|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
Lecture notes, cheat sheets
Computer science. Fundamentals of working in local and global computer networks (lecture notes)
Directory / Lecture notes, cheat sheets Table of contents (expand) Topic 5. Basics of working in local and global computer networks 5.1. The evolution of computer networks The concept of computer networks is a logical result of the evolution of computer technology. The first computers in the 1950s were large, bulky and expensive. Their main purpose was a small number of selected operations. These computers were not used for interactive user work, but were used in batch processing mode. Batch processing systems have typically been based on the mainframe, which is a powerful and reliable general-purpose computer. Users prepared punched cards containing data and program commands and transferred them to the computer center. The operators entered these cards into a computer and gave the results to the users the next day. At the same time, one incorrectly stuffed card could lead to at least a daily delay. For users, it would be much more convenient to have an interactive mode of operation, which implies the ability to quickly manage the data processing process from the terminal. However, at this stage, it was the batch mode that was the most efficient mode of using computing power, since it allowed more user tasks to be performed per unit of time than any other modes. At the forefront was the efficiency of the most expensive device of a computer, which was the processor, to the detriment of the efficiency of the specialists using it. In the early 1960s processor production costs have decreased and new ways of organizing the computing process have appeared that allow taking into account the interests of users. The development of interactive multi-terminal time-sharing systems began. In these systems, several users worked on the computer at once. Each of them received at the disposal of the terminal, which helped him to communicate with the computer. At the same time, the reaction time of the computing system was short enough so that the user did not notice the parallel work with the computer of other users. By dividing the computer in this way, users could enjoy the benefits of computerization for a relatively small fee. Terminals, when leaving the computer center, were dispersed throughout the enterprise. Although computing power remained completely centralized, many operations, such as data input and output, became distributed. These multi-terminal centralized systems outwardly became very similar to local area networks. In fact, each user perceived working at the mainframe terminal in much the same way as now working at a PC connected to the network. He had access to shared files and peripherals and was convinced that he was the sole owner of the computer. This was due to the fact that the user could run the program he needed at any time and get the result almost immediately. Thus, multi-terminal systems operating in the time-sharing mode were the first step towards the creation of local area networks. However, before the advent of local networks, it was still necessary to overcome a long way, since multi-terminal systems, although they had the external features of distributed systems, still retained the centralized nature of information processing, and the need for enterprises to create local networks by this point in time had not yet matured. This was explained by the fact that in one building there was simply nothing to network. The high cost of computing technology prevented businesses from purchasing multiple computers. During this period, the so-called Grosz's law was valid, empirically reflecting the level of technology of that time. According to this law, the performance of a computer was proportional to the square of its cost, therefore, for the same amount it was more profitable to buy one powerful machine than two less powerful ones, since their total power turned out to be much lower than the power of an expensive machine. However, the need to connect computers that were at a great distance from each other by this time was quite ripe. The development of computer networks began with solving a simpler problem - access to a computer from terminals many hundreds or even thousands of kilometers away from it. Terminals were connected to computers via telephone networks via modems. Such networks allowed numerous users to remotely access the shared resources of several powerful computers of the supercomputer class. After that, systems appeared in which, along with remote connections of the terminal-to-computer type, remote connections of the computer-to-computer type were also used. Computers were able to exchange data automatically, which is the basic mechanism of any computer network. Based on this mechanism, the first networks organized a file exchange service, synchronization of databases, e-mail and others, which have now become traditional network services. So, chronologically, global computer networks were the first to be developed and applied. It was during the construction of global networks that almost all the basic ideas and concepts of existing computer networks were proposed and worked out, for example, the multilevel construction of communication protocols, packet switching technology, and packet routing in composite networks. In the 1970s there was a technological breakthrough in the production of computer components, which resulted in the emergence of LSI. Their low cost and huge functionality made it possible to create mini-computers that became real competitors to mainframes. Grosz's law was no longer valid because ten minicomputers were able to perform some tasks much faster than one mainframe, and such a minicomputer system cost less. Small divisions of enterprises could now purchase computers for themselves. Minicomputers were able to perform the tasks of managing technological equipment, a warehouse, and solving other problems corresponding to the level of an enterprise division, i.e., the concept of distributing computer resources throughout an enterprise appeared, but at the same time, all computers of one organization continued to work independently. Over time, the needs of computer users increased, there was a need to be able to exchange data with other closely spaced computers. For this reason, businesses and organizations began to use the connection of their minicomputers and developed the software necessary for their interaction. As a result, this led to the emergence of the first local area networks. They were still significantly different from modern networks, in particular in the interface device. Initially, a wide variety of non-standard devices were used to connect computers to each other with their own methods of presenting data on communication lines, their own types of cables, etc. Such devices were able to connect only those types of computers for which they were designed. This situation gave rise to a great scope for creativity of students. The names of many course and diploma projects were dedicated to the interface device. In the 1980s the state of affairs in local networks began to change dramatically. Standard technologies for connecting computers to a network appeared - Ethernet, Arcnet, Token Ring. A strong impetus for their development was given by the PC. These mass products have become ideal elements for building networks. On the one hand, they were quite powerful and capable of working with network software, and on the other hand, they needed to combine their computing power to solve complex problems. Personal computers began to predominate in local networks, not only as client computers, but also as data storage and processing centers, i.e. network servers, while displacing minicomputers and mainframes from their usual roles. Conventional network technologies have turned the process of building a local network from an art into a chore. In order to create networks, it was enough to purchase network adapters of the appropriate standard, such as Ethernet, a standard cable, connect the adapters and cable with standard connectors, and install any of the available network operating systems, such as NetWare, on the computer. Now the network started to work, and connecting a new computer did not lead to problems. The connection occurred naturally if a network adapter of the same technology was installed on it. Local networks in comparison with the global ones have introduced a lot of new technologies for organizing the work of users. Access to shared resources became much more convenient, since the user could simply examine the lists of available resources, rather than remembering their identifiers or names. When connecting to a remote resource, it was possible to work with it using the commands already known to the user for working with local resources. The consequence and at the same time the driving force behind such progress was the emergence of a large number of non-professional users who did not need to learn special (and rather complex) commands for networking at all. Local network developers got the opportunity to use all these conveniences with the appearance of high-quality cable communication lines, with the help of which even first-generation network adapters could provide data transfer rates up to 10 Mbps. However, the developers of global networks did not suspect such speeds, since they had to use the communication channels that were available. This was due to the fact that the laying of new cable systems for computer networks thousands of kilometers long would cause enormous capital investments. Only telephone communication channels were available at that time, poorly adapted for high-speed transmission of discrete data - a speed of 1200 bit / s was a good achievement for them. For this reason, the economical use of the bandwidth of communication channels has become the main criterion for the effectiveness of data transmission methods in global networks. Under such conditions, various procedures for transparent access to remote resources, which are standard for local networks, remained an unaffordable luxury for global networks for a considerable time. At the moment, computer networks are constantly evolving, and quite quickly. The separation between local and global networks is constantly decreasing, largely due to the emergence of high-speed territorial communication channels that are not inferior in quality to cable systems of local networks. In global networks, resource access services have emerged that are as convenient and transparent as local network services. Such examples are shown in great numbers by the most popular global network - the Internet. Local networks will also be transformed. The passive cable connecting computers was replaced by various types of communication equipment - switches, routers, gateways. Due to the use of such equipment, it became possible to build large corporate networks that include thousands of computers and have a complex structure. There was a renewed interest in large computers. This was because, after the euphoria about the ease of working with PCs subsided, it became clear that systems consisting of hundreds of servers were more difficult to maintain than several large computers. Therefore, at a new stage of evolution, mainframes are returning to corporate computing systems. At the same time, they are full-fledged network nodes that support Ethernet or Token Ring, as well as the TCP / IP protocol stack, which has become the de facto networking standard thanks to the Internet. Another important trend has emerged, affecting equally both local and global networks. They began to process information that was previously unusual for computer networks, such as voice, video images, and drawings. This has led to the need to make changes in the operation of protocols, network operating systems and communication equipment. The difficulty of transmitting this multimedia information over the network is due to its sensitivity to delays in the case of transmission of data packets. Delays most often cause distortion of such information in the end nodes of the network. Since conventional computer network services such as file transfer or e-mail generate latency-insensitive traffic and all network elements were invented with it in mind, the advent of real-time traffic has caused great problems. At the moment, these problems are solved in various ways, for example, with the help of ATM technology specially designed for the transmission of different types of traffic. However, despite the great efforts made in this direction, it is still far from an acceptable solution to the problem, and much more needs to be done in this area in order to achieve the fusion of technologies not only for local and global networks, but also for technologies of any information networks - computer, telephone, television, etc. Despite the fact that today this idea seems unrealistic to many, experts believe that the prerequisites for such an association already exist. These opinions differ only in the estimation of the approximate terms of such an association - the terms are called from 10 to 25 years. At the same time, it is believed that the basis for the synthesis will be the packet switching technology used today in computer networks, and not the circuit switching technology used in telephony. 5.2. Main software and hardware components of the network As a result of even a superficial examination of network operation, it is clear that a computer network is a complex set of interconnected and coordinated software and hardware components. The study of the network as a whole involves the study of the principles of operation of its individual elements, among which are: 1) computers; 2) communication equipment; 3) operating systems; 4) network applications. All software and hardware of the network can be described by a multilayer model. The first is the hardware layer of standardized computer platforms. At the moment, computers of various classes are widely and successfully used in networks - from PCs to mainframes and supercomputers. The set of network computers must be compared with the set of various tasks that are solved by the network. The second layer is the communication equipment. Although computers are central to the processing of information in networks, communication devices such as cabling, repeaters, bridges, switches, routers, and modular hubs have come to play an important role. At present, a communication device may be a complex, dedicated multiprocessor that must be configured, optimized, and administered. To make changes in the principles of operation of communication equipment, it is necessary to study the many protocols used in both local and wide area networks. The third layer, which forms the software platform of the network, is the operating system. The type of management concepts for local and distributed resources underlying the network operating system determines the efficiency of the entire network. When designing a network, one should take into account how easily this system can interact with other operating systems of the network, how much it is able to ensure the safety and security of data, and to what extent it allows increasing the number of users. The fourth, topmost layer of networking 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 applications, as well as that they are compatible with other network applications and OS. 5.3. Types of local networks In order to connect two PCs together, they are connected with a special null-modem cable. This cable is connected when the PC is 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 hosted on another computer. With direct access, one of the computers is the master, and the second is the slave. Manages the operation of computers interconnected, the user from the host PC. In this case, it is important to perform the following preparatory operations: ▪ installation of software components Client, Protocol, Services; ▪ installation of the Microsoft network file and printer access service. The flag must be checked on the computer that provides the resources. Files on this computer can be shared; ▪ ensuring 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 performed by the Direct Connection Wizard using successive windows of the Direct Connection dialog. These windows indicate which of the computers is the slave and which is the master; port used for communication; the login password to use. In the last Direct Connection window, if the parameters are set correctly, click on the Receive Commands button on the host computer, and on the Manage button on the slave computer. After that, 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. With remote control, the server is, as it were, an extension of the client. The basic synchronization scheme includes the following steps: 1) combination of stationary and portable computers. The desktop computer must be the host, and the folders containing the necessary files must be shared; 2) copying files from a stationary computer to a portable computer in the Portfolio folder; 3) disconnecting a portable computer from a stationary one and further editing files in the Portfolio folder; 4) reconnecting the portable computer to the stationary computer from which the source files were originally copied to the Portfolio folder. In this case, the portable computer must be the slave computer, and the folders with source files on the desktop computer must be shared; 5) opening the Portfolio folder and executing the Portfolio/Refresh command. If the original files have remained unchanged over the past period, all modified files in the Portfolio folder will be automatically copied to the 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 a laptop PC; ▪ update on a desktop PC; ▪ cancel any update. Not all objects can be synchronized using the Portfolio/Update command, but only a group of files marked in the folder. 5.4. Organization of the domain structure of the network When computers are networked on the Windows NT platform, they are grouped into workgroups or domains. A group of computers that make up an administrative block and do not belong to domains is called a work computer. It is formed on the Windows NT Workstation platform. Any computer in a workgroup includes its own information on user and group budgets and does not share it with other computers in the workgroup. Members who are members of workgroups log on only to the workstation and can browse the directories of other workgroup members over the network. Peer-to-peer network computers form workgroups, which should be formed based on the organizational structure of the enterprise: accounting workgroup, planning department workgroup, personnel department workgroup, etc. A workgroup can be created based on computers with different operating systems. Members of this group can play the role of both users of resources and their providers, i.e. they are equal. The right to provide other PCs with access to all or some of the local resources at their disposal belongs to the servers. When the network includes computers of different capacities, the most productive computer in the network configuration can be used as a non-dedicated file server. At the same time, it can store information that is constantly needed by all users. The rest of the computers operate in network client mode. When you install Windows NT on a computer, you specify whether it is a member of a workgroup or a domain. A logical grouping of one or more network servers and other computers that share a common security system and information in the form of a centrally managed database of user budgets is called a domain. Each of the domains has an individual name. Computers belonging to the same domain can be located on a local network or in different countries and continents. They can be connected by various physical lines, such as telephone, fiber optic, satellite, etc. Each computer in a domain has its own name, which, in turn, must be separated by a dot from the domain name. A member of this name is a computer, and the domain forms the fully qualified domain name for the computer. A domain controller is the organization of a domain structure in the network, the establishment of certain rules in it, and the management of interaction between the user and the domain. A computer that runs Windows NT Server and uses a single shared directory to store user budgeting and domain-wide security information is called a domain controller. Its task is to manage within the domain the interaction between the user and the domain. All changes to the information about the budgets of the domain are selected, stored in the catalog database, and constantly replicated to the backup domains by the main domain controller. This ensures centralized management of the security system. Several models for building a network with a domain architecture are used: ▪ single-domain model; ▪ model with a master domain; ▪ model with several master domains; ▪ model of completely trusting relationships. 5.5. Multilevel approach. Protocol. Interface. protocol stack Communication between devices on a network is a complex task. To solve it, a universal technique is used - decomposition, which consists in dividing one complex task into several simpler tasks-modules. Decomposition consists of a clear definition of the functions of each module that solves a particular problem, and the interfaces between them. As a result, a logical simplification of the task is achieved, in addition, it becomes possible to transform individual modules without changing the rest of the system. When decomposing, a multilevel approach is sometimes used. In this case, all modules are divided into levels that form a hierarchy, i.e., there are overlying and underlying levels. The modules that make up each level are formed in such a way that, in order to perform their tasks, they make requests only to those modules that are directly adjacent to the lower levels. However, the results of the work of all modules that belong to a certain level can only be transferred to the modules of the neighboring higher layer. With this hierarchical decomposition of the problem, it is necessary to clearly define the function of each level and the interfaces between the levels. An interface establishes a set of functions provided by a lower layer to a higher layer. As a result of hierarchical decomposition, significant independence of levels is achieved, i.e., the possibility of their easy replacement. Means of network interaction can also be presented in the form of a hierarchically organized set of modules. In this case, the lower level modules are able, in particular, to solve all issues related to the reliable transmission of electrical signals between two neighboring nodes. Higher-level modules will create message transport throughout the entire network using the lower-level tools for this. At the top level, there are modules that provide users with access to various services, including a file service, a print service, and so on. However, this is only one of many possible ways to divide the overall task of organizing networking into private, smaller subtasks. The multi-level approach applied to the description and implementation of system functions is used not only in relation to network facilities. This action model is used, for example, in local file systems, if an incoming request for access to a file is processed in turn by several program levels, first of all, by the top level, which sequentially parses the compound symbolic name of the file and determines the unique file identifier. The next level finds by a unique name all the remaining characteristics of the file: address, access attributes, etc. After that, at a lower level, the access rights to this file are checked, and then, after calculating the coordinates of the file area containing the necessary data, a physical exchange is performed with an external device using the disc driver. The multilevel representation of network interaction tools has its own specifics, which is related to the fact that two machines participate in the exchange of messages, i.e., in this case, the coordinated work of two "hierarchies" should be organized. When transmitting messages, both participants in the network exchange must accept many agreements. For example, they need to agree on the levels and shape of electrical signals, how to determine the length of messages, agree on ways to check the validity, etc. Thus, agreements must be accepted for all levels, from the lowest, which are the levels of transmission of bits, to the very high, which performs a service for network users. Modules that implement the protocols of neighboring layers and are located in the same node also interact with each other in accordance with well-defined norms and using standardized message formats. These rules are called interface. An interface is a set of services that a given layer provides to its neighbor layer. In fact, the protocol and the interface define the same concept, but traditionally in networks they have been assigned different scopes: protocols assign rules for the interaction of modules of the same level in different nodes, and interfaces define modules of neighboring levels in the same node. The means of any of the levels must work out, firstly, their own protocol, and secondly, interfaces with neighboring levels. A hierarchically organized set of protocols, which is sufficient to organize the interaction of nodes in a network, is called communication protocol stacks. Communication protocols can be implemented both in software and in hardware. Lower layer protocols are most often implemented by a combination of software and hardware, while upper layer protocols are usually implemented purely in software. A software module that implements a protocol is often also referred to as a protocol for short. In this case, the relationship between a protocol - a formally defined procedure and a protocol - a software module that performs this procedure, is similar to the relationship between an algorithm for solving a certain problem and a program that solves this problem. The same algorithm can be programmed with varying degrees of efficiency. Similarly, a protocol may have several software implementations. Based on this, when comparing protocols, it is necessary to take into account not only the logic of their work, but also the quality of software solutions. In addition, the quality of the entire set of protocols that make up the stack affects the efficiency of interaction between devices in the network, in particular, how rationally the functions are distributed between the protocols of different levels and how well the interfaces between them are defined. Protocols are organized not only by computers, but also by other network devices, such as hubs, bridges, switches, routers, etc. In general, the connection of computers in a network is not carried out directly, but through various communication devices. Depending on the type of device, it requires certain built-in tools that implement one or another set of protocols. 5.6. Organization of accounts. User group management All information about a user that is necessary to identify him and work on a Windows NT network is called an account. It is created for each user and contains a unique name, which is typed by the user when registering on the network, and a password to enter the network. When creating an account, you must enter the following information: 1) a user group that includes a user; 2) the path to the user profile, which defines the user's environment and the programs available to him; 3) the time at which the user is allowed to enter the network; 4) a workstation through which a given user can enter the network; 5) the validity period of the account and the type of account; 6) user rights to remote access and callback facilities. Use account management to make changes to accounts. These changes may include: changing the password, renaming the account, changing the user group (deleting from one and including in another), blocking access, deleting the account. Domain controller accounts can be valid for other domains as well, and those domains must be trusted. Windows NT 4 introduced the concept of managing user groups. The basis of this concept is the assignment of rights to a whole group of users at once and the execution of access control by adding and removing users from different groups. This account management approach grants all access rights to the group that the account is placed in. User accounts that have access to servers and workstations in their own and other domains with which a trust relationship has been established are called global groups. They are managed by the user manager for domains. Local groups consist of user accounts that have access only to resources on the local system within its own domain, and user accounts of global groups that have access to servers that are part of their domain. Administrators are a group responsible for the overall configuration of a domain and its servers. This group has the most rights. It includes the domain administrators global group, which has the same rights as administrators. Budget operators have the right to create new groups and user accounts. However, they have limited rights to administer accounts, servers, and domain groups. Groups of users, domain users, domain guests, guests also have rights with significant limited capabilities. It is possible to copy, correct and delete user-created groups. The group management wizard has the right to add and create users. It works semi-automatically and provides step-by-step assistance with the following administrative tasks: ▪ creation of user accounts; ▪ group management; ▪ controlling access to files and folders; ▪ input of printer drivers; ▪ installation and uninstallation of programs; ▪ Licensing management; ▪ Administration of network clients. 5.7. Security policy management One of the most important administrative tasks is to manage the security policy. It includes: interactive user authentication, user access control to network resources, audit. Interactive user authentication is performed by pressing the Ctrl + Alt + Del keys, which leads to the launch of the WINLOGIN utility, which opens the Login window. When a user joins a workgroup, their account is created and stored in the SAM (computer RAM) of their workstation, and the local authentication software contacts the workstation's SAM database to validate the logon parameters entered. If a user registers in a domain, then the call to verify the entered registration parameters occurs to the SAM database of the domain to which his machine belongs. User access to network resources is controlled by applying the user's budget, user or user group rules, object access rights, etc. The user's budget is formed by the administrator after the account is created. The budget includes the network time, the scope of the OP that is granted to the user, and other user rights in the system. The rules that set the actions available for use are called the rights of a user or user group. The granted rights and restrictions that are imposed on an individual user or group of users determine the user's ability to access network resources. The user can have ordinary and advanced rights. Typically, extended rights are granted only to programmers and sometimes administrators of workstations, but not to user groups. The system policy editor is used to adjust and set new rights for a certain user by the administrator. In Windows NT, administrative functions are most often performed using the User Manager, Server Manager, and others. User rights are set by the administrator when the user account is created. System elements in Windows NT are objects, and each object is defined by a type, a set of services, and attributes. Object types in Windows NT are directories, files, printers, processes, devices, windows, and so on; they affect the allowable sets of services and attributes. The set of actions performed by or with an object is a set of services. The object name, data, and access control list are part of the attributes. The access control list is a required property of an object. This list contains the following information: a list of the object's services, a list of users and groups that have permission to perform each action. If necessary, some user rights can be protected: access rights to objects are determined by the security descriptor. NTFS file system permissions (write, read, execute, delete, change permissions) are included in local rights. Control over. remote rights is exercised by shared resources, which, in turn, are controlled by a network resource that allows users of remote computers to access objects over the network. Audit is used to record all events that occur in the local network; it informs the administrator about all prohibited user actions, provides an opportunity to obtain information about the frequency of access to certain resources, and establish the sequence of actions that users performed. There are three levels of audit management: 1) enabling and disabling auditing; 2) audition of any of the seven possible types of events; 3) checking specific objects. 5.8. Network resource management Network resource management is multifaceted and includes the following tasks: 1) selective compression of NTFS volumes, folders and files, carried out to save disk space. Spreadsheets, text files, and some graphic files can shrink by several times; 2) archiving data and solving similar problems; 3) development of scenarios that are set by a set of commands. Among them are: a script for automatically executing tasks when a user registers in the system, a script for a certain user's own directory, establishing appropriate network links when using different user names, surnames, etc.; 4) folder replication to other computers, which authorizes the replication of registration scripts from one domain controller to another, databases from one server to another in order to maintain and organize trust relationships; 5) management of the launch and operation of services jointly with the service manager. These may include applications that run on the server in the background and provide support for other applications; 6) system performance monitoring, carried out using the System Monitor program; 7) disk management using the Disk Administrator program, including creating basic and extended partitions, formatting partitions, creating spanned volumes, etc.; 8) optimizing the operation of Windows NT 4 as a file server, as an application server (controlling the application server processor, controlling virtual memory, eliminating network problems), etc. In this case, the operation of hard drives is optimized, disk access problems are eliminated at the program level, network bandwidth; 9) print service management. Maintenance of printers is carried out through the use of a program that is accessed through the Printers folder from the control panel or Settings; 10) managing the entry of computers into the domain of your server, organizing domains, deleting computers, assigning a server as the main domain controller, replicating data to other servers, merging domains, managing trust relationships between domains, auditing network resources for each user, etc. All of the above actions are performed using Server Manager and User Manager for Domains; 11) management of shared resources. When a computer boots into Windows NT, default system shares are created for each of the system's disks to support networking and manage internal operations; 12) setting remote access control. The installation of the remote access client and server is carried out using the Network utility from the control panel. Modems, protocols and communication ports are installed using the same utility; 13) management of all connections in the network and access to information of the remote access server for which the Remote Access Management utility is used; 14) Troubleshooting the network using Network Monitor, which you can use to view packets coming into and out of Windows NT. 5.9. Network Services For the user, the network is not computers, cables and hubs, and not even information flows, but is primarily a set of network services that allow you to view a list of computers available on the network or a remote file, print a document on a "foreign" printer or send a mail message. It is the combination of these features - how wide their choice is, how convenient, reliable and safe they are - that sets the look of each of the networks for the user. In addition to the data exchange itself, network services are designed to solve other, more specific, tasks, in particular, those generated by distributed data processing. These are tasks aimed at ensuring the consistency of several copies of data hosted on different machines (replication service), or organizing the execution of one task simultaneously on several network machines (remote procedure call service). From network services, administrative services can be distinguished, i.e., focused not on a simple user, but on an administrator and designed to organize the correct operation of the network as a whole. These include: the user account administration service, which allows the administrator to maintain a common database of network users; network monitoring system, which functions include capturing and analyzing network traffic; a security service that, among other things, performs login procedures followed by password verification, etc. The operation of network services is performed by software. The main services are the file service and the print service, which are usually provided by the network OS, while the secondary services are the database, fax, or voice services, which are performed by system network applications or utilities that work closely with the network OS. The distribution of services between the OS and utilities is quite arbitrary and varies in specific implementations of this system. When developing network services, it is necessary to solve problems inherent in any distributed applications, including the definition of an interaction protocol between the client and server parts, the distribution of functions between them, the choice of an application addressing scheme, etc. One of the main indicators of the quality of a network service is its convenience. For the same resource, you can develop several services that solve the same task in different ways. The main problems lie in the performance or level of convenience of the services provided. For example, a file service might be based on a command to transfer a file from one computer to another by file name, and this requires the user to know the name of the desired file. The same file service can be organized so that the user mounts the remote file system to a local directory and then accesses the remote files as if they were his own, which is much more convenient. The quality of the network service is determined by the quality of the user interface - intuitiveness, clarity, rationality. In the case of determining the degree of convenience of a shared resource, the term "transparency" is often used. Transparent access is such that the user does not notice where the resource he needs is located - on his computer or on a remote one. After mounting a remote file system into its directory tree, access to remote files becomes completely transparent to it. The mount operation itself can also have varying degrees of transparency. In networks with less transparency, the user needs to know and specify in the command the name of the computer that stores the remote file system; in networks with a greater degree of transparency, the corresponding software component of the network searches for shared file volumes, regardless of where they are stored, and then shows them to the user in a form convenient for him , such as a list or a set of icons. To achieve transparency, the way of addressing (naming) shared network resources is important. The names of such resources should not depend on their physical location on a particular computer. At best, the user should not change anything in their work if the network administrator has moved the volume or directory between computers. The administrator and the network OS have information about the location of file systems, but it is hidden from the user. This degree of transparency is still rare in networks. Most often, to gain access to the resources of a particular computer, you should establish a logical connection with it. This approach is used, in particular, in Windows NT networks. 5.10. Tools that provide interaction with other network operating systems A network operating system can be called an OS that interacts with network equipment and provides intercomputer communications. The user interface to the network allows you to share files and peripherals. The Windows NT operating system is capable of interacting and exchanging data with many existing networks based on various network support systems. Circumstances that may lead to this need may be: the presence of networks already built on the basis of other operating systems, resources required by Windows NT users; creation of new networks based on Windows NT, and other operating systems supporting networks to improve their efficiency. Interoperability of networks built on Windows NT with other network support operating systems are designed to provide the following facilities. 1. Open network structure, dynamic loading and unloading mechanisms built-in network support for various network components. These mechanisms can be used to load and unload third-party software, allowing Windows NT to support many different network protocols, network cards, and drivers. 2. Protocols compatible with other networks and communicating with them that support Windows NT. The remote access service uses the following protocols to transfer data from one local network to another remote local network via the Internet: РРР - parallel connection protocol over several telephone channels; SLIP - Internet protocol for a serial link; PPTP is a protocol containing an encryption mechanism for the Internet. 3. Network drivers and interfaces. They allow Windows NT to connect to different types of networks and interact with different types of computing systems. 4. Multi-user remote access service for systems with Windows NT Server and single-user remote access for Windows NT Workstation systems. It provides remote WAN access to a Windows NT system. Network connections that are based on different operating systems that support networks are able to serve the remote access service server. This is done thanks to the ability to translate messages from one format to another, as well as the presence of a multi-network access router that performs the establishment and termination of a network connection, remote printing and data transmission over the network to a network component that processes resource requests. 5. The ability to run many applications for different operating systems due to the presence of various APIs in Windows NT. The Win-32 I/O API protocol is required when processing file I/O requests that are located on a remote machine, etc. 6. Built-in support for various types of file systems (NTFS, FAT, CD-ROM, VFAT, Macintosh), which has the ability to convert FAT and HPFS partitions to NTFS partitions, support for Macintosh format directories in NTFS partitions. 7. Support for Windows NT and NetWare shared directory services NTDSmNDS. For example: secure directory base, distributed architecture, network single sign-on, simple administration. 8. Ability to connect new users to domains, such as users of other networks, maintaining the required level of system security by establishing trust relationships between domains. These include built-in WANs, which are used to connect LANs to LANs over the WAN. 5.11. Organization of work in a hierarchical network Hierarchical networks have one or more servers. They contain information that is used simultaneously by different users. There are file servers, database servers, print servers and mail servers. The file server hosts shared files and shared programs. Workstations host only a small portion of these programs, which require negligible resources. Programs that allow this mode of operation are called network installable programs. On the database server there is a database, for example, "ConsultantPlus", "Garant", "Bank customer accounts", etc. The database on the server can be replenished from various workstations or information can be provided upon request from a workstation. In this case, there are three fundamentally different modes of processing requests from a workstation or editing records in the database: 1) database records are sequentially sent from the server to the workstation, where the records are filtered and the necessary ones are selected. In this case, the requirements for the server are reduced, but the load on the network channels and the requirements for the computing power of workstations increase; 2) the server selects the required records from the database and sends them to the workstation. This reduces the load on the network and reduces the level of requirements for workstations. In this case, the requirements for the computing power of the server increase dramatically. This method is the best and is implemented by special tools for working with modern network databases; 3) the "drain-spill" mode is used with low power of the server, workstation or network. It is used to enter new records or edit them if the database record can be changed no more than once a day. To create a print server, a fairly productive printer is connected to a low-power computer, which is used to print information simultaneously from several workstations. The mail server is designed to store information sent and received both via the local network and from the outside via a modem. At the same time, the user can view the information received for him at any convenient time or send his own through the mail server. For each user, three areas are allocated on the server hard disk: 1) personal, available only to a user with all rights, for example, creating folders and files in it, editing and applying files, deleting them. Other users are not granted access to "other people's private areas", they do not see them using the file system, since private areas are used to store the user's confidential information; 2) general, to which all network users have simultaneous access with the right to read and write. This area is used to exchange information between different network users or workstations. To do this, information from the user's personal area or from the workstation's local disk is written to the public area. From this area, another user overwrites it to his personal area or to the local disk of another PC; 3) a reading area in which the user can only read information. In order to access the private area on the server, the user must complete the network logon or network registration procedures. The procedure for logging on to the network is carried out after turning on or restarting the computer. 5.12. Organization of peer-to-peer networks and technology of work in them The user can install the peer-to-peer software. The software components for managing this network allow you to organize a direct cable connection between two PCs using a null modem cable. Peer-to-peer networks are called peer-to-peer computers (workstations) in which there is no server part of the software. Each workstation installs client software, which consists of four components: 1) client - a program that implements the general functions of managing the interaction of a workstation with other computers on the network; 2) services - a program that sets the type of access to resources and ensures the transformation of a specific local resource into a network one and vice versa; 3) protocol - a program that controls the transfer of information in the network; 4) network card - a driver that controls the operation of the network adapter, however, when organizing a direct cable connection between a PC, this component may be absent. Keep the following in mind when installing network software components. 1. To organize a peer-to-peer network (as a client), you must install the Client for Microsoft Networks program. Peer-to-peer networks allow reading and editing shared information resources, as well as launching a program from a "foreign computer". At the same time, each user can have their own desktop view, a set of icons on it, personal settings for working on the Internet, etc. 2. Select File and Printer Sharing for Microsoft Networks as the Service for Microsoft Peer-to-Peer Networks or direct cable connection. 3. The type of protocol is determined by the type of installed client and the type of network card. In this case, the protocol is often automatically installed during installation. 4. For network cards of the Rpr class, the software component Network card should be used. The card is installed automatically when the PC is restarted, if drivers for the network card are included in the Windows drivers. When organizing work in a peer-to-peer network, you should use the resources of different computers. A workstation resource in a peer-to-peer network is any of the following elements: ▪ long-term memory devices, including logical disks of HDDs, drives and other similar devices (information); ▪ folders, with or without lower-level subfolders (informational); ▪ connected to a computer, including printers, modems, etc. (technical). A computer resource that is accessible from other computers on a network is called a shared or network resource, as well as a shared resource. Allocate shared information resources and shared technical devices. The concepts of local and shared resource are dynamic; this means that any local resource can be converted to a network resource and back at any time by the "master" of the workstation. Before using a network resource in peer-to-peer networks, the following organizational measures must be taken: ▪ clarify the composition of shared resources and select the computers on which they will be located; ▪ determine the circle of users who gain access to them; ▪ give information to future consumers of this resource about the names of the PCs on which they were created, the network names of the resources, rights and passwords to access them; ▪ create groups, if necessary, and include in it all PCs that will be given access to this resource. 5.13. Modem types of networks A modem is a device that allows the exchange of information between computers using the telephone network. For the duration of the communication session, both computers must be connected to a telephone line using a modem. Fax modems have a special scheme that allows you to exchange information not only between computers, but also between computers and fax devices. Fax modems are capable of operating in two modes: modem mode and fax modem mode, and at the same time exchange fax messages. In both cases, the individual elements of work are similar in a number of respects, the capabilities of each mode and the technology of working with them differ significantly. The use of a modem makes it possible to produce the following network information technologies and information services. 1. Direct connection. This is the simplest way to connect two computers and organize the exchange of information between them without intermediaries and additional fees. If the system of hourly payment for telephone calls is not applied, then modem operation within the local telephone network is free of charge. When a modem connection has been established using a cellular or long-distance connection, payment is made according to the time-based tariff established for this type of connection. Direct communication is provided by special switching programs. Once a connection is established between the computers, the circuit programs immediately allow you to transfer files between them. When direct switching is used, any type of file or text information directly typed on the keyboard can be transferred. The type of document that is transmitted or received during the transmission of messages may either be the same or differ depending on the transmission method used. 2. Communication with the bulletin board (BBS). In this case, there is a connection to a computer or local network, in which there is a database and special software that implements the query language, searches the database for the necessary information and copies it to the subscriber's computer. Within the local telephone network, the services of these information systems are provided to all users and are free of charge. To work with the BBS, you can use circuit programs and special software that is read from the BBS itself after the first call to it using the circuit program. In addition to copying files, some BBS offer additional features - address correspondence between its subscribers or the placement of messages addressed to a specific group of subscribers or all BBS subscribers. 3. Remote access. This is one way to connect to a separate computer or office LAN. After this connection, the remote computer acquires the status of a full-fledged workstation of this network, and the modem simultaneously performs the functions of a network card. 4. Connection to global networks. A global network is a network of computers distributed around the world, which provides information and other types of services on a commercial basis to everyone. Connection to the global network is carried out after connecting to a computer or local network via an intermediary modem - provider. Sites are called powerful information nodes, which are computers or local networks of providers connected by high-speed channels with nodes of other providers around the world and together forming a global network. The most famous global network is the Internet. The provider provides services on a commercial basis, and in order to receive them, a contract must be concluded in advance. 5.14. Installing and configuring the modem Working with the modem includes a one-time installation stage and operations that are performed during each communication session. Modem installation is understood as its physical and software connection. The physical connection method is determined by the type of modem. The modem can be internal or external. The internal modem is a board that plugs into an expansion slot on the motherboard. When applied, an additional asynchronous (COM) port is created. Configuring this port may require a certain degree of user skill. In this case, the modem is not transportable. The advantages of an internal modem include its cheapness, and the fact that it does not require a separate connection to the electrical network, does not use a COM port, and is ready to work immediately after turning on the computer. External modems are stand-alone devices that are connected by special cables to a PC through asynchronous ports. This type of modem requires a connection to the mains, most often through the voltage converter supplied with it. Both types of modem, when physically connected, can interface with a voice phone. There are the following connection methods: ▪ the modem is connected to the telephone socket, and the telephone is connected to the modem; ▪ Both the telephone and the modem are connected to the telephone socket through the connector on it. Connection with the subscriber with both connection methods is carried out both using a telephone and via a modem. Only the device (modem or telephone) from which the telephone number is dialed first is active (holding the line). In switching programs, when using the first connection method, after talking on the phone and without breaking the connection, transfer control to the modem, after which, after hanging up the handset, to carry out a modem communication session. This connection method is convenient when you need to call the subscriber in advance in order to warn him about the beginning of the session and specify the communication parameters. But the second way of pairing the modem and phone, and the presence of a parallel phone or fax machine, makes the modem work worse. The modem in Windows programmatically connects to the OS as a new device. A software connection is performed using the New Device Connection Wizard, which is called by the Control Panel / Hardware Installation / Modem command. The brand of the connected modem is indicated by the user in the list of modems recognized by the OS, or it is determined automatically. When modem drivers are supplied by the modem manufacturer, it is installed in the usual way: by clicking the Install from Disk button or by using the installation program with the Start/Run command. After programmatically connecting the modem in the Windows system, you can configure its parameters by performing the following sequence of actions: 1) activate the My Computer/Control Panel/Modems icon; 2) select a specific modem in the opened Modems window by clicking on the Properties button; 3) set the necessary values for the configuration parameters of the modem operation in the fields of the General and Establish connection tabs. The port speed characterizes the speed of information exchange between the PC and the modem. In this case, the port speed is set in the Maximum speed field of the General tab of the Modem Properties window. If it is necessary to limit the transmission speed on the line, then reduce the speed on the port, but the connection parameters in the Connection tab are not changed. 5.15. Establishing a connection with a remote personal computer When using a modem, any communication session begins with establishing a connection with a remote computer. This connection in Windows is provided by the Remote Network Access program, which is automatically installed when Windows is installed. In this case, at the time of installation, the modem must be physically connected to the PC and turned off. In the window of this program, for each telephone number, a special Connection element is automatically created, the properties of which indicate the telephone number. To create a Connection icon, follow the steps below, only the first step is required. 1. Create a new icon. In the Remote Connection program window, click on the New Connection icon, and then in the subsequent windows of the Connection Creation Wizard, specify the name of the connection and the subscriber's telephone number. After this, an icon is created with the specified name, the recipient's phone number and some standard set of parameters that control the process of connecting with the subscriber. These parameters can be changed using the steps in the next paragraph. 2. Configure dialing parameters. The parameters in this group depend on the type of telephone line used; they control the connection establishment technology. To change parameters, double-click on the icon of the desired connection, and in the Connection Establishment window that opens, click on the Parameters button. You need to make all the necessary changes in the Dialing Options window. The meaning of most parameters is as follows: ▪ the dialing type determines the dialing system used, which can be pulse or tone. When a new connection is made, the tone mode is set by default, so most often it needs to be changed to pulse. This is advisable if the measures described below are not applied, otherwise the connection will not be established (this applies to all types of connections, including connections to the Internet); ▪ the Call location field allows you to have several types of number parameters for the same connection. This is convenient to use when you have to establish a connection from a laptop computer from different places that differ in the method of calling the subscriber. For example, in one case directly, and in the other - through a switch, or in one case from a line with tone dialing, and in the other - with pulse dialing. In this case, click on the Create button, after which in the Call Place field you must enter a name that defines the corresponding set of parameters. After this, you need to set the necessary parameter values, the setting of which is completed by clicking the Apply button. The call location is then selected during the call establishment process. 3. Coordination of communication parameters with the PC-subscriber, which sets the protocols for data transfer to the subscriber and other characteristics that are necessary for connecting to a remote computer. The most important parameters are set in the Server type tab. These settings are especially important when establishing a connection to the Internet. Connection with a specific subscriber is made using: ▪ double-click the Connection icon in the Remote Access program window. Frequently used connections can have their icons displayed on the desktop for ease of access; ▪ double-click on the connection icons that appear in the windows of the switching programs; ▪ specifying the name of the desired connection, which is made in special fields of Internet programs. It is required to ensure that the required connection is automatically established. 5.16. Working with circuit programs Switching, or terminal, programs allow using a modem to organize the exchange of information between two remote PCs, as well as work with BBS. With direct switching, it is possible to exchange text information in an interactive mode, when the text typed on the keyboard of one PC is immediately reproduced on the subscriber's monitor. With the help of such switching, you can transfer files from one PC to another. To do this, both computers must be connected to a telephone line via a modem, and HyperTerminal must be loaded on them. After that, one of the computers becomes the caller, and the other - the waiter. The distribution of functions between computers is determined by the preliminary agreement of subscribers. When establishing a connection between computers, the actions should include the following steps: 1) on the waiting computer in the HyperTerminal window, double-click the Hypertrm icon, and then click the Cancel button. An empty New connection window will open, which is the working window of HyperTerminal, and in the menu of this window you need to execute the commands Communication / Wait for a call; 2) after performing the above actions on the waiting PC, on the calling PC, in the NuregTerminal window, double-click the icon of the receiving PC or double-click the HyperTerminal icon to create the Connection icon. After that, the connection between the calling computer and the waiting computer begins. The connection to the BBS is made using a circuit program. The control program will require a user login name and a password when connecting to the BBS for the first time. Both the password and the name are assigned by the user himself. To receive mail addressed to the user on a subsequent connection to the BBS, you must enter the correct name and password in the Connection window. After that, the control program, like the Wizards in modern operating systems, will generate a menu sequence on the monitor. For example, menu items assign the following actions: ▪ return to the previous menu; ▪ calling the BBS system operator to exchange messages interactively; ▪ viewing the contents of text files or archives; ▪ selecting a file search topic from the list of topics provided; ▪ view a list of files in the selected area; ▪ specifying a list of files to copy to your computer; ▪ uploading files to BBS; ▪ viewing mail and sending it to specific recipients; ▪ logout and end of session, etc. A modem is used for remote access to a single computer and network. With its help, you can organize remote control of one master computer by another, slave computer. In this case, the keyboard of the master computer becomes, as it were, the keyboard of a slave; To do this, the Remote Access Server program must be installed on the slave computer. Its installation in the first case should be requested during the installation of Windows, and in the second case, it should be done a little later using the Start / Settings / Control Panel / Add or Remove Programs command. After that, in the Communication group, mark the flag of the Remote Access Server program. When it is installed, to allow control of this computer from a remote computer, launch the Remote Access program and execute the menu command Connections/Remote Access Server in its window. Then, in the windows that open, you need to set the protocols and password for access to the user's computer. Next, you need to create a Connection to access this computer, specifying in its properties and parameters all the values \uXNUMXb\uXNUMXbnecessary for connection and access. 5.17. Working with a fax modem When exchanging information not only with other computers, but also between PCs and facsimile devices, modern modems are used. Using a modem, it is possible, for example, to send a message from a computer to a fax machine and vice versa. A modem operating in this mode is called a fax modem. Work with this device is carried out with the help of special switching programs or universal organizer programs. Fax setup is carried out after installing the modem or when installing fax programs, or when accessing fax for the first time. A fax icon is placed in the Printers group, and the fax itself, like the printer, is connected to a special "logical" port. After installing the fax, this port can also be accessed from other applications as a printer. One way to fax a document created by an application is to print it using the Print command. In this case, the installed fax is indicated as a printer. Changing the fax operation parameters and setting it up is done in the Properties window for the corresponding fax in the Printers group. A fax message can be sent using: 1) the program in which the document was prepared. This method is easiest if the File menu of the program that prepared the document has Print or Send commands. An appropriate fax is set as a printer and a print command is issued; 2) organizer programs; 3) switching programs that have the ability to send fax messages. When sending a message, a window appears in which it is necessary to fill in the message header containing the following fields: ▪ To - with one or more addresses of message recipients; ▪ Copy - with the addresses of recipients of copies, while in some systems the main recipients may or may not be notified of the presence of copies; ▪ Subject - brief information about the message. To simplify the assignment of addresses, there are address books that include a list of frequently used addresses, as well as message forms that contain entire headers of various types. Messages can contain text directly typed in a special window, and an attachment (text, graphic and other files or a spreadsheet). The message can only include attachments. It looks like this when sent from an application program on a Print or Send command. Messages are protected from illegal access in various ways: password, keys, electronic signature, etc. When sending a message, you can specify: ▪ urgency of delivery - immediately, exactly on the specified date and time, within a certain time interval at a “cheap rate”; ▪ the presence and type of title page separating one message from another; ▪ print quality and paper size; ▪ the need to confirm receipt of the message and the method of protection; ▪ the number of repeated attempts to resend a message when this cannot be done immediately; ▪ the need to save the message. You can receive messages automatically and manually. The modem and computer must be turned on during automatic reception, and the communication program must be running when sending a message (if the mail server is not involved in the exchange process). Auto Receive Fax must be set to Receive Fax Automatically. Author: Kozlova I.S. << Back: Fundamentals of user work in the operating environment of a personal computer (Operating systems. Classification of software. Purpose of operating systems. Evolution and characteristics of operating systems. Operating system of new technologies. WINDOWS NT architecture. Installation of WINDOWS NT. Registry and configuration of the WINDOWS NT operating system. Features of the WINDOWS 2000 operating system. Network operating systems. Family UNIX operating systems. Linux operating system. Novell family of network operating systems) >> Forward: Internet networks (The emergence of the Internet. Possibilities of the Internet. Software for working on the Internet. Transfer of information on the Internet. Addressing system. Addressing and protocols on the Internet. Problems of working on the Internet with Cyrillic texts. Establishing a connection with a provider (entrance to the Internet). World Wide Web , or WORLD WIDE WEB. Intranet. Creating a Web page using Front Page. File information resources FTP. Electronic mail (E-mail). News or conferences. E-commerce. Online store. Internet payment systems. Internet auctions. . Internet banking. Internet insurance. Internet exchange. Internet marketing. Internet advertising)
▪ The budget system of the Russian Federation. Lecture notes
The existence of an entropy rule for quantum entanglement has been proven
09.05.2024 Mini air conditioner Sony Reon Pocket 5
09.05.2024 Energy from space for Starship
08.05.2024
▪ Digital Signal Processor C6713-300 ▪ Creation of new plants without DNA insertion ▪ Gadgets cause accelerated aging ▪ Artificial cartilage is superior to real
▪ site section Power supplies. Article selection ▪ article A million torments. Popular expression ▪ article Methodist, instructor-methodologist. Job description
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
We recommend interesting articles Section 
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page