What is a network OS. Network OS: functions, types, various OS. Network services and network services

A network operating system is an OS that has built-in capabilities for working with computer networks. These unique opportunities may include:

• various support for network equipment and;
• setting up support and filtering of network traffic,
• the presence in this system of network services that would allow remote users to use the resources of this computer.

Network OS- an example of such shells:

• Novell NetWare.
• Many GNU/Linux systems.
• Microsoft Windows(95, NT and later).
• Many UNIX systems such as Solaris, FreeBSD.
• IOS; ZyNOS by ZyXEL.

The main tasks of system operating systems are the division of network resources (for example, disk spaces) and its administration. Using network functions System Administrator defines shared resources, sets passwords, defines access rights for each user or group of users.

Which are given above, are divided into:

• network OS for servers;
• network OS for users.

There are special operating systems of this type, which are given the functions of typical designs (Windows NT) and simple operating systems (Windows XP), which are given network functions. Nowadays, virtually all operating systems used have integrated functions.

Network-wide OS structure

The network auto-operational concept is the basis for any computing system. Any computing device is independent in its operation. As a result, a network OS in the modern sense means a complex of several individual PCs that interact with each other by sending information to each other and distributing resources in accordance with general laws - protocols.

In a narrower sense, such operating systems, an example of which can be seen on most modern devices is a set of programs installed on a computer that allows it to function in conjunction with other devices.

Peculiarities

It is worth highlighting a number of elements thanks to which an OS of this type can function:

• allocation of temporary memory for managing processors in multiprocessor devices;
• ability to control remote computers.

In other words, the ability to provide one's resources and information for common use is an inseparable element of the network OS. In addition, operating systems, examples of which were discussed above, necessarily include the following functions:

• locking files and records (which is necessary when devices are shared);
• managing directories of network resource names;
• processing requests for access to the file system and various information in remote form;
• managing the queues of requests from remote users to their own devices.

Components

The means for requesting access to remote resources and the possibility of using them is a client element of the OS, called a redirector. This item determines and forwards network requests to remote resources from users and various applications. In this case, the request originates from the application in local form, and goes to the network in a different format that meets the conditions of the server.

The client part, in addition, receives responses from other servers and modifies them into local formats. Therefore, remote and local requests are treated the same by applications.

Network operating systems, an example of the functioning of which is described above, also have communication tools that ensure the exchange of information on the network. These tools guarantee addressing and buffering of incoming notifications, selection of a transmission route for messages on the network, transmission security, etc. In other words, this element is responsible for transporting information on the network.

Based on the functions available in a particular computer, its OS may not have a server or client component.

Examples of first generation network operating systems

The first network operating systems looked like a complex of an existing local OS and a network shell in the form of a superstructure on top of it. In this case, the local OS had a minimum number of network functions, since they were carried out directly by the shell. The most famous system of this type, which has become widespread throughout the world, is MS DOS. Since the third distribution of this shell, it has integrated functions such as record and file locking required for general file access. Modern commonly used network operating systems - LANtastic and PersonalWare - have a similar principle of operation.

Modern stages of development

However, the most promising way is to develop network operating systems, initially specialized for running on the network. The functions of such shells are integrated deeply into their key system modules, which guarantees their logical coherence, ease of operation and updating, and good efficiency. Today, a lot of resources are allocated specifically to improve such operating systems. Examples of programs of this type are various Windows NT distributions Microsoft.

Structure of a network operating system.

The network operating system forms the basis of any computer network. Each computer on the network is largely autonomous, therefore, a network operating system in the broad sense is understood as a set of operating systems of individual computers that interact to exchange messages and share resources according to uniform rules - protocols. In a narrow sense, a network OS is the operating system of a separate computer that provides it with the ability to work on a network.

Rice. 1.1. Network OS structure

In the network operating system of an individual machine, several parts can be distinguished (Figure 1.1):

• · Tools for managing local computer resources: distribution functions random access memory between processes, scheduling and dispatching processes, managing processors in multiprocessor machines, managing peripheral devices and other functions for managing local OS resources.
• · Means of providing your own resources and services for public use - the server part of the OS (server). These tools provide, for example, file and record locking, which is necessary for their sharing; maintaining name directories network resources; processing requests remote access to your own file system and database; request queue management remote users to their own peripheral devices.
• · Tools for requesting access to remote resources and services and their use - the client part of the OS (redirector). This part recognizes and forwards requests to remote resources from applications and users to the network, where the request comes from the application in a local form and is transmitted to the network in another form that meets the server's requirements. The client part also accepts responses from servers and converts them into a local format, so that the application is indistinguishable from executing local and remote requests.
• · Communication means of the OS, with the help of which messages are exchanged on the network. This part provides addressing and buffering of messages, selection of the route for transmitting messages over the network, reliability of transmission, etc., that is, it is a means of transporting messages.

Depending on the functions assigned to a particular computer, its operating system may lack either a client or server part.

Figure 1.2 shows the interaction of network components. Here, computer 1 plays the role of a “pure” client, and computer 2 plays the role of a “pure” server, respectively, on the first machine there is no server part, and on the second there is no client part. The figure separately shows the client side component - the redirector. It is the redirector that intercepts all requests coming from applications and analyzes them. If a request is issued to a resource on a given computer, then it is forwarded to the appropriate subsystem of the local OS, but if it is a request to a remote resource, then it is forwarded to the network. In this case, the client part converts the request from a local form into a network format and transmits it to the transport subsystem, which is responsible for delivering messages to the specified server. The server part of the operating system of computer 2 receives the request, transforms it and passes it on to its local OS for execution. After the result is received, the server contacts the transport subsystem and sends a response to the client that issued the request. The client part converts the result into the appropriate format and addresses it to the application that issued the request.

Rice. 1.2. Interaction of operating system components when computers interact

In practice, several approaches to building network operating systems have emerged (Figure 1.3).

Rice. 1.3. Options for building network operating systems

The first network operating systems were a combination of an existing local operating system and one built on top of it network shell. At the same time, the minimum network functions necessary for the operation of the network shell, which performed the main network functions, were built into the local OS. An example of this approach is the use of the MS DOS operating system on each network machine (which, starting with its third version, has built-in functions such as file and record locking necessary for file sharing). The principle of building network operating systems in the form of a network shell over a local operating system is also used in modern operating systems, such as LANtastic or Personal Ware.

However, it seems more effective to develop operating systems that are initially designed to work on the network. The network functions of this type of OS are deeply built-in into the main modules of the system, which ensures their logical harmony, ease of operation and modification, as well as high performance. An example of such an OS is the Windows NT system from Microsoft, which, due to its built-in network tools provides higher performance and information security compared to the LAN Manager network operating system from the same company (joint development with IBM), which is an add-on to the local OS/2 operating system.

Peer-to-peer network OS and OS with dedicated servers.

Depending on how the functions are distributed between computers on the network, network operating systems, and therefore networks, are divided into two classes: peer-to-peer and two-toe (Figure 1.4). The latter are more often called networks with dedicated servers.

Rice. 1.4. (a) - Peer-to-peer network, (b) - Two-peer network

If a computer provides its resources to other network users, then it plays the role of a server. In this case, the computer accessing the resources of another machine is a client. As already mentioned, a computer operating on a network can perform the functions of either a client or a server, or combine both of these functions.

If performing some server functions is the main purpose of the computer (for example, sharing files with everyone else on the network, or sharing a fax, or allowing everyone on the network to run on this computer applications), then such a computer is called a dedicated server. Depending on which server resource is shared, it is called a file server, fax server, print server, application server, etc.

Obviously, on dedicated servers it is advisable to install OSes that are specially optimized for performing certain server functions. Therefore, in networks with dedicated servers, network operating systems are most often used, which include several OS options that differ in capabilities server parts. For example, the Novell NetWare network operating system has a server version optimized for operation as a file server, as well as shell options for workstations running various local operating systems, and these shells perform exclusively client functions. Another example of an OS aimed at building a network with a dedicated server is the Windows NT operating system. Unlike NetWare, both versions of this network OS - Windows NT Server (for a dedicated server) and Windows NT Workstation (for a workstation) - can support both client and server functions. But the server version of Windows NT has more opportunities for providing the resources of your computer to other network users, since it can perform a wider range of functions, supports a larger number of simultaneous connections with clients, implements centralized network management, and has more developed security features.

It is not customary to use a dedicated server as a computer to perform routine tasks not related to its main purpose, as this may reduce the performance of its work as a server. In connection with such considerations, in the Novell NetWare OS on the server side, the ability to perform conventional application programs is not provided at all, that is, the server does not contain a client part, and workstations do not have server components. However, in other network operating systems, functioning of the client part on a dedicated server is quite possible. For example, under Windows control NT Server can run normal local user programs, which may require the execution of client OS functions when requests for resources from other computers on the network appear. In this case, workstations on which Windows NT Workstation is installed can perform the functions of a non-dedicated server.

It is important to understand that despite the fact that in a network with a dedicated server, all computers in the general case can simultaneously perform the roles of both server and client, this network is not functionally symmetrical: in hardware and software, two types of computers are implemented in it - one, to a greater extent focused on performing server functions and running specialized server OSes, while others primarily perform client functions and run the OS version appropriate for this purpose. Functional asymmetry, as a rule, also causes hardware asymmetry - for dedicated servers, more powerful computers with large amounts of RAM and external memory. Thus, functional asymmetry in networks with a dedicated server is accompanied by asymmetry of operating systems (OS specialization) and hardware asymmetry (computer specialization).

In peer-to-peer networks, all computers have equal access rights to each other's resources. Each user can, at his own discretion, declare any resource on his computer as shared, after which other users can exploit it. In such networks, the same OS is installed on all computers, which provides all computers on the network potentially equal opportunities. Peer-to-peer networks can be built, for example, based on LANtastic OS, Personal Ware, Windows for Workgroup, Windows NT Workstation.

In peer-to-peer networks, functional asymmetry may also arise: some users do not want to share their resources with others, and in this case, their computers act as a client; the administrator has assigned only functions for organizing the sharing of resources to other computers, which means they are servers; case when local user does not object to the use of his resources and does not exclude the possibility of accessing other computers, the OS installed on his computer must include both server and client parts. Unlike networks with dedicated servers, in peer-to-peer networks there is no OS specialization depending on the predominant functional focus - client or server. All variations are implemented by configuring the same OS version.

Peer-to-peer networks are easier to organize and operate, but they are used mainly to unite small groups of users who do not have great requirements for the volume of stored information, its security from unauthorized access and access speed. With increased requirements for these characteristics, two-rank networks are more suitable, where the server better solves the problem of serving users with its resources, since its equipment and network operating system are specially designed for this purpose.

OS for workgroups and OS for enterprise networks.

Network operating systems have different properties depending on whether they are intended for workgroup (department)-scale networks, campus-scale networks, or enterprise-scale networks.

• · Department networks - used by a small group of employees solving common problems. The main purpose of a department network is to share local resources such as applications, data, laser printers and modems. Departmental networks are not typically divided into subnets.
• · Campus networks - connect several networks of departments within a separate building or within one territory of an enterprise. These networks are still local area networks, although they can cover an area of ​​several square kilometers. Services of such a network include interaction between department networks, access to enterprise databases, access to fax servers, high-speed modems and high-speed printers.
• · Enterprise networks (corporate networks) - unite all computers of all territories of a separate enterprise. They can cover a city, a region, or even a continent. These networks provide users with access to information and applications located in other workgroups, departments, divisions, and corporate headquarters.

The main purpose of the operating system used in a department-wide network is to organize the sharing of resources such as applications, data, laser printers, and possibly low-speed modems. Typically department networks have one or two file servers and no more than 30 users. Management tasks at the department level are relatively simple. The administrator's tasks include adding new users, eliminating simple failures, installing new nodes and installing new versions software. The operating systems of departmental networks are well-developed and varied, as are the departmental networks themselves, which have been in use for a long time and are quite well-functioning. Such a network usually uses one or at most two network operating systems. Most often this is a network with a dedicated NetWare 3.x or Windows NT server, or a peer-to-peer network, for example Windows network for Workgroups.

Users and administrators of departmental networks soon realize that they can improve their efficiency by gaining access to information from other departments in their enterprise. If a sales person can access specific product features and include them in a presentation, the information will be more current and have a greater impact on buyers. If the marketing department can access the characteristics of a product that is still being developed by the engineering department, then it can quickly prepare marketing materials immediately after development is completed.

So, next step in the evolution of networks is the unification of local networks of several departments into single network buildings or groups of buildings. Such networks are called campus networks. Campus networks can extend over several kilometers, but do not require wide-area connections.

The operating system running on the campus network must provide employees in some departments with access to some files and resources on the networks of other departments. The services provided by campus network OSes go beyond simple file and printer sharing and often provide access to other types of servers, such as fax servers and high-speed modem servers. An important service provided by operating systems of this class is access to corporate databases, regardless of whether they are located on database servers or on minicomputers.

It is at the campus network level that integration problems begin. In general, departments have already chosen the types of computers, networking equipment, and network operating systems. For example, the engineering department may use the UNIX operating system and Ethernet network equipment, the sales department may use DOS/Novell operating environments and equipment Token Ring. Very often, a campus network connects disparate computer systems, while department networks use the same type of computers.

The corporate network connects the networks of all departments of the enterprise, which are generally located at considerable distances. Corporate networks use WAN links to connect local networks or individual computers.

Enterprise network users require all of the applications and services found on departmental and campus networks, plus some additional applications and services, such as access to mainframe and minicomputer applications and global communications. When an OS is developed for local network or workgroup, its main responsibility is to share files and other network resources (usually printers) among locally connected users. This approach is not applicable at the enterprise level. Along with the basic services associated with sharing files and printers, a network OS that is being developed for corporations must support a broader set of services, which usually includes postal service, teamwork tools, remote user support, fax service, processing voice messages, organization of video conferences, etc.

In addition, many existing methods and approaches to solving traditional problems of smaller-scale networks for the corporate network turned out to be unsuitable. Tasks and problems came to the fore that were either of secondary importance or did not appear at all in the networks of work groups, departments, and even campuses. For example, the simplest task for a small network of maintaining user accounting information has grown in complex problem for an enterprise-scale network. And the use of global communications requires enterprise operating systems to support protocols that work well on low-speed lines, and to abandon some traditionally used protocols (for example, those that actively use broadcast messages). The tasks of overcoming heterogeneity have acquired particular importance - numerous gateways have appeared on the network, ensuring coordinated operation of various operating systems and network systems new applications.

The following features may also be included in the characteristics of corporate operating systems.

Application support. IN corporate networks are being carried out complex applications, requiring a lot of computing power to perform. Such applications are divided into several parts, for example, on one computer the part of the application associated with executing queries to the database is executed, on the other - queries to the file service, and on client machines - the part that implements the application data processing logic and organizes the user interface. Computing part common to the corporation software systems may be too large and overwhelming for client workstations, so applications will run more efficiently if the most computationally complex parts of them are moved to a dedicated powerful computer - applications server.

The application server must be based on a powerful hardware platform (multiprocessor systems, often based on RISC processors, specialized cluster architectures). The application server OS must provide high computing performance, and therefore support multithreaded processing, preemptive multitasking, multiprocessing, virtual memory and the most popular application environments (UNIX, Windows, MS-DOS, OS/2). In this regard, the NetWare network operating system can hardly be classified as a corporate product, since it lacks almost all the requirements for an application server. At the same time good support universal applications in Windows NT actually allows it to claim a place in the world of corporate products.

Help Desk. An enterprise OS must be able to store information about all users and resources in a way that can be managed from one central point. Like a large organization, a corporate network needs centralized storage of as complete background information as possible about itself (from data about users, servers, workstations to data about the cable system). It is natural to organize this information in the form of a database. Data from this database can be required by many network system applications, primarily management and administration systems. In addition, such a database is useful for organizing e-mail, group work systems, security services, network software and hardware inventory services, and for almost any large business application.

A database that stores reference information provides the same variety of capabilities and poses the same many problems as any other large database. It allows you to carry out various search operations, sorting, modification, etc., which makes life very much easier for both administrators and users. But these conveniences come at the price of solving the problems of distribution, replication and synchronization.

Ideally network reference Information should be implemented as a single database, and not be a set of databases specializing in storing information of one type or another, as is often the case in real operating systems. For example, Windows NT has at least five various types reference databases. The main domain directory (NT Domain Directory Service) stores information about users, which is used to organize their logical login to the network. Data about the same users may be contained in another directory used by email Microsoft Mail. Three more databases support low-level address resolution: WINS - matches Netbios names to IP addresses, the DNS directory - a domain name server - is useful when connecting an NT network to the Internet, and finally, the DHCP protocol directory is used to automatically assign IP addresses network computers. Closer to ideal are the directory services provided by Banyan (Streettalk III) and Novell (NetWare Directory Services), which offer a single directory for all network applications. Availability of a single help desk for a network operating system - one of the most important signs of its corporate identity.

Safety. Data security issues are of particular importance for the OS of a corporate network. On the one hand, in a large-scale network, there are objectively more opportunities for unauthorized access - due to the decentralization of data and the large distribution of “legitimate” access points, due to the large number of users whose trustworthiness is difficult to establish, and also due to the large number of possible points unauthorized connection to the network. On the other hand, enterprise business applications work with data that has vital important for the successful operation of the corporation as a whole. And to protect such data in corporate networks, along with various hardware, the entire range of protection tools provided by the operating system is used: selective or mandatory access rights, complex user authentication procedures, software encryption.

A computer operating system is often defined as an interconnected set system programs, which provides efficient management of computer resources (memory, processor, external devices, files, etc.), and also provides the user with a convenient interface for working with computer hardware and developing applications. Speaking of network operating systems, we obviously must expand the boundaries of managed resources beyond the boundaries of a single computer.

Network operating system (OS) is a computer operating system that, in addition to managing local resources, provides users and applications with the ability to efficiently and effectively easy access to information and hardware resources of other computers on the network.

Today, almost all operating systems are network-based.

In network operating systems, remote access to network resources is provided:

• network services;
• means of transporting messages over the network (in the simplest case - network interface cards and their drivers).

Network OS functions

• directory and file management;
• resource management;
• communication functions;
• protection against unauthorized access;
• ensuring fault tolerance;
• network management.

Directory and file management is one of the primary functions of a network operating system, served by a special network file subsystem. The user receives from this subsystem the ability to access files physically located on the server or in another data station, using language tools familiar to local work. When exchanging files, the necessary level of exchange confidentiality (data secrecy) must be ensured.

Resource management involves requesting and provisioning resources.

Communication functions provide addressing, buffering, routing.

Protection against unauthorized access is possible at any of the following levels: restriction of access to certain time, and (or) for certain stations, and (or) a certain number of times; limiting the set of directories available to a specific user; limiting the list of possible actions for a specific user (for example, only reading files); marking files with symbols such as “read only”, “secrecy when viewing a list of files”.

Fault tolerance is determined by the presence of an autonomous power source in the network, display or duplication of information in disk drives. Mapping means storing two copies of data on two drives connected to the same controller, while duplication means connecting each of those two drives to a different controller. A network OS that implements disk duplication provides more high level fault tolerance.

Further increase in fault tolerance is associated with duplication of servers.

Network OS components

Functional modules (network services and means of transporting messages over the network) must be added to the OS so that it can be called networked:

Among the network services, we can distinguish those that are aimed not at the ordinary user, such as a file service or a print service, but at the administrator. Such services are aimed at organizing the operation of the network. For example, centralized help desk, or directory service(For example, Active Directory in Windows), is designed to maintain a database of network users and all its software and hardware components1. Other examples include network monitoring service, which allows you to capture and analyze network traffic, security service, whose functions may include, in particular, performing a logical login procedure with password verification, service Reserve copy and archiving.

Its position in the general range of network operating systems depends on how rich a set of network services the operating system offers to end users, applications and network administrators.

In addition to network services, the network OS must include software communication (transport) tools that, together with hardware communication tools, ensure the transmission of messages exchanged between the client and server parts of the network services. The problem of communication between network computers is solved drivers and protocol modules. They perform functions such as generating messages, breaking a message into parts (packets, frames), converting computer names into numeric addresses, duplicating messages in case of loss, determining a route in a complex network, etc.

Both network services and transports can be integral (built-in) components of the OS or exist as separate software products. For example, a network file service is usually built into the OS, but a web browser is most often purchased separately. A typical network OS includes a wide range of drivers and protocol modules, but the user, as a rule, has the opportunity to supplement this standard set with the programs he needs. The decision on how to implement network service clients and servers, as well as drivers and protocol modules, is made by developers based on a variety of considerations: technical, commercial, and even legal. For example, it was on the basis of US antitrust law that Microsoft was prohibited from including it Internet browser Explorer is part of this company's OS.

Types of network operating systems

A network service can be represented in the OS either by both (client and server) parts, or only by one of them.

In the first case, the operating system, called peer-to-peer, not only allows you to access the resources of other computers, but also provides your own resources
at the disposal of users of other computers. For example, if all computers on the network have both clients and servers installed file service, then all network users can share each other's files. Computers that combine client and server functions are called peers.

An operating system that primarily contains client portions of network services is called client. Client operating systems are installed on computers that make requests to the resources of other computers on the network. These computers, also called client computers, are used by ordinary users. Typically, client computers are relatively simple devices.

Another type of operating system is server OS- it is focused on processing requests from the network to the resources of your computer and includes mainly
server parts of network services. A computer with a server OS installed on it that is solely engaged in servicing requests from other computers is called dedicated server networks. As a rule, ordinary users do not work behind a dedicated server.

Network OS examples

I repeat that today almost all operating systems are network-based. The most common of them:

• Novell NetWare
• Microsoft Windows(95, NT, XP, Vista, Seven)
• Various UNIX systems such as Solaris, FreeBSD
• Various GNU/Linux systems
• ZyNOS companies ZyXEL
• Chrome OS from Google

Look at the review of one of the modern network operating systems - cloud-based Chrome OS:

In the case when users are faced with the task of optimal division of network resources (for example, disk space), they can use network systems. Such systems provide the opportunity to transfer many administration functions to network space. With the help of network resources that are significantly superior to user ones, the administrator has the opportunity to professionally define shared resources and, by assigning unique passwords to each of them, make them autonomous and accessible to each individual user or group of users. This division also determines the classification of network operating systems into server operating systems and operating systems intended for users.

Today, special network operating systems have been developed and are widely used, but they have the characteristics of operating systems familiar to us. Special network operating systems have been developed that have the parameters of conventional ones, such as, for example, the Windows xp operating system. It should also be noted that today, almost all conventional systems have built-in options and functions of network systems.

Consequently, a network OS is a built-in optional feature that allows you to work effectively in the network space. These properties include:

Providing support for a wide range of network equipment;

Possibility of use network protocols;

Ensuring the use and support of routing;

Traffic filtering;

Ensuring uninterrupted access to remote network resources (disks and printers);

Implementation of remote access capabilities to solve network problems.

The most common network operating systems are: Novell NetWare, various versions of GNU/Linux, ZyNOS, and, of course, the most common Microsoft Windows (95, NT, XP, Vista, 7).

Modern networks and their diversity are due to the fact that today there are many types of computers in the world. That is why systems are being developed and distributed for mobile devices, home workstations, server systems, corporate OS. This classification itself emphasizes the diversity of the performance characteristics and optionality that distinguish the resources under consideration. This variety, positive on the one hand (provides choice to the user, the OS according to its financial capabilities and in accordance with the tasks at hand), creates certain inconveniences, on the other. This inconvenience lies in the need to ensure OS compatibility, especially for corporate divisions operating within the same network policy. A very important property that characterizes the parameters of a particular network OS is the accessible loading of the operating system and the ability to quickly update it.

Such operating systems are most widely used in various enterprises and institutions that require processing large amounts of data. The question naturally arises of how to choose the right network operating systems to effectively run a business without spending extra money. It seems that the main criterion when choosing the appropriate OS should be the following. If you need a resource on the scale of a large enterprise or corporation, then pay attention to such a parameter as scalability, i.e. stability of operation in various network conditions. It is also important high degree compatibility - the ability to effectively use the online update mode. In addition, such an OS should preferably provide integration of heterogeneous resources - servers and computers.

Of course, it is quite difficult to find and select an operating system that fully satisfies the requirements of a particular user. Therefore, it is advisable to select them taking into account a critical assessment of the real problems and specific situation that this software will solve.

Network operating system structure

The network operating system forms the basis of any computer network. Each computer on the network is largely autonomous, therefore, a network operating system in the broad sense is understood as a set of operating systems of individual computers that interact to exchange messages and share resources according to uniform rules - protocols. In a narrow sense, a network OS is the operating system of a separate computer that provides it with the ability to work on a network.

Rice. 4.1.

In the network operating system of an individual machine, several parts can be distinguished (Figure 4.1):

Tools for managing local computer resources: functions for distributing RAM between processes, scheduling and dispatching processes, managing processors in multiprocessor machines, managing peripheral devices and other functions for managing local OS resources.

Means of providing own resources and services for general use - the server part of the OS (server). These tools provide, for example, file and record locking, which is necessary for their sharing; maintaining directories of names of network resources; processing requests for remote access to your own file system and database; managing queues of requests from remote users to their peripheral devices. Means for requesting access to remote resources and services and their use - the client part of the OS (redirector). This part recognizes and forwards requests to remote resources from applications and users to the network, where the request comes from the application in a local form and is transmitted to the network in another form that meets the server's requirements. The client side also accepts responses from servers and converts them into a local format, so that the application makes no difference between local and remote requests. Communication means of the OS, with the help of which messages are exchanged on the network. This part provides addressing and buffering of messages, selection of the route for transmitting messages over the network, reliability of transmission, etc., that is, it is a means of transporting messages.

Depending on the functions assigned to a particular computer, its operating system may lack either a client or server part.

Figure 4.2 shows the interaction of network components. Here computer 1 plays the role of a “pure” client, and computer 2 plays the role of a “pure” server, respectively, the first machine does not have a server part, and the second one does not have a client part. The figure separately shows the client side component - the redirector. It is the redirector that intercepts all requests coming from applications and analyzes them. If a request is issued to a resource on a given computer, then it is forwarded to the appropriate subsystem of the local OS, but if it is a request to a remote resource, then it is forwarded to the network. In this case, the client part converts the request from a local form into a network format and transmits it to the transport subsystem, which is responsible for delivering messages to the specified server. The server part of the operating system of computer 2 receives the request, transforms it and passes it on to its local OS for execution. After the result is received, the server contacts the transport subsystem and sends a response to the client that issued the request. The client part converts the result into the appropriate format and addresses it to the application that issued the request.

Rice. 4.2.

In practice, several approaches to building network operating systems have emerged (Figure 4.3).

Rice. 4.3.

The first network operating systems were a combination of an existing local operating system and a network shell built on top of it. At the same time, the minimum network functions necessary for the operation of the network shell, which performed the main network functions, were built into the local OS. An example of this approach is the use of the MS DOS operating system on each network machine (which, starting with its third version, has built-in functions such as file and record locking necessary for file sharing). The principle of building network operating systems in the form of a network shell over a local operating system is also used in modern operating systems, such as LANtastic or Personal Ware.

However, it seems more effective to develop operating systems that are initially designed to work on the network. Network functions of this type of OS are deeply built into the main modules of the system, which ensures their logical harmony, ease of operation and modification, as well as high performance. An example of such an OS is the Windows NT system from Microsoft, which, due to the built-in network tools, provides higher performance and information security compared to the LAN Manager network OS from the same company (joint development with IBM), which is an add-on over the local OS/2 operating system .

Peer-to-peer network OS and OS with dedicated servers

Depending on how the functions are distributed between computers on the network, network operating systems, and therefore networks, are divided into two classes: peer-to-peer and two-toe (Figure 4.4). The latter are more often called networks with dedicated servers.

Rice. 4.4. (a) - Peer-to-peer network,

(b) - Two-rank network

If a computer provides its resources to other network users, then it plays the role of a server. In this case, the computer accessing the resources of another machine is a client. As already mentioned, a computer operating on a network can perform the functions of either a client or a server, or combine both of these functions.

If performing some server functions is the main purpose of the computer (for example, providing files for general use by all other network users or organizing fax sharing, or allowing all network users to run their applications on this computer), then such a computer is called a dedicated server. Depending on which server resource is shared, it is called a file server, fax server, print server, application server, etc.

Obviously, on dedicated servers it is advisable to install OSes that are specially optimized for performing certain server functions. Therefore, in networks with dedicated servers, network operating systems are most often used, which include several OS options that differ in the capabilities of the server parts. For example, the Novell NetWare network operating system has a server version optimized for operation as a file server, as well as shell options for workstations running various local operating systems, and these shells perform exclusively client functions. Another example of an OS aimed at building a network with a dedicated server is the Windows NT operating system. Unlike NetWare, both versions of this network OS - Windows NT Server (for a dedicated server) and Windows NT Workstation (for a workstation) - can support both client and server functions. But the server version of Windows NT has more opportunities for providing the resources of your computer to other network users, since it can perform a wider range of functions, supports a larger number of simultaneous connections with clients, implements centralized network management, and has more developed security features.

It is not customary to use a dedicated server as a computer to perform routine tasks not related to its main purpose, as this may reduce the performance of its work as a server. In connection with such considerations, the Novell NetWare OS does not provide the ability to run conventional application programs on the server side at all, that is, the server does not contain a client part, and there are no server components on workstations. However, in other network operating systems, functioning of the client part on a dedicated server is quite possible. For example, Windows NT Server can run regular local user programs that may require OS client functions to be executed when requests for resources from other computers on the network appear. In this case, workstations on which Windows NT Workstation is installed can perform the functions of a non-dedicated server.

It is important to understand that despite the fact that in a network with a dedicated server, all computers in the general case can simultaneously perform the roles of both server and client, this network is not functionally symmetrical: in hardware and software, two types of computers are implemented in it - one, to a greater extent focused on performing server functions and running specialized server OSes, while others primarily perform client functions and run the OS version appropriate for this purpose. Functional asymmetry, as a rule, also causes asymmetry in the equipment - for dedicated servers, more powerful computers with large amounts of RAM and external memory are used. Thus, functional asymmetry in networks with a dedicated server is accompanied by asymmetry of operating systems (OS specialization) and hardware asymmetry (computer specialization).

In peer-to-peer networks, all computers are equal in access rights to each other's resources. Each user can, at his own discretion, declare any resource of his computer as shared, after which other users can exploit it. In such networks, all computers have the same OS installed, which provides all computers on the network with potentially equal capabilities. Peer-to-peer networks can be built, for example, on the basis of LANtastic, Personal Ware, Windows for Workgroup, Windows NT Workstation OS.

In peer-to-peer networks, functional asymmetry may also arise: some users do not want to share their resources with others, and in this case, their computers act as a client; the administrator has assigned only functions for organizing the sharing of resources to other computers, which means they are servers; In the case where a local user does not object to the use of his resources and does not exclude the possibility of accessing other computers, the OS installed on his computer must include both server and client parts. Unlike networks with dedicated servers, in peer-to-peer networks there is no OS specialization depending on the predominant functional focus - client or server. All variations are implemented by configuring the same OS version.

Peer-to-peer networks are easier to organize and operate, but they are used mainly to unite small groups of users who do not have great requirements for the volume of stored information, its security from unauthorized access and access speed. With increased requirements for these characteristics, two-rank networks are more suitable, where the server better solves the problem of serving users with its resources, since its equipment and network operating system are specially designed for this purpose.

OS for workgroups and OS for enterprise networks

Network operating systems have different properties depending on whether they are intended for workgroup (department)-scale networks, campus-scale networks, or enterprise-scale networks.

Departmental networks - used by a small group of employees solving common problems. The main purpose of a department network is to share local resources such as applications, data, laser printers, and modems. Departmental networks are not typically divided into subnets. Campus networks - connect multiple networks of departments within a single building or within the same enterprise area. These networks are still local area networks, although they can cover an area of ​​several square kilometers. Services of such a network include interaction between department networks, access to enterprise databases, access to fax servers, high-speed modems and high-speed printers. Enterprise networks (corporate networks) - unite all computers of all territories of a separate enterprise. They can cover a city, a region, or even a continent. These networks provide users with access to information and applications located in other workgroups, departments, divisions, and corporate headquarters.

The next step in the evolution of networks is the consolidation of local networks of several departments into a single network of a building or group of buildings. Such networks are called campus networks. Campus networks can extend over several kilometers, but do not require wide-area connections.

The operating system running on the campus network must provide employees in some departments with access to some files and resources on the networks of other departments. The services provided by campus network OSes go beyond simple file and printer sharing and often provide access to other types of servers, such as fax servers and high-speed modem servers. An important service provided by operating systems of this class is access to corporate databases, regardless of whether they are located on database servers or on minicomputers.

It is at the campus network level that integration problems begin. In general, departments have already chosen the types of computers, networking equipment, and network operating systems. For example, the engineering department may use the UNIX operating system and Ethernet network equipment, the sales department may use the DOS/Novell operating environment and Token Ring equipment. Very often, a campus network connects disparate computer systems, while departmental networks use similar computers.

The corporate network connects the networks of all departments of the enterprise, which are generally located at considerable distances. Corporate networks use WAN links to connect local networks or individual computers.

Enterprise network users require all of the applications and services found on departmental and campus networks, plus some additional applications and services, such as access to minicomputer applications and global communications. When an OS is designed for a local network or workgroup, its main responsibility is to share files and other network resources (usually printers) among locally connected users. This approach is not applicable at the enterprise level. Along with the basic services associated with sharing files and printers, a network OS that is being developed for corporations must support a wider range of services, which usually includes mail service, collaboration tools, remote user support, fax service, voice message processing, organization of video conferences, etc.

In addition, many existing methods and approaches to solving traditional problems of smaller-scale networks for the enterprise network have proven unsuitable. Tasks and problems came to the fore that were either of secondary importance or did not appear at all in the networks of work groups, departments, and even campuses. For example, the simplest task of maintaining user records for a small network has grown into a complex problem for an enterprise-scale network. And the use of global communications requires enterprise operating systems to support protocols that work well on low-speed lines, and to abandon some traditionally used protocols (for example, those that actively use broadcast messages). The task of overcoming heterogeneity has acquired particular importance - numerous gateways have appeared on the network, ensuring the coordinated operation of various operating systems and network system applications. The following features may also be included in the characteristics of corporate operating systems.

Application support. Enterprise networks run complex applications that require a lot of computing power to run. Such applications are divided into several parts, for example, on one computer the part of the application associated with executing queries to the database is executed, on the other - queries to the file service, and on client machines - the part that implements the application data processing logic and organizes the user interface. The computing part of the software systems shared by a corporation can be too voluminous and overwhelming for client workstations, so applications will run more efficiently if their most computationally complex parts are transferred to a powerful computer specially designed for this purpose - an application server. The application server must be based on a powerful hardware platform, multiprocessor systems, often based on RISC processors, specialized cluster architectures. The application server OS must provide high computing performance, and therefore support multithreaded processing, preemptive multitasking, multiprocessing, virtual memory and the most popular application environments (UNIX, Windows, MS-DOS, OS/2). In this regard, the NetWare network operating system can hardly be classified as a corporate product, since it lacks almost all the requirements for an application server. At the same time, the good support for universal applications in Windows NT actually allows it to claim a place in the world of corporate products.

Help Desk. An enterprise OS must be able to store information about all users and resources in a way that can be managed from one central point. Like a large organization, a corporate network needs centralized storage of as complete background information as possible about itself (from data about users, servers, workstations to data about the cable system). It is natural to organize this information in the form of a database. Data from this database can be required by many network system applications, primarily management and administration systems. In addition, such a database is useful for organizing e-mail, group work systems, security services, network software and hardware inventory services, and for almost any large business application. Ideally, network reference information should be implemented as a single database, and not be a set of databases specializing in storing information of one type or another, as is often the case in real operating systems. For example, Windows NT has at least five different types of help databases. The main domain directory (NT Domain Directory Service) stores information about users, which is used to organize their logical login to the network. Data about the same users may also be contained in another directory used by Microsoft Mail. Three more databases support low-level address resolution: WINS - matches Netbios names to IP addresses, the DNS directory - a domain name server - is useful when connecting an NT network to the Internet, and finally, the DHCP protocol directory is used to automatically assign IP addresses network computers. Closer to ideal are the directory services provided by Banyan (Streettalk III) and Novell (NetWare Directory Services), which offer a single directory for all network applications. The presence of a single help desk for a network operating system is one of the most important signs of its corporate character.

Safety . Data security issues are of particular importance for the OS of a corporate network. On the one hand, in a large-scale network, there are objectively more opportunities for unauthorized access - due to the decentralization of data and the large distribution of “legitimate” access points, due to the large number of users whose trustworthiness is difficult to establish, and also due to the large number of possible points unauthorized connection to the network. On the other hand, enterprise business applications work with data that is vital to the success of the corporation as a whole. And to protect such data in corporate networks, along with various hardware, the entire range of protection tools provided by the operating system is used: selective or mandatory access rights, complex user authentication procedures, software encryption.