called...

Write down the answer: __________________________________________

17. Data on the network is transmitted in packets no larger than:

1.5 GB

1.5 KB

1.5 Bytes

18. Types of computer networks:

Personal, local, corporate, territorial, global

Personal, local, corporate, city, global

Personal, satellite, 4-G

19. Communication lines are of two types:

Satellite and Glonass

Wireless and WAN

Wireless and wired

20. Bluetooth operates within a radius

10 meters 2) 20-30 meters 3) 100 meters

21. The LAN can connect as much as possible

1000 computers

100 computers

20 computers

22. Eight-pin connector with a latch for connecting a PC to the network:

COM 2. R.J.-48 3. R.J.-45

23 Switches or switches used for:

to select a route

connecting computers into a single network

signal amplification

24. The capacity of the information channel is measured:

1.Hertz 2.Seconds 3.Mbps

25.The lowest throughput and noise immunity is:

Coaxial cable

Telephone cable 3. Twisted pair

Answers

Local computing network

Star, Tire, ring

Hub (switch) and switch (hub)

Optical fiber

Client

Grade

21-25 "5"

16-21 "4"

Lesson topic: Local computer networks.

Lesson objectives:

1. Master the types of local computer networks;
2. Have an idea of ​​their capabilities

Lesson Objectives

Educational:

• give an idea of ​​the purpose of computer networks and their types.
• introduce students to the structure of local networks.
• teach to identify different types of local network topologies.

Educational:

• develop students’ ability to exchange files on a local computer network.
• instill in students basic techniques for working online.
• develop skills in identifying network topology.

Educational

• instill interest in the subject.
• to develop skills of independence and discipline, the basics of communicative communication.

Students must:

1. Know the concept of computer networks, their types.
2. Know the concept of a local network, its purpose and organization.
3. Be able to correctly determine the topology of a local network and identify the shortcomings of each topology.

Equipment: Classroom LAN, computer, screen, projector, presentation on the topic.

Lesson plan:

1. Organizational moment – ​​2 min.
2. Explanation of a new topic – 25 min.
3. Consolidating new material – 8 min.
4. Lesson summary and homework – 5 min.

Introduction

The emerging problem of transmitting information between users over a certain distance is solved by using various information transmission channels that can use different physical principles. For example, when people communicate directly, information can be transmitted using sound waves; when talking on the phone, information can be transmitted using electrical signals propagating along communication lines. Using communication channels of various physical natures (cable, fiber optic, radio channels, etc.), you can transfer information between computers. The practical need for quick access to the information resources of other computers, printers, and other peripheral devices was the reason for the emergence of computer networks. According to the method of mutual arrangement of computers connected to a network, networks are divided into two types:

• Local networks.
• Global networks.

Let's get acquainted with the concept and capabilities of Local Computer Networks.

I. Let's define a computer network:

A computer network is a system of computers connected by information transmission channels.

Small-scale computer networks operating within one room, building, at a relatively short distance are called local networks(LS).

An example of a local computer network is a computer network in a computer science class, a school-wide LAN that connects computers installed in subject rooms. Also, various departments of enterprises, firms, and institutions are united in the LS. Typically, LAN computers are located no more than 1 km from each other.

Let's answer the question “How does offline work on a PC differ from work on the same PC that is part of the LAN?” using the example of drugs at school.

(There is a discussion going on that should lead to a conclusion about the benefits of networking.)

So there are two basic goals in use PM:

• Sharing files between network users;
• Use of publicly available resources: large disk space, printers, centralized database, software, etc.

Users of a shared local network are usually called working group , and computers connected to the network – workstations .

If all computers on the network have equal rights, i.e. the network consists only of workstations (PCs) - it is called peer-to-peer

II. Computer network topology

Local networks (LANs), depending on their purpose and technical solutions, may have different structures for connecting computers. This structure is called configuration, architecture, network topology.

The general scheme of connecting computers on a local network is called network topology.

There are two main classes of networks, distinguished by the way computers are connected:

1. broadcast configuration (each computer transmits information that can be perceived by all other computers on the network);
2. sequential configuration (a computer can only transmit information to its nearest neighbor). The most common network topologies are:

• Bus topology;
• Star topology;
• Ring topology.

In broadcast configurations Each personal computer transmits signals that can be perceived by other computers. Such configurations include “common bus”, “tree”, “star with a passive center” topologies. A star-type network can be thought of as a type of “tree” that has a root with a branch to each connected device.

In sequential configurations Each physical sublayer transmits information to only one personal computer. Examples of sequential configurations are: random (random connection of computers), hierarchical, “ring”, “chain”, “star with an intellectual center”, “snowflake”, etc.

Let's briefly look at the three most common (basic) LAN topologies: star, bus, and ring.

Consider the following schemes:

1. Linear bus topology.

The option of connecting computers to each other, when a cable runs from one computer to another, sequentially connecting computers and peripheral devices to each other (as shown in Fig. 1), is called linear bus.

Rice. 1. Bus topology

An example of such a configuration would be the following connection. Information on the bus is transmitted to all PCs on the network, but only the PC for which this information is intended receives it.

2. Ring type topology.

Type topology "ring" implies the connection of computers in a closed curve network - a transmission medium channel. The output of one network node is connected to the input of another. Information is transmitted in a closed loop from PC to PC. In a relatively small space, this topology is advantageous, although the failure of one of the “ring” computers disrupts the integrity of the network.

At ring topology data is transferred from one computer to another via relay race (Fig. 2). If a computer receives data that is not intended for it, it passes it on further along the ring. The recipient does not transmit the data intended for him anywhere.

Rice. 2. Ring topology

A special form of ring topology is a logical ring local area network. Physically, it is mounted as a connection of star topologies. Individual stars are switched on using special switches. Hub– concentrator), which in Russian are also sometimes called “hub”. Depending on the number of workstations and the length of the cable between workstations, active or passive hubs are used. Active hubs additionally contain an amplifier for connecting from 4 to 16 workstations. The passive hub is purely a splitter device (for a maximum of three workstations). Managing an individual workstation in a logical ring local area network occurs in the same way as in a regular ring local area network. Each workstation is assigned an address corresponding to it, through which control is transferred (from senior to junior and from junior to senior). The connection is broken only for the downstream (closest) node of the local computer network, so that only in rare cases can the operation of the entire local computer network be disrupted.

3. Star topology.

The connection option when a separate cable comes to each computer from one central node is called a “star” configuration.

When star topology each computer is connected via a special network adapter with a separate cable to the central node (Fig. 3). The central node is a passive connector or active repeater.

Rice. 3. Star topology

Typically, with this connection scheme, the central node is a more powerful computer. A variation of the star topology is the radial topology.

4. Tree topology.

Network computers can be located on different levels (floors). In this case, a configuration can be applied, which is often called "snowflake".

Let's consider the capabilities of networks with different topologies.

The structure of the network influenced the creation of the information support system itself, called the information space, which also has a network structure. The entire information space can be represented as a navigation system, a certain set of programs that allow the user to navigate the entire variety of information posted on the network and find the factual data, historical information, and useful programs he needs. Most often, the navigation system is organized through a system of nested menus. The user does not need to remember the address or name of the resource and the sequence of commands necessary to access it: by moving through the program menu, you can navigate through the contents of various computers connected to the network.

The topology of a real LAN may be exactly the same as one of the above or include a combination of them. The structure of the network is generally determined by the following factors: the number of computers being connected, requirements for reliability and efficiency of information transfer, economic considerations, etc.

Connecting computers into a single network provides network users with new opportunities that are incomparable to the capabilities of individual computers. A network is not an addition, but a multiplication of the capabilities of individual computers. A local network allows you to organize the transfer of files from one computer to another or others, share computing and hardware resources, combine distributed data processing on several computers with centralized storage of information, and much more. With the help of a computer local network, the collective use of technical resources is carried out, which has a beneficial effect on the psychology and behavior of the user not only online, but also in real life.

Network hardware resources

Network hardware resources- This is additional equipment that can be connected to the network and shared between users. Hardware resources enhance network capabilities.

Printers, scanners, modems and fax modems, CD-ROMs are all network hardware resources.

Peer-to-peer, decentralized or peer-to-peer(from English peer-to-peer, P2P– equal to equal) networks are computer networks based on equality of participants. In such networks there are no dedicated servers, and each node (peer) is both a client and a server. Unlike the client-server architecture, this organization allows the network to remain operational with any number and any combination of available nodes. So to speak, “Eye to eye.”

The phrase “peer-to-peer” was first used in 1984 by Parbawell Yohnuhuitsman when developing IBM's Advanced Peer to Peer Networking architecture.

Literature used to prepare the lesson:

1. Computer Science and ICT 8. Textbook for 8th grade. Ugrinovich N.D. – M.: BINOM, 2008;
2. Workshop on computer science and information technology: Textbook. / Ugrinovich N.D. and others - M.: BINOM. Knowledge Laboratory, 2007.
3. Teaching the course “Informatics and ICT”. Ugrinovich N.D. Methodological manual - 4th ed., revised - M.: BINOM, 2007;
4. Simonovich S.V., Evseev G.A., Alekseev A.G. General computer science: Textbook for high school. – M.: Ast-press, Informkom-press, 2001. – 592 p.
5. Methods of teaching computer science: Proc. aid for students ped. universities / M.P. Lapchik, I.G. Semakin, E.K. Henner; Under the general editorship. M.P. Lapchika. – M.: Publishing center “Academy”, 2001. – 624 p.

| §4.1 Local and global computer networks

Lesson 24
§4.1 Local and global computer networks

Keywords:

Message
link
computer network
information transfer rate
the local network
global network

4.1.1. Transfer of information

We have already said earlier that information transfer is one of the most important information processes. Information is transmitted from the source to the receiver in the form of a certain sequence of signals, symbols, signs. For example, during direct conversation between people, sound signals are transmitted - speech; When reading a text, a person perceives graphic symbols - letters. The transmitted sequence of signals, symbols, signs is called a message.

A communication channel (information transmission) is a system of technical means and a signal propagation medium for transmitting messages from a source to a receiver. When people communicate directly, information is transmitted using sound waves, when talking on the phone - using acoustic and electrical signals distributed along communication lines, when reading - using light waves.

Any transformation of information coming from a source into a form suitable for its transmission over a communication channel is called coding. Currently, digital communications are widely used, when the transmitted information is converted into binary code.

Insufficient technical quality of communication channels and some other reasons can lead to distortion of the transmitted signal and loss of information. To avoid such situations, the code transmitted over the communication line is made redundant. Due to this, the loss of some part of the information during transmission can be compensated. In addition, in modern digital communication systems, all messages are divided into parts (packets, blocks). For each block, a checksum (the sum of binary digits) is calculated, which is transmitted along with this block. At the receiving site, the checksum of the received block is recalculated, and if it does not coincide with the original sum, then the transmission of this block is repeated.

For centuries, humanity has used postal services to transmit letters; in the second half of the 19th century, sound transmission technology (telephone) was invented; Since the 30s of the 20th century, telefax began to be used to transmit images. Nowadays, computers are widely used to transmit text, images, sound and many other types of information. computer networks- two or more computers connected by information transmission lines. With the advent of computer networks, it became possible to send a letter that reaches faster than a telegram, receive an answer, find out the latest news, talk to a friend sitting at a computer hundreds of kilometers away as if he were in the next room, book a plane ticket or a room in hotel, “download” the desired program, melody or movie.

An important characteristic of a computer network is information transfer rate, or channel capacity. This value is defined as the amount of information in bits per second (bps) and in derived units: kilobits per second (1 Kbps = 1000 bps), megabits per second (1 Mbps = 1000 Kbps), gigabits per second (1 Gbit/s = 1000 Mbit/s).

There are local and global computer networks.

4.1.2. What is a local computer network

A local computer network unites computers installed in one room (for example, a school computer lab) or in one building (for example, all computers located in a school building can be combined into a local network). A local network allows users to share access to computer resources, as well as to peripheral devices (printers, scanners, disks, modems, etc.) connected to the network.

Local networks are peer-to-peer and dedicated server.

In small local networks, all computers have equal rights, that is, each of them can use the resources of the other. Users independently decide which resources of their computer (files, folders, disks) to make available to the entire network. Such networks are called peer-to-peer networks.

In networks with a large number of users, it is not desirable for all of them to have access to all computers on the network. When combining more than 10 computers, it is advisable to select the most powerful computer - the server. The server's hard drive contains files (data and programs) that can be accessed by other computers on the network - clients. In addition, peripheral equipment connected to the server (for example, a printer or scanner) can be available to all network users.

Each computer connected to a local network must have a special card - a network adapter. Its function is to transmit and receive signals distributed through communication channels.

Connecting computers (their network cards) to a local network is carried out using various types of cables (twisted pair, optical fiber - Fig. 4.1) or via wireless channels (such as Wi-Fi).

Rice. 4.1. Cables:
twisted pair and optical fiber

A twisted pair consists of two insulated copper wires twisted relative to each other. Twisting the wires this way reduces the effect of interference on the signals transmitted through this cable. A twisted pair connection consists of several twisted pairs (2 or 4) covered with a plastic sheath. Data transfer speed - from 10 Mbit/s to 1000 Mbit/s.

A fiber optic cable transmits light through a glass fiber. This type of connection provides a very high transmission speed, the length of the channel is hundreds and thousands of kilometers, and it is absolutely not susceptible to electromagnetic interference. Data transfer speed - from 100 Mbit/s to 10 Gbit/s.

Wireless Wi-Fi connection provides data transfer speeds of up to 300 Mbps.

4.1.3. What is a global computer network

Local networks, connecting dozens of computers in a small area, do not provide shared access to information to users located at a considerable distance from each other (for example, in different localities).

Global computer network is a system of interconnected computers located at an arbitrarily large distance from each other (for example, in different countries and on different continents).

Examples of global computer networks include regional and corporate networks. Regional computer networks provide the unification of computers within one region (city, region, region, country). Corporate computer networks are created to support the activities of various types of corporate structures that have geographically remote divisions (for example, banks with their branches).

The best known and most extensive global computer network is the Internet. This network unites numerous local, regional and corporate networks, as well as individual user computers distributed throughout the world.

The basis of any global computer network is computer nodes and communication channels.

A node is a powerful computer that is constantly connected to the network. Subscribers - personal computers of users or local networks - are connected to the nodes of the computer network.

A wide variety of physical channels are used to transmit data in global networks: electrical cable; radio communication through repeaters and communication satellites; infrared rays (as in television remote controls); modern fiber optic cable; regular telephone network.

An organization that provides users with connections to the global network through their computers is called provider(English provider - supplier) of network services.

Task. The data transfer rate through a certain connection is 128,000 bps. How much time (in seconds) will it take to transfer a 625 KB file over this connection?

THE MOST IMPORTANT

Computer network- these are two or more computers connected by information transmission lines.

Local computer network connects computers installed in the same room or building, and provides users with the ability to share access to computer resources, as well as peripheral devices connected to the network. Local networks can be peer-to-peer or with a dedicated server.

Global computer network- this is a set of interconnected computers located at an arbitrarily large distance from each other (for example, in different countries and on different continents).

Questions and tasks

1. Read the presentation materials for the paragraph contained in the electronic appendix to the textbook. What can you say about the forms of presentation of information in the presentation and in the textbook? What slides could you add to your presentation?

2. How do you understand the meaning of the phrase: “The ability to transfer knowledge and information is the basis for the progress of society as a whole and each person individually”? Discuss this question in a group.

3. Since ancient times, people have exchanged information in various ways, notified of danger or conveyed important and urgent information. Prepare a short report about one of the previously used methods of transmitting information.

4. What is a computer network?

5. What is a communication channel? How is the bandwidth of a communication channel determined?

6. How does a peer-to-peer local network work?

7. How does a local network with a dedicated server work?

8. What type of local network is installed in your computer lab? What functions does it perform?

9. What networks are called global? Give examples of such networks.

10. What communication channels are used to transmit data in global computer networks?

11. The data transmission speed over a certain communication channel is 512 000 bit/s. Transferring a file over this channel takes 16 seconds. Determine the file size in kilobytes.

12. Find out the names of network service providers in your area.

13. Construct a graph of relations connecting the concepts discussed in this section.