. Questions + on topic computer networks

2016-02-10

Questions + on the topic of computer networks

Tests on the topic "Local networks" - computer science, lessons

Testing on the topic "Computer networks"

Option number 2.

Question 1. (Difficulty - A) Global network- This.
Answer 1. a system of interconnected computers
Answer 2. interconnected system local networks
Answer 3. a system of interconnected local telecommunications networks
*Answer 4. a system of interconnected local networks and computers of individual users
Question 2. (Difficulty - A) To connect two computers via telephone lines connections you need to have:
Answer 1. Modem * Answer 2. two modems
Answer 3. telephone, modem and special software
Answer 4. via modem on each computer and special software
Question 3. (Difficulty - A) E-mail is:
Answer 1. search program Answer 2. mail server name
Answer 3. mail program
*Answer 4. exchange of letters on computer networks (e-mail)
Question 4. (Difficulty - A) The HTTP protocol is used to:
*Answer 1. hypertext transfer Answer 2. file transfer
Answer 3: Messaging Control
Answer 4. Run the program from a remote computer
Question 5. (Difficulty - A) What components computer network necessary to organize a peer-to-peer local network?
*Answer 1. modem, server computer
Answer 2: network card, network software
Answer 3. server computer, workstations,
Answer 4. communication lines, network card, network software
Question 6. (Difficulty - A) The following are intended for viewing WEB pages:
Answer 1. search engines *Answer 2. browsers
Answer 3. Teleconferences Answer 4. providers
Question 7. (Difficulty - A) Which of the following computer connection diagrams is a closed chain?
Answer 1. Tire *Answer 2. Ring
Answer 3. Star Answer 4. No correct answer
Question 8. (Difficulty - A) Which cable provides data transfer speeds of up to 10 Mbit/s?
*Answer 1. Coaxial Answer 2. twisted pair Answer 3. fiber optic
Answer 4. There is no correct answer.
Question 9. (Difficulty - A) A protocol is used to transfer files over a network.
Response 1. POP3 Response 2. HTTP Response 3. CMPT *Response 4. FTP

Question 10. (Difficulty - A) Select the correct email address:
Answer 1. ivanpetrov@mail
Answer 2. ivan_petrov.mail.ru
Answer 3. ivan petrov.mail.ru
*Answer 4. [email protected]
Question 11. (Difficulty - A) The data transfer speed is 6000 Mbit/min. This amounts to. Mbit/s
Answer 1. 10
*Answer 2. 100
Answer 3. 3600
Answer 4. 36000
Question 12. (Difficulty - A) The email address on the Internet is given: [email protected]. What is the mail server name?
Answer 1. [email protected]
Answer 2. fortune
*Answer 3. list.ru
Answer 4. list
Question 13. (Difficulty - A) A computer connected to the Internet must have
Answer 1. URL;
*Answer 2. IP address
Answer 3. WEB page;
Answer 4. domain name;
Question 14. (Difficulty - A) Select the correct IP address of the computer on the network
*Answer 1. 108.214.198.112
Answer 2. 18.274.198.0
Answer 3. 1278.214.198
Answer 4. 10,0,0,1225
Question 15. (Difficulty - A) The topology of a computer network in which all computers on the network are connected to a central node is called
Answer 1. Tire
Answer 2. Ring
*Answer 3. Star
Answer 4. There is no correct answer
Question 16. (Difficulty - A) What top-level domain means "educational site"?
Answer 1. mil
Answer 2.gov
Answer 3.com

*Answer 4. edu
Question 17. (Difficulty - A) Determine the 2nd level domain www.klyaksa.inform.net
Answer 1. klyaksa
Answer 2. inform
Answer 3. www
*Answer 4. net
Question 18. (Difficulty - B) Determine the computer number on the network by IP 215.128.255.106
Answer 1. 215.128.255.106
Answer 2. 128.255.106
Answer 3. 255.106
*Answer 4. 106
Question 19. (Difficulty - A) The protocol is.
Answer 1. the ability of a computer to send files through communication channels
Answer 2. device for running a local network
*Answer 3. standard for data transmission over a computer network
Answer 4. Standard for sending messages via email
Question 20. (Difficulty - B) How long will it take to transfer a 128 KB file over a network whose speed is 128 KB/s?
*Answer 1. 8 p.
Answer 2. 1 p.
Answer 3. 1 min.
Answer 4. 10 s.

Test: Local Network

Question No. 1: This is a local network.

• Fishing net
• A computer network that unites a group of computers that are located in one place
• A computer network that connects all computers Answer: 2;

Question No. 2: In order to connect a computer to the network you must have.

• Network cable
• Keyboard
• Network adapter
• Network drive Answer: 1.3;

Question #3: There are networks.

Select multiple answer options:

• Local
• Global
• High
• Deep
• Regional Answer: 1,2,5;

Question #4: If there are several computers, then an additional device is needed to connect them into a network.

Select one of the answer options:

• Connector
• Switch
• Networker Answer: 2;

Question #5: The data transfer rate is characterized.

Select one of the answer options:

• kb/cm
• kb/s Answer: 4;

Question #6: Specify the procedure to follow when sharing your folder.

Indicate the order of the answer options:

• Enable the option to share this folder
• Right click on your folder
• select Properties
• select the access tab
• click Apply Answer: 2-3-4-1-5;

Question No. 7: What can't be done using a local network?

Select one of the answer options:

• Communicate
• To play together
• Work on one document
• Pass the candy Answer: 4;

Question #8: What is the name of the icon in Windows with which we can log into other computers on our local network?

Select one of the answer options:

• Network folder
• network
• Network icon Answer: 2;

View the contents of the document Tests on the topic "Local Networks"

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 PCs and communications equipment are located on 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.

2.List 3 basic topologies networks:

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. optical fiber

4. there is no right answer

8.The largest network size (up to 20 km) has the 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. The 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 public access network users, 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"

3.5. Local area networks

Local area network (LAN) called the joint connection of several separate computers to a single data transmission channel. The concept of LAN (English LAN - Local Area Network) refers to geographically limited (territorially or production) hardware and software complexes, in which several computer systems connected with each other using appropriate means of communication.

A LAN provides the ability to simultaneously use programs and databases by several users, as well as the ability to interact with other workstations connected to the network. Through a LAN, the system combines personal computers located at many remote workplaces that share equipment, software and information. Employees' workplaces are no longer isolated and are combined into a single system.

The most important characteristic LAN is the speed of information transfer. Ideally, when sending and receiving data over a network, the response time should be almost the same as if it were received from the user's PC rather than from somewhere else on the network. This requires data transfer speed 10 Mbit/s and higher. The following speeds are actually achieved:

· Coaxial cable – 10¸ 50 Mbaud;

· Twisted pair – up to 10 Mbaud;

· Special twisted pair cable of category 5 – up to 100 Mbaud;

· Optical fiber - up to 1 Gbaud;

· Telephone line - from 2400 baud to 56 kbaud;

· Satellite 10,000 computers at the same time and the speed is about 1 Mbaud.

LAN components: network devices and means of communication.

The LAN implements the principle of modular organization, which allows you to build networks of various configurations with different functionality. The main components from which the network is built are the following:

transmission medium – coaxial cable, telephone cable, twisted pair, fiber optic cable, radio broadcast, etc.;

workstations– PC, workstation or network station itself. If the workstation is connected to a network, it may not require a hard drive or floppy disks. However, in this case it is necessary network adapter– special device for remote downloading operating system from the network;

interface boards – network cards for organizing the interaction of workstations with the network;

servers– separate computers with software that perform the functions of managing shared network resources;

network software .

Let's look at some of the listed network components in more detail.

Servers

A network may have one or more servers. Various servers can be used to manage the network ( network servers), storing information in the form of files ( file servers), searching and retrieving information from databases ( database servers), information distribution ( mail servers), network printing ( print servers) etc. Server disks are accessible from all other workstations on the network if users have the appropriate permissions.

The interaction of the server with workstations occurs approximately according to the following scheme. As necessary, the workstation sends a request to the server to perform any actions: read data, print a document, send email and so on. The server performs the requested action and issues a confirmation.

Transmission medium

Transmission media are characterized by the speed and range of information transmission and reliability.

The most commonly used means of communication in a LAN are twisted pair cables, coaxial cables, and fiber optic lines. When choosing a transmission medium, the following indicators must be taken into account:

· information transfer speed;

· range transfer of information;

· security of information transmission;

· reliability of information transmission ;

· cost of installation and operation.

Simultaneously meeting the requirements for the transmission medium is a difficult task. For example, high data transmission speeds are often limited by the maximum permissible distance for reliable data transmission, while ensuring the necessary level of protection of the transmitted data. The cost of communication means affects the ability to build and expand the network.

Let us consider in more detail the properties of some transmission media.

twisted pair

Twisted pair, the cheapest among transmission media. Allows you to transmit information at speeds of up to 10 Mbit/s, easy to expand, low noise immunity. The cable length does not exceed 1000 m with a transmission speed of 1 Mbit/s. To increase the noise immunity of information, shielded twisted pair, placed in a shell similar to the screen of a coaxial cable. The price of such a pair is close to the price of a coaxial cable.

Coaxial cable

Coaxial cable is used for communication over distances of up to several kilometers, has good noise immunity at an average price. Information transfer speeds range from 1 to 10 Mbit/s, in some cases reaching 50 Mbit/s. Coaxial cable can be used for broadband transmission of information.

Broadband coaxial cable.

Such a coaxial cable is weakly susceptible to interference, is easy to expand, but has high price. The information transfer speed reaches 500 Mbit/s. To transmit information over a distance of more than 1.5 km in the base frequency band, it is necessary repeater(amplifier), while the stable transmission distance increases to 10 km. For a LAN with a bus or tree topology, the cable must have a Terminator (terminating resistor).

Ethernet cable

Thick Ethernet

Coaxial cable with a characteristic impedance of 50 Ohms (thick Ethernet. or yellow cable). Uses 15-pin standard connection. The maximum permissible transmission distance without a repeater does not exceed 500 m, and the total length of the Ethernet network is 3000 m. Thick Ethernet, due to the backbone topology, uses only one terminator at the end. In terms of noise immunity, it is an expensive alternative to conventional coaxial cable.

Thin Ethernet

Coaxial cable with a characteristic impedance of 50 ohms (thin Ethernet) and an information transfer rate of 10 7 bps, cheaper than thick Ethernet.

LANs with thin Ethernet cable are characterized by low cost, minimal costs when extending and do not require additional shielding. The cable is connected to network cards workstations using tee connectors ( T-connectors ) with small-sized bayonet connectors (CP-50). Repeaters are required when connecting thin Ethernet segments. The distance between workstations without repeaters cannot exceed 300 m, and the total length of the network is 1000 m.

Fiber optic cable

The most expensive transmission medium for a LAN is fiber optic cable, also called fiberglass cable. The speed of information transfer through it reaches several gigabits per second with an allowable length of more than 50 km. The noise immunity of fiber optic cable is very high, so LANs based on it are used where electromagnetic interference occurs and information transmission over long distances is required without the use of repeaters. The networks are resistant to eavesdropping because the branching technique in fiber optic cables is very complex. Typically, LANs based on fiber optic cable are built in a star topology.

Characteristics of typical transmission media are given in the table.

Indicators	Transmission medium
	twisted pair	Coaxial cable	Fiber optic cable
Price	Low	Average	High
Building up	Very simple	Problematic	Problematic
Eavesdropping protection	Bad	good	Very good
Grounding	No	Required	No
Noise immunity	Low	High	Very high

IVS topology

Topology, i.e. configuration of connection of elements in a LAN , attracts attention to a greater extent than other network characteristics. This is due to the fact that it is the topology that largely determines the most important properties of the network, such as reliability and performance.

There are different approaches to classifying LAN topologies. According to one of them, local network configurations are divided into two main classes: broadcast And sequential .

IN broadcast configurations, each PC transmits signals that can be perceived by other PCs. Such configurations include a common bus, a tree (connecting several common buses using repeaters), and a star with a passive center. The advantages of configurations of this class are the simplicity of network organization.

IN consecutive configurations, each physical sublayer transmits information to only one PC. Such configurations include a star with an intellectual center, a ring, a hierarchical connection, and a snowflake. The main advantage is the simplicity of the software implementation of the connection.

To prevent collisions in information transmission, it is most often used time division method , according to which each connected workstation V certain moments time, the exclusive right to use the information transmission channel is granted. Therefore, the requirements for network throughput under increased load, i.e. when new workstations are introduced, they decrease.

Different topologies implement different principles of information transfer . In broadcast it is information selection, in successive – information routing.

In a broadband LAN, workstations are assigned a frequency on which they can send and receive information. The transmitted data is modulated at the appropriate carrier frequencies. The technology of broadband messages makes it possible to simultaneously transport a fairly large amount of information in a communication environment.

Star topology .

Network topology in the form stars with an active center inherited from the area mainframes , where the head machine receives and processes all data from the terminal devices as the active data processing node. All information between peripheral workstations passes through the central node of the computer network.

Network throughput is determined by the computing power of the central node and is guaranteed for each workstation. Collisions, i.e. There are no collisions in data transmission.

The cabling of the topology is relatively simple because each workstation is connected to a central node, but the cost of laying communication lines is high, especially when the central node is not geographically located in the center of the topology.

When expanding a LAN, it is impossible to use previously made cable connections: a separate cable from the central network node must be laid to the new workstation.

Star topology with good central node performance is one of the fastest topologies LAN, since the transfer of information between workstations occurs over dedicated lines used only by these workstations. The frequency of requests to transfer information from one station to another is low compared to other topologies.

Figure 1. Star topology

The performance of a star topology LAN is primarily determined by the parameters of the central node, which acts as network server. It may turn out to be a network bottleneck. If the central node fails, the operation of the network as a whole is disrupted.

In a LAN with a central control node, it is possible to implement an optimal mechanism for protecting against unauthorized access to information.

Ring topology.

In a ring network topology, LAN workstations are connected to each other in a circle. The last workstation is connected to the first, i.e. communication link closes in a ring.

Laying communication lines between workstations can be quite expensive, especially if the workstations are located far from the main ring.

Messages in the LAN ring circulate in a circle. The workstation sends information to a specific address, having previously received a request from the ring. The transmission of information turns out to be quite efficient since messages can be sent one after another. For example, you can make a ring request to all stations. The duration of information transfer increases in proportion to the number of workstations included in the LAN.

Rice. 2. Ring topology

The main problem of the ring topology is that each workstation must participate in the transfer of information, and if at least one of them fails, the entire network is paralyzed. Faults in the cable system are easily localized.

Expanding a network with a ring topology requires stopping the network because the ring must be broken. There are no special restrictions on the size of the LAN.

A special form of ring topology is logical ring .

Physically, it is mounted as a connection of star topologies. Individual stars are switched on using special switches (English: Hub), which in Russian are also sometimes called “hubs”. 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 network is the same as in a regular ring 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 computer network, so that only in rare cases can the operation of the entire network be disrupted.

Bus topology

In a LAN with a bus topology, the main transmission medium ( tire) – common for all workstations. The functioning of the LAN does not depend on the state of the individual workstation, i.e. workstations can be connected to or disconnected from the bus at any time without disrupting the operation of the network as a whole.

Rice. 3. Bus topology

However, in the simplest network Ethernet with a bus topology uses a thin Ethernet cable with a tee connector as the transmission medium ( T -connector), therefore expanding such a network requires breaking the bus, which leads to disruption of the functioning of the network. More expensive solutions involve installation instead T - connectors of passive plug boxes.

Since the expansion of a LAN with a bus topology can be carried out without interrupting network processes and breaking the communication medium, the removal of information from the LAN and, accordingly, eavesdropping on information is quite easy, as a result of which the security of such a LAN is low.

Characteristics of computer network topologies are given in the table.

Characteristic	Topology
	Star	Ring	Tire
Price extensions	Low	Average	Average
Connecting subscribers	Passive	Active	Passive
Defence from failures	Low	Low	High
Eavesdropping protection	good	good	Bad
Behavior at high	good	Bad	Bad
Work in real time	good	good	Bad
Wiring cable	good	Bad	good

Tree topology.

It is formed by various combinations of the LAN topologies discussed above. The base of the tree (root) is located at the point where communication lines (tree branches) gather.

Networks with a tree structure are used where it is impossible direct application basic network structures. To connect workstations, devices called hubs .

There are two types of such devices. Devices to which a maximum of three stations can be connected are called passive concentrators. To connect more devices needed active hubs with the possibility of signal amplification.

Types of LAN construction based on information transmission methods.

Token Ring Network

This standard was developed by IBM. Unshielded or shielded twisted pair or optical fiber are used as the transmission medium. Data transfer rates from 4 Mbit/s to 16 Mbit/s. As access control method workstations to the transmission medium are used marker ring (Token Ring). Basic principles of the method:

¨ ring LAN topology;

¨ the workstation can transmit data only after receiving the token, i.e. permission to transmit information;

¨ At any given time, only one station in the network has this right.

In LAN To k e n Ring uses three main types of packets:

¨ control/data package (Data/Command Frame);

¨ token;

¨ reset package (Abort).

Management/Data Package . Using such a packet, data or network control commands are transmitted.

Marker.The station can start transmitting data only after receiving such a packet. There can be only one marker in the ring and, accordingly, only one station with the right to transmit data.

Reset Pack.Sending such a packet causes the transmission of information to cease.

Network To k e n Ring allows you to connect computers in a star topology.

Arknet local network.

Arknet (Attached Resource Computer NETWork) is a simple, inexpensive, reliable and flexible LAN architecture. Developed by Datapoint Corporation in 1977. Subsequently, the license for Arcnet was acquired by SMC Corporation (Standard Microsistem Corporation), which became the main developer and manufacturer of equipment for Arcnet networks. Twisted pair, coaxial cable with a characteristic impedance of 93 Ohms and fiber optic cable are used as transmission media. Data transfer speed is 2.5 Mbit/s. When connecting devices to bus and star topologies are used. Access control method stations to the transmitting medium – marker tire (Token Bus). The method provides the following rules:

¨ devices connected to the network can transmit data only after receiving permission to transmit (token);

¨ at any given time, only one station in the network has this right;

Work principles

Each byte is transmitted to Arcnet by sending an ISU (Information Symbol Unit) consisting of three service start/stop bits and eight data bits. At the beginning of each packet, the initial separator AB (Alegt Burst), which consists of six service bits, is transmitted. The start delimiter acts as a packet preamble.

Arcnet defines 5 types of packets:

1. ITT package(Information To Transmit) – an invitation to transmit. This message transfers control from one network node to another. Station that received the packet ITT , receives the right to transfer data.

2. FBE package(Free Buffet Inquiries) – request for readiness to receive data. This packet checks the node's readiness to receive data.

3. Data package.Data transmission is carried out using this parcel.

4. ASK package (ACKnowledgments) – confirmation of reception. Confirmation of readiness to receive data or confirmation of receipt of a data packet without errors, i.e. response to FBE and data packet.

5. Package NAK(Negative AcKnowledgments) unpreparedness to receive. The node is not ready to receive data in response to an FBE or received a packet with an error.

Ethernet LAN

The Ethernet specification was proposed by Xerox in the late seventies. Later, Digital Equipment Corporation (DEC) and Intel joined this project. In 1982, the Ethernet specification version 2.0 was published. The IEEE 802.3 standard was developed based on Ethernet.

Basic operating principles

¨ bus topology at the logical level;

¨ all devices connected to the network have equal rights, i.e. any station can start transmitting at any time (if the transmitting medium is free);

¨ Data transmitted by one station is available to all stations in the network.

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 selection various types 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 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. Practical need quick access to the information resources of other computers, printers, and other peripheral devices was the cause of 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 "What autonomous operation on a PC is different from working 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 public resources: large space disk memory, 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 (LAN), depending on the 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.

A variant of connecting computers to each other, when a cable runs from one computer to another, connecting computers in series and peripherals among themselves (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 transmitted from one computer to another via relay (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). Management of an individual workstation in a logical ring local area network occurs in the same way as in a conventional 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 such a connection scheme, the central node is 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.

Network topology	Advantages	Flaws
Bus topology	simplification of the logical and software architecture of the network; ease of expansion; simplicity of management methods; minimal cable consumption; no need for centralized management; reliability (failure of one PC will not disrupt the operation of others).	there is only one cable connecting all stations, therefore PCs can only “communicate” one by one, which means that special means are needed to resolve conflicts; Troubleshooting the cable is difficult; if it breaks, the operation of the entire network is disrupted.
Star topology	reliability (failure of one station or cable will not affect the operation of others).	requires a large amount of cable; reliability and performance are determined by the central node, which may turn out to be a “bottleneck” (therefore, this equipment is often duplicated).
Ring topology	low cost; high efficiency of mono channel use; ease of expansion; simplicity of control methods.	if at least one computer fails, the entire network is paralyzed; Each workstation requires a buffer for intermediate storage of transmitted information, which slows down data transfer; connecting a new station requires disconnecting the network, so special devices are being developed to block circuit breaks.

The structure of the network influenced the creation of the system itself information support, called information space, which also has a network structure. All information space can be represented as 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 and historical information he needs, useful programs. 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: Tutorial. / 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: A 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.