Software and hardware of local computer networks. Hardware and software. Unshielded twisted pair
The network adapter is installed on the network node and connects it to the data transmission channel. To communicate with other network nodes, it performs the following operations: data buffering, packet formation, access to the transmission medium, data conversion, encoding and decoding, and, finally, transmission and reception.
The purpose of network hubs and switches is similar - connecting several LAN nodes lying within the same segment. The difference is that a hub broadcasts traffic from one node to all available nodes, while a switch broadcasts traffic directly to the recipient node. This or that LAN hardware can be selected depending, first of all, on the information load of the network and the requirements for data transmission security. In networks whose nodes are not critical to traffic volumes, hubs are sufficient. Networks that place increased demands on performance and data security must be equipped with switches that eliminate the need and ability of network nodes to process information not intended for them.
Bridges and routers are LAN hardware, providing communication between network segments. Routers, unlike bridges operating at the data link layer - the second in the OSI model, use the third layer of the model - the network. This allows you to transmit packets taking into account the specifics of protocols, to select the optimal route for transmitting a packet based on an analysis of information received from other routers about the topology and state of the network. The bridge is transparent to all network protocols and, like switches, makes a decision about transmitting a packet only on the basis Recipient MAC addresses.
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Structural is a graphic document that displays the physical location and connection of the components of the structure.
You should trust only qualified specialists officially approved to work in electrical installations.
Local network tasks: File sharing. The network allows many users to work on one file at the same time. File separation. The network allows many users to work on the same file at the same time. File transfer. The network allows you to quickly copy files of any size from one machine to another without using magnetic media. File transfer. The network allows you to quickly copy files of any size from one machine to another without using magnetic media. Separation of application programs. The network allows different users to use the same copy of a program. Separation of application programs. The network allows different users to use the same copy of a program. Printer separation. A network allows multiple users to share one or more printers. Printer separation. A network allows multiple users to share one or more printers. Email. The network allows you to install a mail service to send messages, reports, and memos to other network users. Email. The network allows you to install a mail service to send messages, reports, and memos to other network users. It is possible to install software on the basis of a local network, which makes it possible to use global Internet technologies when preparing, publishing, and using documents. It is possible to install software on the basis of a local network, which makes it possible to use global Internet technologies when preparing, publishing, and using documents.
Peer-to-peer local network In a peer-to-peer local network, all computers have equal rights. Shared devices can be connected to any computer on the network. In a peer-to-peer local network, all computers have equal rights. Shared devices can be connected to any computer on the network.
Network with a dedicated server Server (from the English server - service device) is a computer that distributes resources between network users. The server has a powerful processor, large RAM and disk memory, and stores the bulk of software and network data that can be used by all network users. Less powerful computers with less disk and RAM memory are usually used as workstations.
Local network topology The simplest type of topology is bus. In such a network, all computers are connected to one cable. The structure called a ring is also similar to a tire. For local networks based on a file server, the star scheme can be used. The composition of the equipment and software depends on the scheme. The topology is chosen based on the needs of the enterprise. If an enterprise occupies a multi-story building, then it can use a snowflake design, in which there are file servers for different workgroups and one central server for the entire enterprise.
Local network equipment: cables for information transmission; cables for information transmission; connectors for connecting cables; connectors for connecting cables; matching terminators; matching terminators; network adapters; network adapters; repeaters; repeaters; transceivers; transceivers; concentrators; concentrators; bridges; bridges; routers; routers; gateways. gateways.
Network adapters (aka controllers, cards, boards, interfaces, NIC Network Interface Card) are the main part of the local network equipment, without which the network is impossible. The purpose of a network adapter is to connect a computer (or other subscriber) to the network, that is, to ensure the exchange of information between the computer and the communication channel in accordance with accepted exchange rules.
Repeaters, or repeaters, perform a simpler function than transceivers. They do not convert signal levels or their appearance, but only restore weakened signals (their amplitude and shape), bringing their shape to its original form. The purpose of this signal relay is to increase the length of the network.
Bridges, routers and gateways are used to combine into a single network several heterogeneous networks with different lower-level exchange protocols, in particular, with different packet formats, different encoding methods, different transmission rates, etc.
Network software To work on a local network, you need special network software. To work on a local network, you need special network software. The Windows operating system already has everything you need to set up a network.
Network software To organize a local network you need to: determine the name of the Working Group; assign each computer a unique name and IP address in this Workgroup, and also set a subnet mask address (in some cases, an explicit IP address and subnet mask address may not be set).
PURPOSE AND CLASSIFICATION OF COMPUTER NETWORKS
Global Internet services.
Global Internet. Addressing.
Purpose and classification of computer networks.
INTERNET TECHNOLOGIES
Plan:
Computer network– communication system between computers and computer equipment.
Depending on the territorial location of subscriber systems, computer networks can be divided into three main classes:
Wide Area Network (WAN) is a system of networked computers located at large distances from each other.
Regional computer network (MAN – Metropolitan Area Network) connects subscribers located at a considerable distance from each other (tens - hundreds of kilometers).
Local area network (LAN, LAN – Local Area Network) unites subscribers located within a small area (2 – 2.5 km).
Local area network hardware includes workstations, server, communication equipment
Work station– a personal computer connected to a network and providing user access to its resources.
Server– a specialized computer on a network designed to run service software on it.
To connect a workstation with a communication channel, use network adapter.
Communication channel in a computer network is a physical medium for transmitting information.
Communication channels differ in three main properties: throughput, noise immunity, and cost.
Bandwidth– this is the maximum speed of information transmission over the channel. It is usually expressed in kilobits per second (Kbps) or megabits per second (Mbps).
Let's consider communication channels.
twisted pair characterized by poor noise immunity and low information transmission speed 0.25 – 1 Mbit/s. Low cost.
Coaxial cable has high noise immunity and provides information transmission speeds of up to 10-50 Mbit/s.
Fiber optic cable It is not affected by electromagnetic fields and has practically no radiation. Information transfer speed is more than 50 Mbit/s.
Wireless network. Wireless communication technologies in computer networks are based on the coding and transmission of signals in the form of electromagnetic radiation.
The most common standards for data transmission in the radio wave range are: Bluetooth, Wi-Fi, GPRS, Wi-Max, 3G, LTE.
There are standards for data transmission in the light range: infrared - IrDa, etc.
Communication equipment:
Network hub or hub– a network device designed to connect several Ethernet devices to a common network segment. Devices are connected using twisted pair, coaxial cable or optical fiber.
Currently, hubs are almost never produced - they have been replaced by network switch (switches)- devices designed to connect several network nodes within one or more network segments.
Router (router)– a device that provides connection of administratively independent communication networks.
Bridge is a device that connects two networks using the same data transfer methods
Gateway is a device that allows you to organize data exchange between two networks using different communication protocols.
After studying this topic, you will learn:
What types of networks exist;
- what are the main components of the network;
- how information is exchanged between computers;
- what technical means ensure the operation of a computer network;
- what communication channels are used in computer communications;
- about the role of modems and network adapters in the network.
Types of computer networks
Computer networks occupy an increasingly important place in the life of mankind. Networks can combine information resources of both small enterprises and large organizations occupying premises remote from each other, sometimes even located in different countries. This determines the way computers are connected to each other and, accordingly, the type of network: local, regional, corporate, global.
Local networks
Imagine a clinic computer network with a central computer containing information about all patients. In each doctor's office there is a computer, on the screen of which, if necessary, information about a specific patient is displayed. The doctor updates them, saves them in the database of the central (main) computer, and they become available to other specialists, for example, a physiotherapist, neurologist, cardiologist. In addition, the same information is displayed on the registration computer, where the patient can order a referral for examination or an appointment with the desired doctor. The computer can also store information about the work schedule of specialists, the issuance of coupons for appointments with them, etc.
A commercial enterprise can also be equipped with a computer network. Here, with its help, you can store information about goods and their costs, process information about sales, keep records of the quality of goods sold, etc. All this information is stored centrally, on the server.
A computer network can unite computers throughout the school, installed in a variety of workplaces: in administration offices, in the library, in computer science classes and other offices. You can connect, for example, two or three home computers of students living in the same neighborhood using a network.
In an office environment, working online, different employees have access to the same internal sources of information to prepare various reports, schedule and plan overall business activities. Special network programs allow you to automatically schedule meetings, selecting the most suitable time for all employees; the boss can check whether his instructions that he sent over the network have been completed, etc. All the examples of networks described above are designed for processing information of local importance. As a rule, such networks connect computers located at short distances (about 50-100 meters) within a building, and therefore they are called local (local). About 90% of the information circulating in such networks is information from a local organization.
Local network is a connection of computers located at short distances from each other.
Regional and corporate networks
Often in the same office, school or clinic there is a need to obtain information from other similar organizations. In such cases, computers located not only in one or several rooms are connected to each other.
Imagine a system for storing information in libraries. Here it is necessary to have a variety of information for each book: title, information about the authors, publisher, number of copies available, annotation of the contents, etc. If such information is made available to a large number of libraries, then it is possible to improve service to readers and improve the organization of the interlibrary collection for the exchange of books. Integrating libraries into a centralized computer network allows all libraries to have access to any necessary information about books.
Both a library with only one computer and a library with a local network can be connected to the central library. A telephone line can be used to connect computers. Such a network already has regional significance. An example is the network of libraries in St. Petersburg and the Leningrad region.
A regional network is a combination of computers and local networks to solve common problems on a regional scale.
Let's remember how train tickets are booked. At the request of any cashier-operator, information about the availability of free seats on the train, the cost of travel tickets, etc. is displayed on his monitor. At the passenger’s direction, the cashier enters a request to purchase a ticket through the network into the central computer and formalizes its sale. Moreover, the paid space is immediately withdrawn from further sale. Imagine if all these computers were not connected to a network. Then the point of using them would be completely lost, since after each working day you would have to make general changes about the availability of free seats in each individual computer, inform other cashiers about unsold tickets and think about how to organize the sale of tickets the next day.
A centralized network easily solves such problems. Tickets for the same routes can be sold from several cities. And such a network can no longer be called local. It serves to process information from one company or an association of companies and is therefore called corporate (from the word “corporation” - association).
A corporate network is an association of local networks within one corporation.
Corporate networks are designed to serve customers in various remote locations, such as hotels. They can connect branches located in different countries within one corporation. Information may be changed by employees who have access to it. The networks described above may have access to other external networks, for example, in order to obtain information from remote global databases or send messages by e-mail to another network, send a fax.
Global networks
Centralized data processing is not always reliable, since the failure of the central computer can lead to the loss of important information or even paralyze the network for some time. Therefore, there was a need for decentralized information processing on the network. The development of means and methods for transmitting information over long distances made possible the emergence of global networks. The idea behind their construction is that powerful computers are interconnected and can exchange information on a transcontinental scale.
Global network servers provide other computers registered on them with access not only to their resources (information and software, e-mail, computer conferences), but also to the resources of other network servers and provide their users with the opportunity to work with information outside their computer, opening access to resources of remote machines.
In recent years, global networks have united with each other, and this association is called the Internet. Internet users can find anything they want on this network. These are files, images, sounds created in various computer environments and stored in file server archives. They can be copied to your computer and opened using the applications in which they were created. From the Internet you can receive daily changing information: weather forecasts, exchange rates, statistical reports, theater repertoire and restaurant menus, any programs, etc.
Remote access (access to information from a long distance via a network) allows you to organize training at any distance (distance learning). For example, you can conduct a lesson simultaneously in different schools around the world, communicating directly with everyone present at such a lesson, or organize lectures by Famous professors for a wide range of listeners from different countries of the world. Communication at a distance makes consultations of major specialists possible during surgical operations, consultations, and demonstrations of these operations for the training of medical personnel.
The use of global networks has become especially attractive in connection with the development of multimedia, that is, graphics, video and sound. Documents containing such components have become the most popular information available on the Internet.
In order not to get confused in huge flows of information, there are special search engines on network servers. They search for information, analyze it and provide the user, upon request, with the addresses of the location of the necessary information.
The global network provides efficient access to information on a global scale.
Global network - associations of computers located at a remote distance for the common use of world information resources.
Communication channels for exchanging information between computers
The main purpose of creating any computer network (local or global) is to ensure the exchange of information between objects (servers and clients) of the network. Obviously, for this it is necessary to communicate between computers. Therefore, the mandatory components of any network are all kinds of communication channels (wired and wireless), for which they use different physical media. In accordance with this, networks distinguish between such communication channels as telephone and fiber optic lines, radio communications, space communications, etc.
The purpose of communication channels in a computer network is easy to understand if you compare them with the transport channels of a freight or passenger transportation system. Transportation of passengers can occur by air, by railways or by water (sea or river) routes. Depending on the transportation environment, the vehicle is chosen. Information is transported through computer networks. The environments in which network computers communicate determine the means by which computers are connected. If it is an environment that requires telephone communication, then the connection is made through a telephone cable. Connecting computers using electrical cables, radio waves, fiber optic cables, etc. is widely used.
These are all different communication channels. The efficiency of communication in computer networks significantly depends on the following main characteristics (parameters) of communication channels:
♦ throughput (data transfer speed), measured by the number of bits of information transmitted over the network per second;
♦ reliability - the ability to transmit information without distortion or loss;
♦ cost;
♦ expandability (connecting new computers and devices).
Compare the characteristics of communication channels shown in Table 22.1.
Table 22.1. Characteristics of communication channels
From this table it can be seen that electrical cable communication has greater capacity than telephone communication. The table shows two types of electrical cables. Two-core cable (or twisted pair) is cheaper and has a higher data transfer rate, but is not immune to interference.
Coaxial (shielded) cable has better noise immunity, and this is one of its most important characteristics. Anti-interference is costly, so these cables are more expensive.
Using electrical cables is much more expensive than using regular telephone lines. Therefore, electrical cables are used as communication channels over short distances, that is, in local networks. In global networks, the cheapest is the telephone channel. However, its main disadvantages include low noise immunity. The table shows that the best communication channel is fiber optic cable, but its cost is very high.
Purpose of network adapters
To transmit information over communication channels, it is necessary to convert computer signals into signals of physical media, that is, to make it possible to transmit them along electrical, optical, and telephone paths. For example, when transmitting information over a fiber optic cable, computer data will be converted into optical signals. For this purpose, special technical devices are used - network adapters.
Network adapters (network cards) are technical devices that perform the functions of pairing computers with communication channels.
Network adapters must match the communication channels. Each type of communication channel requires its own type of network adapter.
The adapter is inserted into a free slot on the computer's motherboard and connected with a cable to the network adapter of another computer. Network cards contain the addresses of computers on the network, without which transmission is impossible. When information circulates across the network, each network computer selects from the general flow only the data that is intended for it. This selection is made in accordance with the computer address.
There are also software tools that set the network addresses of computers. A large number of special network system shells have been developed. These add-ons allow you to assign computer addresses, order the required number of network users if the network is limited in the number of clients, allow or deny access to directories or hardware resources for various client computers on the network, giving them certain rights, etc. In these programs the possibility of protecting information is also provided. Some directories can be made read-only, others can be read and written, and some can be hidden altogether, making them inaccessible. In the latter case, only part of the server information is visible to users. Network programs allow you to grant different access rights to different users. This measure is necessary to ensure the safety of information and maintain its confidentiality.
Modem purpose
A distinctive feature of the global network is the significant distance of computers from each other. Telephone lines and modems are widely used for their communication. The telephone network transmits the sounds of human voices (in the form of analog signals). The digital signals from the computer are converted (modulated) by the modem into signals that can be transmitted over the telephone network, and at the other end of the connection they are received by another modem and converted (demodulated) from analog to digital computer signals.
Modem is a device that performs modulation (converting digital signals into analog) and demodulation (converting analog signals into digital).
The modem connects the computer to the telephone line. To work with it, a special control program must be loaded into the RAM - the modem driver. With its help, the corresponding parameters of the modem are configured (installation of the modem), without which work with it, and therefore communication with the network, is impossible.
The other end of the phone line must also have a modem connected to another computer. Then the receiver computer will be able to receive signals from the network, that is, the modem is used in the global network instead of a network adapter. If a computer is a client of the network, then it must have a defined address of the computer to which it accesses as a server. These settings are made during the protocol and software settings.
Modems can be external (made as a separate unit and connected to the system unit via a serial port) and internal (in the form of a board installed in the motherboard socket). They differ in the maximum data transfer speed.
Modems now common among users have speeds of 28,800, 33,600, 56,000 bits per second. Modems with higher transfer rates are also available.
Because modems are used instead of network adapters in networks where telephone lines serve as communication channels, they can be used in areas of the network that cover long distances. If you use the modem for long-term work on the network, you will have to occupy the telephone channel. Communication via telephone channels is unreliable, and, in addition, the transmission speed through it is not as high as through cables. Therefore, in local networks it is common to use electrical cables for connections.
The role of protocols in information exchange in networks
In order for information transmitted by one computer to be understood by another computer after receiving it, it was necessary to develop uniform rules for transmitting data over the network, called protocols. During their development, all communication problems were taken into account and standard algorithms for information delivery were developed.
During any transportation, the rules must be strictly followed. What rules, for example, must be followed when transporting passengers on trains? Passengers buy tickets and take the seats indicated on them. Otherwise, there will be a disorderly movement of passengers in the carriages, wanting to take better seats. The passenger has no right to carry tigers, bears and other wild animals with him. There are rules for transporting pets. The conductor is obliged to monitor the sanitary condition of the carriage and the bathroom, the availability of water, otherwise passengers may arrive at their station sick. The train follows the schedule, making the necessary stops. When moving to European countries, the wheels of the carriages are replaced to travel on narrow-gauge tracks (otherwise the train will derail). You see how much needs to be taken into account during transportation. The same is true when transmitting information.
Indeed, data transmission is a complex process and can be considered at different levels. We will not discuss them all in detail. However, let's touch on some issues.
The transfer protocol establishes an agreement between communicating computers. In order for communication between computers to be established, their addresses must be specified. These addresses are determined by network adapters, phone numbers, and communications programs. The rules for forming computer addresses on a global network must be absolutely identical, despite the fact that computers on the network may be heterogeneous and use different operating systems.
Transmitting data in one continuous stream may result in data loss or corruption. Therefore, they are divided into blocks (packets) of information of a strictly defined length. Each such block is accompanied by service information, including identification marks of its beginning and end. Transmission protocols contain a mechanism to recognize the beginning and end of a block. They manage data flows, distribute them, and queue them. At the other end, the information receiver must work according to the same rules (protocols). Only then will computers understand what they are transmitting to each other.
Each packet receives a number in order to recognize information sent erroneously or lost during communication, as well as to request again exactly the packet whose forwarding there were problems. You can compare the delivery of these packages with the delivery of parcels by mail in identical boxes and with a standard address design. After all, each parcel is also accompanied by service information. If they send you several parcels and one of them has not arrived, you can, of course, request it.
Due to the numerous tasks that must be solved in a standard way, there are different types of data transfer protocols, error correction and correction, etc.
The Internet uses the international protocol TCP/IP, created in the 70s. Network management is decentralized. This means that if any node (computer) of the network fails, the functioning of all other computers is maintained. Data packets move across the network to the computer with the desired address and if an accident occurs on one of the computers, they are automatically sent along a different route. For the recipient, it does not matter at all what route this or that packet will take to reach him. At their destination they will unite into one. So packets can reach the destination through roundabout routes.
Test questions and assignments
1. What types of networks exist?
2. What is the purpose of each type of network?
3. How do networks with terminals and a central machine differ from computer networks?
4. What is called a client and what is a server?
5. Come up with examples of using a local network.
6. Come up with examples of how to use a corporate network.
7. Come up with examples of using the global network.
8. Name the main types of communication channels.
9. What is taken into account when organizing a network?
10. How to connect computers in one room?
11. Determine the time it will take to transfer a 6 MB file over coaxial cable9 over the telephone network and over fiber optic cable.
12. Why are telephone lines used in computer networks?
13. What is a network card?
14. What is a modem? What types of modems are there?
15. What are network adapters and modems used for?
16. Describe the functions and characteristics of modems.
17. Why do users strive to buy modems with higher transmission speeds?
18. Where is it better to use a modem, and where is the network adapter for organizing a network?
19. What is called a protocol? Explain the functions of transmission protocols.
LAN hardware components: workstations, servers, interface cards and cables.
Workstations (PCs) – personal computers, - workplaces of network users. Sometimes PCs may not have hard drives. Such workstations are called diskless PCs. Their advantage is low cost, high security against penetration into the system by foreigners and computer viruses; disadvantage - there is no possibility to work offline, to have your own archives of data and programs.
Servers on the LAN perform the functions of distributing network resources. A server is a fairly powerful personal computer, mini-computer or special computer server. There can be several servers on one network. A personal server computer can combine the functions of a server and a workstation. The collection of server computers and server-related workstations is called a domain.
The network adapters used in a LAN have three main characteristics: the type of computer bus to which they are connected (ISA, EISA, Micro Channel, etc.), the bit depth (8, 16, 32, 64) and the method used to access the network data channel.
The main schemes for connecting computers to a LAN are: “star”, “ring” and “common bus”.
Widely used network channel access methods:
o Ethernet (supports bus topology);
o Arcnet (supports star topology);
o Token-Ring (supports ring topology).
In the classification of LAN topologies, there are two main classes: broadcast and serial.
In broadcast configurations, each personal computer transmits signals that can be received by other computers. These configurations include bus, tree, and star topologies.
In sequential configurations, each physical sublayer transmits information to one computer. Examples: arbitrary (random connection of computers), hierarchical, “ring”, “chain”, “star with an intellectual center”, “snowflake”.
To connect computers on a LAN, coaxial (thin and thick) cables, twisted pair cables and optical fiber are used, and work is underway to introduce wireless radio networks.
Additional LAN equipment – uninterruptible power supplies, modems, transceivers, repeaters and connectors (connectors, terminators).
Management principles
There are two main principles of management in a LAN: centralized and decentralized. In centralized networks there is a central node (server computer (CS)) and workstations.
The main purpose of a server computer is to manage data transfer on a network and store files used by many workstations. Laser printers, faxes, modems, scanners, etc. are usually connected to server computers.
Network operating systems that implement centralized management: Microsoft Windows NT Server, Novell NetWare (versions 3.X and 4.X) and others.
The advantages of centralized networks: high security of network resources from unauthorized access, ease of network administration, the ability to create networks with a large number of nodes.
Disadvantages: vulnerability of the system when the file server malfunctions, as well as high demands on server resources.
Networks with decentralized management (peer-to-peer networks) do not contain a server computer. Network management functions are transferred one by one from one workstation to another. The core resources of all workstations are usually publicly available. Peer-to-peer networks are built on the following programs and packages: Novell NetWare Lite, Windows for Workgroups, Windows95/98 and others.
Deploying a peer-to-peer network across a small number of workstations allows for a more efficient and resilient distributed computing environment. Network software is simpler compared to centralized networks. However, such networks are weaker in terms of information security and administration.
A resource consumer on the network is called client , and the resource-providing network component is server . The main types of resources: hardware (entire computer, disk drive, printing device, etc.), software and information. Typical network clients are: a computer, a user or a program. For a hardware resource, the terms used are disk server (file server or file server). Processing of incoming messages is performed by message servers, processing of database requests by database servers, and execution of user applications by application servers. Sometimes the same term refers to different (hardware and hardware-software) components of a computer system. For example, a print server is a computer with a printer connected to it, a printing program, or a computer with print management software.
