In modern working conditions, when several employees simultaneously need access to the Internet, databases and various files, a local network is. It is also necessary in order to speed up collaboration on documents and projects, as well as for remote printing of documents. If an enterprise is moving towards optimizing its work and getting additional profit, organizing a local network becomes not a luxury, but a necessity.

What are the benefits of a local network

With the right organization, the local network will enable the enterprise to use a high-speed channel to transfer and exchange information. The network includes a large number of elements such as servers, computers operating as work nodes, various peripheral devices. office or even whole group offices with a local network can boast much more efficient work, as well as higher productivity.

Through the network, employees are provided with the ability to access the Internet, share access to all open network resources, and can share peripheral devices. Convenient and fast data exchange between employees of the enterprise is also provided by local networks. The electronic document management of the enterprise also becomes more efficient, due to the fact that all employees can use the program for it via the local network at the same time.

With a competent network organization, the level of security of corporate information, access to which should have a limited circle of employees, increases, and there is no need to constantly upgrade it. Thus, not only does the company save time and money, but it also becomes possible to simultaneously manage work nodes.

Principles of building local networks

To create a local network you will need:

• draw up a technical task;
• design work;
• select the necessary equipment;
• mount it;
• lay a cable;
• test and hand over the network, and then finally launch it.

For an efficient and successful network operation, it is necessary to determine the needs of the company as accurately as possible. Data will be required on the number of computerized workstations, estimated data transfer rates and the degree of integration of various intelligent systems. The terms of reference should contain all this information. In addition, you need to choose a program for the subsequent automation of the company's workflow.

Preliminary launch and testing of the network must be carried out without fail. At this stage, it is possible to eliminate minor defects, as well as make additional changes to the system. When the local network is fully put into operation, the work of the entire company becomes not only more comfortable, but also much more efficient.

Network options

Wireless networks are relevant for one-story premises of a small area. Multi-storey buildings or premises with an area of ​​​​more than a thousand square meters are best equipped with complex wired networks.

For those cases when offices are located in different places, for example, in different districts or even cities, it is possible to create secure closed channels based on VPN (Virtual Privat Network).

The network topology can be different:

• stellate;
• ring;
• logical ring;
• tire.

For different needs, different types of networks are used, depending on the initial conditions. To determine the required type, it is required to collect the necessary information for the terms of reference.

Section: Local networks

Subject:Basic concepts local networks. Features of the organization of local networks

networks– a group of connected computers and other devices.

Goals:

Getting an idea about the components of the local network;

Identification of a peer-to-peer network, a server-based network.

Network classification

local networks- a network that unites computers located in one or more buildings.

if the PC is located in different parts of the city or in different cities, then the network is called distributed

distributed networks through which not individual PCs are connected, but local networks create corporate net.

global net distributed networks of the world scale.

Overwhelming majority personal computers in the world work in networks. Local area networks of personal computers (often called local area networks - LAN) are very widespread, since 80-90% of information circulates near the places of its occurrence and only 10-20% is associated with external interactions. Local area networks link computers located at a short distance from each other. The main distinguishing ability of local networks – a single high-speed data transmission channel and a low probability of errors in communication equipment. A twisted pair, coaxial or fiber optic cable, etc. is used as a data transmission channel. The distances between computers in a local network are small - up to 10 km, when using radio communication channels - up to 20 km. Channels in local networks are the property of organizations and this simplifies their operation. The main purpose of computer networks– resource sharing and constant real-time communication 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. Servers can 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. Special attention should be given to one of the types of servers - the file server (File Server). In common terminology, the abbreviated name for it is the file server. File Server stores the data of network users and provides them with access to this data. This is a computer with a large amount of RAM, high capacity hard drives, and optional tape drives (streamers). It runs under the control of a special operating system, which provides simultaneous access of 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. Work station - a personal computer connected to the network, through which the user gets access to its resources. The network workstation operates in both network and local modes. It is equipped with its own operating system (MS DOS, Windows, Unix, etc.) and provides the user with all the necessary tools for solving applied problems.

Purposes of creation and advantages of using local networks

Basic the purpose of creating local computer networks is the sharing of resources and the implementation of interactive communication both within the same firm and outside it. Resources - these are data and applications (programs) stored on network drives, and peripheral devices such as an external drive, printer, modem, etc. concept interactive communication computers involves real-time messaging. Main the advantages of working in a local network are: 1. Ability to store personal and general use data on file server disks. This ensures the simultaneous work of several users with data of common use (viewing and reading texts, spreadsheets and databases), multidimensional data protection at the level of directories and files, the creation and updating of common data by network application software such as Excel, Access. 2. Possibility of permanent storage of software required by many users in a single copy on the disks of the file server. Note that such storage of software does not violate the user's usual ways of working. The software tools needed by many users are primarily application programs. general purpose, such as text and graphic editor, spreadsheets, database management systems, etc. 3. Exchange of information between all computers in the network. This provides a dialogue between network users, as well as the possibility of organizing the work of e-mail. 4. Simultaneous printing by all network users on network-wide printers (one or more). This ensures the availability of a network printer to any user, the possibility of using a powerful and high-quality printer with its protection from unskilled handling. 5. Providing access to the user from any computer on the local network to the resources of global networks in the presence of a single communication node of the global network.

Features of the organization of local networks

Information systems built on the basis of computer networks provide solution next tasks: data storage, data processing, organization of user access to data, transfer of data and results of data processing to users. Computer networks implement distributed data processing. Data processing in this case is distributed between two objects: the client and the server. Client – a task, workstation, computer network user or PC that accesses network resources provided by servers. In the process of data processing, the client can form a request to the server to perform complex procedures, read a file, search for information in databases, etc.

Servers - PCs whose resources are available to network users

Server executes a request from a client. The results of the request are sent to the client. The server provides storage of public data, organizes access to this data and transmits data to the client. The client processes the received data and provides the processing results in a user-friendly way. In principle, data processing can also be performed on the server.

There are 2 types of networks:

server-based peer-to-peer

The choice of network type depends on many factors:

Size of the enterprise Degree of security required Type of business Availability of administrative support Needs of network users Level of funding

Peer-to-Peer Network

In it is a rank network, all PCs are equal, i.e. there is no hierarchy among PCs and there is no dedicated server. Usually, each PC functions both as a client and as a server, in other words, there is no separate PC responsible for the entire network, users themselves decide what data on their PC to make available over the network. Peer-to-peer networks most often combine no more than 10 PCs. Peer-to-peer networks are relatively simple because each PC is both a client and a server, there is no need to install a powerful central server and other components required for complex networks, this usually explains the high cost. In a peer-to-peer network, the performance and security requirements of network software are the rule is lower than the same requirements of dedicated server software.

The feasibility of using peer-to-peer networks

no more than 10 users users are compactly located data protection issues are not practical no expansion of networks in the near future

If these conditions are met, then the choice of a peer-to-peer network will most likely be correct.

Server based networks

B

Most networks have the following configuration - they work on the basis of a dedicated server. A dedicated server is called, which only works as a server and is not used as a client or workstation. It is optimized for fast processing of requests from network clients.

Specialized servers:

file and print servers application servers mail servers fax servers communication servers directory services servers

The advantage of server-based networks

resource provisioning – Access and data are administered and managed centrally. Resources are also usually located centrally, which ensures that the search is centralized. protection - the main argument determining the choice of a server-based network is, as a rule, reliable data protection. One administrator can deal with the security problem, he forms a single security policy and applies it to each network user. data backup - since vital information is located centrally, it is easy to back it up regularly. redundancy - thanks to redundant systems, data on any server can be duplicated in real time, so if the main storage is damaged, information will not be lost, you can always use backup. the number of users in these networks - server-based networks are capable of supporting 1000 users. hardware - since the client PC does not act as a server, the requirements for its characteristics are determined by the user himself. A typical PC client has at least a Pentium processor and 32 to 64 MB of RAM.

Combined networks

They combine the best qualities of peer-to-peer and server-based networks.

Combined networks most fully meet the needs of modern users, but for their correct implementation, reliable protection, certain knowledge and planning skills are required.

Topic: Topology of local networks. The role and functions of the local network administrator

Goals:

Learn to distinguish between basic topologies and their combinations;

Learn how to choose the appropriate topology for a specific task.

The computers that make up the LAN can be located in the most random way in the territory where the computer network is being created. It should be noted that for network management it is not indifferent how the subscriber computers are located. Therefore, it makes sense to talk about LAN topology. Network topology is the physical location of computers, cables, and other network components. Topology is a standard term that is used to describe the basic layout of a network. The topology of a network determines its characteristics. In particular, the choice of a particular topology affects:

on the composition of the required network equipment; on the characteristics of network equipment; on the possibility of expanding the network; on the way to manage the network.

The topologies of computer networks can be very different, but only three are typical for local area networks: ring, tire, star-shaped. Sometimes, for simplicity, the terms “ring”, “tire” and “star” are used. It should not be thought that the types of topologies under consideration represent an ideal ring, an ideal line, or a star. Any computer network can be viewed as a collection of nodes. Knot – any device directly connected to the transmission network.

Bus topology

Tire- such a topology in which PCs are connected along one cable (segment). This topology is often called linear. It uses one cable called a backbone or a segment to which all the PCs of the network are connected. In a network with a bus topology, PCs address data to a specific PC., Transmitting them over the cable in the form of electrical signals. To understand the process of PC interaction on the bus, one should define the following concepts:

signal transmission signal reflection terminator

Data in the form of electrical signals is transmitted to all PCs in the network, however, information is received only by the PC whose address corresponds to the address of the recipient encrypted in these signals, and only one PC can transmit at a time. Tire- this is a passive topology - electrical signals propagate from one cable to another, if no special measures are taken, the signal reaching the end of the cable will be displayed, creating interference, so the signals at the ends of the cable must be extinguished, this is used Terminator, which absorbs these signals.

Expansion of the local area network.

In a network with a bus topology, the cable is usually extended in two ways:

they use a barrel-connector, but you should not abuse it, because the signal weakens, it is better to buy a long cable than to connect several short ones. With a large number of connections, signal distortion occurs. use a repeater that amplifies the signal when transmitting to the next segment

Topology star

IN

All PCs are connected via cable segments to a single central component - a hub ( Hub), the signal from the transmitting PC goes through the hub to everyone else.

In networks with a star topology, the connection of the PC to the network is performed centrally.

Cons: s significant cable consumption, if the central component fails, the network falls.

Advantages: e If one PC fails, the entire network continues to function.

T

opology ring

In this topology, the PC is also connected to the cable in a ring, so the cable cannot have a free ring and no terminator is required. Signals travel around the ring in one direction and pass through each PC. roles repeater, amplifying the signal, transmitting to the next PC.

Cons: e If one PC fails, the entire network stops functioning.

Hubs

Concentrators are:

active - must be connected to electrical network passive - no need to connect to the electrical network hybrid

Active Hubs regenerate and transmit signals in the same way as repeaters. Repeaters - amplify signals and transform them into additional segments, thereby increasing the overall length of the cable. Passive hubs pass the signal through themselves, like switching nodes, without amplifying or restoring it. Hybrid Hubs to which various types of cables can be connected. Networks built on hubs are easy to expand by connecting additional hubs.

Mesh topology

WITH

A mesh network is highly redundant and reliable because each computer on the network is connected to every other single cable. The signal from the sending computer to the receiving computer can take different routes, so a cable break does not affect network performance. Basic flaw such a topology - high costs for laying the cable, which is compensated high reliability and easy maintenance. Mesh topology is usually used in combination with other topologies when building relatively large networks. In a mesh network, each computer is connected to any other separate cable.

Combined topologies

WITH Today, network layouts are increasingly using hybrid topologies that combine the individual properties of a bus, star, and ring. Star-tire(star-bus) is a combination of bus and star topologies. Typically, the scheme looks like this: several networks with a star topology are combined using a backbone linear bus. In this case, the failure of one computer will not affect the operation of the entire network - the rest of the computers still interact with each other. And the failure of the hub will cause only the computers and hubs connected to it to be disconnected from the network. Z

everywhere-ring (star-ring) - somewhat similar to a star-tire. In both topologies, computers connect to hubs. The difference is that the hubs in the star-bus are connected by a backbone line bus, while in the star-ring all the hubs are connected to the main hub, forming a star. The ring is implemented inside the main hub.

The role and functions of the local network administrator

A network that can work on its own has not yet been invented. From time to time, you need to connect new users, and delete some of the existing ones. You have to install new resources and share them, in addition, grant access rights to them. These problems are dealt with network administrator. Centralized management of a LAN is a very difficult task. Until now, there is no universal set of tools for performing the functions of a computer network administrator. There are only software and hardware tools to partially perform this work. The network administrator must be very skilled and creative in applying certain tools to solve non-standard situations occurring in computer networks. He should have a reasonable understanding of network configurations, network performance, accounting and planning, data protection and application programs. Administrator functions include:- accounting of users and differentiation of access rights; - data protection; - user training and support; - modernization of existing software and installation of new; - data archiving and backup; - data loss prevention; - protection of the network from viruses; - monitoring and management of storage space on the server; - modernization and replacement of network components, etc.

Verification work

№ 1. Indicate the letter corresponding to the most accurate, in your opinion, answer to the question:

1. What is true about peer-to-peer networks?

a) Provide a stronger level of security and control than server-based networks.

c) A powerful central server is needed

What is most characteristic of a ring topology network?

a) requires less cable than other topologies

c) equal access for all PCs

d) terminators are required for proper operation

What is most characteristic of a "bus" network topology?

a) requires more cable than other topologies

b) the transmission medium is inexpensive and easy to operate

c) resolving problems is much easier than in other topologies

d) the number of PCs in the network does not affect its performance

4. What is the most characteristic for a bus topology network?

a) requires significantly less cabling than other topologies

b) a break in one cable disables the entire network

c) harder to reconfigure than other topologies

d) centralizes control and manages the network

What topology is passive?

b) passing the token

d) star-ring

What tool will help you build a cable in a network with a "linear bus" topology?

a) network adapter card

b) terminator

c) Barrel Connector

d) communication media connection module

№ 2. Confirm or refute the statement

Answer Yes if the statement is true, otherwise No. Justify the answer.

Server-based networks are also called workgroups.

Server-based networks always have a dedicated server

If data protection issues are important for the enterprise, it is necessary to configure a server-based network

Hypertext is a textual method of representing files linked to each other by an arbitrary associative network.

Email systems can include voice and video in messages

The network printer must be near the network administrator for the network administrator to manage printing

№ 3 List the three most famous servicesInternet.

Answer "Yes" if it is a LAN, otherwise answer "No".

Three PCs and a printer located in the same office are connected by cable, and employees can share the printer. Two PCs in Arizona and one in New York share an email program. More than 150 standalone PCs on the 47th floor in New York use Word for word processing. More than 200 PCs on 14,15,16 floors of a large business center are connected by cable and share files, printers and other resources.

№4 Fill in the gaps in the following statements:

The main reason for using computer networks is the ability to ______________ __________________. The main resources shared on the network are _________ _____________, such as laser printers. Applications _________ ____________ allow users to quickly and efficiently interact with each other. In a peer-to-peer network, each PC can act both as a server and as a __________. There are no dedicated __________________ in a peer-to-peer network. In a peer-to-peer network, each user manages the network resources of their PC, so each user can be considered ______________________. A peer-to-peer network is fine if ______________ questions are not of fundamental importance. The standard model for a network with more than 10 users is a _______ based network. A dedicated server is a PC that does not function as _______________. To meet the increasing demands of users, servers in large networks have become ____________________. The term ____________ defines the network layout. Any network layout is based on the following topologies: _______, __________, ___________. Since when the cable is connected (to lengthen it), the signal is attenuated, _______________ is used, which amplifies the signal before transmitting it to the next segment. The "Bus" topology is a _____________ topology in which PCs do not participate in the transmission of data from the sender to the receiver. With a bus topology, __________ must be connected to the ends of the cable, which will absorb the signal, preventing its reflection. In networks with a star topology, the cable segments diverge from _______________. In networks with a "ring" topology, all PCs act as ___________, amplifying the signal during its transmission. The hubs that generate and transmit the signal are called __________.

№5 In the statements, answer "Yes" or "No"

In star networks, the disconnection of one PC brings the entire network to a halt. The ring topology is passive. Ring topology networks use terminators. In networks with a star topology, the failure of the central node to which all PCs are connected leads to a shutdown of the entire network.

Practical work

Job #1

The company has 8 people. Each employee has their own PC. To get the information you need, you have to verbally ask colleagues or copy data using floppy disks. All agents deal only with their clients and this information is strictly confidential. An eight-year-old laser printer is at the office administrator. Each agent has its own dot matrix printer.

Simultaneously with the installation of the network, it was decided to purchase a high-speed laser printer.

Task. You are tasked with setting up a network for this small company. To make it easier to solve the problem, answer the following questions.

Your choice

What type of network would you use in this company

Single Rank Server Based

Which topology is more suitable for this situation

Tire Ring Star Tire-star Star-ring Justify the answer.

Job #2

Situation

Christina sends the document for printing. Only the top half of the document is printed. No one else has such a problem: other users safely print similar documents.

Known Facts

The printer remains the same. Christina always printed documents on it. She is used to working Microsoft Windows for Workgroups, but recently moved to a new operating system.

Your choice

Cause of the problem

Name one reason why Christina started having trouble printing.

Possible Solution

What advice would you give Christina to get her print output back to normal?

1. Quarterly report Open Joint Stock Company Moscow United Electric Grid Company Issuer code

   public report

   The information contained in this quarterly report is subject to disclosure in accordance with the law Russian Federation about securities

2. Modem communication and computer networks

   Essay

   Rare serious business man, professional programmer or a system operator can imagine a full-fledged operation without using such a powerful, responsive and convenient combination as a regular telephone line, modem and computer network.

3. Virtual Social Networks basic concepts 9 Introduction to the theory of social networks 10 Classical and online social networks 10 Structure, types and parameters of networks 12 law

   Law

   Your attention is invited to study the possibilities of socially-oriented network technologies for the development of civil society and its modernization.

Computer networks and work in them

Local Area Networks

Network architecture

Net is a collection of computers connected by means of data transmission. Data transmission means in the general case may consist of the following elements: communication computers, communication channels (satellite, telephone, digital, fiber-optic, radio and others), switching equipment, repeaters, various types of signal converters and other elements and devices.

Network architecture The computer determines the principles of construction and operation of the hardware and software of the network elements.

Modern networks can be classified according to various criteria: remoteness of computers, topology, purpose, list of services provided, management principles (centralized and decentralized), switching methods (without switching, telephone switching, circuit switching, messages, packets and datagrams, etc. ), types of transmission media, etc.

Depending on the remoteness of computers, networks are conditionally divided into local Andglobal.

Free global network may include other global networks, local networks, as well as computers connected to it separately ( remote computers) or separately connected I/O devices. There are four main types of global networks: urban, regional, national and transnational. As input-output devices, for example, printers and copiers, cash and banking machines, displays (terminals) and faxes can be used. The listed elements of the network can be removed from each other by a considerable distance.

INlocal area networks (LAN) computers are located at a distance of up to several kilometers and are usually connected using high-speed communication lines with an exchange rate of 1 to 10 or more Mbit / s (the case of connecting computers using low-speed telephone lines is not excluded). LANs are usually deployed within some organization (corporation, institution). Therefore they are sometimes called corporate systems or networks. Computers in this case, as a rule, are located within the same room, building or neighboring buildings.

Regardless of the network on which a computer operates, the functions of the software installed on it can be conditionally divided into two groups: resource management the computer itself (including in the interests of solving problems for other computers) and exchange management with other computers (network functions).

The OS traditionally manages the computer's own resources. Functions network management implements network software, which can be done both as separate packages network programs, and in the form of a network OS.

When developing network software, a hierarchical approach is used, which involves the definition of a set of relatively independent levels and interfaces between them. This makes it easy to modify the algorithms of programs of an arbitrary level without significantly changing other levels. In the general case, the simplification of the functions of a certain level or even its complete elimination is allowed.

To streamline the development of network software and ensure the interoperability of any computing systems, the International Standard Organization (ISO) has developed Reference model of open systems interaction(Open System Interconnection - OSI).

The OSI reference model defines the following seven functional layers:

• physical (physical layer);
• transmission line (link) control or channel (data link);
• network (network layer);
• transport (transport layer);
• session (session layer);
• representative (presentation layer);
• application, or application layer (application layer).

Physical layer provides an interface between the network computer and the discrete signal transmission medium. At the physical layer, sequences of bits are transmitted through subscriber channels. The control of the physical channel is reduced to the selection of the beginning and end of the frame that carries the transmitted data, as well as to the formation and reception of signals of a certain physical nature.

The physical layer standards include recommendations X.21 or X.21 bis that define the mechanical, electrical, functional, and procedural characteristics necessary to establish (activate), maintain, and terminate (deactivate) physical connections.

Functions link layer consist in managing the input-output of information in the communication channel. To improve the reliability of the transmission, the link layer procedures may include the introduction of redundant codes, retransmission of data, and other methods. The data generated by this level is grouped into so-called frames

Data exchange between two link-layer objects can be carried out in one of three ways: duplex(simultaneously in both directions), half duplex(alternate in both directions) or simplex(in one direction).

network the level provides transmission of network blocks (packets) between network nodes. Here, the tasks of choosing a route from among the possible ones (when the load or network configuration changes), controlling the incoming flow, buffering packets, etc. are solved. main function network protocol- laying in each physical channel of a set of logical channels (up to 4096), which significantly increases the efficiency of using the resources of the physical channel.

main function transport layer is the delivery of messages (transport blocks), which consist of network packets. To this end, the transport objects of the network software organize the disassembly of messages at the transmitting end and the assembly of messages from received packets at the receiving end. In addition, the transport layer deals with the negotiation of various network layers using the appropriate gateways (coordination of network objects is fundamentally various networks) and bridges(coordination of network objects similar networks).

To check that all sent packets are accepted and there are no errors, the method of sending receipts is used - acknowledgment. Acknowledgment receipts may be sent by the recipient after receiving one or more packets (usually up to 8). In the latter case, one speaks of the so-called "window" mechanism. The use of this mechanism, with a good quality of communication means, makes it possible to reduce the load on the communication network by the service information transmitted over it.

There are currently five classes of service provided by the transport protocol (0, 1...4). The selected classes differ in the capabilities of priority message transmission, error protection, and data encryption using encryption.

session layer designed to organize communication sessions (interaction) between objects of higher levels When establishing communication sessions, the object's authority to access another object is controlled. This level, like the transport one, provides for several classes of services (A, B, C and D).

Representative level describes methods for converting information (encryption, compression, recoding) transmitted to application-level objects: users and programs.

Application layer Responsible for supporting the user's application software. Three main services are implemented at this level: file transfer and management, job transfer and processing, and the virtual terminal service.

The proposed seven-level model describes the general principles of combining computers separated by a data transmission medium. Protocols and interfaces are used to describe the interaction between software and hardware elements of the levels.

protocol called a set of rules for the interaction of objects of the same level, as well as the formats of data blocks (messages) transmitted between objects. Examples of data link protocols are the HDLC (Higher-level Data Link Control) protocol adopted by ISO and the SDLC (Synchronous Data Link Control) protocol from IBM.

Interfaces describe the procedures for the interaction of objects of adjacent levels and the formats of information transmitted between these objects. An example of one of the interfaces is the X.25 interface for connecting users to public data networks. This interface is described in the relevant recommendations (X.25), which define the order and rules for the interaction of terminal equipment. processing DTE (Data Terminal Equipment) data and circuit termination equipment transmission DCE data (Data Circuit-terminating Equipment). The role of DTE is performed by a modem or digital interface device for connecting to a data network. The DCE can be a host machine (Host), a controller or hub serving remote terminals, an interface computer for connecting to another network, etc.

The development by ISO of a set of recommendations for organizing network exchange between computers has made a significant contribution to the theory of creating both global and local networks. However, it should be noted that the adoption of international standards has not completely eliminated the diversity of architectures of real existing networks.

The differences between networks are caused by the features of the hardware and software used, the different interpretation of the recommendations by the developers, the difference in the requirements for the system on the part of the tasks being solved (requirements for information security, exchange rate, data transmission error-free, etc.) and other reasons. LAN networking software often sees a reduction in the number of layers implemented.

More intensive exchange of information occurs in local networks than in global ones. In a LAN, in essence, the management of hardware and software resources of all computers included in the network is organized. The network software implements these functions. In the global network, the main type of interaction between independent computers is the exchange of messages.

This section deals with the organization of distributed computing in a LAN environment. The issues of building and functioning of global networks on the example of the Internet are presented in the next section.

LAN hardware

The main hardware components of a LAN are:

• workstations;
• servers;
• interface boards;
• cables.

Workstations (PC) are, as a rule, personal computers, which are the workstations of network users.

The requirements for the composition of the PC are determined by the characteristics of the tasks solved in the network, the principles of the organization of the computing process, the OS used, and some other factors. So, if the network uses the MS Windows for Workgroups operating system, then the PC processor must be at least 80386 or 80486.

Sometimes a PC directly connected to a network cable may not have magnetic disk drives. Such PCs are called diskless workstations. However, in this case, in order to boot an operating system from a file server to a PC, it is necessary to have a remote boot chip in the network adapter of this station. The latter is supplied separately, is much cheaper than drives and is used as an extension of the basic BIOS input / output system. The microchip contains a program for loading the OS into the PC's RAM. Main advantage diskless PC is a low cost, as well as high security against unauthorized entry into the user system and computer viruses. Flaw Diskless PC is the inability to work offline (without connecting to the server), as well as to have their own archives of data and programs.

Servers in the LAN perform the functions of distributing network resources. Usually, its functions are assigned to a sufficiently powerful PC, mini-computer, main computer or a special server computer. One network can have one or more servers. Each of the servers can be separate or combined with a PC. In the latter case, not all, but only a part of the server's resources is publicly available.

If there are several servers on the LAN, each of them controls the operation of the PCs connected to it. The collection of server computers and related PCs is often referred to as domain. Sometimes there are multiple servers in the same domain. Typically, one of them is the main one, while the others act as a backup (in case the main server fails) or a logical extension of the main server.

The most important parameters that should be considered when choosing a server computer are the type of processor, the amount of RAM, the type and amount hard drive and disk controller type. The values ​​of these characteristics, as well as in the case of a PC, essentially depend on the tasks being solved, the organization of computations in the network, the network load, the operating system used, and other factors.

So, minimum requirements The processor and memory requirements of the Novell NetWare 2.2 and Novell NetWare Lite simple network operating systems are the 80286 processor with 4 MB of memory. If it is supposed to use Novell NetWare 386 or MS Windows for Workgroups, then it is desirable to have a processor no lower than 80386 with 8 or more MB of RAM.

RAM in the server is used not only for the actual execution of programs, but also for placing disk I/O buffers in it. By determining the optimal number and size of buffers, you can significantly speed up the execution of I / O operations.

For a server with more than 16 MB of RAM, it is advisable to use a 32-bit disk controller. Otherwise, there may be difficulties with the 16-bit DMA (Direct Memory Access) channel of direct memory access.

The drive you select should be large enough to accommodate the required software (especially for diskless PCs) as well as shared files and databases.

PCs and servers in the network location are connected to each other via data lines, in the role of which cables most often act. Connecting computers to the cable is carried out using interface boards - network adapters.-

Recently there have been wireless network, the data transmission medium in which is a radio channel. In such networks, computers are installed at short distances from each other: within one or several neighboring rooms.

The network adapters used have three main characteristics: tire type the computer to which they are connected (ISA, EISA, Micro Channel, etc.), bit depth (8, 16, 32.64) and topology formed network (Ethernet, Arcnet, Token-Ring). So, for networks with Ethernet topology and network operating systems Novell NetWare or MS Windows for Workgroups, it is best to use Novell network adapters: NE1000 (8 bit), NE2000 (16 bit) or NE3200 (32 bit).

If the file server is a computer with a memory of at least 16 MB, then it is better to use a 32-bit network adapter and a disk controller for it.

The choice of a network cable (it can be thin and thick) is determined by the specification given in the documentation for the network adapter. It is better to use an imported cable. For Ethernet networks based on a thin cable of short length, domestic cable RK-50 can also be used.

TOadditional LAN equipment refer sources uninterruptible power supply, modems, transceivers, repeaters, as well as various connectors (connectors, terminators).

Uninterruptible power supplies (UPS) are used to increase the stability of the network and ensure the safety of data on the server. In the event of a power failure, the UPS connected to the server through a special adapter will give a signal to the server, providing a stable voltage for some time. On this signal, the server performs a shutdown procedure that prevents data loss. The main criterion for choosing a UPS is the power, which must be no less than the power consumed by the server connected to the UPS.

transceiver - this is a device for connecting a PC to a thick coaxial cable. Repeater designed to connect network segments. Connectors (connectors) needed to connect network adapters computers with a thin cable, as well as for connecting cables to each other. Terminators are used for connecting to open network cables, as well as for grounding (the so-called grounding terminators).

Modem used as a device for connecting a LAN or a separate computer to a global network through telephone connection. For more details on the functioning and use of the modem, see section 29.

Structural and functional organization of the LAN

LAN topology

Network connection configuration (topology) largely determines the most important characteristics network, such as its reliability, performance, cost, security, etc.

One of the approaches to the classification of LAN topologies is to distinguish two main classes of topologies: broadcast Andconsecutive.

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

IN successive configurations, each physical sublayer transmits information to only one personal computer. Examples of sequential configurations are: arbitrary (arbitrary connection of computers), hierarchical, "ring", "chain", "star with an intelligent center", "snowflake" and others.

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

When star topologies each computer is connected via a special network adapter with a separate cable to the central node (Fig. 28.1). The central node is either a passive connector or an active repeater.

Fig.28.1. Star topology

The disadvantage of such a topology is low reliability, since the failure of the central node leads to a shutdown of the entire network, as well as usually a large length of cables (this depends on the actual placement of computers). Sometimes, to increase reliability, a special relay is installed in the central node, which allows you to turn off failed cable beams.

Topology "common bus" involves the use of one cable to which all computers are connected. Information on it is transmitted by computers in turn (Fig. 28.2).

Fig.28.2. Topology "common bus"

The advantage of such a topology is, as a rule, a shorter cable length, as well as higher reliability than that of a "star", since the failure of an individual station does not disrupt the network as a whole. The disadvantages are that a break in the main cable leads to the inoperability of the entire network, as well as the weak security of information in the system at the physical level, since messages sent from one computer to another, in principle, can be received on any other computer.

At ring topology data is transmitted from one computer to another in a relay race (Fig. 28.3). If a computer receives data that is not intended for it, it passes it along the ring. The recipient does not transfer the data intended for him anywhere.

Fig.28.3. Topology "ring"

The advantage of a ring topology is that the system is more reliable in case of cable breaks than in the case of a common bus topology, since there are two access paths to each computer. The disadvantages of the topology include a large length of the cable, low performance compared to the "star" (but commensurate with the "common bus"), as well as poor information security, as in the topology with a common bus.

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

Management principles

There are two main principles of management in local networks: centralization and decentralization.

In networks with centralized management data exchange management functions are assigned to file servers. Files stored on the server are available on the PC network. One PC has no access to the files of another PC. True, the exchange of files between PCs can also occur bypassing the main paths, for example, using the NetLink program. After running this program on two computers, you can transfer files between them in the same way as copying using Norton Commander.

There are many network operating systems that implement centralized management. Among them are Microsoft Windows NT Server, Novell NetWare (versions 3.X and 4.X), Microsoft Lan Manager, OS/2 Warp Server Advanced, VINES 6.0 and others.

The advantage of centralized networks is the high security of network resources from unauthorized access, ease of network administration, the ability to create networks with a large number of nodes. The main drawback is the vulnerability of the system in case of a file server failure (this can be overcome by having several servers or taking some other measures), as well as rather high demands on server resources.

decentralized (peer-to-peer) networks do not contain dedicated servers. The network management functions in them are alternately transferred from one PC to another. The resources of one PC (disks, printers, and other devices) are made available to other PCs.

The most common software products that allow you to build peer-to-peer networks are following programs and packages: Novell NetWare Lite, Windows for Workgroups, Artisoft LANtastic, LANsmart, Invisible Software NET-30 and others. All of them can run under DOS. For peer-to-peer networking, Windows 95 and Windows NT can also be used.

Deploying a peer-to-peer network for a small number of PCs often results in a more efficient and robust distributed computing environment. network software in them is simpler than in centralized networks. It does not require the installation of a file server (both a computer and related programs), which significantly reduces the cost of the system. However, such networks are weaker in terms of information security and administration.

Access Methods and Communication Protocols

To organize the exchange between LAN computers, standard protocols developed by the International Institute of Electrical and Electronics Engineers IEEE (Institute of Electrical and Electronic Engineers) are most often used.

Let us briefly consider the exchange protocols set forth in the IEEE802.3, IEEE802.4 and IEEE802.5 standards for local networks, which describe, respectively, the access methods to network data channels: Ethernet, Arcnet and Token Ring. These access methods implement the link layer functions of the OSI model. The name of the method used in the LAN is often identified with the type of network topology.

Ethernet access method. Developed by Xerox. Provides high transmission speed and reliability. Supports shared bus topology. The ownership of a message transmitted over the public bus is determined by the source and destination addresses included in the header.

This method is Carier Sense Multiple Access with Collision Detection (CSMA/CD).

The essence of the method is that the PC starts transmission if the channel is free, otherwise the transmission of messages is delayed for some time (each station has its own). Possible cases of simultaneous data transfer are recognized automatically by the hardware.

Network speed is noticeably reduced when 80-100 PCs are running at the same time. This is due to delays associated with channel conflicts.

Arcnet access method. Developed by Datapoint Corp. Used in star topology.

Messages from one PC to another via this access method are transmitted using marker, which is created on one of the PC. If the PC wants to send a message, then it waits for the token to arrive and attaches its own message to it, provided with the sender and recipient addresses. If the PC is waiting to receive, then it waits for the arrival of the token, and upon its arrival, it analyzes the header of the message attached to it. If the message is intended for this PC, then it detaches it from the marker, and also attaches a new one, if any.

Equipment for networks such as Arcnet is cheaper than Ethernet and Token Ring, but inferior to them in terms of reliability and performance.

Token Ring access method. Developed by IBM for ring topology. In addition to IBM, network equipment suppliers with this access method are Proteon, 3Com and Undermann-Bass, and network software suppliers are 3Com, Novell and Univation. This method is similar to the Arcnet method. The main difference is that there is a priority mechanism whereby individual PCs can get the token faster than others and hold onto it for longer.

To use typical programs on a LAN, it is important to know which messaging (packet) protocol is supported on the network. There are several such protocols. Among them, the following are widely used: IPX, SPX and NETBIOS

IPX (Internetwork Packet Exchange) is a transport layer protocol of the OSI model. It has an interface with the underlying network layer. The SPX protocol (Sequenced Packet Exchange) is a protocol of a higher session layer. It is based on the use of the IPX protocol. NETBIOS (Network Basic Input/Output System) is a network basic input/output system developed by IBM. Implements the functions of the network, transport and session layers of the OSI model.

Client-server technology

The "client-server" technology has replaced the centralized scheme for managing the computing process based on a medium or large computer (mainframe).

INcentralized scheme management, all computing resources, data and programs for their processing were concentrated in one computer. Users had access to machine resources using terminals (displays). The terminals were connected to the computer through interface connections or remote telephone communication lines (the so-called remote terminals). The main function of the terminal was to display information presented to the user. The advantages of this scheme include ease of administration, software modification and information protection. The disadvantage of the scheme is its low reliability (computer failure entails the destruction of the computing process), the difficulty of scaling (increasing power) modification of hardware and software, as a rule, a sharp decrease in efficiency with an increase in the number of users of the system, and others.

In architecture "client-server" the place of the terminal was taken by a PC (client), and the mainframe - by one or more powerful computers specially allocated for solving common problems of information processing (server computers). The advantage of this model is the high survivability and reliability of the computing system, ease of scaling, the possibility of simultaneous user work with several applications, high efficiency of information processing, providing the user with a high-quality interface, etc.

Note that this very promising and far from exhausted technology has been further developed. More recently, we have been talking about technology. intranet, which appeared as a result of the transfer of the ideas of the Internet (see Section 29) to the environment of corporate systems. Unlike client-server technology, this technology is focused not on data, but on information in its final form ready for consumption. Intranet technology combines the advantages of the two previous schemes. Computing systems built on its basis include central information servers and distributed components for presenting information to the end user (navigator programs or browsers). A detailed discussion of this technology is beyond the scope of this manual.

Let us dwell briefly on the concepts associated with the "client-server" technology, since it still dominates local area networks.

In the interaction of any two objects in the network, it is always possible to single out a party that provides a certain resource (service, service), and a party that consumes this resource. The resource consumer is traditionally called client, and the supplier server.

A resource can be considered a hardware component (disk, printer, modem, scanner, etc.), a program, a file, a message, information, or even the computer as a whole. Hence the origin of many terms: file server or disk server, print server or print server, message server, SQL server (database query processing program formulated in SQL), server computer, etc. Obviously, these servers have corresponding clients.

From the point of view of software, the "client-server" technology implies the presence of client programs and server programs. Client programs are typically programs such as word processors and spreadsheets. Most often, database management systems act as server programs. An example of a typical pair of programs of the "client-server" type is the TCKCTOBOI program on the processor, which processes a document that contains a table with information from a database.

A certain program running on the network can act as a client for some programs and at the same time be a server for other programs. Moreover, over a certain period of time, the roles of the client and server between the same programs can change.

A variety of more complex client-server models is three-link model"application server" - AS-model(Application Server). This model describes the process of functioning of networks using databases. According to the AS-model, each of the three main functions (data management, application processing and presentation of information to the end user) is implemented on a separate computer.

LAN software

The concept of a network operating system

LAN software as a set of computers can be divided into system software and application software. SystemicBY, used in a LAN, it implements two main functions: managing the resources of each individual computer (memory, I / O devices, printer, disks, etc.) and managing network-shared resources ( network printer, network scanner, shared drives, messages, etc.). Application software network includes end-user application packages.

Systemic software, managing processes in the LAN, united by a common architecture, communication protocols and mechanisms for the interaction of computing processes, are called network OS.

A network OS can be organized in two ways: as a combination of a conventional non-network OS (such as MS DOS, Unix, OS / 2) and some auxiliary network package, or as an independent network OS itself. Network packages, as well as independent network operating systems, will be referred to as network operating systems in the narrow sense, or simply network operating systems (NOS).

The structure and composition of SOS installed on LAN computers depend on the type of control in the network.

So, in peer-to-peer networks workstations contain functionally equal components, such as, for example, Windows for Workgroups. The main part of these components are communication programs that implement communication protocols.

In networks with centralized control SOS programs installed on servers and workstations differ significantly. For such networks, it is often said that the NOS consists of two main components: the NOS of the server and the NOS of the workstation (client). The communication functions between these components, as well as in peer-to-peer networks, are performed by the corresponding communication programs.

Main task SOS server is the management of shared LAN network resources. Programs workstation SOS, mainly ensure the normal functioning of client programs. The interaction between programs that provide server resources (server programs) and programs running on a PC (client programs) in modern LANs is usually based on the "client-server" technology, which is described below. In a LAN, programs developed by different companies can act as a network operating system for a server and a PC. Popular systems tend to support co-operation with other known products.

Since there are currently many network operating systems for LAN users and administrators, the problem of choice is of interest.

Characteristics of network OS

There are many SOS, differing in their capabilities and operating conditions. The main parameters that are taken into account when comparing systems are the following:

• dependence of performance on the number of PCs;
• reliability of the network;
• level of service (volume and quality of services provided, the possibility of developing application programs in the network, operation management, ease of installation, configuration, prevention and other operations);

• protection of information from unauthorized access;
• consumption of resources by network means (the amount of RAM and disk memory, the required share of the performance of the computing system);
• the ability to use multiple servers in the network;
• types of supported network topologies, as well as the ability to change the composition of the network;
• list of supported network devices (network cards, printers, scanners, modems, etc.);
• availability of interfaces with other LANs and access to the Internet, etc.

Definitely leaning in favor of one or another SOS when choosing it is not easy. This is due to several reasons:

• the difference in the importance of certain indicators of the quality of SOS;
• features of the tasks being solved;
• hardware structure;
• cost;
• the constant appearance of new versions of the SOS, in which some parameters are improved compared to competing systems, etc.

In the case of a network that is geographically scattered, heterogeneous in terms of hardware and software, as well as with complex application programs, an environment based on several SOS may be necessary.

Let's take a look at the pros and cons of the following most widely used server NOSs: Microsoft Windows NT Server 3.51 (Microsoft), NetWare 4.1 (Novell), OS/2 Warp Server Advanced (IBM), and VINES 6.0 (Banyan Systems).

Microsoft Windows NT Server 3.51. Highly scalable, this system is a complete NOS that is equally suitable for small to medium sized, single and multi-server enterprise networks.

As part of the MS BackOffice application suite, the Microsoft Windows NT Server 3.51 operating system is closest to the idea of ​​an ideal modern network environment.

The main advantages of this system include the following:

• the presence of a unified graphical interface;
• simplicity and ease of use and administration;
• reliability of file and print services;
• advanced API (Application Program Interface) for application programming, which facilitates the process of developing application programs;
• the possibility of implementing single- and multi-processor (up to 32 processors) processing in one package;
• support for various processor architectures (CISC and RISC) and different hardware platforms (Intel, Alpha, MIPS, etc.).

Among the shortcomings, the following are usually noted:

• weak flexibility of the directory service (domain model) compared to similar services SOS NetWare 4.1 and Banyan VINES 6.0;
• the complexity of the security system in managing access within and between domains.

Netware 4.1. Still remains attractive to many users, especially those working in DOS. Stands out for the power of file and printer management services, as well as management capabilities in large networks.

The advantages of the system are:

• well-designed and powerful file and print services;
• availability of means of operational compression of information on disks;
• powerful administration tools for large multi-user, multi-server Novell networks;
• the ability to create networks with increased fault tolerance (NetWare SFTIII package);
• a large number of application programs developed by independent vendors;
• convenient hierarchical structure of the distributed directory. The disadvantages of the system include:
• system orientation to Intel processors;
• the need to purchase a separate NetWare SMP package for multiprocessing;
• lack of simple tools application development;
• Weak memory protection when running server applications, which makes it difficult to debug programs and can lead to a system crash during its operation.

OS/2 Warp Server Advanced. In this SOS, in addition to the basic network file and print services, the LAN Distance remote access program and a number of utilities are provided for performing basic system management functions, accounting for software and hardware, network Reserve copy and recovery. It better than others meets the requirements of small or medium networks.

The advantages of the system are the following:

• good system performance as an application server, such as DB2 DBMS (IBM), messaging and group work Lotus Notes (Lotus Development), IBM Internet Connection Server and others;
• good opportunities use of network drives and printers;
• powerful means of administrative management and control.

The main disadvantages of the system are the inability to provide symmetric multiprocessing and the lack of a full-fledged global directory service (here, a domain structure is used, as in Windows NT Server 3.51).

VINES 6.0. Of the four COSs compared here, VINES 6.0 has the most powerful directory service. This is its main advantage.

In addition, the advantages of VINES 6.0 include a good implementation of the file and print service, as well as the ability of the system to work in multiprocessor systems.

The disadvantages of the system are the following:

• limited app service capabilities (files cannot be larger than 2 GB; few pre-built apps have been developed);
• means of working with the Internet and remote access are limited;
• insufficiently convenient means of installation;
• limited set of equipment on which the system can operate.

Software technology "client-server"

For the successful application of the "client-server" technology, appropriate software must be used, including the client and server parts. In particular, the widely used Microsoft package Office is a suite of programs for the client computer. It consists of: word processor Word, spreadsheet Excel, preparation system PowerPoint presentations, the Access database management system, and the Outlook information management program.

Due to the success of the distribution of this package, Microsoft decided to put together a set of programs for the server - this is how the MS BackOffice package appeared.

This package includes the following components:

• Windows NT Server - network operating system;
• System Management Server - network administration system;
• SQL Server - database management server;
• SNA Server - server for connecting to host computers;
• Exchange Server- e-mail system server;
• Internet Information Server - a server for working with the Internet.

Windows-NT Server is capable of sharing files, printing devices, providing services for connecting to workstations ( client computers) and another service.

There are two flavors of Windows NT:

• Windows NT Workstation is designed to be used on offline computer,
• Windows NT Server is designed to be used as network operating system and can be used on a workstation to implement additional features.

Windows NT Server it is advisable to use in cases where several processors are expected (usually up to four). In addition, Windows NT Server provides sharing of resources among many users, the ability to connect to remote networks through the remote access service - RAS (Remote Access Service), as well as through means of communication with networks of other companies (Novell, Digital Pathworks and Apple).

System Management Server (SMS) allows network administrator centrally manage the entire network. This provides the ability to administer each computer connected to the network, including the software installed on it. SMS provides the following service:

• inventory management of software and hardware;
• automating the installation and distribution of software, including its updates;
• remote troubleshooting and giving full control to the administrator over the keyboard, mouse and screens of all computers on the network running MS-DOS or Windows;
• network application management.

SQL Server is a relational database management system that uses the principles of "client-server" technology. MS SQL Server supports transaction processing system, referential integrity preservation system, distributed transaction mechanism, data replication.

SNA Server provides the ability to communicate with IBM AS/400 and IBM mainframes (EC computers). This product allows multiple desktop PCs running MS-DOS, Windows, Windows NT, Macintosh, Unix, or OS/2 to "see" host computers.

Exchange Server provides a means of transmitting and receiving messages in the organization's information network. This service includes electronic mail (E-mail) and exchange of informational messages for working groups. Microsoft Exchange Server is built on the principles of "client-server" technology and scales in accordance with the increasing computing capacity of the network.

Internet Information Server provides the ability to create Web, FTP and Gopher servers for the Internet, supports their management using the built-in Internet programs service manager.

The local network - combining several computers located at a short distance from each other (usually within the same building) for the joint solution of information, computing, educational and other tasks. In a small local network there can be 10-20 computers, in a very large one - about 1000.

Purpose of local networks

 Sharing common hardware (printer drives, modems)

 Data exchange

 information system of the enterprise (institution)

Organization of local networks.

Although there are many different ways to connect computers, there are essentially two types of computer networks: peer-to-peer network and client-server network.

peer-to-peer network is an association of equal computers. Typically, a peer-to-peer network unites no more than 10 computers and is organized in homes or small offices.

Client server network more common in organizations such as a school, business, or library rather than in the home. In this type of network, one computer, called the server, is the heart of the network. It stores information and resources and makes them available to other computers on the network. Other computers that use the network to obtain this information are called clients.

Client-server networks are the best option for networking more than ten computers. They are more expensive, but in cases where you need to store a large amount of information, this is the best choice.

Models of various network configurations

Back to top

Topologies of local networks

Local networks depending on the purpose and technical may have different configurations. The general scheme of connecting computers in a local network is called the network topology. Network topologies can be different. Most often, local networks can have a "bus" and "star" topology. In the first case, all computers are connected to one common cable (bus), in the second case, there is a special central device (hub), from which "beams" go to each computer, i.e. each computer is connected to its own cable.

IN tire topology, computers are connected to a common channel (bus) through which they can exchange messages.

The bus-type structure is simpler and more economical, since it does not require an additional device and consumes less cable. But it is very sensitive to cable system failures. If the cable is damaged in at least one place, then there are problems for the entire network. The fault location is difficult to locate.

IN radial topology ("star" topology) in the center there is a concentrator that sequentially communicates with subscribers and connects them with each other.

In this sense, the "star" is more stable. A damaged cable is a problem for one particular computer; it does not affect the operation of the network as a whole. No troubleshooting required

IN annular topology information is transmitted over a closed channel. Each subscriber is directly connected to the two closest ones, although in principle it is able to contact any subscriber in the network.

In a network having a "ring" type structure, information is transmitted between stations along the ring with hopping in each network controller. Reception is carried out through buffer drives made on the basis of random access memory devices, therefore, if one network controller fails, the operation of the entire ring may be disrupted. The advantage of the ring structure is the ease of implementation of devices, and the disadvantage is low reliability.

hybrid a topology is a combination of different topologies in a single network. For example, you can connect multiple star networks with a single cable.

Back to top

LAN equipment

How do computers communicate with each other?

The operation of the network is based on the fact that all elements of the equipment are connected to each other in one way or another. Each computer and equipment such as printers, scanners, laptops are connected using a cable of various sizes, satellite communications or telephone lines. Today, there are even wireless networks that connect computers using radio waves.

LAN equipment generally includes:

 computers (servers and workstations);

 network boards (adapters);

 communication channels;

 special devices that support the functioning of the network (routers, hubs, switches).

Each computer connects to the network using a network card - adapter.

The network card is connected to the network cable. If radio or infrared communication is used, no cable is required. In modern local networks, two types are most often used. network cables:

 unshielded twisted pair;

 fiber optic cable.

Typically, the choice of a cable for a network depends on the following indicators: the cost of installation and maintenance, the data transfer rate, the limitation on the amount of information transfer distance without additional repeater amplifiers (repeaters), data transfer security.

twisted pair is a set of eight wires twisted in pairs in such a way as to provide protection against electromagnetic interference.

Twisted pair is the cheapest type of cable. Twisted pair allows a maximum transmission rate of up to 10 Mbps. The cable length should not exceed 1000 meters, and the data transfer rate will not exceed 1 Mbps. Shielded twisted-pair cables are used to increase noise immunity. Each twisted-pair cable connects only one computer to the network, so a connection failure affects only that computer, which allows you to quickly find and fix problems.

fiber optic cables transmit data in the form of light pulses along glass wires. Fiber optic cables provide the highest transmission speed; they are more reliable, as they are not subject to electromagnetic interference.

Optical cable is very thin and flexible, making it easier to transport than heavier copper cable. The data transfer rate over optical cable is hundreds of thousands of megabits per second, which is about a thousand times faster than over twisted pair wires.

An optical fiber line is the most expensive type of connection today, but the speed of information propagation in it reaches several gigabits per second with an allowable distance of up to 50 kilometers. At the same time, communication lines built on the use of optical fiber are practically insensitive to electromagnetic interference.

Where to "plug" the cable in the computer? You need an intermediate (interface) device, which is called a network card or network adapter, and in English speech NIC– Network Interface Controller.

Network adapter, or NIC, is an embedded device that allows you to connect your computer to a network. Each computer has software installed that allows it to communicate with other computers.

Wireless communication on radio waves can be used to organize networks within large premises where the use of conventional communication lines is difficult or impractical. In addition, wireless lines can connect remote parts of the local network at distances up to 25 km (subject to line of sight).

In addition to cables and network adapters, twisted-pair LANs use other network devices - hubs, switches, and routers.

concentrator(also called a hub) - a device that combines several (from 5 to 48) branches of a star-shaped local network and transmits information packets to all branches of the network in the same way.

Switch(switch) does the same, but, unlike the hub, ensures the transfer of packets to the specified branches. This provides optimization of data flows in the network and increased security against unauthorized intrusion.

router(router) - a device that transfers data between two networks, including between local and global networks. The router, in fact, is a specialized microcomputer, has its own processor, RAM and permanent memory, operating system.

Gateway: interface device that connects two different types of networks. It receives the information, translates it into the required format, and then forwards the translation to its destination.

Shared External Devices include external memory drives connected to the server, printers, plotters and other equipment that becomes available from workstations.

Back to top

Organization of data transfer in the network

A necessary condition for the operation of a single local area network is the use network operating system. Such OS ensure the sharing of not only network hardware resources (printers, drives, etc.), but also distributed collective technologies when performing a variety of jobs. The most widely used network operating systems NovellNetWare, linux And Windows.

Computers can communicate with each other because there are sets of rules, or protocols which help computers understand each other. Protocols are necessary for the communication process to proceed without errors. Protocols help define how information is sent and how it is received.

Control questions

What is a computer network?

Why are local computer networks created?

What is a server? Work station?

What types of lines (channels) are used to connect computers in local networks?

What are the topologies of local networks?

What are the characteristics of client-server technologies?

What technical and social problems are solved by means of global computer networks?

What is a global network? What is the Internet?

How about development computer technology Has the perception of computer literacy changed?

What is the difference between a host computer and a network user PC? Indicate the difference in the following positions: purpose, mode of operation, software.

What is an IP address and a domain address?

Compare different types of communication channels according to their properties: price and quality.

What is a modem used for?

How does the "client-server" technology manifest itself in the organization of the work of the Network?

Explain why the packet principle of information transfer improves the reliability of the Network?

What is the difference between TCP and IP protocols?

What is the main difference between hypertext documents and conventional documents?

What software do you need to have on your computer to be able to use the WWW service?

How can you visually determine whether graphic image hyperlink without clicking on it with the mouse?

Explain the difference between communication and information services on the Web.

Explain the difference between "basic Internet protocol" and "application protocols".

Why do email server and client use different protocols?

What is the difference between a chat conference and a teleconference?

What is the advantage of Internet telephony over traditional telephony?

What is the purpose of the FTP service?

What was the significance of the WWW service for the development of the Internet?

What is a Web server?

Which of the following site addresses cannot exist (does not comply with the rules for naming):

Back to top

Task 1: how a computer network works

1 . Create in the directory specified by the teacher folder With name SETI.

2 . Run the program Notebook and type in it the following information about yourself: last name, first name, school, class, date of birth, home address, home phone number.

4 . Make to the folder you created full access for all users.

5 . Using the network environment, go to one of the neighboring computers (as directed by the teacher) and make the SETI folder network drive.

6 . Copy file aboutN. txt to the created network drive.

7 . Copy file aboutN. txt to a folder SETI to all other computers without creating network drives).

8 . Disable network drive.

9 . Delete folder SETI from your computer (after the teacher's permission).

Back to top

Task number 2: establish a correspondence between concepts

Match each term with its definition. Each definition may be used more than once or not at all. Good luck!

A. The most famous and largest computer network in the world, connecting millions of computers into one huge network of networks.

B. Software that displays web pages, including text, graphics, and other multimedia content such as music.

C. Message sent over the Internet.

D. On a network, a client-server is a computer that stores all information and resources and makes them available to other computers on the network.

E. A set of special rules, or protocol, that governs the movement or copying of files from one computer to another.

F. A network in which a dedicated computer contains all information and resources, providing access to them to other computers located on the network.

G. A computer on a network connecting to a server to receive information.

H. A network that connects peer computers.

I. A networking conference on USENET organized for discussion and news sharing.

J. Hardware installed inside a computer that connects it to a network.

K. A set of rules that help computers "understand" each other.

L. A group of computers connected in some way so that people can exchange information and share equipment.

Back to top

Task 3: work with the mail program

1. Run mail program.

2. Create message, containing information about you (last name, first name, school, class, hobby) and any two questions for recipients.

3 . send a message at the addresses indicated by the teacher (at least five).

4. Get messages sent to you.

7 . Clear folders "Inbox" And "Sent"(with the permission of the teacher).

Back to top

Task 4: work with a free mail server

1. Login to the website http:// www. mail. en

2. Create on this mail server own email box and go into it.

3. Create message, containing information about you (last name, first name, school, class, hobby) and any two questions for recipients.

4 . send a message at three addresses of your classmates (as directed by the teacher).

5. Get messages sent to you.

8 . Clear folders "Inbox" And "Sent"(with the permission of the teacher).

Back to top

Task 5: practice test "Internet and the World Wide Web"

1. Go on the website http:// www. gismeteo. en and to know weather for the next three days in your locality.

2. Go to the website of the RTR channel http:// www. rutv. en and find TV program on current day.

3. Go on the website Kaspersky Labs / and find descriptions malware (their classification).

4. Go on the website Russian iron roads http:// www. rzd. en and find information about schedule And availability tickets for tomorrow on trains running on the route Novosibirsk-Moscow.

5. Go to newspaper website "From hand to hand" / your locality and find information about all sold cars FordFocus(any year of issue).

6 . Login to the server Novosibirsk State University http:// www. nsu. en and learn about admission conditions at the Faculty of Mechanics and Mathematics.

PREPARING FOR THE USE

The data transfer rate through an ADSL connection is 128000 bps. A 625 KB file is transmitted through this connection. Specify the file transfer time in seconds.

The universal resource locator looks like: /catalog2005/index.htm. Then the server name is:

 catalog2005/index.htm

Let the universal resource locator look like: /catalog2005/index.htm. Then the path to the file:

 catalog2005/index.htm

Petya wrote down the school server's IP address on a piece of paper and put it in his jacket pocket. Petya's mother accidentally washed the jacket along with the note. After washing, Petya found four scraps with fragments of the IP address in his pocket. These fragments are labeled A, B, C, and D. Restore the IP address. In your response, provide a sequence of letters representing the fragments, in the order corresponding to the IP address.

What type of servers are used to host websites?

 mail server

 WWW server

 FTP server

 HTTP Server

Which of these entries can be an email address?

The name of the mail server is old-horse, which is located in Russia. Name given mailbox ann. Please select a valid email address.

Purpose of local networks

Although the creation of local networks took on a massive character after the advent of personal computers, communication between computers over short distances existed long before that.

One of the first tasks that arose in the course of the development of computer technology, which required the creation of a network of at least two computers, was to ensure high reliability in real-time control of a critical process. So, when controlling the launch of a spacecraft, the failure of the control computer threatens with irreparable consequences. A redundant computer is used to increase the reliability of the control system. In the event of a failure in the operation of the active machine, the contents of its processor and OED are very quickly transferred to the second one, which picks up control.

Another example is joining big computers the second or third generations of numerous terminals - devices for input / output of data and programs. These terminals did practically no information processing, but they made it possible to divide the machine time of a powerful and expensive computer between different users. The corresponding mode of operation was called the time-sharing mode, since the computer sequentially solved the tasks of many users in time.

Shortly after the advent of personal computers in the early 1980s, they began to be connected on networks, which allowed the sharing of files, databases, and hardware resources (such as printers). Today, local area networks are systems that require complex technical and software maintenance.

Computer networks have given rise to new information processing technologies - network technologies that allow sharing hardware and software: high-capacity drives, printers, databases and data banks. It has become customary for employees of many institutions to use email to exchange messages and documents, to collaborate on projects. In schools and universities, local networks help to conduct lessons, organize access to educational resources, libraries, etc. At enterprises, local networks are used to create automated systems enterprise and technological process management.

Information systems built on the basis of local area networks provide the solution of the following tasks:

o data storage;

o data processing;

o organization of user access to data;

o transfer of data and results of their processing to users.

LAN Hardware

LAN equipment generally includes:

• computers (servers and workstations);
• network cards;
• channels of connection;
• special devices that support the operation
• networks (routers, hubs, switches).

On the basis of the distribution of functions, local computer networks are divided into peer-to-peer and dual-rank (hierarchical networks or networks with a dedicated server).

In peer-to-peer Network computers are equal in relation to each other. Each user on the network decides for himself what resources of his computer he will provide for general use. Thus, the computer acts as both a client and a server. Peer-to-peer sharing of resources is quite acceptable for small offices with 5-10 users, combining them into a workgroup.

dual rank the network is organized on the basis of a server on which network users register.

For modern computer networks, a typical is a mixed network that combines workstations and servers, with some of the workstations forming peer-to-peer networks, and the other part belonging to dual-rank networks.

More advanced networks beyond end user computers - workstations , include special computers - servers. Server - this is a computer dedicated to the network that performs the functions of servicing workstations. Eat different types servers: file servers, database servers, etc. For example, a computer that performs the functions of a file server is used for only one purpose: to provide users with access to the hardware and software resources of the server, and not each other's computers, which improves the protection of personal data.

Each computer connects to the network using a network adapter card that supports a specific connection scheme. So, Ethernet adapters with a bandwidth of 10 or 100 Mbps are widespread. A network cable is connected to the network board. If radio or infrared communication is used, no cable is required.

In modern local networks, two types of network cables are most often used:

• unshielded twisted pair;
• fiber optic cable.

twisted pair is a set of eight wires twisted in pairs in such a way as to provide protection against electromagnetic interference. Each twisted pair connects only one computer to the network, so only that computer is affected by a connection failure, allowing for quick troubleshooting.

Fiber optic cablestransmit data in the form of light pulses along glass wires. Most LAN technologies now allow the use of fiber optic cables. Fiber optic cable has significant advantages over any copper cable options. Fiber optic cables provide the highest transmission speed; they are more reliable, as they are not subject to electromagnetic interference. Optical cable is very thin and flexible, making it easier to transport than heavier copper cable. The data transfer rate over optical cable is hundreds of thousands of megabits per second, which is about a thousand times faster than over twisted pair wires.

Wireless connectionon radio waves can be used to organize networks within large premises where the use of conventional communication lines is difficult or impractical. In addition, wireless lines can connect remote parts of the local network at distances up to 25 km (subject to line of sight).

Shared external devices include external memory drives connected to the server, printers, plotters and other equipment that becomes available from workstations.

In addition to cables and network adapters, twisted-pair LANs use other network devices - hubs, switches, and routers.

1. Repeater - a device that provides signal amplification and filtering without changing its information content. As you move along the communication lines, the signals fade. Repeaters are used to reduce the effect of attenuation. Moreover, the repeater not only copies or repeats the received signals, but also restores the characteristics of the signal: it amplifies the signal and reduces interference.

2. Bridge - a device that performs the functions of a repeater for those signals (messages) whose addresses satisfy pre-imposed restrictions. One of the problems of large networks is heavy network traffic (the flow of messages on the network). This problem can be solved in the following way. Computer network is divided into segments. The transfer of messages from segment to segment is carried out only purposefully, if the subscriber of one segment sends a message to the subscriber of another segment. A bridge is a device that restricts traffic across a network and prevents messages from passing from one network to another without being validated.

Bridges can be local or remote.

Local bridges connect networks located in a limited area within an already existing system.

Remote bridges connect geographically dispersed networks using communication channels and modems.

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

Internal bridges are usually located on the same computer and combine the function of the bridge with the function of the subscriber computer. The expansion of functions is carried out by installing an additional network board.

External bridges involve the use of a separate computer with special software.

3. Router is a device that connects networks of different types, but using the same operating system. This is, in fact, the same bridge, but with its own network address. Using the addressing capabilities of routers, hosts on a network can send messages destined for another network to the router. Routing tables are used to find the best route to any destination on the network. These tables can be static or dynamic.

4. Gateway - a special hardware and software complex designed to ensure compatibility between networks using different communication protocols. The gateway transforms the form of presentation and data formats when transferring them from one segment to another. The gateway performs its functions at a level above the network. It does not depend on the transmission medium used, but depends on the communication protocols used. Usually the gateway performs conversions between protocols.

Network topologies

Local networks, depending on the purpose and technical solutions, can have different configurations (topologies, architectures) shown in the figure.

In the roundabout topology information is transmitted over a closed channel. Each subscriber is directly connected to two nearest neighbors, although in principle it is able to communicate with any subscriber in the network. Ring . The nodes are connected in a network of a closed curve. The workstation sends information to a certain end address, having previously received a request from the ring. Data is transmitted in only one direction. Each node, among other things, implements the functions of a relay. He receives and transmits messages, and perceives only addressed to him. Using ring topology, you can connect a large number of nodes to the network, solving the problems of interference and signal attenuation using the network card of each node. Message forwarding is very efficient as most messages can be sent "on the road" over the cable system one after the other. It is very easy to make a ring request to all stations. The duration of information transfer increases in proportion to the number of workstations included in the computer network.

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

Connecting a new workstation requires a short-term shutdown of the network, since the ring must be open during installation. There is no limit on the extent of the computer network, since it is ultimately determined solely by the distance between two workstations.

In the radial topology ("star" topology) in the center there is a concentrator that sequentially communicates with subscribers and connects them with each other. Star . Network nodes are connected to the center by beams. All information is transmitted through the center, which makes it relatively easy to troubleshoot and add new nodes without interrupting the network. However, the cost of organizing communication channels is usually higher here than for a bus and a ring.

In the tire shop topology, computers are connected to a common channel (bus) through which they can exchange messages. Tire . A communication channel that connects nodes into a network forms a broken line - a bus. Any node can receive information at any time, and transmit only when the bus is free. Data (signals) are transmitted by the computer to the bus. Each computer checks them, determining to whom the information is addressed, and accepts the data if they are sent to it, or ignores it.

In a tree topology implemented hierarchical subordination of computers. Computing networks withtree structureare used where it is impossible to directly apply the basic network structures in their pure form. To connect a large number of workstations, according to adapter cards, network amplifiers and / or switches are used. A switch that simultaneously has the functions of an amplifier is called an active hub.

In practice, two varieties are used, providing the connection of eight or sixteen lines, respectively.

A device to which a maximum of three stations can be connected is called a passive hub. A passive hub is usually used as a splitter. It doesn't need an amplifier. The prerequisite for connecting a passive hub is that the maximum possible distance to the workstation must not exceed several tens of meters.

New technologies offer passive plug boxes through which workstations can be turned off and/or turned on while the computer network is running.

Due to the fact that workstations can be turned on without interrupting the network processes and communication environment, it is very easy to listen to information, i.e. branch information from the communication medium.

In a LAN with a direct (not modulated) transmission of information, there can always be only one station that transmits information. To prevent collisions, in most cases, a temporary separation method is used, according to which for each connected workstation, at certain points in time, the exclusive right to use the data transmission channel is granted. Therefore, the requirements for the bandwidth of a computer network with increased load are reduced, for example, when new workstations are introduced. Workstations are connected to the bus by means of TAP (Terminal Access Point) devices. TAP is a special type of connection to coaxial cable. The needle-shaped probe is introduced through the outer shell of the outer conductor and the dielectric layer to the inner conductor and is attached to it.

In a broadband modulated LAN, different workstations receive, as needed, the frequency at which these workstations can send and receive information. The transmitted data is modulated on the respective carrier frequencies, i.e. between the information transmission medium and the workstations there are respectively modems for modulation and demodulation. The technology of broadband communications allows you to simultaneously transport a fairly large amount of information in a communication medium. For the further development of discrete data transportation, it does not matter what initial information is fed into the modem (analogue or digital), since it will be converted in the future anyway.

Characteristics of topologies of computer networks are given in the table.

Characteristics	Topology
	Star	Ring	Tire
Expansion cost	Minor	Medium	Medium
Joining subscribers	passive	Active	passive
Failure protection	Minor	Minor	high
Characteristics	Topology
	Star	Ring	Tire
System dimensions	Any	Any	Limited
eavesdropping protection	Good	Good	Minor
Connection cost	Minor	Minor	high
System behavior under high loads	Good	Satisfactory	bad
Ability to work in real time	Very good	Good	bad
Cable routing	Good	Satisfactory	Good
Service	Very good	Average	Average

Organization of data transfer in the network

A necessary condition for the operation of a single local area network is the use of a network operating system. Such operating systems ensure the sharing of not only network hardware resources (printers, drives, etc.), but also distributed collective technologies when performing a variety of jobs. The most widely used network operating systems are Novell, NetWare, Linux and Windows.

Information in networks is transmitted in separate portions - packets, and the length of these packets is strictly limited (usually a few kilobytes). This method of transmission is due to the fact that the local network must provide high-quality communication for all computers on the network within a reasonable access time - the time the user waits for the start of communication. Naturally, it should not be too large. Since networks of the most common non-coin configurations have several transfers simultaneously to avoid mixing of information, without dividing the transmitted data into packets, some users could actually be cut off from the network. Thus, the process of information exchange in the network is the circulation of packets, each of which contains data (or part of the data) transmitted from subscriber to subscriber.

As mentioned above, networks have given rise to new (network) information processing technologies. A common way to organize information processing in a network is called technology "client-server". It assumes a deep separation of the functions of computers in the network. At the same time, the functions of the client (workstation) include:

• providing a user interface focused on the needs of the user;
• formation of requests to the server, and not necessarily with informing the user about it; ideally, the user does not delve into the technology of communication between his computer and the server at all;
• analysis of server responses to requests and their presentation to the user.

The main function of the server is to perform specific actions at the request of the client (for example, solving a complex mathematical problem, searching for data in a database, connecting a client to another client, etc.). slide 2

A local area network is an association of several computers located at a short distance from each other (usually within the same building) for the joint solution of information, computing, educational and other tasks. In a small local network there can be 10-20 computers, in a very large one - about 1000.

LAN hardware computers (servers and workstations); network cards; channels of connection; special devices that support the functioning of the network (routers, hubs, switches).

Server and workstations More developed networks, in addition to computers of end users - workstations, include special computers - servers. A server is a computer dedicated to the network that performs the functions of servicing workstations. There are different types of servers: file servers, database servers, etc. For example, a computer that acts as a file server is used for only one purpose: to provide users with access to the hardware and software resources of the server, and not to each other's computers, which improves protection personal data.

Network card Each computer connects to the network using a network adapter card that supports a specific connection scheme. So, Ethernet adapters with a bandwidth of 10 or 100 Mbps are widespread. A network cable is connected to the network board. If radio or infrared communication is used, no cable is required.

Types of network cables unshielded twisted pair; fiber optic cable.

Twisted Pair A twisted pair is a set of eight wires twisted in pairs to provide protection against electromagnetic interference. Each twisted pair connects only one computer to the network, so only that computer is affected by a connection failure, allowing for quick troubleshooting.

Fiber optic cables transmit data in the form of pulses of light along glass wires. Fiber optic cable has significant advantages over any copper cable options. Fiber optic cables provide the highest transmission speed; they are more reliable, as they are not subject to electromagnetic interference. Optical cable is very thin and flexible, making it easier to transport than heavier copper cable. The data transfer rate over optical cable is hundreds of thousands of megabits per second, which is about a thousand times faster than over twisted pair wires. fiber optic cable

Wireless communication on radio waves can be used to organize networks within large premises where the use of conventional communication lines is difficult or impractical. In addition, wireless lines can connect remote parts of the local network at distances up to 25 km (subject to line of sight).

Shared external devices include external storage drives attached to the server, printers, plotters, and other equipment that is made available from workstations. In addition to cables and network adapters, twisted-pair LANs use other network devices - hubs, switches, and routers.

A concentrator (h ub) also called a hub is a device that combines several (from 5 to 48) branches of a star-shaped local network and transmits information packets to all branches of the network in the same way.

The switch (switch) does the same thing, but, unlike the hub, ensures the transmission of packets to the specified branches. This provides optimization of data flows in the network and increased security against unauthorized intrusion.

Router (router) - a device that transfers data between two networks, including between local and global networks. The router, in fact, is a specialized microcomputer, has its own processor, RAM and permanent memory, operating system.

Network topologies Depending on the purpose and technical solutions, local networks can have different configurations (topologies, architectures),

Ring In a ring topology, information is transmitted over a closed channel. Each subscriber is directly connected to two nearest neighbors, although in principle it is able to communicate with any subscriber in the network.

Radial (star) In a radial (star) topology, there is a hub in the center that communicates with subscribers in series and connects them to each other.

Bus In a bus topology, computers are connected to a common channel (bus) through which they can exchange messages.

Tree-like The tree-like topology implements a hierarchical subordination of computers.

Client-server technology. A common way to organize information processing in a network is called "client-server" technology. It assumes a deep separation of the functions of computers in the network. At the same time, the functions of the client (workstation) include: providing a user interface focused on the needs of the user; formation of requests to the server, and not necessarily with informing the user about it; ideally, the user does not delve into the technology of communication between his computer and the server at all;

Thank you for your attention!