Transmission with the establishment of a virtual channel differs from the transmission with the establishment of a logical connection in that the connection parameters include a route previously laid by the network, along which all packets within the framework of this connection pass. The virtual circuit for the next session may follow a different route.

Packets on a network can move in three main ways: datagram transmission, connection-oriented transmission, and virtual circuit-establishment transmission.

In a datagram transmission, a single packet is treated as an independent transmission unit (datagram), no connection is established between nodes, and all packets move independently of each other. Connection-oriented transmission involves the establishment communication sessions with the definition of a procedure for processing a set of packets within one session.

Since computers and network equipment can be of different manufacturers, the problem of their compatibility arises. Without the adoption by all manufacturers of generally accepted rules for constructing equipment, the creation of a computer network would be impossible. Therefore, the development and creation of computer networks can only take place within the framework of approved standards for:

Interaction of the user's software with a physical communication channel (via a network card) within one computer;

Interaction of a computer through a communication channel with another computer.

In the implementation of communications, there are three levels: hardware, software and information. In terms of hardware and software levels communications- is the organization of a reliable connection channel and the transfer of information without distortion, the organization of information storage and effective access to it.

Modern computer software has a multi-level modular structure, i.e. The program code written by the programmer and visible on the monitor screen (upper-level module) goes through several levels of processing before it turns into an electrical signal (lower-level module), which is transmitted to the communication channel.

When computers interact through a communication channel, both computers must comply with a number of agreements (on the size and shape of electrical signals, message length, reliability control methods, etc.).

In the early 80s of the twentieth century, a number of international organizations developed a standard model for networking - model of interconnection of open systems (OSI - Open System Interconnection)... In the OSI model, all network protocols are divided into seven layers: physical, channel, network, transport, session, representative and applied.

Formalized rules that determine the sequence and format of messages exchanged by modules that are at the same level, but are called in different computers protocols.

Modules that implement adjacent layer protocols and reside in the same computer also interact with each other in accordance with well-defined rules and using standardized message formats. These rules are called interface and define a set of services provided by this layer to the neighboring layer.

A hierarchically organized set of protocols for the interaction of computers on a network is called a stack of communication protocols, which can be implemented in software or hardware. The lower layer protocols are usually implemented by a combination of firmware and the higher layer protocols are implemented purely in software.

The protocols of each layer are independent from each other, i.e. a protocol of any layer can be changed without having any effect on the protocol of another layer. The main thing is that the interfaces between the layers provide the necessary connections between them.

In the OSI standard, special names are used to denote units of data with which protocols of various layers are dealt with: frame, packet, datagram, segment.

The OSI model has published, publicly available specifications and standards adopted by agreement between many developers and users. If two networks are built in compliance with the rules of openness, then they have the ability to use hardware and software from different manufacturers adhering to the same standard, such networks are easily interfaced with each other, easy to learn and maintain. An example of an open system is the global computer network Internet.

In local networks, the following main methods of computers access to communication lines for data transmission are used: priority, marker and random. Priority access was implemented in the 100G-AnyLAN standard, and token access in Token Ring technology. These methods are currently not widely used due to the complexity of the equipment that implements them.

Ethernet is the most common data transmission standard in local networks today, implemented at the data link layer of the OSI model, according to which computers access the communication line is provided randomly. The standard uses a carrier-sense multiple access method with collision detection. It is used in networks with a shared bus topology.

Recently, it has become widespread radio Ethernet(the corresponding standard was adopted in 1997) for the organization of a wireless local area network (WLAN - Wireless LAN). Radio networks are convenient for mobile, but also find applications in other areas (hotel chains, libraries, airports, hospitals, etc.).

Radio Ethernet uses two main types of equipment: a client (computer), an access point that acts as a link between a wired and wireless network. The wireless network can operate in two modes: client / server and point-to-point. In the first mode, several computers can be connected to one access point via a radio channel, in the second, communication between end nodes is established directly without a special access point.

The most famous modification of radio-Ethernet is WiFi (Wireless Fidelity) a technology that provides transmission rates up to 11 Mbps and uses carrier sense multiple access and collision avoidance (the corresponding standard was adopted in 2001). Omnidirectional and narrow-beam antennas (the latter for point-to-point connections) are used for communication. An omnidirectional antenna guarantees communication for distances up to 45 meters, and a narrow-beam antenna up to 45 km. It can serve up to 50 clients at the same time.

Unlike wired Ethernet, for radio networks, it is important that radio signals from different sending nodes do not overlap at the input of the receiving node. Otherwise, a collision will occur on the network. To prevent collisions in radio-Ethernet, it is necessary to strictly observe the radio signal operating distances of individual nodes.

Using methods on the Internet packet switching allowed to make it fast enough and flexible. Unlike circuit switching in packet switching, there is no need to wait for the connection to be established with the receiving computer; the packets move independently of each other. This allows various services (e-mail, www, IP-telephony, etc.) to transfer information.

The Internet is based on the idea of ​​combining many independent networks of almost arbitrary architecture. An open network architecture implies that individual networks can be designed and developed independently, with their own unique interfaces provided to users and / or other network service providers, including Internet services.

The key to the rapid growth of the Internet has become free, open access to the main documents, especially to the protocol specifications. An important role in the formation of the Internet was played by her commercialization, which includes not only the development of competitive, private network services, but also the development of commercial products (hardware and software networking) that implement Internet technologies.

The basis of data transmission over the Internet is a stack of punctures TCP / IP (Transmission Control Protocol / Internet Protocol) which provides:

- independence from the network technology of a separate network - TCP / IP only defines the transmission element - datagram, and describes how it moves through the network;

- universal connectivity of networks, by assigning to each computer a logical address used by 1) the transmitted datagram to identify the sender and the recipient, 2) intermediate routers for making routing decisions;

- the confirmation - TCP / IP protocol provides confirmation of the correctness of information passing during data exchange between the sender and the receiver;

- support for standard application protocols - e-mail, file transfer, remote access, etc.

The TCP / IP stack defines 4 levels of interaction, each of which assumes a specific function for organizing the reliable operation of the global network.

The TCP / IP protocol software module is implemented in the computer operating system as a separate system module (driver). The user can independently configure the TCP / IP protocol for each specific case (the number of network users, the throughput of physical communication lines, etc.).

The main task of TCP is the delivery of all information to the recipient's computer, control of the sequence of transmitted information, re-sending of undelivered packets in case of network failures. Reliability of information delivery is achieved as follows.

On the sending computer, TCP splits the block of data coming from the application layer into separate segments, assigns segment numbers, adds a header, and passes the segments to the interworking layer. For each segment sent, the sending computer expects a special message to arrive from the receiving computer - a receipt confirming that the computer has received the required segment. The waiting time for the receipt of the corresponding receipt is called timeout time.

Setting the timeout time and the size of the sliding window is very important to network performance. The TCP protocol provides for a special automatic algorithm for determining these values, taking into account the throughput of physical communication lines.

TCP is tasked with determining what type of application the data received from the network is. To distinguish between application programs, special identifiers are used - ports... Port numbers are assigned either centrally if the application is popular and publicly available (for example, the FTP remote file service has port 21, and the WWW service has port 80), or locally, if the application developer simply associates any available, randomly available with the application. selected number.

TCP can operate as a User Datagramm Protocol (UDP), which, unlike TCP, does not ensure the reliability of packet delivery and protection against information transmission failures (does not use receipts). The advantage of this protocol is that it requires a minimum of settings and parameters to transfer information.

IP protocol is the core of the entire architecture of the TCP / IP stack and implements the concept of transmitting packets to the desired address (IP address). The appropriate level of interaction ( Internet level, see figure 4.1 ) provides the ability to move packets across the network using the route that is currently optimal.

The IP addressing of computers on the Internet is based on the concept of a network of hosts. Host is a network entity that can transmit and receive IP packets, such as a computer, workstation, or router. Hosts are connected to each other through one or more networks. The IP address of any of the hosts consists of from the address (number) of the network (network prefix) and the address of the host on this network.

By convention when the IP protocol was developed, an address is represented by four decimal numbers separated by periods. Each of these numbers cannot exceed 255 and represent one byte of a 4-byte IP address. The allocation of only four bytes for addressing the entire Internet is due to the fact that at that time the mass distribution of local networks was not foreseen. There was no talk at all about personal computers and workstations. As a result, 32 bits were allocated for the IP address, of which the first 8 bits designated the network, and the remaining 24 bits - the computer on the network. The IP address is assigned by the network administrator when configuring computers and routers. For convenience, they are represented as four decimal digits separated by a comma, for example, 195.10.03.01. There are five classes of IP addresses - A, B, C, D, E. Depending on the class of IP address on the network, there will be a different number of addressable subnets and the number of computers on a given subnet.

Since it is extremely inconvenient to use digital addressing of networks when working on the Internet, symbolic names are used instead of numbers - domain names. A domain is a group of computers united by one name. Symbolic names give the user the opportunity to better navigate the Internet, since remembering a name is always easier than a numeric address.

In addition, all countries in the world have their own symbolic name that denotes the top-level domain of that country. For example, de - Germany, us - USA, ru - Russia, by - Belarus, etc.

The structural components of the Internet include:

- routers- special devices that connect individual local networks with each other by directly addressing each of the subnets using IP addresses. Forwarding packets between subnets according to destination addresses is called routing;

- proxy server(from the English proxy - "representative, authorized") - a special computer that allows users of the local network to receive information stored on computers on the Internet. First, the user connects to the proxy server and requests some resource (for example, e-mail) located on another server. Then the proxy server either connects to the specified server and gets the resource from it, or returns the resource from its own memory. The proxy server also allows you to protect the client computer from some network attacks;

- DNS server - a special computer that stores domain names.

To protect the local network from unauthorized access (hacker attacks, viruses, etc.), software and hardware systems are used - firewalls. In the network, it filters the passage of information in both directions and blocks unauthorized access to a computer or local network from the outside. The firewall allows you to control the use of ports and protocols, "hide" unused ports to exclude attacks through them, and also prohibit / allow access of specific applications to specific IP addresses, i.e. control everything that can become a tool of a hacker and unscrupulous firms. In general, firewalls work at the network layer and carry out packet filtering, although you can organize protection at the application or data link layer. Packet filtering technology is the cheapest way to implement a firewall because in this case, packets of different protocols can be checked at high speed. The filter analyzes packets at the network level and is independent of the application being used.

Firewall is a kind of software firewall, a means of controlling incoming and outgoing information. Firewall software is built into standard operating systems.

ISP- is a provider of access to the Internet - any organization that provides individuals or organizations with access to the Internet. Providers are generally divided into two classes:

Internet Access Providers (ISP);

Online Service Providers (OSP).

The ISP can be a business that pays for a high-speed connection to one of the companies that are part of the Internet (AT&T, Sprint, MCI in the US, etc.). It can also be national or international companies that have their own networks (such as WorldNet, Belpak, UNIBEL, etc.)

OSPs, sometimes referred to simply as "interactive services," may also have their own networks. They provide additional information services available to customers by subscribing to these services. For example, Microsoft's OSPs offer users access to an Internet service from Microsoft, America Online, IBM, and others. ISP providers are the most common.

Typically, a large provider has its own POP (point-of-presence) in cities where local users connect.

To interact with each other, various providers agree on connections to so-called NAP (Network Access Points) access points, through which the information flows of networks belonging to a particular provider are combined.

Hundreds of large providers operate on the Internet, their backbone networks are connected through NAP, which provides a single information space of the global computer network Internet.

The main services of the Internet include:

- e-mail (e-mail);

- WWW (World Wide Wed, world wide web);

- FTP (File Transfer Protocol);

- UseNet - newsgroups, the corresponding NNTP (Network News Transport Protocol) is designed to replicate articles in the UseNet distributed discussion system;

- remote terminal Telnet service provides the ability to work on a remote computer in a network that supports the Telnet service;

- IP-telephony service (IP-Telephony)- allows you to use the Internet as a means of voice information exchange and fax transmission in real time using the technology of compression of voice signals. To ensure the operation of IP telephony, the H.323 protocol stack is used, which splits the data stream into packets, assembles the packets in the correct sequence, identifies packet loss, ensures synchronization and continuity of data arrival. Voice data is transmitted over UDP without waiting for a receipt.

In addition to these most popular protocols on the Internet, others are also used - network file system (NSF), network monitoring and management (SNMP), remote procedure execution (RPC), network printing, etc.

There are several organizations responsible for the development of the Internet:

- Internet Society (ISOC)- a professional community that deals with the growth and evolution of the Internet as a global communication infrastructure;

- Internet Architecture Board (IAB) - an ISOC-managed organization that oversees the technical oversight and coordination of work for the Internet. The IAB coordinates research and development for the TCP / IP protocol and is the ultimate authority in defining new Internet standards. It includes: Internet Engineering Task Force (IETF) - an engineering group that deals with the immediate technical problems of the Internet and Internet Research Task Force (IRTF)- coordinates long-term projects on TCP / IP protocols;

- Internet Corporation for Assigned Names and Numbers (ICANN) - international non-profit organization for endowing local and regional networks with a specific IP-address . This organization has a special information center - InterNIC (Internet Network Center);

- World Wide Web Consortium, W3C (W3 Consortium) - coordinating organization for the promotion of the Internet as an environment for the implementation of positive social and economic transformations of society.

A corporate network (CS) is an organization's infrastructure that supports the solution of urgent tasks and ensures its implementation missions... It unites in a single space the information systems of all objects of the corporation and is created as the systemic and technical basis of the information system, as its main system-forming component, on the basis of which other subsystems are constructed.

Creation of a corporate network allows:

Create a single information space;

Promptly receive information and generate consolidated reports at the enterprise level;

Centralize financial and informational data flows;

Collect and process information promptly;

Reduce costs when using server solutions and moving from solutions for workgroups to solutions of the enterprise level;

Process multimedia data streams between departments;

Reduce the cost of communication between departments and organize a single numbering space;

Provide high-quality communication at high speeds;

Organize a video surveillance system.

Basic requirements for modern corporate networks:

- scalability means the possibility of increasing the capacity of servers (performance, volume of stored information, etc.) and territorial expansion of the network;

- network reliability- is one of the factors that determine the continuity of the organization;

- performance- the growth in the number of network nodes and the volume of processed data makes constantly increasing demands on the bandwidth of the communication channels used and the performance of devices that ensure the functioning of the corporate information system;

- economic efficiency- saving money on the creation, operation and modernization of the network infrastructure with the constant growth of the scale and complexity of corporate networks;

- Information Security - ensures the stability and security of the business as a whole, protects the storage and processing of confidential information in the network.

The following basic principles of building a corporate network are distinguished:

- comprehensive character - the network extends to the entire corporation;

- integration - the corporate network provides the ability for its users to access any data and applications, taking into account the information security policy;

- global - The CC provides information on the life of the organization, regardless of policy and state borders;

- adequate performance- the network has the property of controllability and has a high level of reliability, survivability, serviceability with support for applications critical to the corporation's activities;

Maximum use standard solutions, standard unified components.

The corporate network can be viewed from different points of view:

- structures ( system and technical infrastructure );

- system functionality(services and applications);

- performance characteristics to (properties and services).

From a systemic and technical point of view, it is an integral structure consisting of several interconnected and interacting levels: a computer network, telecommunications, computer and operating platforms, middleware, applications.

From a functional point of view, the CS is an effective medium for the transmission of relevant information necessary for solving the problems of the corporation.

From the point of view of system functionality, the CS looks like a single whole, providing users and programs with a set of useful services ( services), system-wide and specialized applications, which has a set of useful qualities and contains service, guaranteeing the normal functioning of the network.

Typically, CS provides users and applications with a number of universal services - DBMS service, file service, information service (Web service), e-mail, network printing, and others.

TO system-wide applications include automation tools for individual labor, used by various categories of users and focused on solving typical office tasks - word and spreadsheet processors, graphic editors, etc.

Specialized applications are aimed at solving problems that are impossible or technically difficult to automate using system-wide applications, and within the corporation define the application functionality.

The corporate network provides the ability to deploy new applications and their effective operation while maintaining investment in it, and in this sense should have the properties of openness, performance and balance, scalability, high availability, security and manageability. These properties determine performance characteristics the information system being created.

System-wide services Is a set of tools that are not directly aimed at solving applied problems, but are necessary to ensure the normal functioning of the CIS. Information security, high availability, centralized monitoring and administration services must be included in the COP.

CS is a mixed topology network that includes several local area networks.

The speed and ease of deployment of a local network;

Low cost of purchasing equipment;

Low operating costs and no monthly fees;

Preservation of investments in the local network when moving and changing office.

The main disadvantage of such networks is that the data transfer rate decreases with increasing distance.

The use of the Internet as a transport medium for data transmission when building a corporate network of an enterprise (Fig.4.4) provides the following advantages:

Low subscription fee;

Ease of implementation.

Figure 4.4 - Using the Internet as a transport medium
data transmission

The disadvantages of such a network include low reliability and safety, the lack of a guaranteed data transfer rate.

Combining local networks of an enterprise into a single corporate network based on leased data transmission channels (Fig. 4.5) brings the following advantages:

High quality of the provided data transmission channels;

High level of services and services provided by the provider;

Guaranteed data transfer rate.

Figure 4.5 - Combining local networks into a single network based on leased data transmission channels

A properly designed and implemented corporate network, the choice of reliable and efficient equipment determines the efficiency of the corporate information system, the possibility of its effective and long-term operation, modernization and adaptation to rapidly changing business conditions and new challenges.

The infrastructural components of the corporate network are:

The cable system that forms the physical medium of data transmission;

Network equipment that provides data exchange between terminal equipment (workstations, servers, etc.).

When creating corporate networks, the main task is to build building-scale networks ( local) and groups of nearby buildings ( campus), consolidation using communication channels of territorially remote subdivisions. The Internet or city network can act as a unifying means.

When building local and campus networks, switches, and when building geographically distributed networks - routers... Switches provide high-speed communication within the local network, transmitting information only to the destination nodes. The switches operate with the addresses of the channel protocol, which is usually Ethernet / Fast Ethernet / Gigabit Ethernet, which ensures transparent network operation, and the switches can perform their basic functions without laborious configuration. When transmitting information, routers operate logical addresses - for example, addresses of the IP, IPX, etc. protocols, which allows them to use a hierarchical representation of the structure of a network that is large in scale or consists of disparate and heterogeneous segments when processing information.

Office wireless networks provide an alternative to traditional cabling systems. Their main difference from cable systems is that data between computers and network devices is transmitted not through wires, but through a highly reliable wireless channel. Due to the use of a wireless network built in accordance with the Wi-Fi specification, the flexibility and scalability of the local network is provided, the ability to easily connect new equipment, workstations, mobile users, regardless of the type of computer used. The use of wireless networking technologies allows you to receive additional services: access to the Internet in a conference room or meeting room, organizing a Hot-Spot access point, etc.

Benefits of using wireless networks:

Speed ​​and ease of deployment of a wireless network;

Network scalability, the ability to build multi-cell networks;

Preservation of investments in the local network when changing the location of the office;

Fast restructuring, changing the configuration and size of the network;

User mobility in the network coverage area.

In fig. 4.6 shows an office network consisting of several wireless cells, in the center of which there are access points united by a single wired channel or wireless bridges. Such a network provides the highest performance, scalability, free movement of users within the radio coverage areas of the access points.

To organize uninterrupted operation and ensure data security in the CS, a network administration service is required. Administration- This is a management process, activities for the management of the assigned area of ​​work through administrative management methods.

Figure 4.6 - Wireless network in the organization

Administration of a computer network presupposes informational support of users, allows minimizing the influence of the human factor on the occurrence of failures in its work.

System Administrator- an employee who ensures the network security of the organization, the creation of optimal performance of the network, computers and software. Often, the functions of a system administrator are performed by IT outsourcing companies.

The administrator solves the issues of network planning, selection and purchase of network equipment, monitors the progress of network installation and ensures that all requirements are met. After installing the network equipment, he checks it and installs network software on servers and workstations.

The administrator's responsibilities include monitoring the use of network resources, registering users, changing user access rights to network resources, integrating heterogeneous software used on file servers, database management systems (DBMS) servers, on workstations, timely copying and backing up data and restoring normal operation of network equipment and software after failures.

In large organizations, these functions can be distributed among several system administrators ( security administrators, users, Reserve copy, databases and etc.).

Web Server Administrator - is engaged in the installation, configuration and maintenance of web server software.

Database administrator- specializes in database maintenance and design.

Network administrator- is engaged in the development and maintenance of networks.

System engineer(or system architect) - is engaged in building a corporate information infrastructure at the application level.

Network security administrator- deals with information security problems.

When administering a network connected to the Internet and in which Internet services are installed, the following problems arise:

Networking based on TCP / IP protocols;

Connecting a local or corporate network to the Internet;

Routing of information transfer in the network;

Obtaining a domain name for an organization;

Exchange of e-mail within the organization and with addressees outside of it;

Organization of information services based on Internet and Intranet technologies;

Network security.

Classification of telecommunication network services (filled areas correspond to traditional services of telecom operators)

Corporate network Is a network that supports the operation of a particular enterprise that owns a given network. Only employees of the given enterprise are users of the corporate network. In general, services are not provided to third-party organizations and users.

Typically, the term corporate network is used for a large enterprise network. Such a network is composite, including various local area networks.

The structure of the corporate network as a whole corresponds to the generalized structure of the telecommunications network (Figure 13.1.). However, there are also some differences. For example, local area networks connecting end users are included in the corporate network. Further, the names of the structural units of the corporate network reflect not only the coverage area, but also the organizational structure of the enterprise. So, it is customary to divide the corporate network into a network of departments and work groups, a network of buildings and territories, a highway.

In fig. 13.2 shows an example of a department network architecture. The main purpose of the department network is to separate local resources (applications, data, laser printers, modems). Typically, departmental networks have one or two file servers and no more than thirty users. Most of the enterprise traffic is localized on these networks. Department networks are usually built around a single networking technology — Ethernet, Token Ring, or FDDI. Such a network is characterized by one or at most two types of operating systems.

Rice. 13.2. Department network

The building and area network connects the networks of different departments of the same enterprise within an individual building or within the same area, covering an area of ​​several square kilometers. For the construction of such networks, appropriate technologies of local networks are used.

Typically, a building (territory) network is built on a hierarchical basis with its own backbone built on the basis of Gigabit Ethernet technology, to which the networks of departments using Fast or Internet technology are connected (Figure 13.3).

The main feature of corporate networks is their scale. The number of users and computers in a corporate network can be measured in thousands, and the number of servers in hundreds; the distances between the networks of individual territories may turn out to be such that the use of global connections becomes necessary (Figure 13.4). An indispensable attribute of a corporate network is a high degree of heterogeneity (heterogeneity) - it is impossible to satisfy the needs of thousands of users using the same type of software and hardware. A corporate network necessarily uses different types of computers - from mainframes to personal computers, several types of operating systems, and many different applications.

Corporate information network

“A corporate network is a network whose main purpose is to support the operation of a particular enterprise that owns the network. Only the employees of this enterprise are users of the corporate network. " The primary purpose of a corporate network is to provide comprehensive information services to employees of an enterprise, in contrast to a simple local network, which provides only transport services for the transfer of digital information streams.

Information flows in the modern world are critical. Today, no one needs to be convinced that a reliable and easily manageable information system is necessary for the successful operation of any corporate structure. Any enterprise has internal connections that ensure interaction between management and structural divisions, and external relations with business partners, enterprises, authorities. External and internal communications of the enterprise can be considered as informational. But at the same time, an enterprise can be viewed as an organization of people united by common goals. To achieve these goals, various mechanisms are used to facilitate their implementation. One of these mechanisms is effective production management, based on the processes of obtaining information, processing it, making decisions and communicating them to the performers. The most important part of management is decision making. To work out the right decision requires complete, prompt and reliable information.

The completeness of information characterizes its volume, which should be sufficient for making a decision. The information must be up-to-date, i.e. such that during its transmission and processing the state of affairs does not change. The reliability of information is determined by the degree to which its content corresponds to the objective state of affairs. The information should come to the workplace of the head of the enterprise or the executor in a form that facilitates its perception and processing. But how to organize a high-quality information system at the lowest cost? What equipment should you give preference to when choosing?

A significant part of the telecommunications equipment market is occupied by hardware designed to provide corporate structures with intra-industrial communication and data transmission services. Moreover, these concepts can mean a fairly wide range of modern services. Using the technologies of modern automatic telephone exchanges, it is possible to deploy a digital network with the integration of ISDN services and provide users with access to databases and the Internet, organize a mini-cellular communication system of the DECT standard, introduce a videoconference or intercom mode.

Modern automatic telephone exchanges use digital technologies, a modular construction principle, have a relatively high reliability, provide a full set of basic functions (call routing, administration, etc.), provide the ability to connect additional equipment such as voice mail, billing systems, etc.

Any organization is a set of interacting elements (departments), each of which can have its own structure. The elements are interconnected functionally, i.e. they perform certain types of work within the framework of a single business process, as well as informational, exchanging documents, faxes, written and oral orders, etc. In addition, these elements interact with external systems, and their interaction can also be both informational and functional. And this situation is true for almost all organizations, no matter what type of activity they are engaged in - for a government institution, a bank, an industrial enterprise, a commercial firm, etc.

This general view of the organization allows us to formulate some general principles of building corporate information systems, i.e. information systems throughout the organization.

A corporate network is a system that provides information transfer between various applications used in a corporation's system. A corporate network is a network of a separate organization. A corporate network is any network that uses the TCP / IP protocol and uses Internet communication standards, as well as service applications that provide data delivery to network users. For example, a business might set up a Web server to publish announcements, production schedules, and other service documents. Employees access the documents they need using Web content viewers.

Web servers on the corporate network can provide users with services similar to those of the Internet, such as working with hypertext pages (containing text, hyperlinks, graphics, and sound recordings), providing the necessary resources when requested by web clients, and accessing databases.

A corporate network, as a rule, is geographically distributed, i.e. uniting offices, divisions and other structures located at a considerable distance from each other. The principles by which a corporate network is built are quite different from those used to create a local network. This limitation is fundamental, and when designing a corporate network, all measures should be taken to minimize the amount of data transferred. For the rest, the corporate network should not impose restrictions on which applications and how they process the information carried over it. An example of a corporate network is shown in Figure 9.

The process of creating a corporate information system

The main stages of the process of creating a corporate information system can be distinguished:

Conduct an information survey of the organization;

Based on the results of the survey, select the architecture of the system and the hardware and software for its implementation, based on the results of the survey, select and / or develop the key components of the information system;

Corporate database management system;

Business operations and document management automation system;

Electronic document management system;

Special software tools;

Decision support systems.

When designing a corporate information network of an organization, it was necessary to be guided by the principles of consistency, standardization, compatibility, development and scalability, reliability, security and efficiency.

The principle of consistency implies that during the design and creation of the corporate information system, its integrity must be maintained by creating reliable communication channels between subsystems.

The principle of standardization provides for the use of standard equipment and materials that comply with international standards ISO, FCC, Gosstandards of the Republic of Kazakhstan.

Example of a corporate network

Figure 9

The principle of compatibility, directly related to the principle of standardization, ensures the compatibility of equipment, interfaces and data transfer protocols throughout the organization and the global network.

The principle of development (scalability) or openness of the corporate information system is that even at the design stage, the corporate information system should be created as an open system that allows replenishment, improvement and updating of subsystems and components, the connection of other systems. The development of the system will be carried out by replenishing it with new subsystems and components, modernizing existing subsystems and components, updating the used computer technology with more advanced ones.

The principle of reliability consists in duplicating important subsystems and components in order to ensure the uninterrupted operation of the EIS, to create a stock of materials and equipment for prompt repair and replacement of equipment.

The principle of corporate information system security implies the use of hardware and software tools and organizational methods in building corporate information systems that exclude unauthorized access to equipment and information retrieval from the corporate information system by external and internal objects and subjects that do not have special permission.

The principle of efficiency is to achieve a rational ratio between the costs of designing and creating the corporate information system and the target effects obtained as a result of the practical implementation and operation of the integrated information system. The economic essence of the creation and implementation is to ensure an effective and efficient exchange of information between the divisions of the organization to solve production, financial and economic issues, expressed in reducing the cost of telephone communications and postage.

We will analyze the specific implementation of the foregoing later at the design stage of the computer information network of the organization under study.

A corporate network is a network whose main purpose is to support the operation of a particular enterprise that owns a given network. The users of the corporate network are the employees of the given enterprise. Depending on the scale of the enterprise, as well as on the complexity and variety of tasks to be solved, there are department networks, campus networks and corporate networks (that is, a large enterprise network).

Department networks- These are networks that are used by a relatively small group of employees working in one department of the enterprise.

The main purpose of the department network is to separate local resources such as applications, data, laser printers and modems. Typically, departmental networks have one and two file servers, no more than thirty users, and are not subdivided into subnets (Figure 55). Most of the enterprise traffic is localized in these networks. Department networks are usually created on the basis of any one network technology - Ethernet, Token Ring. Such a network is characterized by one or at most two types of operating systems. The small number of users enables the network to be used by departments of peer-to-peer network operating systems such as Microsoft's Windows.

There is another type of networks, close to department networks - working group networks... These networks include very small networks, including up to 10-20 computers. The characteristics of workgroup networks are practically the same as those of departmental networks. Properties such as network simplicity and homogeneity are most pronounced here, while departmental networks can in some cases approach the next largest type of network - campus networks.

Campus networks got their name from the English word "campus" - a campus. It was on the territory of university campuses that it was often necessary to combine several small networks into one large network. Now this name is not associated with student campuses, but is used to refer to the networks of any enterprises and organizations.

The main features of campus networks are that they connect many networks of different departments of the same enterprise within a single building or within a single territory covering an area of ​​several square kilometers (Fig. 56). However, global connections are not used on campus networks. The services of such a network include interoperability between departmental networks. Access to shared enterprise databases, access to shared fax servers, high-speed modems and high-speed printers. As a result, employees of each department of the enterprise gain access to some files and resources of networks of other departments. An important service provided by campus networks has become access to corporate databases, regardless of what types of computers they are located on.

It is at the campus network level that the challenges of integrating heterogeneous hardware and software arise. The types of computers, network operating systems, network hardware may vary from department to department. Hence the complexities of managing campus networks. In this case, administrators should be more qualified, and the means of operational management of the network should be more advanced.

Corporate networks also called enterprise-wide networks, which corresponds to the literal translation of the term "enterprise - wide network". Enterprise-wide networks (corporate networks) unite a large number of computers in all areas of an individual enterprise. They can be complexly connected and cover a city, region, or even a continent. The number of users and computers can be measured in thousands, and the number of servers - in hundreds, the distances between the networks of individual territories can be such that the use of global connections becomes necessary (Fig. 57). To connect remote local networks and individual computers in the corporate

networks use a variety of telecommunication means, including telephone channels, radars, satellite communications. A corporate network can be thought of as "islands" of local networks "floating" in the telecommunications environment. An indispensable attribute of such a complex and large-scale network is a high degree of heterogeneity (interogeneity) - it is impossible to satisfy the needs of thousands of users using the same type of hardware. In a corporate network, various types of computers are necessarily used - from mainframes to personal computers, several types of operating systems and many different applications. The heterogeneous parts of the corporate network should work as a whole, providing users with the most convenient and easy access to all the necessary resources.

The emergence of the corporate network is a good illustration of the well-known philosophical postulate about the transition from quantity to quality. When connecting separate networks of a large enterprise with branches in different cities and even countries into a single network, many quantitative characteristics of the united network exceed a certain critical threshold, beyond which a new quality begins. Under these conditions, the existing methods and approaches to solving traditional problems of smaller-scale networks for corporate networks turned out to be unsuitable. Tasks and problems have come to the fore that, in the distributed networks of workgroups, departments, and even campuses, either were of secondary importance or did not appear at all.

In distributed local networks, consisting of 1-20 computers and approximately the same number of users, the necessary information data is moved to the local database of each computer, to the resources of which users must have access, that is, data is retrieved from the local account database and based on their access provided or not provided.

But if there are several thousand users on the network, each of whom needs access to several dozen servers, then, obviously, this solution becomes extremely ineffective, since the administrator must repeat the operation of entering the credentials of each user several dozen times (according to the number of servers). The user himself is also forced to repeat the logon procedure every time he needs access to the resources of the new server. The solution to this problem for a large network is to use a centralized help desk, in the database of which the necessary information is stored. The administrator performs the operation of entering user data into this database once, and the user performs the logical login procedure once, and not to a separate server, but to the entire network. As the scale of the network grows, the requirements for its reliability, performance, and functionality increase. Increasing amounts of data circulate over the network, and the network must ensure their safety and security, along with availability. All this leads to the fact that corporate networks are built on the basis of the most powerful and diverse hardware and software.

Of course, corporate computing has its own challenges. These problems are mainly associated with the organization of effective interaction of individual parts of a distributed system.

First, there are the complexities associated with software - operating systems and applications. Programming for distributed systems is fundamentally different from programming for centralized systems. So, a network operating system, performing all the functions of managing local computer resources, will solve its many problems of providing network servers. The development of network applications is complicated by the need to organize the joint work of their parts running on different machines. A lot of concerns are delivered by ensuring the compatibility of the software installed on the network nodes.

Second, there are many problems associated with transporting messages over communication channels between computers. The main tasks here are to ensure reliability (so that the provided data is not lost or distorted) and performance (so that data exchange occurs with acceptable delays). In the structure of the total cost of a computer network, the costs of solving "transport issues" make up a significant part, while in centralized systems these problems are completely absent.

Thirdly, these are issues related to security, which are much more difficult to solve in a computer network than in an autonomous computer. In some cases, when security is especially important, it is better to refuse to use the network altogether.

However, in general, the use of local (corporate) networks gives the enterprise the following opportunities:

Sharing expensive resources;

Improvement of commutation;

Improving access to information;

Fast and high-quality decision making;

Freedom in the territorial distribution of computers.

A corporate network (enterprise network) is characterized by:

Scale - thousands of user computers, hundreds of servers, huge volumes of data stored and transmitted over communication lines, a variety of applications;

High degree of heterogeneity (heterogeneity) - the types of computers, communication equipment, operating systems and applications are different;

The use of global connections - the networks of branches are connected using telecommunication means, including telephone channels, radio channels, satellite communications.

network of a large enterprise). Before discussing the characteristic features of each of the listed types of networks, let us dwell on the factors that force enterprises to acquire their own computer network.

What gives the enterprise the use of networks

This question can be clarified as follows:

• When to deploy in an enterprise computer networks preferable to using stand-alone computers or multi-machine systems?
• What new opportunities are emerging in the enterprise with the advent of the computer network?
• Finally, does an enterprise always need a network?

If you do not go into details, then the ultimate purpose of using computer networks at the enterprise is an increase in the efficiency of its work, which can be expressed, for example, in an increase in profits. Indeed, if computerization reduced the cost of producing an existing product, shortened the development time for a new model, or accelerated customer service, this means that the enterprise really needed a network.

Conceptual advantage of networks, which follows from their belonging to distributed systems, before autonomous computers is their ability to perform parallel computing... As a result, in a system with several processing units, in principle, it is possible to achieve productivity exceeding the maximum currently possible performance of any separate, no matter how powerful, processor. Distributed systems potentially have a better performance / cost ratio than centralized systems.

Another obvious and important advantage of distributed systems is their higher fault tolerance... Under fault tolerance one should understand the ability of the system to perform its functions (maybe not in full) in the event of failure of individual hardware elements and incomplete data availability. Redundancy is the basis for increased fault tolerance in distributed systems. Redundancy of processing units (processors in multiprocessor systems or computers in networks) allows, if one node fails, to reassign tasks assigned to it to other nodes. For this purpose, dynamic or static reconfiguration procedures can be provided in a distributed system. V computer networks some datasets may be duplicated on external storage devices several computers on the network, so that if one of them fails, the data remains available.

The use of geographically distributed computing systems is more consistent with the distributed nature of applications in some subject areas, such as automation technological processes, banking, etc. In all these cases, there are separate consumers of information dispersed over a certain territory - employees, organizations or technological installations. These consumers autonomously solve their problems, so they should be provided with their own computing facilities, but at the same time, since the tasks they solve are logically closely interconnected, their computing facilities should be combined into a common system. The optimal solution in this situation is to use a computer network.

For the user, distributed systems also provide such advantages as the ability to share data and devices, as well as the ability to flexibly distribute work throughout the system. This separation of costly peripheral devices- such as high-capacity disk arrays, color printers, plotters, modems, optical disks - in many cases it is the main reason for deploying a network in an enterprise. A user of a modern computer network works at his computer, often not realizing that he is using the data of another powerful computer located hundreds of kilometers away. He sends e-mail through a modem connected to a communications server shared by several departments in his enterprise. The user has the impression that these resources are connected directly to his computer, or "almost" connected, since they require minor additional steps to work with compared to using their own resources.

Recently, another incentive for the deployment of networks began to prevail, much more important in modern conditions than the cost savings due to the division of expensive hardware or software among the employees of the corporation. This motive was the desire to provide employees with prompt access to extensive corporate information. In the face of tough competition in any sector of the market, the company ultimately wins, whose employees can quickly and correctly answer any client's question - about the capabilities of their products, about the conditions for their use, about solving various problems, etc. In a large enterprise, even a good manager hardly knows all the characteristics of each of the manufactured products, especially since their nomenclature can be updated every quarter, if not month. Therefore, it is very important that the manager has the opportunity from his computer connected to corporate network, say, in Magadan, transfer the client's question to the server located in the central office of the enterprise in Novosibirsk, and promptly receive an answer that satisfies the client. In this case, the client will not apply to another company, but will continue to use the services of this manager.

Using the network leads to improvement communications between employees of the enterprise, as well as its customers and suppliers. Networks reduce the need for businesses to use other forms of communication, such as telephone or mail. It is often the ability to organize e-mail that is one of the reasons for deploying a computer network in an enterprise. New technologies are becoming more and more widespread, which make it possible to transfer not only computer data, but also voice and video information through network communication channels. Corporate network, which integrates data and multimedia information, can be used for organizing audio and video conferencing, in addition, on its basis, its own internal telephone network can be created.

Benefits of using networks

1. An integral advantage is an increase in the efficiency of the enterprise.
2. Ability to perform parallel computing, due to which productivity can be increased and fault tolerance.
3. More consistent with the distributed nature of some applications.
4. The ability to share data and devices.
5. Possibility of flexible distribution of work throughout the system.
6. Online access to extensive corporate information.
7. Improving communications.

Problems

1. Complexity of system and application software development for distributed systems.
2. Performance issues and reliability data transmission over the network.
3. Security issue.

Of course, when using computer networks there are also problems associated mainly with the organization of effective interaction of individual parts of a distributed system.

First, there are problems in the software: operating systems and applications. Programming for distributed systems is fundamentally different from programming for centralized systems. So, a network operating system, performing in the general case all the functions of managing the local resources of a computer, moreover, it solves numerous problems associated with the provision of network services. The development of network applications is complicated by the need to organize the joint work of their parts running on different machines. A lot of the hassle is also provided by ensuring the compatibility of the software installed on the network nodes.

Second, there are many problems associated with transporting messages over communication channels between computers. The main tasks here are to ensure reliability (so that the transmitted data is not lost or distorted) and performance (so that data exchange occurs with acceptable delays). In the structure of the total cost of a computer network, the costs of solving "transport issues" constitute a significant part, while in centralized systems these problems are completely absent.

Thirdly, these are issues related to security, which are much more difficult to solve in a computer network than in a stand-alone computer. In some cases, when security is especially important, it is better to refuse to use the network.

There are many more pros and cons, but the main proof of the efficiency of using networks is the indisputable fact of their widespread distribution. Today it is difficult to find an enterprise that does not have at least a one-segment network of personal computers; more and more networks with hundreds of workstations and dozens of servers appear, some large organizations acquire private global networks that unite their branches, remote for thousands of kilometers. In each specific case, there were reasons for creating a network, but the general statement is also true: there is still something in these networks.

Department networks

Department networks- These are networks that are used by a relatively small group of employees working in one department of the enterprise. These employees perform some general tasks, such as accounting or marketing. It is believed that a department can have up to 100-150 employees.

The main purpose of the department network is separation local resources such as applications, data, laser printers and modems. Typically, departmental networks have one or two file servers, no more than thirty users (Figure 10.3), and are not subnetted. Most of the enterprise traffic is localized on these networks. Department networks are usually created on the basis of any one network technology - Ethernet, Token Ring. Such a network most often uses one or at most two types of operating systems. A small number of users allows peer-to-peer network operating systems such as Windows 98 to be used in departmental networks.

Rice. 10.3.

Network management tasks at the department level are relatively simple: adding new users, fixing simple failures, installing new nodes, and installing new software versions. Such a network can be managed by an employee who devotes only part of his time to performing the duties of an administrator. Most often, the network administrator of a department does not have special training, but is the person in the department who understands computers best of all, and of course it turns out that he is engaged in network administration.

There is another type of networks that are close to department networks - workgroup networks. These networks include very small networks, including up to 10-20 computers. The characteristics of workgroup networks do not differ much from the characteristics of departmental networks described above. Properties such as network simplicity and homogeneity are most pronounced here, while departmental networks can in some cases approach the next largest type of network - campus networks.

Campus networks

Campus networks get their name from the English word campus - a campus. It was on the territory of university campuses that it was often necessary to combine several small networks into one large one. Now this name is not associated with student campuses, but is used to refer to the networks of any enterprises and organizations.

Campus networks(Figure 10.4) unite many networks of different departments of the same enterprise within a single building or one territory covering an area of ​​several square kilometers. However, global connections are not used on campus networks. The services of such a network include interoperability between departmental networks, access to shared enterprise databases, access to shared fax servers, high-speed modems, and high-speed printers. As a result, employees of each department of the enterprise gain access to some files and resources of networks of other departments. Campus networks provide access to corporate databases no matter what types of computers they are located on.

Rice. 10.4.

It is at the campus network level that the problems of integrating heterogeneous hardware and software arise. The types of computers, network operating systems, network hardware in each department may differ. Hence the complexities of managing campus networks. In this case, administrators should be more qualified, and the means of operational management of the network - more effective.

Enterprise networks

Corporate networks also called enterprise-wide networks, which corresponds to the literal translation of the term "enterprise-wide networks" used in the English literature to refer to this type of network. Enterprise networks ( corporate networks) unite a large number of computers in all territories of an individual enterprise. They can be intricately connected and can cover a city, region, or even a continent. The number of users and computers can be measured in thousands, and the number of servers - in hundreds, the distances between networks of individual territories are such that you have to use corporate network different types of computers will definitely be used - from mainframes to personal computers, several types of operating systems and many different applications. Inhomogeneous parts corporate network should work as a whole, providing users with the most convenient and simple access to all the necessary resources.

Enterprise networks ( corporate networks) unite a large number of computers in all territories of an individual enterprise. For corporate network are characteristic:

• scale - thousands of user computers, hundreds of servers, huge volumes of data stored and transmitted over communication lines, a variety of applications;
• a high degree of heterogeneity - different types of computers, communication equipment, operating systems and applications;
• use of global connections - the networks of branches are connected using telecommunication means, including telephone channels, radio channels, satellite communications.

The emergence corporate networks is a good illustration of the well-known postulate about the transition from quantity to quality. When connecting separate networks of a large enterprise with branches in different cities and even countries, into a single network, many quantitative characteristics of the united network cross a certain critical threshold, beyond which a new quality begins. Under these conditions, the existing methods and approaches to solving traditional problems of smaller-scale networks for corporate networks proved to be unusable. Tasks and problems have come to the fore that in the networks of workgroups, departments and even campuses either were of secondary importance or did not appear at all. An example is the simplest (for small networks) task - maintaining credentials about network users.

The easiest way to solve this problem is to put the credentials of each user in the local credentials database of each computer that the user should have access to. When an attempt is made to access, this data is retrieved from the local account base and, based on this, access is granted or denied. In a small network of 5-10 computers and about the same number of users, this method works very well. But if the network has several thousand users, each of whom needs access to several dozen servers, then, obviously, this solution becomes extremely ineffective. The administrator must repeat the operation of entering the credentials of each user several dozen times (according to the number of servers). The user himself is also forced to repeat the logon procedure every time he needs access to the resources of the new server. A good solution to this problem for a large network is to use a centralized help desk that stores the accounts of all users on the network in a database. The administrator performs the operation of entering user data into this database once, and the user performs the logical login procedure once, and not to a separate server, but to the entire network.

When moving from a simpler type of network to a more complex one - from department networks to corporate network- the coverage area is increasing, it becomes more and more difficult to maintain connections between computers. As the scale of the network grows, the requirements for its reliability, performance, and functionality increase. An increasing amount of data circulates over the network, and it is necessary to ensure their safety and security, as well as availability. All this leads to the fact that corporate networks are built on the basis of the most powerful and diverse hardware and software.