As a result of even a superficial examination of the work on the network, it is clear that computer network is a complex set of interconnected and coordinated software and hardware components. Studying the network as a whole involves studying the operating principles of its individual elements, among which are:
1) computers;
2) communication equipment;
3) operating systems;
4) network applications.
All network hardware and software can be described by a multilayer model. The first is the hardware layer of standardized computer platforms. Currently, computers of various classes are widely and successfully used in networks - from PCs to mainframes and supercomputers. The set of computers on the network must be compared with the set of diverse tasks that the network solves.
The second layer represents the communications equipment. Although computers are the central elements of information processing in networks, communication devices are now playing a larger role, e.g. cable systems, repeaters, bridges, switches, routers and modular hubs. At present communication device may be a complex, specialized multiprocessor that must be configured, optimized, and administered. To make changes to the operating principles of communications equipment, it is necessary to study the many protocols used in both local and wide area networks.
The third layer forming software platform network is an operating system. The type of concepts for managing local and distributed resources that form the basis of the network OS determines the efficiency of the entire network. When designing a network, you should consider how easily this system can interact with other operating systems on the network, how capable it is of ensuring the safety and security of data, and to what extent it allows you to increase the number of users.
The fourth, topmost layer of network tools includes various network applications, such as network databases, mail systems, data archiving tools, collaboration automation systems, etc. It is important to know the range of capabilities that applications provide for various application areas, as well as that they are compatible with other network applications and operating systems.
Types of local networks
In order to connect two PCs together, they are connected with a special null modem cable. This cable connect with the PC turned off, and for each connection method you should use a different type of cable.
If a direct PC connection is used, then there are two types of their interaction:
1) direct access, in which only the transfer of information from one computer to another is possible;
2) remote control, in which it is possible to execute a program located on another computer.
At direct access one of the computers is the master, and the second is the slave. The user controls the operation of interconnected computers from the host PC. It is important to carry out the following preparatory operations:
installation of software components Client, Protocol, Services;
installing the Microsoft network file and printer access service. The flag must be checked on the computer that provides the resources. Files of this computer can be made common;
providing access at the resource level;
definition as shared resources of the PC server participating in the exchange;
connection from a client computer to shared information resources.
All actions on the Direct Connection command are carried out by the Direct Connection Wizard using successive Direct Connection dialog windows. These windows indicate which computer is the slave and which is the master; port used for communication; the login password used.
In the last Direct Connection window, if the parameters are set correctly, you need to click on the Receive commands button on the master computer, and on the Control button on the slave computer. After this, the master PC can use the shared resources of the slave and the entire local network, if the slave PC is connected to the network.
At remote control the server is like a continuation of the client. The basic synchronization scheme includes the following steps:
1) combining desktop and laptop computers. The desktop computer must be the master computer, and the folders containing the necessary files must be shared;
2) copying files from a desktop computer to a portable one in the Portfolio folder;
3) disconnecting the laptop computer from the desktop one and further editing files in the Portfolio folder;
4) reconnecting the laptop computer with the desktop computer from which they were originally copied to the Briefcase folder source files. In this case, the laptop computer should be a slave, and the folders with source files on the desktop computer should be shared;
5) opening the Briefcase folder and executing the Briefcase/Update command. If the source files have remained unchanged over the past period, all changed files in the Portfolio folder will be automatically copied in place of the original ones. For files modified on a desktop PC, a warning will be issued, after which you must select any of the following actions:
update on laptop;
update on desktop PC;
canceling any update.
Using the Portfolio/Update command, you can synchronize not all objects, but only a group of files marked in the folder.
Topic 6
Internet networks
The emergence of the Internet
In 1962, D. Licklider, the first director of the Experimental Network computer research project whose goal was to transmit packets to the Defense Advanced Research Projects Agency (DARPA), published a series of notes discussing the concept of a “galactic networks" (Galactic Network). It was based on the assertion that in the near future a global network of interconnected computers would be developed, allowing each user to quickly access data and programs located on any computer. This idea was the beginning of the development of the Internet.
In 1966, at DARPA, L. Roberts began working on the concept of a computer network, and the ARPANET plan soon appeared. At the same time, the main protocols for data transmission on the network - TCP / IP - were created. Many public and private organizations wanted to use the ARPANET network for daily data transfer. Because of this, ARPANET transitioned from an experimental network to a working network in 1975.
In 1983, the first standard for the TCP/IP protocols was developed and officially implemented, which was included in the Military Standards (MIL STD). In order to facilitate the transition to new standards, DARPA put forward a proposal to the company's managers Berkley Software Design on the implementation of TCP/IP protocols in Berkeley (BSD) UNIX. After some time, the TCP/IP protocol was reworked into a common (public) standard, and the term “Internet” began to be used. At the same time, MILNET was separated from ARPANET, after which MILNET became part of the Defense Data Network (DDN) of the US Department of Defense. After this, the term "Internet" began to be used to refer unified network: MILNET plus ARPANET.
In 1991, the ARPANET network ceased to exist. But the Internet exists at the moment and is developing. Moreover, its dimensions are much larger than the original ones.
The history of the development of the Internet can be divided into five stages:
1) 1945–1960 – the emergence of theoretical works on interactive interaction between man and machine, as well as the first interactive devices and computers;
2) 1961–1970 – the beginning of the development of technical principles of packet switching, the introduction of ARPANET;
3) 1971–1980 – expansion of the number of ARPANET nodes to several dozen, installation of special cable lines that connect some nodes, start of operation email;
4) 1981–1990 – implementation of the adoption of the TCP/IP protocol, division into ARPANET and MILNET, introduction of the “domain” name system – Domain Name System (DNS);
5) 1991–2007 – the latest stage in the development of the history of the global Internet.
Internet capabilities
The Internet is a global computer network that covers the whole world and contains a huge amount of information on any topic, available on a commercial basis to everyone. On the Internet, in addition to receiving information services, you can make purchases and commercial transactions, pay bills, order tickets for various types of transport, make hotel reservations, etc.
Any local network is knot, or website. The legal entity that ensures the operation of the site is called provider. The site includes several computers – servers, used to store information of a certain type and in a certain format. Each site and server on the site are assigned unique names with which they are identified on the Internet.
To connect to the Internet, the user must enter into a service contract with any of the existing providers in his region. To start working on the network, you need to connect to the provider’s website. Communication with the provider is carried out either via a dial-up telephone channel using a modem, or using a permanent dedicated channel. When connecting to a provider via a dial-up telephone line, communication is carried out using a modem and means remote access. If the connection with the provider is made through a permanent dedicated channel, then a simple call to the appropriate program for working on the Internet is used. The opportunities available to the user are determined by the terms of the contract concluded with the provider.
By using keywords throughout the Internet, each information system has its own search tools necessary information. The network includes the following information systems:
1) World Wide Web(WWW) – World Wide Web of Information. Information in this system consists of pages (documents). Using WWW you can watch movies, listen to music, play computer games, contact various information sources;
2) FTR system ( File Transfer program). It is used to transfer files that are available for work only after copying to own computer user;
3) electronic mail (E-mail). Each subscriber has his own email address With " by mailbox" It is somewhat analogous to a postal address. Using email, the user is able to send and receive text messages and binary files of any kind;
4) news (teleconference system – Use Net Newsgroups). This service consists of a collection of documents grouped according to specific topics;
5) IRC and ICQ. Using these systems, information is exchanged in real time. These functions are in Windows system are performed by the MS NetMeeting application, which allows you to create shared pictures and add text together with other users on remote workstations.
Internet search, management and control tools include:
WWW search systems – used to search for information organized in one of the above methods (WWW, FTR);
Telnet mode remote control any computer on the network used to run the necessary program on the server or any computer on the Internet;
official Ping program– allows you to check the quality of communication with the server;
Whois and Finger programs are used to find the coordinates of network users or determine the users currently working on a specific host.
Definition of a computer network
Lecture 7. Local and global networks COMPUTER.
Computing (computer) network– a complex system of software and hardware components interconnected with each other. The main functions of all types of computer networks are as follows:
1) provision sharing hardware and software network resources;
2) provision sharing to data resources.
Network hardware components include:
Computers (workstations and servers);
Communication equipment (cable systems, hubs, repeaters, routers, bridges, etc.).
Workstations- These are user computers connected to the network. According to availability local disk There are two types of workstations:
1) workstation with local disk – operating system boots from this disk,
2) diskless workstation - the operating system is loaded from the network server disk, and the boot program is stored in the network adapter chip.
There are three main ways to connect to the network:
Direct connection to the network cable system via a network adapter card (this is the most reliable and fastest method, but is used only for networks concentrated in a small area),
Connecting the station via a dedicated (non-switched) line,
Connecting the station via a dial-up (for example, telephone) line.
Network server – a network computer for providing certain services to network users. Based on the functions they perform, the following groups of servers are often distinguished:
File server– a computer with a large capacity disk space, used for storing, archiving data, coordinating data changes made by different users, and transferring data.
Database server– a network computer that performs the functions of storing, processing and managing database files with coordination of their sharing and restriction of user access.
Server backup data– a device for creating, storing and restoring copies of data existing on network computers.
Application Server – powerful computer, on which user applications are executed based on their requests.
Main elements communication equipment serve:
1) repeaters(splitters, HUB), amplifying or regenerating the signal received at it and relaying it to the inputs of other network segments. By connecting different network segments with many computers, repeaters simultaneously connect only two workstations;
2) switch(swich) – a device for combining network segments, but capable, unlike a repeater, of supporting simultaneous data exchange between several pairs of workstations from different segments;
3) router(router) – a device connecting networks of one or different types using one data exchange protocol. Analyzing the addresses of senders and recipients, routers send data along the optimally chosen route;
4) gateway(gateway) – a device for organizing data exchange between networks with different data exchange protocols.
TO software components include:
- network operating systems, designed to control work network of computers,
- network applications– software packages that expand the capabilities of network operating systems ( mail programs, teamwork systems, etc.).
Even as a result of a fairly superficial examination of networking, it becomes clear that a computer network is a complex set of interconnected and coordinated software and hardware components. Studying the network as a whole presupposes knowledge of the operating principles of its individual elements:
computers;
communication equipment;
operating systems;
network applications.
The entire network hardware and software complex can be described by a multilayer model. At the heart of any network is a hardware layer of standardized computer platforms. Currently, computers of various classes are widely and successfully used in networks - from personal computers to mainframes and supercomputers. The set of computers on the network must correspond to the variety of tasks solved by the network.
The second layer is communications equipment. Although computers are central to data processing in networks, communications devices have recently begun to play an equally important role. Cabling systems, repeaters, bridges, switches, routers and modular hubs have gone from being ancillary network components to being core components, along with computers and system software both in terms of impact on network performance and cost. Today, a communications device may be a complex, specialized multiprocessor that must be configured, optimized, and managed. Learning how communications equipment works requires familiarity with a large number of protocols used in both local and wide area networks.
The third layer that forms the network software platform is operating systems (OS). The efficiency of the entire network depends on which concepts for managing local and distributed resources form the basis of the network OS. When designing a network, it is important to consider how easily a given operating system can interact with other operating systems on the network, how secure and secure it is for data, the extent to which it allows you to increase the number of users, whether it can be transferred to a different type of computer, and many other considerations.
The topmost layer of networking tools are various network applications, such as network databases, mail systems, data archiving tools, collaboration automation systems, etc. It is very important to understand the range of capabilities provided by applications for different application areas, as well as to know how compatible they are with other network applications and operating systems.
The simplest case of interaction between two computers
In the simplest case, the interaction of computers can be realized using the same means that are used to interact a computer with peripherals, for example, through the RS-232C serial interface. In contrast to the interaction of a computer with a peripheral device, when a program usually works only on one side - the computer side - in this case there is interaction between two programs running on each computer.
A program running on one computer cannot gain direct access to the resources of another computer - its disks, files, printer. She can only “ask” the program running on the computer to which these resources belong. These "requests" are expressed as messages transmitted over communication channels between computers. Messages can contain not only commands to perform certain actions, but also actual information data (for example, the contents of a file).
Consider the case when a user working with text editor on personal computer A, you need to read part of some file located on the disk personal computer B (Fig. 4). Let's assume that we connected these computers via a communication cable through COM ports, which, as is known, implement the RS-232C interface (such a connection is often called a null modem). To be sure, let the computers run MS-DOS, although this is not of fundamental importance in this case.
Rice. 4. Interaction between two computers
The COM port driver together with the COM port controller work in approximately the same way as in the case of interaction between the control unit and the computer described above. However, in this case, the role of the PU control device is performed by the controller and driver of the COM port of another computer. Together they ensure the transfer of one byte of information over a cable between computers. (In “real” local networks, similar functions of transferring data to the communication line are performed by network adapters and their drivers.)
The driver of computer B periodically polls the reception completion sign, set by the controller when the data is transferred correctly, and when it appears, reads the received byte from the controller buffer into RAM, thereby making it available to programs on computer B. In some cases, the driver is called asynchronously, by interrupts from the controller.
Thus, the programs of computers A and B have at their disposal the means to transmit one byte of information. But the task considered in our example is much more complicated, since it is necessary to transfer not one byte, but a certain part of a given file. All additional problems associated with this must be solved by higher-level programs than COM port drivers. For definiteness, we will call such programs of computers A and B application A and application B, respectively. So, application A must generate a request message for application B. The request must specify the file name, the type of operation (in this case, reading), the offset and the size of the file area containing the required data.
To transmit this message to computer B, application A contacts the COM port driver, telling it the address in RAM, where the driver finds the message and then transmits it byte by byte to application B. Application B, having received the request, executes it, that is, reads it the required area of the file from the disk using local OS tools to the buffer area of its RAM, and then, using the COM port driver, transmits the read data via a communication channel to computer A, where it reaches application A.
The described functions of application A could be performed by the text editor program itself, but it is not very rational to include these functions in every application - text editors, graphic editors, database management systems and other applications that need access to files. It is much more profitable to create a special software module, which will perform the functions of generating request messages and receiving results for all applications on the computer. As mentioned earlier, such a service module is called a client. On the side of computer B, another module must be running - a server, constantly waiting for requests for remote access to files located on the disk of this computer. The server, having received a request from the network, accesses the local file and performs specified actions with it, possibly with the participation of the local OS.
The software client and server perform system functions for servicing requests from applications on computer A for remote access to files on computer B. In order for applications on computer B to be able to use files on computer A, the described scheme must be symmetrically supplemented with a client for computer B and a server for computer A.
The interaction diagram of the client and server with applications and the operating system is shown in Fig. 5. Despite the fact that we have considered a very simple hardware communication scheme for computers, the functions of programs that provide access to remote files are very similar to the functions of modules of a network operating system operating on a network with more complex hardware connections of computers.
Rice. 5. Interaction of software components when connecting two computers
Very convenient and useful function client program is the ability to distinguish a request to remote file from a request to a local file. If the client program can do this, then applications do not have to care about which file they are working with (local or remote), the client program itself recognizes and redirects request to a remote machine. Hence the name often used for the client part of a network OS - redirector. Sometimes recognition functions are separated into a separate software module; in this case, not the entire client part is called a redirector, but only this module.
Along with autonomous operation A significant increase in the efficiency of using computers can be achieved by combining them into computer networks.
A computer network in the broad sense of the word refers to any set of computers connected to each other by communication channels for data transmission.
There are a number of good reasons for connecting computers together in a network. First, resource sharing allows multiple computers or other devices to share access to a separate disk (file server), CD-ROM drive, tape drive, printers, plotters, scanners and other equipment, which reduces the cost of each individual user.
Secondly, in addition to sharing expensive peripheral devices, it is possible to similarly use network versions of application software. Thirdly, computer networks provide new forms of interaction between users in one team, for example, when working on a common project.
Fourthly, it becomes possible to use general funds connections between various application systems (communication services, data and video transmission, speech, etc.). Of particular importance is the organization of distributed data processing. In the case of centralized storage of information, the processes of ensuring its integrity, as well as backup, are significantly simplified.
2. Basic software and hardware components of the network
Computer network is a complex complex of interconnected and coordinated software and hardware components.
Studying the network as a whole presupposes knowledge of the operating principles of its individual elements:
Computers;
Communication equipment;
Operating systems;
Network applications.
The entire network hardware and software complex can be described by a multilayer model. At the heart of any network is a hardware layer of standardized computer platforms, i.e. the system of the end user of the network, which can be a computer or a terminal device (any input/output or information display device). Computers on network nodes are sometimes called host machines or simply hosts.
Currently, computers of various classes are widely and successfully used in networks - from personal computers to mainframes and supercomputers. The set of computers on the network must correspond to the variety of tasks solved by the network.
The second layer is communications equipment. Although computers are central to data processing in networks, communications devices have recently begun to play an equally important role.
Cabling systems, repeaters, bridges, switches, routers, and modular hubs have gone from being ancillary network components to becoming essential components, along with computers and system software, in both their impact on network performance and cost. Today, a communications device may be a complex, specialized multiprocessor that must be configured, optimized, and managed.
The third layer that forms the network software platform is operating systems (OS). The efficiency of the entire network depends on which concepts for managing local and distributed resources form the basis of the network OS.
When designing a network, it is important to consider how easily a given operating system can interact with other operating systems on the network, how secure and secure it is for data, the extent to which it can increase the number of users, whether it can be transferred to a different type of computer, and many other considerations.
The topmost layer of network tools are various network applications, such as network databases, mail systems, data archiving tools, teamwork automation systems, etc.
It is important to understand the range of capabilities that applications provide for different applications and how compatible they are with other network applications and operating systems.
Purpose and brief description main components of computer networks.
Computer network called a set of interconnected and distributed computers over a certain territory.
computer network– a computing complex that includes a geographically distributed system of computers and their terminals combined into a single system.
According to the degree of geographical distribution, computer networks are divided into local, city, corporate, global, etc.
The computer network consists of three components:
Data transmission networks, including data transmission channels and switching facilities;
Computers connected by a data network;
Network software.
computer network- this is a complex complex interconnected software and hardware components:
computers(host computers, network computers, workstations, servers) located in network nodes;
network operating system and application software, managing computers;
communication equipment– equipment and data transmission channels with accompanying peripheral devices; interface cards and devices (network cards, modems); routers and switching devices.
Software and hardware components of a computer network
Computer network- a spatially distributed system of software and hardware components connected by computer communication lines.
Among the hardware Computers and communications equipment can be distinguished. Software components consist of operating systems and network applications.
Currently, computers of various types and classes with different characteristics. This is the basis of any computer network. Computers and their characteristics determine the capabilities of a computer network. But recently, communication equipment (cable systems, repeaters, bridges, routers, etc.) has begun to play an equally important role. Some of these devices, given their complexity, cost and other characteristics, can be called computers that solve very specific tasks to ensure the operability of networks.
For efficient work networks are used special network operating systems (network OS), which, unlike personal operating systems, are designed to solve special problems of managing the operation of a network of computers. Network operating systems are installed on specially dedicated computers.
Network Applications- These are application software systems that expand the capabilities of network operating systems. Among them are email programs, group work systems, network databases, etc.
As network operating systems evolve, some network application functions become regular operating system functions.
All devices connected to the network can be divided into three functional groups:
1) workstations;
2) network servers;
3) communication nodes.
1) Workstation A workstation is a personal computer connected to a network on which a network user performs his or her work. Each workstation processes its own local files and uses its own operating system. But at the same time, network resources are available to the user.
There are three types of workstations:
Workstation with local disk,
Diskless workstation,
Remote workstation.
On a workstation with a disk (hard or floppy), the operating system boots from that local disk. For a diskless station, the operating system is loaded from the file server disk. This capability is provided by a special chip installed on the network adapter of the diskless station.
A remote workstation is a station that connects to a local network via telecommunications channels (for example, using a telephone network).
2) Network server, a network server is a computer connected to a network and providing certain services to network users, such as storing public data, printing jobs, processing a request to a DBMS, remote processing of jobs, etc.
Based on the functions they perform, the following groups of servers can be distinguished.
File server, file server - a computer that stores data of network users and provides user access to this data. Typically, this computer has a large amount of disk space. The file server allows users to access shared data simultaneously.
The file server performs the following functions:
Data storage;
Data archiving;
Data transfer.
Database server - a computer that performs the functions of storing, processing and managing database files (DB).
The database server performs the following functions:
Storing databases, maintaining their integrity, completeness, and relevance;
Receiving and processing queries to databases, as well as sending processing results to the workstation;
Coordination of data changes made by different users;
Support distributed databases data, interaction with other database servers located in another location.
Server application programs, application server - a computer that is used to run user applications.
Communication server, communications server - a device or computer that provides local network users transparent access to their serial ports input/output.
Using a communications server, you can create a shared modem by connecting it to one of the server's ports. The user, having connected to the communication server, can work with such a modem in the same way as if the modem was connected directly to the workstation.
An access server is a dedicated computer that allows remote processing of tasks. Programs initiated from a remote workstation are executed on this server.
Commands entered by the user from the keyboard are received from the remote workstation, and the results of the task are returned.
Fax server, fax server - a device or computer that sends and receives fax messages to local network users.
Data backup server, backup server - a device or computer that solves the problem of creating, storing and restoring copies of data located on file servers and workstations. One of the network file servers can be used as such a server.
It should be noted that all of the listed types of servers can operate on one computer dedicated for these purposes.
3) The communication nodes of the network include the following devices:
Repeaters;
Switches (bridges);
Routers;
The length of the network and the distance between stations are primarily determined by the physical characteristics of the transmission medium ( coaxial cable, twisted pair, etc.). When transmitting data in any environment, signal attenuation occurs, which leads to distance limitations. To overcome this limitation and expand the network, special devices are installed - repeaters, bridges and switches. The part of the network that does not include the expansion device is usually called a network segment.
Repeater, repeater - a device that amplifies or regenerates a signal received by it. The repeater, having received a packet from one segment, transmits it to all others. In this case, the repeater does not decouple the segments attached to it. At any given time, in all segments connected by the repeater, data exchange is supported only between two stations.
Switch, switch, bridge, bridge is a device that, like a repeater, allows you to combine several segments. Unlike a repeater, a bridge decouples the segments connected to it, that is, it simultaneously supports several data exchange processes for each pair of stations of different segments.
Router- a device that connects networks of the same or different types using the same data exchange protocol. The router analyzes the destination address and routes the data along the optimal route.
Gateway is a device that allows you to organize data exchange between different network objects using different data exchange protocols.
The main hardware components of the network are the following:
1. Subscriber systems: computers (workstations or clients and servers); printers; scanners, etc.
2. Network equipment: network adapters; concentrators (hubs); bridges; routers, etc.
3. Communication channels: cables; connectors; devices for transmitting and receiving data in wireless technologies.
The main software components of the network are the following:
1. Network operating systems, where the most famous of them are: MS Windows; LANtastic; NetWare; Unix; Linux, etc.
2. Network software(Network Services): network client; network card; protocol; remote access service.
LAN (Local Area Network) is a collection of computers, communication channels, network adapters running a network operating system and network software.
In a LAN, each PC is called a workstation, with the exception of one or more computers that are designed to serve as servers. Each workstation and server has network cards (adapters), which, through physical channels connect with each other. In addition to the local operating system, each workstation runs network software that allows the station to communicate with the file server.
The computers included in the LAN client-server architecture are divided into two types: workstations, or clients, intended for users, and servers, which, as a rule, are inaccessible to ordinary users and are designed to manage network resources.
Workstations
A workstation is a subscriber system specialized for solving certain tasks and using network resources. The workstation network software includes the following services:
Client for networks;
File and Printer Access Service;
Network protocols For of this type networks;
Remote access controller.
A workstation differs from a conventional stand-alone personal computer in the following ways:
Availability network card(network adapter) and communication channel;
Additional messages appear on the screen while the OS is loading, informing you that the network operating system is loading;
Before you begin, you must provide your network software with a username and password. This is called the network logon procedure;
After connecting to the LAN, additional network disk drives appear;
it becomes possible to use network equipment, which may be located far from the workplace.
Network adapters
To connect a PC to a network, you need an interface device called a network adapter, interface, module, or card. It fits into the slot motherboard. Network adapter cards are installed on each workstation and on the file server. The workstation sends a request through the network adapter to the file server and receives a response through the network adapter when the file server is ready.
Network adapters, together with network software, are capable of recognizing and handling errors that may occur due to electrical interference, collisions, or bad work equipment.
Various types network adapters differ not only in their methods of accessing the communication channel and protocols, but also in the following parameters:
Transfer speed;
Packet buffer size;
Tire type;
Bus performance;
Compatible with various microprocessors;
Using direct memory access (DMA);
Addressing I/O ports and interrupt requests;
connector design.
