Lecture: Computer architecture and computer networks

Computer architecture

Computer architecture refers to all of its components, as well as the principles of their operation. If we connect several computers together, we can get a ready-made computer network.

There are two main components that are needed to create a computer network:

1. Special equipment for network formation;

2. Software that allows all computers to work together.

Computer network are called several computers connected to each other by special equipment, controlled special programs, thereby ensuring the exchange and general use of information stored on a computer network.

Communication line- this is an environment that can connect computers together into a computer network; it is through communication lines that information is transferred.

If some information is transmitted directly between some subscribers. This happens via a communication channel. Integrated communication lines are channels. One communication line can belong to several communication channels.

Computer networks can be local (locally, at an enterprise), regional (belonging to a specific region), or global networks.

Types of computer network

Let's take a closer look at what a local, regional and global network is.

The local network is a network that connects those computers that are located on a short distance from each other, usually this happens on the territory of a building or even a floor.

The great advantage of this network is that all computers are located within a short distance, which increases the speed of information transfer and also expands the capabilities of such a network.

If a certain network connects users over long distances, then such a network is called global.

Such networks use a wide variety of communication lines, some of which were originally used for other purposes (for example, telephone or telegraph lines). However, thanks to the modern approach, almost all connecting lines have been replaced by radio lines or optical fiber.

If several local networks are combined into one network, then it is called regional.

These networks connect everything local networks city, district or region.

There are also corporate networks– networks that connect computers of one organization or industry for the exchange of working information.

For such networks, computers do not necessarily have to be located in the same building.

Network architecture is a set of parameters, rules, protocols, algorithms, maps that allow you to study the network.

Protocol is a set of rules that indicate the types of data that can be transmitted over the network.

Network topology

Network topology is a plan that describes the connections between computers and their nodes.

There are several types of topologies, which are determined by the number of computers, the distance between computers, what parameters are used, and many other characteristics.

There are several main types of topologies: “Point”, “Bus”. "Ring", "Star".

"Dot"

The Tochka technology connects two computers in series with each other.

Modern computer solutions can be classified based on their assignment to a particular architecture. But what could it be? What are the main approaches to understanding this term?

Architecture of computer systems as a set of hardware components

What is the essence of the concept of "architecture"? computer system"? The corresponding term can first of all be understood as a set electronic components, of which a PC consists, interacting within a certain algorithm using various types of interfaces.

Which are part of the computer system:

• input device;
• main computing chipset;
• data storage devices;
• components designed to display information.

In turn, each of the noted components may include a large number of individual devices. For example, the main computing chipset may include a processor, a motherboard chipset, and a graphics processing unit. Moreover, the same processor may consist of other components: for example, a core, cache memory, registers.

Based, in fact, on the structure of specific PC hardware components, it is determined what kind of computer system architecture is built. Let's consider the main criteria according to which certain computing solutions can be classified.

Classification of computer systems

In accordance with the approach common among experts, computer systems in their architecture can include:

• to mainframe computers;
• to minicomputers;
• to personal computers.

It should be noted that this classification of computing solutions, according to which the architecture of a computer system can be determined, is considered obsolete by many experts. In particular, the same personal computers today can be divided into a large number of varieties, very different in purpose and characteristics.

Thus, as computer systems evolve, they can be classified using changing criteria. Nevertheless, the indicated scheme is considered traditional. It will be useful to consider it in more detail. In accordance with it, the first type of computer is those that belong to the architecture of large machines.

Mainframe computers

Large computers, or mainframes, are most often used in industry - as data processing centers for various production processes. They can be equipped with powerful, exceptionally high-performance chips.

The computer system architecture under consideration can perform up to several tens of billions of calculations per second. Large computers are incomparably more expensive than other systems. As a rule, their maintenance requires the participation of a fairly large number of people with the necessary qualifications. In many cases, their work is carried out within departments organized as the enterprise computing center.

Minicomputer

Architecture computing systems and computer networks based on them can be represented by solutions classified as mini-computers. In general, their purpose may be similar to that of mainframes: the use of the corresponding type of computer in industry is very common. But, as a rule, their use is typical for relatively small enterprises, medium-sized businesses, and scientific organizations.

Modern minicomputers: capabilities

In many cases, these computers are used precisely for the purpose of effectively managing intracorporate networks. Thus, the solutions under consideration can be used, in particular, as high-performance servers. They are also very equipped powerful processors, such as, for example, Xeon Phi from Intel. This chip can operate at speeds of more than 1 teraflops. The corresponding processor is designed for production using a 22 nm process technology and has throughput memory at 240 GB/s5.

Personal computers

The next type of computer architecture is the PC. It is probably the most common. PCs are not as powerful and high-performance as mainframes and microcomputers, but in many cases they are capable of solving problems in both industry and science, not to mention typical user tasks such as running applications and games.

Another remarkable feature that characterizes personal computers is that their resources can be pooled. The computing power of a sufficiently large number of PCs can thus be comparable to the performance of higher-class computer architectures, but, of course, achieving their levels nominally using a PC is very problematic.

However, the architecture of computer systems, networks based personal computers characterized by versatility, from the point of view of implementation in various industries, accessibility and scalability.

Personal computers: classification

As we noted above, PCs can be classified into a large number of varieties. These include: desktops, laptops, tablets, PDAs, smartphones - combining PCs and phones.

As a rule, desktops have the most powerful and productive architectures; the least powerful are smartphones and tablets due to their small size and the need to significantly reduce the resources of hardware components. But many of the corresponding devices, especially top-end models, are, in principle, comparable in speed to leading laptop models and budget desktops.

The noted classification of PCs indicates their versatility: in one variety or another, they can solve typical user tasks, industrial, scientific, and laboratory. Software and the architecture of computer systems of the corresponding type are in many cases adapted for use by an ordinary citizen who does not have the special training that may be required for a person working with a mainframe or mini-computer.

How to assign a computing solution to a PC?

The main criterion for classifying a computing solution as a PC is the fact of its personal orientation. That is, the corresponding one is designed mainly for use by one user. However, many of the infrastructural resources he accesses are undeniably social in nature: this can be seen in the example of Internet use. Given that the computing solution is personal, the practical effectiveness of its use can only be recorded if a person gains access to data sources generated by other people.

Classification of software for computer architectures: mainframes and minicomputers

Along with the classification of computers discussed above, there are also criteria for assigning programs to certain categories that are installed on the corresponding types computer technology. As for mainframes and minicomputers similar in purpose, and in some cases in performance, they, as a rule, have the ability to use several operating systems adapted to solve specific production problems. In particular, these OS can be adapted to run various automation tools, virtualization, implementation of industrial standards, integration with various types Application software.

Software classification: personal computers

Programs for ordinary PCs can be presented in varieties optimized to solve, in turn, user tasks, as well as those production ones that do not require the level of performance that characterizes mainframes and minicomputers. Thus, there are industrial, scientific, and laboratory programs for PCs. Software and the architecture of computer systems of the appropriate type depend on the specific industry in which they are used, on the expected level of qualifications of the user: it is obvious that professional solutions for industrial design may not be designed for a person with only basic knowledge in the field of application of computer programs.

PC programs in one variety or another have, in many cases, intuitive clear interface, various reference documentation. In turn, the power of mainframes and minicomputers can be fully used provided that not only the instructions are followed, but also that the user regularly makes changes to the structure of the programs being launched: this may require additional knowledge, for example, related to the use of languages programming.

Levels of PC software architecture

The concept of “computer systems architecture” can be interpreted in different ways by a computer science textbook, depending on the views of its author. Another common interpretation of the term is that it refers to software layers. In this case, it does not matter in which specific computer system the corresponding software levels are implemented.

In accordance with this approach, computer architecture should be understood as a set of different types of data, operations, software characteristics used to maintain the functioning of the computer's hardware components, as well as creating conditions under which the user is able to use these resources in practice.

Software Layer Architectures

Experts identify the following main computer system architectures in the context of the approach under consideration to understanding the corresponding term:

• digital logical architecture of a computing solution - in fact, a PC in the form of various modules, cells, registers - for example, located in the processor structure;
• microarchitecture at the level of interpretation of various microprograms;
• architecture for broadcasting special commands - at the assembler level;
• architecture for interpreting the corresponding commands and their implementation into program code understandable to the operating system;
• compilation architecture that allows you to make changes to the program codes of certain types of software;
• architecture of high-level languages ​​that allow adapting program codes to solve specific user problems.

Meaning of Software Architecture Classification

Of course, this classification in the context of considering this term as corresponding to software levels can be very conditional. Computer architecture and the design of computer systems, depending on their manufacturability and purpose, may require different approaches from developers in classifying software levels, as well as, in fact, understanding the essence of the term in question.

Despite the fact that these ideas are theoretical, their adequate understanding has great importance, since it contributes to the development of more effective conceptual approaches to building certain types of computing infrastructure, allows developers to optimize their solutions to the needs of users solving specific problems.

Summary

So, we have defined the essence of the term “computer system architecture”, how it can be viewed depending on a particular context. In accordance with one of the traditional definitions, the corresponding architecture can be understood as the hardware structure of a PC, which predetermines the level of its performance, specialization, and requirements for user qualifications. This approach involves the classification of modern computer architectures into 3 main categories - mainframes, minicomputers, and PCs (which, in turn, can also be represented by various types of computing solutions).

As a rule, each type of these architectures is designed to solve specific problems. Mainframes and minicomputers are most often used in industry. Using a PC, you can also solve a wide range of production problems and carry out engineering developments - the corresponding architecture of computer systems is also adapted for this. Laboratory work and scientific experiments with such technology become clearer and more effective.

Another interpretation of the term in question involves its correlation with specific levels of software. In this sense, the architecture of computer systems is working programm, which ensures the functioning of the PC, as well as creating conditions for using its computing power in practice in order to solve certain user problems.

MINISTRY OF EDUCATION AND SCIENCE OF RUSSIA

Federal State Budgetary Educational Institution

higher professional education

"Tula State University"

Department of Robotics and Production Automation

Collection of guidelines for laboratory work

by discipline

Computers, systems and networks

Direction of preparation: 220400 “Mechatronics and robotics”

Speciality: 220402 “Robots and robotic systems”

Forms of training: full-time

Tula 2012

Guidelines for laboratory work have been compiled Associate Professor, Ph.D. Shmelev V.V. and discussed at the department meeting faculty cybernetics ,

protocol No.___ from "___"____________ 20 1 G.

Methodological instructions for laboratory work were revised and approved at a department meeting robotics and production automation faculty cybernetics ,

Protocol No.___ dated "___"____________ 20___

Head Department________________E.V. Larkin

Laboratory work No. 1. Classification of computers and architecture of computer systems 4

2.1 Computer classification 4

Laboratory work No. 2. Composition and structure of a personal computer 9

2.1 Structure of a personal computer 9

Basic devices PC 15

Laboratory work No. 3. Personal computer storage devices 29

2.1 Storage devices 29

Laboratory work No. 4. External PC devices 58

Laboratory work No. 5. Local computer networks 79

2.1 Local area networks 79

Laboratory work No. 6. Software, information and technical support for networks 91

2.1. Software and information support for networks 92

2.2 Basic principles of building computer networks 93

2.3. Technical support for information and computer networks 104

The object of study is software, information and technical support for networks 122

2. Study software, information and technical support of networks 122

Laboratory work No. 7. Global information network Internet 123

2. Basic theory 123

2.1 Global information network Internet 123

Laboratory work No. 8. Communication system 133

1. Purpose and objectives of the work 133

2. Basic theory 133

2.1. TELECOMMUNICATIONS Systems 133

Documented information transmission systems 146

Laboratory work No. 1. Classification of computers and architecture of computing systems

1. Purpose and objectives of the work.

As a result of completing this work, students should

know classification of computers and architecture of computer systems

2. Basic theory.

2.1 Classification of computers

Computer complex technical means, designed for automatic information processing in the process of solving various problems.

There are several criteria by which VMs can be divided. In particular:

according to the operating principle,

By element base and stages of creation,

as intended,

in size and computing power,

by functionality,

According to the operating principle VM: analog, digital and hybrid.

Analog or continuous VM, work with information presented in continuous (analogue) form, i.e. in the form of a continuous stream of values ​​of any physical quantity (most often electric voltage)

AVMs are simple and easy to use. The speed of solving problems is regulated by the operator and can be very high, but the accuracy of calculations is very low. Such machines effectively solve differential calculus problems that do not require complex logic.

Digital, or discrete-action VMs, work with information presented in discrete, or rather digital, form.

Hybrid or combined-action VMs combine the ability to work with both digital and analog information. Typically used in the automation of technical and process control tasks.

In economics and everyday activities, digital computers have become widespread, more often called simply computers or computers.

According to the element base and stages of creation, the following are distinguished:

1st generation, 50s of the twentieth century: computers based on electronic vacuum tubes.

2nd generation, 60s: Computers based on semiconductor devices (transistors).

3rd generation, 70s: computers based on semiconductor integrated circuits with a low and medium degree of integration (hundreds to thousands of transistors in one package, on a chip).

4th generation, 80-90s: computers on large and ultra-large ICs, the main one of which is a microprocessor (tens of thousands to millions of active elements on one chip).

If the electronic equipment of a 1st generation computer occupied a room with an area of ​​100-150 square meters. m, then VLSI 1-2 sq. cm and the distance between the elements on it is 0.11-0.15 microns (the thickness of a human hair is several tens of microns)

5th generation, present time: computing systems with several dozen parallel operating microprocessors.

6th and subsequent generations: computers with massive parallelism and optical-electronic base, which implement the principle of associative information processing; so-called neural computers.

It is important to know:

Each subsequent generation exceeds system performance and storage capacity by more than an order of magnitude.

By purpose It is customary to distinguish between universal computers, problem-oriented and specialized ones.

Universal are designed to solve a wide range of engineering, technical, economic, mathematical and other problems, which are characterized by large volumes of data processing and complexity of algorithms.

Problem-oriented are designed to solve a narrower range of problems related to the management of technological processes (objects), with registration, accumulation and processing of relatively small volumes data, performing calculations using relatively simple algorithms. They include limited hardware and software resources.

Specialized are designed to solve specific problems of controlling the operation of technical devices (units). These can be controllers - processors that control the operation of individual nodes of the computer system.

By size and computing power computers can be divided into extra-large (supercomputers, supercomputers), large, small and ultra-small (microcomputers, microcomputers).

Comparative characteristics of computer classes

Options	Supercomputer			Microcomputer
Performance, MIPS
RAM capacity, MB
VSD capacity, GB
Depth, bits

By revising functionality computers are evaluated:

• processor speed,

  processor register width,

  forms of representing numbers,

  nomenclature, capacity and speed of storage devices,

  nomenclature and specifications external devices,

  ability to perform several programs simultaneously (multitasking),

  the range of operating systems used,

  software compatibility – the ability to run programs written for other types of computers,

  ability to work on a computer network

COLLECTION

LABORATORY WORK

By subject

Computer systems architecture

Fundamentals of architecture, design and operation of computing systems

Laboratory works №1-17

Compiled in accordance with the program approved by director G.E. Kamyshenkov.

for specialties:

230401 - « Information Systems»

230115 - “Programming in computer systems”

work is designed for: 40 hours

Reviewed:

at the meeting of the P(C)K “Information systems and technologies”

Chairman of the commission _________ Shomas E.A.

Protocol No. ____ dated “___”___________ 2011

A collection of laboratory works developed by the teacher

Khodotova E.A.

Samara 2011

LIST OF LABORATORY WORKS

Laboratory work No. 1.

NAME: Basic components of a PC. System parameters

1. OBJECTIVE OF THE WORK:

1.1. Familiarize yourself with the safety rules when working with a PC and computer device.

1.2. Repeat the techniques of using the mouse and the assignment of the main PC keys

2. LITERATURE:

2.1. http://dic.academic.ru/

3.PREPARATION FOR WORK:

3.1. Study the suggested literature.

3.2. Prepare a report form.

4. MAIN EQUIPMENT:
4.1. Personal IBM PC.

5.1. Title and purpose of the work.

5.2. Answers to security questions.

5.3. Description of the practical work performed on a computer (hereinafter referred to as PC).

5.4. Conclusions about the work done.

6. CHECK QUESTIONS:

6.1. List the main components of a PC?

6.2. List which ones you know additional devices, included in the PC?

6.3. Classify the purpose of devices (Input / Output): keyboard, hard drive, CD-ROM, monitor.

6.4. What are they used for? Shift keys, Alt, Ctrl, Enter, Tab, Esc, Page Up, Page Down, Num. Lock, Home, End, Backspace, Delete?

6.5. How to switch from Russian to English alphabet and vice versa?

6.6. How to type the following characters “.”, “,”, “:”, “;”, “№”, “-”, “?”, “--”, “!”?

6.7. What is a system, system parameters?

6.8. How to view system parameters (2 ways)?

7. ORDER OF WORK:

7.1. Turn on the computer using the “Power” button.

7.2. Using the mouse, open the START menu (left mouse button). Find standard program"Calculator".

7.3. Launch this program (left mouse button). Close this program using the close button (top left button with a cross).

7.4. Open "Trash". Close it with Alt+F4 keys.

7.5. Prepare the computer to shut down using the mouse, Start - Shutdown button. Click the CANCEL button with the mouse or press the ESC key.

7.6. Prepare the computer to shut down using the Alt+F4 keys. Click the CANCEL button with the mouse or press the ESC key.

7.7. Run the program date and time ( double click on the computer clock).

7.8. Use the mouse to change the clock readings.

7.9. Use the mouse to set the year and month of your birth on the calendar and determine on what day of the week you were born.

7.10. Cancel your actions using the CANCEL button on the screen.

7.11. Get to know the basic keys on your PC keyboard.

7.11.1 To do this, first download text editor Microsoft Word, execute the commands sequentially

Start-Programs-Microsoft Word.

You see a vertical line blinking at a constant frequency on the white field of the editor. This is a cursor. Information is entered at the cursor position.

7.11.2. Define the action of the Shift key:

a) type any word from the keyboard;

b) press the Spacebar (the longest key on the keyboard) to separate this word from the next one, and type another word while holding down the Shift key. How has the spelling changed?

7.11.3. Define the action of the Enter key:

a) make sure that the cursor is at the end of the line;

b) press the Enter key. How did the cursor position change?

What is the Enter key used for?

7.11.4.Determine the action of the key Caps Lock:

a) enter a word at the cursor position;

b) make a space;

c) press and release the Caps Lock key. Please note: in the upper right part of the keyboard, the light opposite the “Caps Lock” inscription lights up. This means that the caps lock mode is enabled;

d) type any word, press space;

e) Turn off caps lock mode by pressing and releasing the Caps Lock key again. Light bulb on the right top corner the keyboard will go off.

e) enter a new word. What is the Caps Lock key used for?

How does the Caps Lock key differ from the Shift key?

7.11.5. Move to another line yourself.

7.11.6.Determine the action of the left Shift+left Alt key combination:

a) find the icon labeled Ru in the lower right corner of the screen on the taskbar. This means that the Russian alphabet is currently enabled;

b) press the Shift and Alt keys simultaneously with your left hand (in the future, for brevity, this action will be called Shift+Alt) and release them. Please note: the Ru icon has been replaced by En;

c) enter any letters at the cursor position.

What is the function on this computer performed using the Shift+Alt key combination?

7.11.7.Find the cursor keys. Click on each of them. What are these keys for?

7.11.8.Transfer to a new line (do not forget that the cursor should be at the end of the line when pressing the Enter key) and determine the action of the Num Lock key on a small numeric keypad(MCC).

a) If you press the Num Lock key, the “Num Lock” light at the top of the keyboard will light up. This means that the MCC operates in digital mode. Turn on digital mode and enter numbers at the cursor position.

b) Turn off the digital mode and press the arrow keys again. What is the result of your action? How does the MCC work when Num Lock is on? When turned off?

7.11.9. Using the Enter key, go to the last line of the sheet and type any word. Determine for yourself what the Page Up and Page Down keys are for.

7.11.10. Define the actions of the Home and End keys yourself. What is the difference?

7.11.12. Place the cursor on an empty line. Define the actions of the Tab key yourself.

7.11.13. Let's get acquainted with the signs

a) Turn on the Russian alphabet. Place the cursor on a new line and press the last key several times in the lower right corner of the alphanumeric area of ​​the keyboard (before the Shift key). There is a point here.

b) Press this key with the Shift key combination. What sign is hidden under this combination?

d) Hyphen is a key with a minus symbol, dash is the key combination Ctrl+Alt+“-” (type minus on the MCC). It must be turned on.

7.11.14. Remove offers. To delete, use the Backspace key to the left of the cursor, and Delete to the right.

7.12. Look at the system settings: “Start” - Control Panel. In the window that opens, find the “System” shortcut.

7.13. Copy the system parameters into the report.

The work was compiled by teacher Khodotova E.A.

APPLICATION

A computer (English computer - “computer”) is a device or system capable of performing a given, clearly defined sequence of operations. These are most often operations of numerical calculations and data manipulation, but they also include input-output operations. A description of a sequence of operations is called a program. Electronic computer, computer - a set of technical means designed for automatic processing of information in the process of solving computational and information problems. The name "computer", adopted in Russian-language scientific literature, is synonymous with computer. It has now almost fallen into disuse and is primarily used by digital electronics engineers as a legal term in legal documents and also in a historical sense to refer to 1940s-1980s computer technology and large computing devices, as opposed to personal devices. An electronic computer implies the use of electronic components as its functional units, but a computer can also be designed on other principles - it can be mechanical, biological, optical, quantum, etc. (more details: Classes of computers By type working environment), working due to the movement of mechanical parts, the movement of electrons, photons or the effects of other physical phenomena. In addition, according to the type of operation, a computer can be digital (DVM) and analog (ABM).

PC diagram: 1. Monitor 2. Motherboard 3. Processor 4. ATA port 5. RAM 6. Expansion cards 7. Computer power supply 8. Disk drive 9. Hard drive 10. Keyboard 11. Computer mouse

6.2. COMPUTER NETWORK ARCHITECTURE

REFERENCE MODELS FOR SYSTEM INTERACTION

Open Systems Interoperability Model

To determine the tasks assigned to complex object, as well as to highlight the main characteristics and parameters that it should have, general models of such objects are created. General model computer network determines the characteristics of the network as a whole and the characteristics and functions of its main components.

Computer network architecture - description of its general model.

The variety of manufacturers of computer networks and network software products has raised the problem of combining networks of different architectures. To solve this problem, the Ministry of Education and Science has developed a model open systems architectures.

Open system - a system that interacts with other systems in accordance with accepted standards.

The proposed open systems architecture model serves as a basis for manufacturers to develop compatible network equipment. This model is not some kind of physical body, the individual elements of which can be touched. The model represents the most general recommendations for building standards for interoperable network software products. These recommendations should be implemented both in hardware and software of computer networks.

Currently, the Open Systems Interconnection (OSI) model is the most popular network architectural model. The model considers general functions, but not special solutions, so not all real networks they follow it absolutely. The open systems interaction model consists of seven levels (Figure 6.15).

Level 7 - applied- provides support for end-user application processes. This level determines the range of applied tasks implemented in a given computer network. It also contains everything necessary elements service for user application programs. Some tasks of the network operating system can be transferred to the application layer.

Level 6 - representative- defines the data syntax in the model, i.e. data presentation. It guarantees the presentation of data in codes and formats accepted in a given system. In some systems, this level may be combined with the application level.

Level 5 - sessional- implements the establishment and maintenance of a communication session between two subscribers via communication network. It allows data exchange in a mode defined application program, or provides the ability to select the exchange mode. The session layer maintains and terminates a communication session.

The three upper levels are united under a common name - process or application process. These levels determine the functional features of a computer network as an application system.

4th level - transport-provides an interface between processes and the network. It establishes logical channels between processes and ensures the transmission of information packets exchanged between processes through these channels. The logical channels established by the transport layer are called transport channels.

Plastic bag- a group of bytes transmitted by network subscribers to each other.

Rice. 6.15.Open Systems Architecture Reference Model

3rd level - network- defines the interface data terminal equipment user with a packet switching network. It is also responsible for routing packets in the communication network and for communication between networks - it implements internetworking.

Rice. 6.16.Processing of messages by the layers of the OSI model

Note. In communications technology the term is used data terminal equipment. It defines any equipment connected to a communication channel in a data processing system (computer, terminal, special equipment).

2nd level - duct- data link level - implements the process of transmitting information through the information channel. An information channel is a logical channel; it is established between two computers connected by a physical channel. Data Link Layer provides control of the data flow in the form of frames into which information packets are packed, detects transmission errors and implements an algorithm for information recovery in case of detection of failures or data losses.

1st level - physical- performs all necessary procedures in the communication channel. Its main task is to control data transmission equipment and the communication channel connected to it.

When information is transferred from an application process to the network, it is processed by the levels of the open systems interaction model (Fig. 6.16). The meaning of this processing is that each level adds its own to the process information title- service information that is necessary for addressing messages and for some control functions. In addition to the header, the link layer also adds a trailer - a control sequence that is used to verify the correct reception of a message from the communication network.

The physical layer does not add a header. The message, framed by headers and trailers, goes into the communication network and arrives at the subscriber computers of the computer network. Each subscriber computer that receives a message decrypts the addresses and determines whether the message is intended for it.

At the same time, the reverse process occurs in the subscriber computer - reading and cutting off headers by the levels of the open systems interaction model. Each level responds only to its own header. The headers of the upper levels are not perceived or changed by the lower levels - they are “transparent” to the lower levels. Thus, moving through the levels of the OSI model, information finally reaches the process to which it was addressed.

Attention! Each level of the open systems interaction model responds only to its own header.

Note. In Fig. Figure 6.16 shows the process of data passing through layers
models. Each level adds its own heading - 3.

What is the main advantage of the seven-level BOS model? In the process of development and improvement of any system, the need arises to change its individual components. Sometimes this makes it necessary to change other components, which significantly complicates and complicates the process of upgrading the system.

This is where the advantages of the seven-level model come into play. If interfaces are uniquely defined between the levels, then changing one of the levels does not entail the need to make changes to the other levels. Thus, there is a relative independence of the levels from each other.

It is necessary to make one more remark regarding the implementation of the levels of the BOS model in real computer networks. The functions described by the model levels must be implemented either in hardware or in the form of programs.

Functions physical level are always implemented in hardware. These are adapters, data transmission multiplexers, network cards etc.

The functions of the remaining levels are implemented in the form of software modules - drivers.

Interaction model for LAN

In order to take into account the requirements of the physical transmission medium used in the LAN, some modernization was made to the seven-level open systems interaction model for local area networks. The need for such modernization was caused by the fact that to organize the interaction of subscriber computers on a LAN, they use special methods access to the physical transmission medium. The upper levels of the BOS model did not undergo any changes, and the channel level was divided into two sublevels (Fig. 6.17). Sublevel LLC (Logical Link Control ) provides control of a logical link, i.e. performs the functions of the data link layer itself. Sublevel MAC (Media Access Control ) provides access control to the environment. Basic methods for controlling access to the physical transmission medium will be discussed in subsection. 6.3.

COMPUTER NETWORK PROTOCOLS

Protocol concept

As was shown earlier, when exchanging information on a network, each layer of the OSI model responds to its own header. In other words, there is interaction between the same levels of the model in various subscriber computers. Such interaction must be carried out according tocertain rules.

Rice. 6.17.Reference model for local computer networks

Protocol- a set of rules that determines the interaction of two levels of the same name in the open systems interaction model in various subscriber computers.

A protocol is not a program. The rules and sequence of actions during information exchange, defined by the protocol, must be implemented in the program. Typically, the functions of protocols at various levels are implemented in drivers for various computer networks.

In accordance with the seven-level structure of the model, we can talk about the need for the existence of protocols for each level.

The open systems concept involves the development of standards for protocols at various levels. The protocols of the three lower levels of the open systems architecture model are the easiest to standardize, since they define the actions and procedures characteristic of computer networks of any class.

It is most difficult to standardize protocols at the upper levels, especially the application level, due to the multiplicity of application tasks and, in some cases, their uniqueness. If, based on the types of structures, methods of access to the physical transmission medium, the network technologies used and some other features, one can count about a dozen various models computer networks, then according to them functional purpose there are no limits.

Basic types of protocols

It is easiest to imagine the features of network protocols using the example of link-level protocols, which are divided into two main groups: byte-oriented and bit-oriented.

Byte-oriented The protocol ensures the transmission of a message over an information channel in the form of a sequence of bytes. In addition to information bytes

Control and service bytes are also transmitted to the channel. This type of protocol is convenient for a computer, since it is focused on processing data presented in the form of binary bytes. For a communication environment, a byte-oriented protocol is less convenient, since dividing the information flow in a channel into bytes requires the use of additional signals, which ultimately reduces the throughput of the communication channel.

The most famous and widespread byte-oriented protocol is the binary synchronous communication protocol. BSC (Binary Synchronous Communication ), developed by the company IBM . The protocol provides the transmission of two types of frames: control and information. IN management personnel control and service characters are transmitted in information- messages (individual packets, sequence of packets). Protocol operation BSC is carried out in three phases: establishing a connection, maintaining a message transmission session, and disconnecting the connection. The protocol requires for each transmitted frame to send a receipt indicating the result of its reception. Frames transmitted with an error are retransmitted. The protocol defines the maximum number of retransmissions.

Note. A receipt is a control frame that contains confirmation that the message was received (positive receipt) or was rejected due to an error (negative receipt).

Transmission of a subsequent frame is possible only when a positive receipt for receiving the previous one is received. This significantly limits the speed of the protocol and places high demands on the quality of the communication channel.

Bit-oriented The protocol provides for the transmission of information in the form of a stream of bits that are not divided into bytes. Therefore, special sequences - flags - are used to separate frames. An opening flag is placed at the beginning of the frame, and a closing flag is placed at the end.

The bit-oriented protocol is convenient in relation to the communication environment, since the communication channel is precisely oriented towards transmitting a sequence of bits. It is not very convenient for a computer, because it is necessary to select bytes from the incoming sequence of bits for subsequent message processing. However, given the speed of the computer, we can assume that this operation will not have a significant impact on its performance. Potentially bit-oriented protocols are faster than byte-oriented ones, which makes them widespread in modern computer networks.

A typical representative of the group of bit-oriented protocols is the protocol HDLC (High - level Data Link Control - highest level communication channel control) and its subsets. Protocol HDLC controls the information channel using special control frames in which commands are transmitted. Information frames are numbered. In addition, the protocol HDLC allows you to transmit up to three to five frames into the channel without receiving a positive receipt. A positive receipt received, for example, on the third frame shows that the previous two were received without errors and it is necessary to repeat the transmission of only the fourth and fifth frames. This operating algorithm ensures the high performance of the protocol.

Among the top-level protocols of the OSI model, the X.400 protocol (e-mail) and FTAM (File Transfer, Access and Management - file transfer, file access and file management).

Computer Network Protocol Standards

For physical layer protocols, the standards are defined by the CCITT recommendations. Digital transmission involves the use of X.21 and X.21-bis protocols.

The link layer defines the protocol HDLC and its subsets, as well as the X.25/3 protocol.

The widespread use of local area networks required the development of standards for this area. Currently, LAN standards are developed by the Institute of Electrical and Electronics Engineers - IEEE ( IEEE - Institute of Electrical and Electronics Engineers).

IEEE Committees 802 have developed a number of standards, some of which have been adopted by the ISO ( ISO ) and other organizations. Designed for LAN following standards:

802.1 - upper levels and administrative management;

802.2 - logical data link control ( LLC);

802.3 - random media access method ( CSMA/CD - Carrier Sense Multiple Access with Collision Detection - multiple access with transmission control and collision detection);

802.4 - marker bus;

802.5 - marker ring;

802.6 - metropolitan networks.

The interaction of two nodes from different networks is shown schematically in Fig. 6.18. The exchange of information between levels of the same name is determined by the protocols discussed above.

Note. The nodes are connected using a communication channel. This is the environment for whicha swarm distributes messages from one network node to another. Packages andthe frames that were discussed, in the form of a sequence of electrical sigscash comes from one node to another. Interaction of the same levelsThis model is shown with dotted arrows.

6.3. LOCALCOMPUTINGNETWORKS

FEATURES OF LAN ORGANIZATION

Functional groups of devices on the network

The main purpose of any computer network is to provide information and computing resources to users connected to it.

From this point of view, a local area network can be considered as a collection of servers and workstations.

Server- a computer connected to a network and providing its users with certain services.

Serverscan perform data storage, database management, remote job processing, job printing and a number of other functions that network users may need. The server is the source of network resources.

Work station- a personal computer connected to a network through which the user gains access to its resources.

Work stationThe network operates in both network and local modes. It is equipped with its own operating system, providing the user with all necessary tools for solving applied problems.

Special attention should be given to one of the server types - file server ( File Server ). In common terminology, the abbreviated name is accepted for it - file server.

The file server stores the data of network users and provides them with access to this data. This is a computer with large capacity random access memory, high-capacity hard drives and additional magnetic tape drives (streamers).

It operates under a special operating system that provides simultaneous access for network users to the data located on it.

The file server performs the following functions: data storage, data archiving, synchronization of data changes by different users, data transfer.

For many tasks, using a single file server is not enough. Then several servers can be included in the network. It is also possible to use mini-computers as file servers.

Managing the interaction of devices on the network

Information systems built on the basis of computer networks provide solutions to the following tasks: data storage, data processing, organizing user access to data, transferring data and data processing results to users.

In centralized processing systems, these functions were performed by the central computer ( Mainframe, Host).

Computer networks implement distributed data processing. Data processing in this case is distributed between two objects: client And server.

Client- a task, workstation or computer network user.

During data processing, the client can create a request to the server to perform complex procedures, read a file, search for information in a database, etc.

The server defined earlier fulfills the request received from the client. The results of the request are transmitted to the client. The server provides storage of public data, organizes access to this data, and transmits the data to the client.

The client processes the received data and presents the processing results in a form convenient for the user. In principle, data processing can also be performed on the server. For such systems, the terms adopted are systems client-server or architecture client-server.

The client-server architecture can be used both in peer-to-peer local area networks and in networks with a dedicated server.

Peer-to-peer network. In such a network there is no single center for managing the interaction of workstations and there is no single device for storing data. The network operating system is distributed across all workstations. Each network station can perform the functions of both a client and a server. It can service requests from other workstations and forward its own service requests to the network.

The network user has access to all devices connected to other stations (disks, printers).

Advantages of peer-to-peer networks: low cost and high reliability.

Disadvantages of peer-to-peer networks:

dependence of network efficiency on the number of stations;

complexity of network management;

difficulty in ensuring information security;

difficulties in updating and changing station software. The most popular are peer-to-peer networks based on network operating systems. LANtastic, NetWare Lite.

Network with a dedicated server. In a network with a dedicated server, one of the computers performs the functions of storing data intended for use by all workstations, managing interaction between workstations, and a number of service functions.

Such a computer is usually called a network server. A network operating system is installed on it, and all shared devices are connected to it. external devices- hard drives, printers and modems.

Interaction between workstations on a network is usually carried out through a server. The logical organization of such a network can be represented by the topology star. Role central device executed by the server. In networks with centralized management, it is possible to exchange information between workstations, bypassing the file server. To do this you can use the program NetLink . After running the program on two workstations, you can transfer files from the disk of one station to the disk of another (similar to the operation of copying files from one directory to another using the program Norton Commander).

Advantages of a network with a dedicated server:

reliable system information protection;

high performance;

no restrictions on the number of workstations;

ease of management compared to peer-to-peer networks.

Network disadvantages:

high cost due to the allocation of one computer for the server;

dependence of network speed and reliability on the server;

less flexibility compared to a peer-to-peer network.

Dedicated server networks are the most common among computer network users. Network OS for such networks - LANServer (IBM), Windows NT Server versions 3.51 and 4.0 and NetWare (Novell).

TYPICAL TOPOLOGIES AND LAN ACCESS METHODS

Physical transmission medium of LAN

The physical environment ensures the transfer of information between subscribers of a computer network. As already mentioned, the physical transmission medium of a LAN is represented by three types of cables: twisted pair wires, coaxial cable, fiber optic cable.

twisted pairconsists of two insulated wires twisted together (Fig. 6.19). Twisting the wires reduces the influence of external electromagnetic fields on the transmitted signals. The simplest version of twisted pair is telephone cable. Twisted pairs have various characteristics, determined by dimensions, insulation and twist pitch. The low cost of this type of transmission medium makes it quite popular for LAN.

Rice. 6.19. Twisted pair wires

The main disadvantage of twisted pair cables is poor noise immunity and low speed information transmission - 0.25 - 1 Mbit/s. Technological improvements allow higher transmission speeds and noise immunity (shielded twisted pair), but the cost of this type of transmission medium increases.

Coaxial cable (Fig. 6.20) compared to twisted pair, it has higher mechanical strength, noise immunity and provides information transfer speeds of up to 10-50 Mbit/s. There are two types of coaxial cables available for industrial use: thick and thin. Thick cable more durable and transmits signals of the required amplitude over a greater distance than thin. At the same time/race cable is much cheaper. Coaxial cable, like twisted pair, is one of the popular types of transmission media for LANs.

Rice. 6.20. Coaxial cable

Rice. 6.21. Fiber optic cable

Fiber optic cable -ideal transmission medium (Fig. 6.21). It is not affected by electromagnetic fields and has virtually no radiation itself. The latter property allows it to be used in networks that require increased confidentiality of information.

The speed of information transfer via fiber optic cable is more than 50 Mbit/s. Compared to previous types of transmission media, it is more expensive and less technologically advanced to operate.

LANs produced by various companies are either designed for one type of transmission medium, or can be implemented in various versions based on different transmission media.

Basic LAN topologies

Computing machines, included in the LAN, can be located in the most random manner in the territory where it is created computer network. It should be noted that for the method of accessing the transmission medium and methods of network management, it is not indifferent to how the subscriber computers are located. Therefore, it makes sense to talk about LAN topology.

LAN topology- this is the average geometric diagram connections of network nodes.

Computer network topologies can be very different, but for local area networks only three are typical: ring, bus, star.

Sometimes the terms are used to simplify things - ring, tire And star. One should not think that the types of topologies considered are an ideal ring, an ideal straight line, or a star.

Any computer network can be considered as a collection of nodes.

Knot- any device directly connected to the network transmission medium.

Topology averages the connection pattern of network nodes. So, an ellipse, a closed curve, and a closed broken line belong to the ring topology, and an open broken line belongs to the bus topology.

RingThe topology provides for the connection of network nodes in a closed curve - a transmission medium cable (Fig. 6.22). The output of one network node is connected to the input of another. Information is transmitted along the ring from node to node. Each intermediate node between the transmitter and the receiver relays the sent message. The receiving node recognizes and receives only messages addressed to it.

Rice. 6.22. Ring topology network

Ring topology is ideal for networks that occupy a relatively small space. There is no central node, which increases the reliability of the network. Relaying information allows you to use any type of cable as a transmission medium.

Consistent discipline in servicing the nodes of such a network reduces its performance, and the failure of one of the nodes violates the integrity of the ring and requires special measures to be taken to preserve the information transmission path.

Tiretopology is one of the simplest (Fig. 6.23). It is associated with the use of coaxial cable as a transmission medium. Data from the transmitting network node is distributed along the bus in both directions. Intermediate nodes do not broadcast incoming messages. Information arrives at all nodes, but only the one to which it is addressed receives the message. The service discipline is parallel.

Rice. 6.23. Bus topology network

This ensures high performance of a LAN with a bus topology. The network is easy to expand and configure, and adapt to different systems. The bus topology network is resistant to possible failures of individual nodes.

Bus topology networks are the most common today. It should be noted that they are short in length and do not allow the use of different types of cable within the same network.

Star-shapedtopology (Fig. 6.24) is based on the concept of a central node to which peripheral nodes are connected. Each peripheral node has its own separate communication line with the central node. All information is transmitted through a central node, which relays, switches and routes information flows in the network

Rice. 6.24.Star network

The star topology greatly simplifies the interaction of LAN nodes with each other and allows the use of simpler network adapters. At the same time, the performance of a LAN with a star topology depends entirely on the central node.

In real computer networks, more complex topologies can be used, in some cases representing combinations of those considered.

The choice of a particular topology is determined by the scope of the LAN, the geographical location of its nodes and the size of the network as a whole.

Methods of access to the transmission medium

The transmission medium is a common resource for all network nodes. To be able to access this resource from a network node, special mechanisms are needed - access methods.

Media access method - a method that ensures the implementation of a set of rules by which network nodes gain access to a resource.

There are two main classes of access methods: deterministic and non-deterministic.

At deterministic In access methods, the transmission medium is distributed between nodes using a special control mechanism that guarantees the transmission of node data within a certain, fairly small time interval.

The most common deterministic access methods are the polling method and the transfer method. The survey method was discussed earlier. It is used primarily in star topology networks.

The transfer of rights method is used in networks with a ring topology. It is based on the transmission of a special message - a token - over the network.

Marker- a service message of a certain format, which is used Network participants can post their information packages.

The token circulates around the ring, and any node that has data to transmit places it in the free token, sets the token's busy flag, and transmits it around the ring. The node to which the message was addressed receives it, sets the confirmation flag for receiving the information, and sends a token to the ring.

The sending node, having received confirmation, releases the token and sends it to the network. There are access methods that use multiple tokens.

Non-deterministic - random access methods involve competition between all network nodes for the right to transmit. Simultaneous transmission attempts by several nodes are possible, resulting in collisions.

The most common non-deterministic access method is multiple access method with carrier sensing and collision detection ( CSMA/CD ). This is essentially the competitive mode described earlier. Carrier sensing is where a node wanting to transmit a message “listens” on the transmission medium, waiting for it to become free. If the medium is free, the node starts transmitting.

It should be noted that the network topology, the transmission medium access method and the transmission method are closely related to each other. The defining component is the network topology.

LAN purpose

Over the last five years, local computer networks have become widespread in various fields of science, technology and production.

LANs are especially widely used in the development of collective projects, for example, complex software systems. Computer-aided design systems can be created on the basis of a LAN. This makes it possible to implement new technologies for designing mechanical engineering products, radio electronics and computer technology. In the conditions of development of a market economy, it becomes possible to create competitive products, quickly modernize them, ensuring the implementation of the economic strategy of the enterprise.

LANs also allow you to implement new information Technology in systems of organizational and economic management.

In university educational laboratories, LANs make it possible to improve the quality of teaching and introduce modern smart technologies training.

LAN COMBINATION

Causes LAN associations

A LAN system created at a certain stage of development over time ceases to satisfy the needs of all users, and then the problem of expanding its functionality arises. It may be necessary to combine within a company various LANs that appeared in its various departments and branches at different times, at least to organize data exchange with other systems. The problem of expanding the network configuration can be solved both within a limited space and with access to the external environment.

The desire to gain access to certain information resources may require connecting a LAN to higher-level networks.

In the very simple version LAN consolidation is necessary to expand the network as a whole, but technical capabilities the existing network is exhausted, new subscribers cannot be connected to it. You can only create another LAN and combine it with an existing one, using one of the methods listed below.

Methods for combining LANs

Bridge. The simplest option for combining a LAN is to combine identical networks within a limited space. The physical transmission medium imposes restrictions on the length of the network cable. Within the permissible length, a network segment is built - a network segment. To combine network segments, they are used bridges.

Bridge - a device that connects two networks using the same Todas data transmission.

The networks that the bridge connects must have the same network levels of the open systems interaction model; the lower levels may have some differences.

For a network of personal computers, a bridge is a separate computer with special software and additional equipment. A bridge can connect networks of different topologies, but running the same type of network operating systems.

Bridges can be local or remote.

LocalBridges connect networks located in a limited area within an existing system.

DeletedBridges connect geographically dispersed networks using external communication channels and modems.

Local bridges, in turn, are divided into internal and external.

Domesticbridges are usually located on one of the computers of a given network and combine the function of a bridge with the function of a subscriber computer. Expansion of functions is carried out by installing an additional network card.

Externalbridges involve the use of a separate computer with a special software.

Router (router). A complex network, which is a connection of several networks, requires a special device. The task of this device is to send a message to the recipient on the desired network. This device is called router.

Router, or router, - a device that connects networks of different types, but uses the same operating system.

The router performs its functions on network level, so it depends on the communication protocols, but does not depend on the network type. Using two addresses - the network address and the host address, the router uniquely selects a specific network station.

Example6.7. It is necessary to establish a connection with a telephone network subscriber located in another city. First, the address of the telephone network of this city is dialed - the area code. Then - the node address of this network - phone number subscriber The router functions are performed by PBX equipment.

The router can also choose the best way to transmit a message to a network subscriber, it filters the information passing through it, sending to one of the networks only the information that is addressed to it.

In addition, the router provides load balancing in the network by redirecting message flows over free communication channels.

Gateway.To combine LANs of completely different types, operating under significantly different protocols, there are special devices - gateways.

Gateway- a device that allows you to organize data exchange between two networks using different communication protocols.

The gateway performs its functions at levels above the network level. It does not depend on the transmission medium used, but depends on the data exchange protocols used. Typically a gateway converts between two protocols.

Using gateways, you can connect a local area network to the host computer, as well as connect a local network to a global one.

Example 6.8.It is necessary to unite local networks located in different cities. This problem can be solved using a global data network. Such a network is a packet switching network based on the X.25 protocol. Using a gateway, a local area network is connected to the network X.2S . The gateway performs the necessary protocol conversions and ensures data exchange between networks.

Bridges, routers and even gateways are constructed in the form of boards that are installed in computers. They can perform their functions both in the mode of completely separating functions, and in the mode of combining them with functions workstation computer network.