Introduction

In an era of rapid development of technology, problems of information security arise most acutely. The use of automated information processing and management systems has increased the protection of information from unauthorized access. The main problems of information security in computer systems ah arise due to the fact that the information is not strictly associated with the carrier. It can be easily and quickly copied and transmitted over communication channels. Information system exposed to both external and internal threats from violators.

The main problems of information security when working in computer networks can be divided into three types:

· interception of information (violation of confidentiality of information),

· modification of information (distortion of the original message or replacement with other information),

Today, protecting computer systems from unauthorized access is characterized by an increasing role of software and cryptographic mechanisms compared to hardware ones. New problems in the field of information security already require the use of protocols and mechanisms with relatively high computational complexity. One solution to these problems is the creation of virtual private networks (VPN).

ANALYSIS OF LOCAL COMPUTER NETWORK

Structure and characteristics of an unprotected network

Figure 1.1 Unprotected automated system

Background information about an unprotected automated system:

· Addresses on local networks are private.

· At the entrances to local networks there are PROXY computers with real addresses.

· There can be any number of local networks.

Unprotected protection requirements automated system:

· Protection of information exchange when passing through the open Internet is required.

· The secure tunnel is required to be transparent to users who access remote LAN resources.

· It is required that local network users do not have access to open Internet resources, with the exception of resources of other local networks, defined by the administrator, with which secure interaction is organized and, possibly, resources of mobile users.

· It is required to eliminate the need to install ViPNet [Coordinator] software on LAN gateways.

LAN threats and vulnerabilities

Distributed file storage.

Distributed file storage provides users with transparent access to parts of disk memory remote server. Distributed file storage provides capabilities such as remote file management and remote printing. Remote file sharing allows users to access, read, and save files. In general, distant work file sharing is achieved by allowing users to connect to part of a remote disk storage device (file server) as if the device were directly connected. This virtual disk used as if it were a local workstation disk. Remote printing allows the user to print to any printer connected to any LAN component. Remote printing solves two problems for users: organizing background printing during data processing and sharing expensive printers. LAN print servers can accept the entire file immediately after a print request, allowing users to continue working on their workstations rather than waiting for the print job to complete. Many users using the same printer will be able to justify purchasing a fast, high quality printer.

Problems of distributed file storage.

File servers can control user access to various parts of the file system. This is usually done by allowing the user to attach some file system (or directory) to the user's workstation for later use as local disk. This presents two potential problems. First, the server can only provide access security at the directory level, so if a user is allowed access to a directory, then they have access to all files contained in that directory. To minimize risk in this situation, it is important to structure and manage your file system LAN. The next problem is inadequate local workstation protection mechanisms. For example, Personal Computer(PC) may provide minimal or no security for the information stored on it. When a user copies files from the server to the local drive of a personal computer, the file is no longer protected by the security measures that protected it when it was stored on the server. For some types of information this may be acceptable. However, other types of information may require stronger protection. These requirements focus on the need to control the PC environment.

Remote computing.

Remote computing refers to running an application or applications on remote components. Remote computing allows users to: connect remotely to other LAN components; remotely run an application residing on another component, or remotely run an application on one or more components while making it appear to the user that they are running locally.

A remote connection allows users to establish a session with a remote computer (such as a multi-user computer) as if the user were directly connected to the remote computer. The ability to run applications on one or more components allows the user to use the full computing power of the LAN in SPS.

Problems of remote computing.

Remote computing must be controlled so that only authorized users can access remote components and applications. Servers must be able to authenticate remote users requesting services or applications. These requests can also be issued by local and remote servers for mutual authentication. Failure to authenticate may result in unauthorized users having access to remote servers and applications. There must be some guarantees regarding the integrity of applications used by many users over a LAN.

Message exchange.

Messaging applications are linked to email and teleconferencing capabilities. Electronic mail is one of the most important capabilities available through computer systems and networks. Mail servers act like local post offices, allowing users to send and receive messages over a LAN. Teleconferencing capabilities allow users to actively interact with each other, similar to the telephone.

Problems of topologies and protocols.

The topologies and protocols used today require messages to be accessible to a large number of nodes when transmitted to the desired destination. This is much cheaper and easier than having a direct physical path between each pair of machines. In large LANs, direct connections are not feasible. Possible threats resulting from this include both active and passive interception of messages transmitted on the line. Passive interception involves not only reading information, but also analyzing traffic (use of addresses, other header data, message length, and message frequency). Active interception involves altering the flow of messages (including modification, delay, duplication, deletion or unauthorized use of credentials).

Messaging service problems and other problems.

Messaging services increase the risk to information stored on the server or transmitted between the source and the sender. Inadequately protected Email can be easily intercepted, altered, or retransmitted, affecting both the confidentiality and integrity of the message.

Other LAN security issues include:

· inadequate LAN management and security policies;

· lack of training in the specifics of using LAN and security;

· inadequate protection mechanisms for workstations and inadequate protection during information transfer.

Weak security policies also increase the risk associated with the LAN. There should be a formal security policy that defines the rules for using the LAN to demonstrate the organization's management position on the importance of protecting its assets. A security policy is a condensed statement of senior management's position on information assets, responsibilities for their protection and organizational obligations. There should be a strong LAN security policy to provide guidance and support from the top management of the organization. The policy should define the role that each employee has in ensuring that the LAN and the information transmitted on it are adequately protected.

Using a PC in a LAN environment also introduces risk into the LAN. In general, PCs have virtually no security measures regarding user authentication, file access control, auditing of user activity, etc. In most cases, the protection provided to information that is stored and processed on a LAN server does not accompany the information when it is sent to a PC.

The SPS LAN security policy should emphasize the importance of LAN management and support. LAN management must have the necessary financial resources, time and resources. Poor network management can lead to security failures. This may result in the following problems: a weak security configuration, careless implementation of security measures, or even failure to use the necessary security mechanisms.

Lack of user awareness regarding LAN security also increases the risk. Users who are not familiar with security mechanisms, security measures, etc. may use them incorrectly and possibly less safely. Responsibility for implementing security mechanisms and measures, as well as following rules for using a PC in a LAN environment, generally falls on the PC user. Users should be given appropriate instructions and recommendations necessary to maintain an acceptable level of security in the LAN environment.

The quality of network operation is characterized by the following properties: performance, reliability, compatibility, manageability, security, extensibility and scalability.

There are two main approaches to ensuring network quality. The first is that the network guarantees the user compliance with a certain numerical value of the quality of service indicator. For example, frame relay and ATM networks can guarantee the user a given level of throughput. In the second approach (best effort), the network tries to serve the user as efficiently as possible, but does not guarantee anything.

The main characteristics of network performance include: response time, which is defined as the time between the occurrence of a request for a network service and the receipt of a response to it; throughput, which reflects the amount of data transmitted by the network per unit time, and transmission delay, which is equal to the interval between the moment a packet arrives at the input of any network device and the moment of its appearance at the output of this device.

To assess the reliability of networks, they are used various characteristics, including: availability factor, meaning the proportion of time during which the system can be used; security, that is, the ability of the system to protect data from unauthorized access; fault tolerance - the ability of a system to operate under conditions of failure of some of its elements.

Extensibility means the ability to relatively easily add individual network elements (users, computers, applications, services), increase the length of network segments and replace existing equipment with more powerful ones.

Scalability means that the network allows you to increase the number of nodes and the length of connections within a very wide range, while the network performance does not deteriorate.

Transparency - the ability of a network to hide details of its internal structure from the user, thereby simplifying his work on the network.

Network manageability implies the ability to centrally monitor the status of the main elements of the network, identify and resolve problems that arise during network operation, perform performance analysis and plan network development.

Compatibility means that the network is capable of incorporating a wide variety of software and hardware.

Topology– configuration physical connections between network nodes. Network characteristics depend on the type of topology installed. In particular, the choice of a particular topology affects:

On the composition of the necessary network equipment;

Network equipment capabilities;

Possibility of network expansion;

Network management method.

The term “CN topology” can mean physical topology (configuration of physical connections) or logical topology – signal transmission routes between network nodes. The physical and logical topologies of the CS may be the same or different. Local networks are built on three basic topologies known as:

· common bus (bus);

star

In order for the network to successfully cope with the task, it must meet the requirements for performance, reliability, etc.

Network performance determines the amount of data transferred and the time required for their transfer. To evaluate performance, numerical characteristics are used - network response time, average throughput, maximum possible throughput, transmission delay.

Reliability means the probability that the network performs its functions. The reliability of technical devices is usually characterized by time between failures and availability factor (percentage of time during which the system can be used). The reliability of complex systems is also characterized by the probability of message delivery to the recipient.

Safety means the impossibility of unauthorized access to data and ensuring reliability and resistance to deliberate destructive actions.

Extensibility– the ability to relatively easily add new network elements.

Scalability– the ability to significantly increase the size of the network, including by increasing the number of segments.

Transparency– the ability to use network resources in the same way, regardless of their actual location – on local computer or online. In this case, the user does not seem to “notice” the network, working directly with the resources.

Supports various types of traffic– the ability to combine the functions of various networks, for example, television, telephone, computer.

Controllability– the ability to centrally detect and troubleshoot problems, distribute resources and powers between users.

Compatibility– ability to interact with various equipment and software.

Based on territorial characteristics, networks are divided into local, regional and global.

Regional networks cover a city, district, region, small republic. Sometimes corporate networks are highlighted where it is important to protect information from unauthorized access (for example, the Ministry of Defense network, banking networks, etc.). A corporate network can unite thousands and tens of thousands of computers located in different countries and cities (an example is the Microsoft Corporation network).

Local networks (LAN). 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 LAN can be considered as a collection of servers and workstations.

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

Servers can perform data storage, database management, remote job processing, job printing, and a number of other functions that users on the network may need. Server– source of network resources.

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

The network workstation operates in both network and local modes. It is equipped with its own OS and provides the user with all the necessary tools for solving applied problems.

Particular attention should be paid to one of the types of servers - file server.

It stores the data of network users and provides them with access to this data. This is a computer with large capacity OP, hard drives large capacity and additional magnetic tape drives (streamers).

It operates under a special OS, which provides simultaneous access for network users to the data located on it.

The file server performs the following functions: data storage, data archiving, data transfer.

For many tasks, using a single file server is not enough. Then several servers can be included in the network.

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 form a request to the server to perform complex procedures, read a file, search for information in a database, etc.

The server fulfills the request received from the client. The results of the request are transmitted to the client. The server provides data storage common use, organizes access to this data and transfers 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 similar systems accepted terms - systems client-server or architecture client-server.

Architecture client-server can be used both in peer-to-peer LANs and in a network with a dedicated server.

Peer-to-peer network– there is no single center for managing the interaction of workstations and there is no single device for storing data. The network user has access to all devices connected to other stations (disks, printers).

Advantages– low cost and high reliability.

Flaws– dependence of network efficiency on the number of stations; complexity of network management; difficulty in ensuring information security; difficulties updating and changing software stations.

Dedicated server network– in a network, 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 called a network server. A network OS is installed on it, and all shared devices are connected to it. external devices – hard disks, printers, modems.

Advantages – reliable system information protection; high performance; no restrictions on the number of workstations; ease of management compared to peer-to-peer networks.

Flaws– 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.

Related information.

Topology computer networks

One of the most important differences between different types networks is their topology.

Under topology usually understand the relative position of network nodes relative to each other. In this case, network nodes include computers, hubs, switches, routers, access points, etc.

Topology is the configuration of physical connections between network nodes. Network characteristics depend on the type of topology installed. In particular, the choice of a particular topology affects:

• on the composition of the necessary network equipment;
• on the capabilities of network equipment;
• on the possibility of network expansion;
• on the way the network is managed.

The following main types of topologies are distinguished: shield, ring, star, mesh topology And lattice. The rest are combinations of basic topologies and are called mixed or hybrid.

Tire. Networks with a bus topology use a linear monochannel (coaxial cable) for data transmission, at the ends of which special plugs are installed - terminators. They are necessary in order to

Rice. 6.1.

to extinguish the signal after passing through the bus. The disadvantages of the bus topology include the following:

• data transmitted via cable is available to all connected computers;
• If a bus fails, the entire network stops functioning.

Ring is a topology in which each computer is connected by communication lines to two others: from one it receives information, and to the other it transmits it and implies the following data transfer mechanism: data is transmitted sequentially from one computer to another until it reaches the recipient computer. The disadvantages of the ring topology are the same as those of the bus topology:

• public availability of data;
• instability to damage to the cable system.

Star- this is the only network topology with a clearly designated center, called a network hub or “hub”, to which all other subscribers are connected. The functionality of the network depends on the status of this hub. In a star topology, there are no direct connections between two computers on the network. Thanks to this, it is possible to solve the problem of public data availability, and also increases the resistance to damage to the cable system.

Rice. 6.2.

Rice. 6.3. Star topology

is a computer network topology in which each network workstation is connected to several workstations on the same network. It is characterized by high fault tolerance, complexity of configuration and excessive cable consumption. Each computer has many possible ways connections with other computers. A broken cable will not result in loss of connection between the two computers.

Rice. 6.4.

Lattice is a topology in which the nodes form a regular multidimensional lattice. In this case, each lattice edge is parallel to its axis and connects two adjacent nodes along this axis. A one-dimensional lattice is a chain connecting two external nodes (which have only one neighbor) through a number of internal nodes (which have two neighbors - on the left and on the right). By connecting both external nodes, a ring topology is obtained. Two- and three-dimensional lattices are used in supercomputer architecture.

Networks based on FDDI use a double ring topology, thereby achieving high reliability and performance. A multidimensional lattice connected cyclically in more than one dimension is called a "torus".

(Fig. 6.5) - a topology that prevails in large networks with arbitrary connections between computers. In such networks, it is possible to identify individual randomly connected fragments ( subnets ), having a standard topology, therefore they are called networks with mixed topology.

To connect a large number of network nodes, network amplifiers and (or) switches are used. Active hubs are also used - switches that simultaneously have amplifier functions. In practice, two types of active hubs are used, providing the connection of 8 or 16 lines.

Rice. 6.5.

Another type of switching device is a passive hub, which allows you to organize a network branch for three workstations. The low number of connectable nodes means that a passive hub does not require an amplifier. Such concentrators are used in cases where the distance to the workstation does not exceed several tens of meters.

Compared to a bus or ring, a mixed topology is more reliable. The failure of one of the network components in most cases does not affect the overall performance of the network.

The local network topologies discussed above are basic, i.e. basic. Real computer networks are built based on the tasks that a given local network is designed to solve, and on the structure of its information flows. Thus, in practice the topology computer networks is a synthesis of traditional types of topologies.

Main characteristics of modern computer networks

The quality of network operation is characterized by the following properties: performance, reliability, compatibility, manageability, security, extensibility and scalability.

To the main characteristics productivity networks include:

• reaction time – a characteristic that is defined as the time between the occurrence of a request to any network service and the receipt of a response to it;
• throughput – a characteristic that reflects the amount of data transmitted by the network per unit of time;
• transmission delay – the interval between the moment a packet arrives at the input of a network device and the moment it appears at the output of this device.

For reliability assessments networks use a variety of characteristics, including:

• availability factor, meaning the proportion of time during which the system can be used;
• safety, those. the ability of the system to protect data from unauthorized access;
• fault tolerance - the ability of the system to operate in conditions of failure of some of its elements.

Extensibility means the ability to relatively easily add individual network elements (users, computers, applications, services), increase the length of network segments and replace existing equipment with more powerful ones.

Scalability means that the network allows you to increase the number of nodes and the length of connections within a very wide range, while the network performance does not deteriorate.

Transparency – the ability of a network to hide details of its internal structure from the user, thereby simplifying his work on the network.

Controllability network implies the ability to centrally monitor the status of the main elements of the network, identify and resolve problems that arise during network operation, perform performance analysis and plan network development.

Compatibility means that the network is capable of incorporating a wide variety of software and hardware.

Ministry of Education and Science of the Russian Federation

State educational institution

Higher professional education

“Khakass State University named after N.F. Katanova"

Institute of Informatics and Telematics

Department of Informatics and Computer Science

ABSTRACT

Computer networks

in the discipline “Fundamentals of Algorithmic Culture”

Completed by: 1st year student

Specialties "Applied Informatics"

(in economics)

IIT Batch 20

Vorontsov E.E.

Checked:

Abakan, 2010

Introduction………………………………………………………………………………………...3

Beginning…………………………………………………………………………………4

The concept of computer networks……………………………………………………….5

2.1 Classification of computer networks…………………………………….7

The concept of local computer network………………………………...11

3.1 Classification of local computer networks…………………………11

3.2 Structure of local computer networks……………………………….13

3.2.1 Single-node networks……………………………………………………….13

3.2.2 Networks with wired communication lines………………………………………………………13

3.2.3 Radio networks……………………………………………………...14

3.2.4 Ring networks…………………………………………………………….15

3.2.5 Backbone networks…………………………………………………….16

Trunk mono channels……………………………………16

Backbone polychannels……………………………………17

3.2.6 Combined networks……………………………………………………18

Global computer networks……………………………………………………...18

4.1 Classification of global computer networks………………………..18

4.2 Terrestrial multi-node networks………………………………………………………19

4.2.1 General network structure……………………………………………………..19

4.2.2 The principle of modem communication……………………………………………………………20

4.3 Satellite and combined networks……………………………………21

Conclusion………………………………………………………………………………….22

References……………………………………………………………23

Introduction

Currently, computer networks have become very widespread. This is due to several reasons:

Connecting computers into a network allows you to save significantly cash by reducing the cost of maintaining computers (it is enough to have a certain disk space on the file server (the main computer of the network) with software products installed on it, used by several workstations);

Computer networks make it possible to use a mailbox to transfer messages to other computers, which allows you to transfer documents from one computer to another in the shortest possible time;

Computer networks, with special software, are used to organize the sharing of files (for example, accountants on several machines can process entries from the same ledger).

Among other things, in some areas of activity it is simply impossible to do without computer networks. These areas include: banking, warehouse operations of large companies, electronic archives of libraries, etc. In these areas, each individual workstation, in principle, cannot store all the information (mainly due to its too large volume). The network allows selected (registered on the file server) users to access the information that the network operator allows them to access.

The purpose of this work is: Study of computer networks.

To achieve this goal, it is necessary to solve the following tasks:

Find and study literature on this topic;

Learn the term “computer networks”;

Study the classification of computer networks;

Draw a conclusion on this topic.

1. Beginning

Computers appeared in human life not so long ago, but almost any person can say with firm confidence that the future lies with computer technology.

At the dawn of their appearance, computers were bulky devices that ran on lamps and took up so much space that more than one room was required to accommodate them. With all this, the productivity of such machines, compared to modern ones, was incredibly low.

As time went. Gradually, scientific thought and the capabilities of scientists developed so much that the production of smaller, but more powerful computers became a reality.

The process of development of the personal computer is moving with ever-increasing acceleration, and therefore in the near future computers will become a mandatory and indispensable attribute of any enterprise, office and most apartments.

The reason for such an intensive development of information technology is the ever-increasing need for fast and high-quality information processing, the flow of which grows like a snowball with the development of society.

Computers have become firmly established modern world, in all spheres of human activity and science, creating the need to provide them with various software. Of course, this is primarily due to the development of electronic computer technology and its rapid improvement and implementation in various spheres of human activity.

Connecting computers in a network has significantly increased labor productivity. Computers are used for both industrial (or office) needs and for training.

2. Concept of computer networks

A computer network is a collection of nodes (computers, terminals, peripheral devices) that have the ability to communicate with each other using special communication equipment and software.

The sizes of networks vary widely - from a couple of interconnected computers standing on neighboring tables, to millions of computers scattered around the world (some of them may be located in space objects).

Networks use various network technologies. Each technology has its own types of equipment.

Network equipment is divided into active and passive. Active equipment– these are computer interface cards, repeaters, hubs; passive equipment - cables, connectors, patch panels. In addition, there are auxiliary equipment - uninterruptible power supply devices, air conditioning devices and accessories - mounting racks, cabinets, cable ducts of various types. From a physics point of view, active equipment is a device that requires energy to generate signals; passive equipment does not require energy.

Computer network equipment is divided into end systems (devices) that are sources and/or consumers of information, and intermediate systems that ensure the passage of information through the network.

End systems include computers, terminals, network printers, fax machines, cash registers, barcode readers, voice and video communications and any other peripheral devices.

Intermediate systems include hubs (repeaters, bridges, switches), routers, modems and other telecommunications devices, as well as the cable or wireless infrastructure connecting them.

The action that is “useful” to the user is the exchange of information between end devices.

For active communications equipment, the concept of performance applies in two different ways. In addition to the “gross” amount of unstructured information transmitted by the equipment per unit of time (bit/s), they are also interested in the processing speed of packets, frames or cells. Naturally, the size of the structures (packets, frames, cells) for which the processing speed is measured is also specified. Ideally, the performance of communications equipment should be so high that it can process information on all interfaces (ports) at their full wire speed.

To organize information exchange, a set of software and hardware must be developed, distributed across different network devices. At first, developers and suppliers of networking tools tried to follow their own path, solving the whole range of problems using their own set of protocols, programs and equipment. However, solutions from different vendors turned out to be incompatible with each other, which caused a lot of inconvenience for users who, for various reasons, were not satisfied with the set of capabilities provided by only one of the vendors. With the development of technology and the expansion of the range of services provided, there has become a need to decompose network tasks - breaking them down into several interrelated subtasks with defining the rules of interaction between them. The breakdown of the task and the standardization of protocols allows a large number of software and hardware developers, manufacturers of auxiliary and communication equipment to participate in its solution, bringing all these fruits of progress to the end user.

The use of open technologies and adherence to generally accepted standards allows us to avoid the effect of Babylonian pandemonium. Of course, the standard becomes a brake on development, but someone makes a breakthrough, and his new proprietary technology eventually develops into a new standard.

2.1 Classification of computer networks

The entire variety of computer networks can be classified according to various criteria:

1) method of organizing the network;

2) territorial distribution;

3) departmental affiliation;

4) information transfer speed;

5) type of transmission medium;

6) topology;

7) organization of interaction between computers.

Based on the method of organization, networks are divided into real and artificial.

Artificial computer networks (pseudo-networks) allow computers to be connected together via serial or parallel ports and do not require additional devices. Sometimes communication in such a network is called null modem communication (no modem is used). The connection itself is called null modem. Artificial networks are used when it is necessary to transfer information from one computer to another. MS-DOS and Windows are equipped with special programs for implementing a null modem connection. The main disadvantage of these computer networks is the low data transfer speed and the ability to connect only two computers.

Real computer networks allow you to connect computers using special switching devices and a physical data transmission medium. The main disadvantage of real networks is the need for additional devices.

Based on territorial distribution, computer networks are divided into local, global, and regional.

Local computer networks are networks that cover an area of ​​no more than 10 square meters. m. They are closed networks, access to them is permitted only to a limited circle of users for whom work in such a network is directly related to their professional activities.

Regional computer networks are networks located in a city or region

Global computer networks are networks located on the territory of a state or group of states. For example, the World Wide Web. They are open and focused on serving any users.

The term “corporate network” is also used in the literature to denote the combination of several networks, each of which can be built on different technical, software and information principles.

Based on departmental affiliation, departmental and state networks are distinguished.

Departmental computer networks belong to one organization and are located on its territory.

Government computer networks are networks used in government agencies.

Based on the speed of information transfer, computer networks are divided into low-, medium- and high-speed.

Low-speed computer networks are networks with information transfer speeds of up to 10 Mbit/s.

Medium-speed computer networks are networks with information transmission speeds of up to 100 Mbit/s.

High-speed computer networks are networks with information transmission speeds exceeding 100 Mbit/s.

Based on the type of transmission medium, computer networks are divided into wired-coaxial, twisted-pair, fiber-optic, wireless (with information transmitted via radio channels, in the infrared range).

According to the topology of computer networks, they are divided into computer networks with an end node, computer networks with an intermediate node and computer networks with an adjacent node.

End-node computer networks are networks in which the node is located at the end of only one branch.

Computer networks with an intermediate node are networks in which the node is located at the ends of more than one branch.

Adjacent computer networks are networks in which nodes are connected by at least one path that does not contain any other nodes.

A network node is a computer or a network switching device. A network branch is a path connecting two adjacent nodes.

From the point of view of organizing the interaction of computers, networks are divided into peer-to-peer and hierarchical.

All computers in a peer-to-peer network have equal rights. Any network user can access data stored on any computer.

Peer-to-peer networks can be organized using such operating systems, like Windows"3.11, Novell Netware Lite. These programs work with both DOS and Windows. Peer-to-peer networks can also be organized on the basis of all modern 32-bit operating systems and some others.

Advantages of peer-to-peer networks:

1. Most easy to install and operate.

2. DOS and Windows operating systems have all the necessary functions that allow you to build a peer-to-peer network.

Disadvantage: in peer-to-peer networks, it is difficult to resolve information security issues. Therefore, this method of organizing a network is used for networks with a small number of computers.

In a hierarchical network, when the network is installed, one or more computers are pre-allocated to manage data exchange over the network and resource distribution. Such a computer is called a server. Any computer that has access to the server's services is called a network client or workstation.

A server in hierarchical networks is a permanent storage of shared resources. The server itself can only be a client of a server at a higher hierarchy level. Therefore, hierarchical networks are sometimes called dedicated server networks. Servers are usually high-performance computers, possibly with several parallel processors, large-capacity hard drives, and a high-speed network card (100 Mbit/s or more).

The hierarchical network model is the most preferable, as it allows you to create the most stable network structure and more rationally distribute resources. Another advantage of a hierarchical network is a higher level of data protection.

The disadvantages of a hierarchical network, compared to peer-to-peer networks, include:

1. the need for an additional OS for the server.

2. higher complexity of network installation and upgrades.

3. the need to allocate a separate computer as a server

There are two technologies for using a server: file server technology and client-server architecture.

The first model uses a file server on which most programs and data are stored. At the user's request, the necessary program and data are sent to him. Information processing is performed at the workstation.

In systems with a client-server architecture, data is exchanged between a client application and a server application. Data is stored and processed on a powerful server, which also controls access to resources and data. The workstation receives only the results of the query. Developers of information processing applications commonly use this technology.

3. The concept of local computer network

A local network is a set of computers, peripheral devices (printers, etc.) and switching devices connected by cables. Local networks are divided into institutional (office networks of companies, organizational management networks and other networks that differ in terminology, but are almost identical in their ideological essence) and networks for managing technological processes in enterprises.

Local networks are characterized by the fact that the distances between network components are relatively small, usually not exceeding several kilometers. Local networks differ in the role and importance of PCs in the network, structure, methods of user access to the network, methods of data transfer between network components, etc. Each of the networks offered on the market has its own advantages and disadvantages. The choice of network is determined by the number of connected users, their priority, the required speed and range of data transmission, the required throughput, reliability and cost of the network.

3.1 Classification of local computer networks

Local computer networks can be classified according to the following criteria:

1. by the role of a personal computer in the network:

Networks with a server;

Peer-to-peer (peer-to-peer) networks.

2. according to the structure (topology) of the network:

Single-node (“star”);

Ring (“ring”);

Trunk (“bus”);

Combined.

3. by the method of user access to resources and network subscribers:

Networks with user connection at specified subscriber addresses using the circuit switching principle (“star”);

Networks with centralized (software) connection management

users to the network (“ring” and “bus”);

Networks with random user service discipline (“bus”).

4. by type of communication medium for transmitting information:

Networks using existing corporate telephone networks;

Networks on specially laid cable communication lines;

Combined networks combining cable lines and radio channels.

5. according to user service discipline (method of user access to the network):

Priority, specified NCC when users access the network

in accordance with the priorities assigned to them (constant or changing);

Non-priority, when all network users have equal rights to access the network.

6. on placing data in network components:

With a central data bank;

With a distributed data bank;

With a combined data placement system.

3.2 Structure of local computer networks

3.2.1 Single-node networks

In local networks, single-node (star) networks are mainly used. Telephone communication lines and automatic telephone exchanges of organizations, enterprises, firms, etc., specially laid cable lines and radio signal transmission channels can be used as means of communication.

3.2.2 Wired networks

The method of accessing the network is to call a subscriber by his network name with circuit switching in the communication node (CC). The channel switching method ensures the connection of subscribers through the CC during the transmission of the message. At the same time, the management company can organize priority access to the subscriber network.

The advantages of this type of network are:

Simplicity and low cost of connecting network users;

Easy network management;

Ability to connect and disconnect subscribers without stopping the network;

It also has its disadvantages:

The speed of message transmission depends on the number of subscribers, the intensity of receiving and transmitting messages and the technical capabilities of the management company;

The reliability of the network is determined by the reliability of the management company;

Large total length and low efficiency of using the physical signal transmission medium;

To increase reliability, management systems are built according to a modular principle, which includes working and backup modules. The diagnostic system evaluates the functioning of the working module and, if necessary, switches the network to work with the backup module.

An example of a single-node network is Arcnet (USA). Although the network does not have international standard status, it is widely used for building small institutional networks. The network includes an 8-channel CC. The number of subscribers can be increased by connecting new management companies.

3.2.3 Radio networks

The network structure is similar to a single-node network, only messages in the network are transmitted not via wired communication lines, but via radio links. For this purpose, each computer is equipped with a subscriber radio station (ARS). Subscriber radio stations are connected to each other through a central radio station (CRS).

Network access methods are random. The simplest is the ALOHA method - the subscriber seizes the channel and issues a message regardless of whether there are other messages on the network or not. This can lead to collisions of messages on the network and their mutual distortion. Corrupted messages are retransmitted at random intervals. When messages collide, active network time is lost equal to the sum of the transmission time of both messages.

To reduce the likelihood of collisions, modifications of this method are used: carrier sense access (CSMA) and carrier sense access with collision detection (CSMA/CD). Non-entity controlled access means that the subscriber “listens” to the network and transmits the message only to free network. Collisions are possible when two or more subscribers start transmitting at the same time. Corrupted messages are retransmitted.

In carrier sense access with collision detection, the subscriber “listens” to the network, transmits a message to an idle network, and monitors the possibility of message collisions. If subscribers start transmitting at the same time, then colliding messages are immediately destroyed, without taking time to transmit corrupted messages. The CSMA and GSMA/CD methods are used at higher network loads than the ALOHA method.

Random access methods are implemented by means of the EMVOS of each PC, therefore they are more reliable than centralized access methods implemented by NCC software.

Network advantages:

Possibility of communication with moving subscribers;

Ability to connect and disconnect subscribers without stopping the network.

Flaws:

Ability to listen to all subscribers;

Exposure to industrial and atmospheric interference;

The presence of “dead zones” caused by the structures of buildings and premises.

Radio channel networks are now beginning to be increasingly used where communications with existing subscribers are needed.

3.2.4 Ring networks

Network communications include a physical signal transmission medium in the form of a ring connecting computers, access units and storage devices.

The access block is technical device to connect a computer to a physical environment. Access blocks are divided into two groups: access without breaking the integrity of the physical signal transmission medium and access with breaking the physical medium and restoring it using an access block. For example, wired communication lines can be accessed without breaking the physical medium, but fiber optic lines can only be accessed without breaking the signaling medium. The message transmitted by the subscriber enters through the access unit into the physical environment and moves around the ring. The repeater delays the message for the time necessary to determine the subscriber's address and receive it by the subscriber, and restores weakened and distorted electrical signals of the message. The portion of the physical medium between two adjacent repeaters is called a segment.

Network advantages:

Ease of implementation of a point-to-point communication line (at any moment only two points are connected - two subscribers), which reduces the requirements for the physical environment;

Ease of organizing confirmation of message receipt;

Small overall length of the physical medium;

Flaws:

Low reliability, because failure of a section of physical power or a repeater leads to the operation of the entire network;

Inability to connect and disconnect subscribers without stopping the network;

The maximum message transmission delay depends on the number of subscribers;

To increase the reliability and capacity of the network, a double ring is used. Messages in rings travel in different directions. If one ring is disrupted, only the network capacity is reduced. If both rings are violated, those closest to the violation automatically restore the circulation of information in one ring.

An example of a ring network: Token Ring Network (IBM branch in Zurich). The network has the status of a world standard, its length reaches 2 km and serves up to 256 subscribers.

3.2.5 Backbone networks

3.2.5.1 Trunk mono channels

All subscribers are connected to one physical medium, which is a backbone (bus). The message sent by the user arrives through the data block to all network subscribers.

Network advantages:

Higher reliability than ring networks, since subscriber failure does not affect the operation of the network;

The ability to connect and disconnect subscribers without stopping the network in case of non-destructive connection of subscribers to the physical environment;

The shortest length of the physical medium.

Dual mono channels are used to improve reliability and throughput.

An example of a backbone monochannel structure is Ethernet network, which is an industry standard from Intel, DEC and Xerox. The network is the basis of an international standard, serves up to 1000 subscribers with a network length of up to 10 km, access to the network is carried out using CSMA/CD protocols.

3.2.5.2 Backbone polychannels

A polychannel is a group of communications media operating on the same physical medium and intended to organize several networks for various purposes. For this purpose, a broadband physical medium is used, such as broadband coaxial or fiber optic cable.

Network advantages:

High throughput, allowing for the transmission of large flows of various information;

The ability to organize several networks for various purposes on one physical environment (for example, in large financial organizations, information and multi-industry companies).

Network disadvantages:

Difficulty of operation;

High cost of equipment.

Backbone polychannels are developed and manufactured according to specific orders.

3.2.6 Combined networks

Each of the above network structures has certain advantages and disadvantages. Some disadvantages can be overcome and network efficiency can be increased by combining (structuring) different topologies.

Advantages of networks:

Possibility of easy expansion of subscribers and network resources;

Changing the configuration of the network structure;

Improving network reliability;

Life cycle extension.

The disadvantage of such systems is their higher cost due to additional hardware and software network equipment.

4. Global computer networks

4.1 Classification of global computer networks

Global computer networks can be classified according to the following criteria:

1. by type of communication means:

Terrestrial multi-node networks

Satellite radio networks

Combined networks

2. according to the method of message switching

Circuit switching

Message switching

Packet switching

Adaptive Switching

3. by choosing the message transmission route:

Fixed paths

Directed Path Selection

Random paths

Avalanche method

4.2. Terrestrial multi-node networks

4.2.1. General network structure

Working computers of the network can be all classes of computers from personal computers to supercomputers. Separate terminals (T) are also used. Subscribers connect to the network via telephone and telegraph communication channels at connection points (TP). Users access network resources through switching nodes. Each switching node (SM) serves a certain number of users, usually those closest to the node. The architecture of the management company consists of computers with special network software and communication equipment. Management companies can be serviced or unattended, i.e. operating in automatic mode. CMs perform important network functions: analyzing and generating network addresses of subscribers, encoding messages, monitoring and correcting errors that appear during the transmission of information, managing message flows, choosing the optimal message transmission route for a given situation, etc. One of the CMs acts as a gateway or bridge .

A network control center (NCC), where the network administrator works, is combined with one of the management centers. The NCC, as a rule, includes the most powerful computer on the network with special software.

As a rule, main high-speed data transmission channels (MSDC) are laid between the management companies based on coaxial, multi-core and fiber-optic cables. As a last resort, telephone lines with an average data transfer speed are used.

Advantages of a multi-node network:

It is possible to use previously attached communication channels

Acceptable use in different parts networks of different physical media and data rates

Possibility of application in various ways switching and selection of message transmission paths

Disadvantages of a multi-node network:

Difficulty in installing in hard-to-reach places

Inability to communicate with moving subscribers

4.2.2. Modem communication principle

To transmit a discrete binary signal from the output of one computer to the input of another via analog telephone line communication, this signal must be converted into a standard form of signal transmission over a telephone line. This conversion is called modulation, and the device that carries out the conversion is called a modulator. At the input of the computer receiving the message, an inverse conversion must be done, which is called demodulation, and the device must be a demodulator. Since the computer transmits and receives messages, the modulator and demodulator are combined in one device called a modem. Modems are available both as separate units and as built-in ones in computers. Depending on the quality of modems and communication lines, the data transmission speed through modems is 2400,4800,9600 bps.

In order for two computers to exchange information, in addition to a modem and a physical signal transmission medium, special software is needed to coordinate the operation of the computer and support communication tools. Most modems automatically determine the speed at which information is received, test the quality of the communication line, and also encode messages with special noise-resistant codes.

The usual type of modem allows you to transmit only text information, which is why it is sometimes called a telephone modem. In addition to the telephone modem, fax modems are produced that can transmit graphic information: business letters with signatures and seals, drawings, sketches, drawings, photographs. For versatile user work on the network, a scanner must be connected to the computer.

4.3 Satellite and combined networks

The use of space communication satellites has led to the possibility of creating global radio networks. Communications media include communications satellites (CS), ground-based radios (PCs), and wired communications between a computer and terrestrial radios.

Advantages of satellite networks:

Using different frequencies, you can organize several networks that operate in parallel and do not interfere with each other

Easy to communicate with moving subscribers

It is relatively inexpensive to lay communication channels in hard-to-reach places

Disadvantage: high cost of implementing satellite communications.

Currently among global networks Combined networks are becoming increasingly widespread, in which data transmission through terrestrial management systems is supplemented by radio communication between subscribers and the management company, and, if necessary, satellite communications.

Conclusion

Drawing a conclusion after all of the above, we understand that computer networks occupy a special place in our daily life, in our production activities and in other areas. Connecting computers on a network allows people to find the information they need using the resources of other computers, communicate with each other without leaving their room, and communicate with people who are located at vast distances. Also, computer networks provide fast transmission of information over millions of kilometers, which makes it possible to speed up the work of any enterprise.

This abstract discussed such important issues as the concept of computer networks, their classification, as well as the concept of local and global networks. The comparative characteristics, advantages and disadvantages of the currently most popular information technologies were also shown: local computer network and global computer network. They are in this moment the basis of our life. Not a single enterprise, such as a factory, plant or any private firm, could carry out its work without computers connected to a network, since the connection of computers in a network has significantly increased labor productivity.

There are many other effective and useful technologies, their number is increasing every day. Therefore, in order to keep up with the rhythm of modern life, you need to constantly be aware of the latest personal computer hardware, system software and applied computer technologies.

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