Select a network management method. Calculation of energy consumption, LAN installation, artificial lighting, intake ventilation; Management of network resources and network users; Consideration of network security issues; It is necessary to develop a rational, flexible block diagram of the enterprise network, select the hardware and software configuration of the server, as well as work out the issues of ensuring the required level of data protection. 2. ANALYTICAL REVIEW OF LOCAL NETWORKS. 2.1. Review of the existing principles of building networks.

Understanding a local area network (LAN): A local area network (LAN) is a communication system that allows you to share the resources of computers connected to a network, such as printers, plotters, scanners, disks, CD-ROM drives, and other peripherals.

A local area network is usually geographically limited to one or more closely spaced buildings. 2.1.1. LAN classification. Computing networks are classified according to a number of features: 2.1.1.1. Distance between nodes.

Depending on the distances between connected nodes, computer networks are distinguished: territorial - covering a significant geographic area, another name for them - regional, they use global network technologies to combine local networks in a specific geographical region, for example, in a city.

Regional networks are designated MAN (Metropolitan Area Network). global networks are networks that can connect networks around the world, such as networks of several cities, regions or countries.

For interconnections, third-party communications media are usually used. The English name for territorial networks is WAN (Wide Area Network); local (LAN) - are a set of networked computers located within a small physical region, such as one or more buildings.

Local networks stand for LAN (Local Area Network). The only global network of its kind is the Internet (the World Wide Web (WWW) information service implemented in it is translated into Russian as the World Wide Web). It is a network of networks with its own technology.

In the Internet, there is the concept of intranets (Intranet) - corporate networks within the Internet. 2.1.1.2. Topology.

Network topology is the geometric shape of a network. Depending on the topology of node connections, there are bus (backbone), ring, star and mixed topology networks. bus (bus) - a local network in which communication between any two stations is established through one common path, and the data transmitted by any station simultaneously becomes available to all other stations connected to the same data transmission medium (the latter property is called broadcasting); ring (ring) - nodes are connected by a ring data transmission line (only two lines go to each node); data, passing through the ring, in turn become available to all network nodes; stellar (star) - there is a central node, from which data lines diverge to each of the other nodes; mixed (mixed) is a type of network topology that contains some features of the main network topologies (bus, star, ring). a) Bus b) Ring c) Star Fig.1 Types of topologies 2.1.1.3. By way of management.

Depending on the management method, networks are distinguished: client / server - they have one or more nodes (their name is servers) that perform control or special service functions on the network, and the remaining nodes (clients) are terminal, users work in them.

Client/server networks differ in the nature of the distribution of functions between servers, in other words, the types of servers (eg, file servers, database servers). When specializing servers for certain

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Network management tools.

Any complex computer network requires additional special controls beyond those found in standard network operating systems. This is due to a large number of various communication equipment, the operation of which is critical for the network to perform its basic functions. The distributed nature of a large corporate network makes it impossible to maintain its operation without a centralized management system that automatically collects information about the status of each hub, switch, multiplexer and router and provides this information to the network operator. Usually, the control system operates in an automated mode, performing the simplest actions to manage the network automatically, and allowing complex decisions to be made by a person based on the information prepared by the system. The control system must be integrated. This means that the functions of managing heterogeneous devices should serve the common goal of serving the end users of the network with a given quality.

The control systems themselves are complex software and hardware systems, so there is a limit to the expediency of using the control system - it depends on the complexity of the network, the variety of communication equipment used and the degree of its distribution over the territory. In a small network, you can use separate programs to manage the most complex devices, such as a switch that supports VLAN technology. Typically, each device that requires a fairly complex configuration is accompanied by a manufacturer with a stand-alone configuration and management program. However, as the network grows, the problem of integrating disparate device management programs into a single management system may arise, and in order to solve this problem, it may be necessary to abandon these programs and replace them with an integrated management system.

The architecture of a computer network management system is understood as a set of objects and links that combine tools that provide comprehensive administrative management of computing systems, and tools for managing ongoing processes in accordance with the requirements for the efficiency of using network capabilities to provide information and computing services to users.

Conventionally, the entire network in terms of control can be divided into a control system and a control object. The control system includes a set of computing tools designed to generate control actions and analyze information, on the basis of which a decision is made about control. Most network management architectures use the same basic structure and set of relationships.

The basic network management architecture consists of the following main elements:

network management system;

objects of control;

information base of management;

network control protocol.

In this case, as a rule, the network management system includes such elements as a set of control applications that help analyze data and troubleshoot, as well as an interface with which the network administrator can manage the network.

Typically, the system management system performs the following functions:

Accounting for hardware and software used(Configuration Management). The system automatically collects information about computers installed on the network and creates entries in a special database about hardware and software resources. The administrator can then quickly find out what resources he has and where a particular resource is located, for example, which computers need to update printer drivers, which computers have enough memory, disk space, and so on.

Software distribution and installation(Configuration Management). After the survey is completed, the administrator can create distribution packages for new software to be installed on all computers on the network or on a group of computers. In a large network where the advantages of a control system are shown, this installation method can significantly reduce the complexity of this procedure. The system may also allow centralized installation and administration of applications that run from file servers, as well as enable end users to run such applications from any network workstation.

Remote performance and problem analysis(Fault Management and Performance Management). This group of functions allows you to remotely measure the most important parameters of the computer, operating system, DBMS, etc. (for example, processor utilization, page break rate, physical memory utilization, transaction rate). To solve problems, this group of functions can give the administrator the ability to take over remote control of the computer in the mode of emulating the graphical interface of popular operating systems. The management system database typically stores detailed information about the configuration of all computers on the network so that problems can be analyzed remotely.

Network configuration and naming management

· error processing;

· performance and reliability analysis;

security management;

Accounting for the network.

The challenge is configuring switches and routers to support routes and virtual paths between network users. Agreed manual setting routing tables with a complete or partial rejection of the use of a routing protocol (and in some global networks, such as X.25, such a protocol simply does not exist) is a difficult task.

Switching is considered to be one of the most popular modern technologies. Switches on all fronts are crowding bridges and routers, leaving behind the latter only the organization of communication through the global network. The popularity of switches is primarily due to the fact that they allow you to increase network performance through segmentation. In addition to dividing the network into small segments, switches make it possible to create logical networks and easily regroup devices in them. In other words, switches allow you to create virtual networks.

Switch- a device designed as a network hub and acting as a high-speed multi-port bridge; the built-in switching mechanism allows you to segment the local network, as well as allocate bandwidth to end stations in the network.

There are three methods of switching in local networks:

Switching "on the fly" (cut-through);

Fragment-free switching;

Switching with buffering (store-and-forward switching).

At switching on the fly the incoming data packet is transmitted to the output port immediately after reading the destination address. The analysis of the entire package is not carried out. And this means that packets with errors can be skipped. This method provides the highest switching speed. Frames are transmitted in the following sequence:

1. Reception of the first bytes of the frame (including the destination address byte);

2. Search for the destination address in the address table;

3. Construction of a switching path by a matrix;

4. Reception of the remaining bytes of the frame;

5. Forwarding all bytes of the frame to the output port through the switching matrix;

6. Gaining access to the transmission medium;

7. Frame transmission to the network.

In this case, the switch can check the transmitted frames, but cannot remove bad frames from the network, since some of the bytes have already been sent to the network. Using on-the-fly switching provides significant performance gains, but at the expense of reliability. In networks with collision detection technology, the transmission of malformed frames can lead to a violation of data integrity.

At buffered switching the input packet is received completely, then it is checked for errors (the check is performed by the checksum) and only if no errors were found, the packet is transmitted to the output port. This method guarantees complete filtering of erroneous packets, however, at the cost of reducing the throughput of the switch compared to on-the-fly switching.

Fragmentless switching occupies an intermediate position between these two methods: it buffers only the first 64 bytes of the packet. If the packet ends there, the switch checks for checksum errors. If the packet is longer, it is sent to the output port without checking.

On different ports of the switch, errors can occur with different intensity. In this regard, it is very useful to be able to choose the switching method. This technology is called adaptive switching. Adaptive switching technology allows you to set for each port the mode of operation that is optimal for it. At first, switching on ports is carried out “on the fly”, then those ports on which many errors occur are switched to fragmentless switching mode. If, after this, the number of unfiltered packets with errors remains large (which is quite likely if many packets longer than 64 bytes are transmitted over the network), the port is switched to buffered switching mode.

In networks with information routing, the problem of data routing arises. In circuit-switched systems and when creating a virtual circuit, routing is organized once when the initial connection is established. In conventional packet and message switching modes, routing occurs continuously as data travels from one switching node to another. There are two main routing methods: pre-connected, in which before the start of data exchange between network nodes, a connection with certain parameters must be established, and dynamic, which uses datagram-type protocols that transmit a message to the network without first establishing a connection.

Routing consists in the correct choice of the output channel in the switching node based on the address contained in the header of the packet (message).

Routing can be centralized and decentralized. Centralized Routing allowed only in networks with centralized control: the route is selected in the network control center and the switches in the nodes only implement the decision. At decentralized routing control functions are distributed between switching nodes, which, as a rule, have a connecting processor.

A computer network is several computers within a limited area (located in the same room, in one or more closely spaced buildings) and connected to a single communication line. Today, most computer networks are local area networks (Local-Area Networks) that are located within a single office building and are based on a client/server computer model. A network connection consists of two communicating computers and a path between them. It is possible to create a network using wireless technologies, but this is not yet common.

In the client/server model, network communication is divided into two areas: the client side and the server side. By definition, a client requests information or services from a server. The server, in turn, serves the client's requests. Often, each side in a client/server model can act as both a server and a client. When creating a computer network, it is necessary to choose various components that determine which software and equipment you can use, forming your corporate network. A computer network is an integral part of today's business infrastructure, and a corporate network is just one of the applications used in it and, accordingly, should not be the only factor determining the choice of network components. The components necessary for the Intranet should be an addition to the existing network without leading to a significant change in its architectures.

Network management method

Each organization formulates its own network configuration requirements, determined by the nature of the tasks to be solved. First of all, it is necessary to determine how many people will work in the network. From this decision, in essence, all subsequent stages of creating a network will depend.

The number of workstations directly depends on the expected number of employees. Another factor is the hierarchy of the company. For a company with a horizontal structure, where all employees must have access to each other's data, a simple peer-to-peer network is the optimal solution.

A company built on the principle of a vertical structure, in which it is precisely known which employee and what information should have access, should focus on the more expensive version of the network - with a dedicated server. Only in such a network is it possible to administer access rights.

Network type selection.

In this case, the enterprise has 30 workstations, which need to be combined into a corporate network. Moreover, they are grouped into the following groups:

§ director of the enterprise - 1 workstation;

§ Department of direct subordination - 2 workstations;

§ secretary - 1 workstation;

§ departments 1, 2 and 3 of the 2nd department with 3, 3 and 4 workstations, respectively;

§ departments 4 and 5 of the 3rd department, 4 and 4 workstations each;

§ department 6 of the 4th department - 4 workstations.

Following from the scheme for choosing the type of network, we can decide that in this case a server installation is required, since we have a vertical structure of the enterprise, that is, differentiated access to information.

One of the main stages of planning is the creation of a preliminary scheme. In this case, depending on the type of network, the question arises of limiting the length of the cable segment. This may not be significant for a small office, but if the network spans several floors of a building, the problem appears in a completely different light. In this case, it is necessary to install additional repeaters (repeater).

In an enterprise situation, the entire network will be located on the same floor, and the distance between network segments is not so great that the use of repeaters is required.

Server hosting

Unlike setting up a peer-to-peer network, when building a LAN with a server, another question arises - where is the best place to install a server.

Several factors influence the choice of location:

§ due to the high noise level, it is desirable to install the server separately from other workstations;

§ it is necessary to provide constant access to the server for maintenance;

§ for reasons of information security, it is required to restrict access to the server;

The server is located in the network administrator's room, since only this room meets the requirements, that is, the noise level in the room is minimal, the room is isolated from others, therefore, access to the server will be limited.

The network administrator will be able to constantly monitor the operation of the server and perform server maintenance, as when installing the server.

Network architecture

Network architecture is the combination of topology, access method, and standards required to create a workable network.

The choice of topology is determined, in particular, by the layout of the room in which the LAN is deployed. In addition, the cost of acquiring and installing network equipment is of great importance, which is an important issue for the company, the price range here is also quite large.

The star topology is a more productive structure, each computer, including the server, is connected by a separate cable segment to a central hub (HAB).

The main advantage of such a network is its resistance to failures that occur due to malfunctions on individual PCs or due to damage to the network cable.

The most important characteristic of the exchange of information in local networks are the so-called access methods (access methods), which regulate the order in which the workstation gets access to network resources and can exchange data.

The abbreviation CSMA / CD hides the English expression "Carrier Sense Multiple Access with Collision Detection" (multiple access with carrier sense and collision detection). With this method, all computers get equal access to the network. Each workstation checks whether the channel is free before starting data transmission. At the end of the transmission, each workstation checks whether the sent data packet has reached the destination. If the answer is negative, the node performs a repeated transmission/reception control cycle and so on until it receives a message about the successful reception of information by the addressee.

Since this method has proven itself in small and medium-sized networks, this method is suitable for an enterprise. In addition, the Ethernet network architecture that the enterprise network will use uses this particular access method.

The Ethernet specification was proposed by the Xerox Corporation in the late seventies. Later, Digital Equipment Corporation (DEC) and Intel Corporation joined this project. In 1982, the specification for Ethernet version 2.0 was published. Based on Ethernet, the IEEE 802.3 standard was developed by the IEEE.

Twisted-pair (10Base-T) cable technology is currently the most popular. Such a cable does not cause difficulties when laying.

A twisted-pair network, unlike thin and thick coax, is built on a star topology. To build a network in a star topology, more cable is required (but the cost of twisted pair is not high). Such a scheme also has an invaluable advantage - high fault tolerance. The failure of one or more workstations does not lead to the failure of the entire system. True, if the hub fails, its failure will affect all devices connected through it.

Another advantage of this option is the ease of network expansion, since when using additional hubs (up to four in series), it becomes possible to connect a large number of workstations (up to 1024). When using unshielded twisted pair (UTP), the length of the segment between the hub and the workstation should not exceed 100 meters, which is not observed in the enterprise.

Network resources

The next important aspect of network planning is the sharing of network resources (printers, faxes, modems).

The listed resources can be used both in peer-to-peer networks and in networks with a dedicated server. However, in the case of a peer-to-peer network, its shortcomings are immediately revealed. To work with the listed components, they must be installed on a workstation or connected to it with peripheral devices. When this station is disabled, all components and related services become unavailable for shared use.

In networks with a server, such a computer exists by definition. The network server never shuts down except for short maintenance shutdowns. Thus, round-the-clock access of workstations to network periphery is provided.

The enterprise has ten printers: in each separate room. The administration went to the expense to create the most comfortable working conditions for the team.

Now the question of connecting the printer to the LAN. There are several ways to do this.

1.Connection to a workstation.

The printer is connected to the workstation that is closest to it, as a result of which this workstation becomes the print server. The disadvantage of this connection is that when printing jobs are performed, the performance of the workstation decreases for a while, which will negatively affect the work of application programs when the printer is used intensively. Also, if the machine is turned off, the print server will become inaccessible to other hosts.

2.Direct connection to the server.

The printer is connected to the server's parallel port using a special cable. In this case, it is permanently available to all workstations. The disadvantage of this solution is due to the limitation in the length of the printer cable, which ensures correct data transfer. Although the cable can be run for 10 meters or more, it must be run in conduits or floors, which will increase networking costs.

3. Connect to the network through a special network interface.

The printer is equipped with a network interface and connects to the network as a workstation. The interface card acts as a network adapter, and the printer is registered to the server as a LAN node. The server software sends print jobs over the network directly to a connected network printer.

In networks with a bus topology, a network printer, like workstations, is connected to a network cable using a T-connector, and when using a "star" - through a hub.

An interface card can be installed in most printers, but its cost is quite high.

4. Connect to a dedicated print server.

An alternative to the third option is to use dedicated print servers. Such a server is a network interface arranged in a separate housing with one or more connectors (ports) for connecting printers. However, in this case, using a print server is impractical.

In our case, due to the unprofitability of installing a special network printer, buying a separate interface card for the printer, the most suitable way to connect a network printer is to connect to a workstation. This decision was also influenced by the fact that printers are located near those workstations that need the greatest printer.

Ethernet Configuration Calculation Methodology

In order for an Ethernet network consisting of segments of different physical nature to work correctly, three basic conditions must be met:

The number of stations in the network does not exceed 1024 (subject to limitations for coaxial segments).

The double propagation delay (Path Delay Value, PDV) between the two most remote network stations does not exceed 575 bit intervals.

Reducing the interframe distance (Interpacket Gap Shrinkage) when passing a sequence of frames through all repeaters by no more than 49 bit intervals (recall that when sending frames, the station provides an initial interframe distance of 96 bit intervals).

Compliance with these requirements ensures the correct operation of the network even in cases where the simple configuration rules that determine the maximum number of repeaters and the maximum length of segments of each type are violated.

The physical meaning of limiting the signal propagation delay over the network has already been explained - compliance with this requirement ensures timely detection of collisions.

The requirement for a minimum interframe distance is due to the fact that when a frame passes through a repeater, this distance decreases. Each packet received by the repeater is resynchronized to eliminate signal jitter accumulated during the passage of the pulse train through the cable and through the interface circuits. The resynchronization process typically increases the length of the preamble, which reduces the inter-frame interval. When frames pass through multiple repeaters, the interframe interval can decrease so much that the network adapters in the last segment do not have enough time to process the previous frame, as a result of which the frame will simply be lost. Therefore, the total reduction of the interframe interval by more than 49 bit intervals is not allowed. The amount of decrease in the interframe distance during the transition between adjacent segments is usually called in the English literature Segment Variable Value (SVV), and the total amount of decrease in the interframe interval when passing all repeaters is Path Variable Value (PVV). Obviously, the value of PVV is equal to the sum of SVV of all segments except the last one.

Network Management Standards and Tools

Any more or less complex computer network requires additional special management tools in addition to those that are available in standard network operating systems. This is due to the fact that a new class of equipment appears in large networks - intelligent hubs and routers that create an active transport system. Such equipment is characterized by a large number of parameters that require configuration, settings and control by the administrator. And although special control and monitoring tools are built into communication equipment to facilitate this task, the distribution of these devices requires a centralized system that, receiving data from the built-in tools about the status of each device, organizes a consistent and stable operation of the network as a whole.

* Network configuration and naming management - consists of configuring network components, including parameters such as their location, network addresses and identifiers, managing parameters of network operating systems, maintaining a network diagram, and these functions are used to name objects.

Error handling is the identification, definition and elimination of the consequences of failures and failures in the network.

Performance analysis - helps to evaluate the system response time and schedule value based on the accumulated statistical information, as well as plan the development of the network.

Security management - includes access control and maintaining data integrity. These functions include the authentication procedure, privilege checks, support for encryption keys, authority management. This group also includes important mechanisms for managing passwords, external access, and connections to other networks.

Network accounting - includes registration and management of used resources and devices. This function operates on concepts such as usage time and resource charges.

Network management tools are often confused with computer management tools and their operating systems. The former are often referred to as Network Management tools and the latter as System Management tools.

System controls typically perform the following functions:

Accounting for the hardware and software used. The system automatically collects information about scanned computers and creates entries in the database of hardware and software resources. After that, the administrator can quickly find out what he has and where it is located. For example, find out which computers need to update printer drivers, which PCs have enough memory and disk space, and so on.

Distribution and installation of software. After completing the survey, the administrator can create software distribution packages - a very effective way to reduce the cost of such a procedure. The system may also allow centralized installation and administration of applications that run from file servers, as well as enable end users to run such applications from any network workstation.

Remote performance and problem analysis. The administrator can remotely control the mouse, keyboard and see the screen of any PC running on the network running a particular network operating system. The management system database typically stores detailed information about the configuration of all computers on the network so that problems can be analyzed remotely.

As you can see from the above lists, network management tools and system management tools often perform similar functions, but in relation to different objects. In the first case, the object of control is communication equipment, and in the second case, software and hardware of network computers. However, some functions of these two types of control systems may be duplicated (for example, system controls may perform simple network analysis).

Examples of system management tools are products such as Microsoft's System Management Server or Intel's LAN Desk Manager, and typical network management tools are HP's Open View, SunNet Manager, and IBM NetView systems. Naturally, in this course devoted to the study of communication equipment, only network management systems are considered.

Determining system requirements

After an inventory of an existing computing system, it is necessary to determine the requirements for new system. To determine the technical parameters of a network, consider system requirements not from a technical point of view, but from the perspective of leaders, managers, and end users.

To find out the system requirements, you need to answer the following questions:

What needs to be connected? Do employees in any department need to communicate with a small (large) number of people within a small area, or do they need to communicate with a small (large) number of people within a geographically large area? The volume and distribution of the schedule will help determine the required computer power, as well as the types and speeds of communication equipment and services.

What existing hardware and software will be used in the new system? What systems should be left in the developed corporate network? Do these systems need to be networked? Will existing systems work well on the new network? Are there any enterprise standards, are there prevailing applications? What equipment and applications do you need to add to meet your production goals?

How much information will be transferred over the network? The amount of transmitted information determines the required network bandwidth. Will more or less information be transmitted over the corporate network? Determine this by counting the number of network users, the average number of transactions per day per user, and the average transaction volume. Such a calculation will help determine the media access technology (Ethernet, FDDI,...) and global service requirements.

What network response time is acceptable? Will users wait one second, half a second, or two seconds? Such measurements will help determine the speed requirements of hardware, applications, and communication links.

How long is the network essential for the operation of the enterprise? Do you need network 24 hours a day and 7 days a week, or only for 8 hours a day and 5 days a week? Should I increase my current network usage settings?

What are the requirements for mean time to troubleshoot? How do network maintenance and repair operations affect the efficiency of the business? Will the business lose $5 million or $100,000 if the network goes down for one hour? What will be the damage from network downtime for two hours?

What is the planned growth of the system? What is the current network utilization rate and how can it change over the next 6 months, one year, two years? Even if you carefully planned the network, but did not take into account the possibilities of its growth and development, then the system requirements will have to be changed and increased. Network growth must be planned in advance, and not just react to the actual growth of its load.

Let's look at the two main ways to build a wireless network in Windows system XP Professional.

peer-to-peer network

The simplest wireless network consists of two computers equipped with wireless network cards. As you can see in Figure 5.14, there is no need for an access point, and whenever these two computers are within range of each other, they form their own independent network. Such a network is called a peer-to-peer network. These responsive networks are particularly easy to install and configure. They do not need administration and pre-configuration. In this case, each computer gets access only to the resources of another computer, and not to a central server or the Internet. Networks of this type are ideal for home, small business or one-time needs.

Internal networks

As in conventional computer networks, indoor (inside the building) wireless network equipment consists of a PC card, PCI and ISA client adapters, and access points.

Like a typical small local area network, a WLAN can be made up of a pair of computers communicating, or it can use a topology that changes along the way, using only client NICs. To expand a wireless LAN or to increase its functionality, access points are used, which can act as a bridge to an Ethernet network.

Applying WLAN technology to desktop systems gives an organization flexibility that is simply not possible with traditional LANs. Client devices can be placed where the cable cannot be laid. Moreover, clients can be rearranged at any time as needed. All this makes wireless networks Ideal for temporary workgroups or fast growing organizations.

Today's article opens a new section on the blog, which will be called " networks". This section will cover a wide range of issues related to computer networks. The first articles of the rubric will be devoted to explaining some of the basic concepts that you will encounter when working with the network. And today we will talk about what components will be required to create a network and which ones exist. types of networks.

Computer network is a set of computer and network equipment connected via communication channels into a single system. To create a computer network, we need the following components:

• computers that have networking capabilities (for example, a network card that is in every modern PC);
• transmission medium or communication channels (cable, satellite, telephone, fiber-optic and radio channels);
• network equipment (for example, a switch or router);
• network software (usually included with the operating system or supplied with network equipment).

Computer networks are usually divided into two main types: global and local.

Local networks(Local Area Network - LAN) have a closed infrastructure before reaching Internet service providers. The term "local area network" can describe both a small office network and the network of a large factory covering several hectares. In relation to organizations, enterprises, firms, the term is used corporate network - a local network of a separate organization (legal entity), regardless of the territory it occupies.
Corporate networks are networks of a closed type, access to them is allowed only to a limited circle of users (for example, company employees). Global networks are focused on serving any users.

Global network(Wide Area Network - WAN) spans large geographic regions and consists of many local area networks. Everyone is familiar with the global network, which consists of several thousand networks and computers - this is the Internet.

The system administrator has to deal with local (corporate) networks. A typical user computer connected to a local network is called workstation . A computer that shares its resources with other computers on a network is called server ; and the computer accessing the shared resources on the server is client .

There are various types of servers: file (for storing shared files), database servers, application servers (providing remote operation of programs on clients), web servers (for storing web content) and others.

Network load is characterized by a parameter called traffic. Traffic is the flow of messages in a data network. It is understood as a quantitative measurement of the number of data blocks passing through the network and their length, expressed in bits per second. For example, the data transfer rate in modern local networks can be 100Mbps or 1Gbps

Currently, the world has a huge amount of all kinds of network and computer equipment that allows you to organize a variety of computer networks. The whole variety of computer networks can be divided into several types according to various criteria:

By territory:

• local - cover small areas and are located inside individual offices, banks, corporations, houses;
• regional - are formed by combining local networks in separate territories;
• global (Internet).

By way of connecting computers:

• wired (computers are connected via cable);
• wireless (computers exchange information via radio waves. For example, by WI-FI technologies or bluetooth).

Control method:

• with centralized management - one or more machines (servers) are allocated to manage the process of data exchange in the network;
• decentralized networks - do not contain dedicated servers, network management functions are transferred in turn from one computer to another.

According to the composition of computing facilities:

• homogeneous - combine homogeneous computing tools (computers);
• heterogeneous - combine various computing tools (for example: PCs, trading terminals, webcams and network storage).

By type of transmission medium networks are divided into fiber-optic, with the transmission of information via radio channels, in the infrared range, via a satellite channel, etc.

You may come across other classifications of computer networks. As a rule, the system administrator has to deal with local wired networks with centralized or decentralized control.

Classification according to the interaction model.

The client-server model.

Server means:

1. A computer on a network that provides its services to others, i.e. performing certain functions at the request of others.

2.Server program. It is installed on the server computer.

Served computers communicate with the server through the appropriate (client-) program designed to work in tandem with the server program. The client program runs directly on the workstation.

Client. Client means:

1.User.

2. An application program that works on behalf of the user to provide

some services from a server somewhere in some network.

Client-server is a technology for the operation of various programs on the network. A program that works according to this scheme consists of two interacting parts: a client and a server. The client is on

user's machine, server on the corresponding server (computer). The server, at the command of the client, performs certain actions, providing services to the client. That is, for the provision of services in such a scheme, the presence and simultaneous coordinated work of both of these parts is necessary.

The provision of services on the Internet is built according to this scheme, i.e. it is carried out by the joint work of 2 processes: on the user's computer and on the server computer.

According to the level of management, networks are divided into peer-to-peer and dual-rank

Peer-to-peer networks have a dedicated server that manages message forwarding between workstations and all communications between network devices, stores shared information resources.

The main problems of computer networks are related to data transmission. The speed and reliability of data transfer is greatly influenced by distance. The cost of physical channels, communication equipment makes a significant contribution to the total cost of the network. Therefore, the main classification features of computer networks are the spatial characteristics of the territories they cover. From this point of view, networks can be divided into local, regional, territorial and global. It is currently not possible to accurately indicate the boundary between these classes of networks. However, we can approximately say that local ones are located within buildings, small areas (with a radius of up to 10 km). Increasing the transmission speed in local networks is accompanied by tougher requirements for distances (of the order of hundreds of meters). Regional networks cover the territories of cities and regions. Territorial networks include networks of countries, a set of regional networks. Global networks cover the territories of several countries and continents.

1.2 Purpose of LAN

In local networks, the user's work with network resources is the same as with local resources, but the use of a LAN provides the following advantages:

Providing users with shared access to shared network resources: powerful drives (including drives with removable disks), high-speed laser printers, graphics devices. For example, NetWare 4.1 can support up to 32 TB of disk space and up to 4 GB of RAM. For modern hardware, NetWare 4.1 supports 256 MB of RAM and 2048 GB of disk space;

Meeting the needs of many users in expensive software tools located on network drives. Since the necessary data and programs can be accessed from every workplace, labor productivity increases;

More effective protection of centralized databases than for a standalone computer. If necessary, the most important data can be backed up;

Provide effective means for users to interact with each other, such as through email. It is possible to hold conferences;

Increasing the reliability of the entire information system, since if one computer fails, another, backup computer, can take over its functions and workload.

2. Architecture of computer networks. Reference model of interaction of open systems. Computer network protocols.

2.1. Link architecture

For data transmission in networks, an International Standard is used - the Basic Model of Open Systems OSI, developed by the International Organization for Standardization (ISO). This model serves as a basis for manufacturers to develop compatible network equipment. It provides the most general guidelines for building standards for interoperable network software products. These recommendations should be implemented both in hardware and software of computer networks.

The model contains 7 levels. The main idea of ​​the model is that each level has a specific role. Therefore, the general task of data transmission is formalized and divided into separate, easily visible tasks. In the process of development and improvement of any system, there is a need to change individual components, and since the interfaces between levels are uniquely defined, it is possible to change the functions of one or more of them, while maintaining the possibility of error-free operation of the network as a whole. In networks, there is an interaction between the same-name levels of the model in different computers. Such interaction must be carried out according to certain rules, called a protocol.

Description of model levels:

7 - applied. Defines a set of application tasks implemented in a given network and all service elements for their implementation. At this level, already processed information is presented to the user. At the application level, network applications are implemented, as well as functions that are not implemented for some reason at the lower level. Application level functions are implemented in user network programs, applications. As a rule, network programs implement the functions of the top three levels.

6 - data presentation level. Converts transmitted data to screen format or printable format of the target system. The presentation layer is responsible for presenting network services to the application layer in a standardized manner. The representative level includes such concepts as "virtual terminal", "virtual disk";

5 - session. Organizes a communication session (establishment, support and termination of a session) between subscribers through a network. Designed to synchronize data exchange at the level of large portions of information, to organize a ".dialogue. It provides the upper level with the means of organizing a network dialogue, a communication session, .;

4 - transport. Supports continuous data transfer between two interacting user processes. It is engaged in the transfer of transport blocks between the data source node and the destination node. Transport blocks are usually larger chunks of bits than packets. Therefore, they are broken into packets when transmitted to the network layer. At the transport level, a number of tasks are solved that are not solved at the lower levels - transmission reliability, data flow control. To the upper layer, the transport layer provides a virtual transport connection for the reliable transmission of transport blocks. A typical representative of the transport layer is the TCP protocol popular on the Internet;

3 - network. Establishes communication between subscribers and carries out packet routing in the network, i.e. transmission of information to a specific address. The main functions of the network layer are:

transmission of packets between nodes that are not connected by physical channels;

choice of routes for data transmission.

The network layer provides the upper layer with a virtual channel for transmitting packets between any pair of network nodes, regardless of the presence of a physical connection between them. The functions of the lower three layers are implemented by routers. In addition, modern routers implement the functions of gateways that connect networks using different protocols.

determines the path of the data on the network, allowing 1 them to find the recipient. This means that it determines the network transmission speed and data integrity control. This level can be thought of as a delivery service. The network layer serves as an interface between computers and packet switches. A routing table is used to route data on a network. This is a database that describes the location of possible recipients of packages. Network Layer Using such a table, the router is able to find the path of a packet to any destination on the network.

The routing table can be static or dynamic. In a static table, the information is updated by the operator. In dynamic - by various programs when starting each new session or when a new routing package appears.

Connecting new computers to the network leads to an increase in the flow of packets through it. The network layer controls the flow of data when routing packets (traffic). In this case, it becomes necessary to take into account traffic in different parts of the network to resolve the issue of payment. Traffic information is provided by the network layer.

2 - channel. . The main purpose of the link layer is the reliable transmission of a group of bits, commonly referred to as frames. between nodes connected by physical channels. Sometimes data blocks of the channel, level .; are called packets, but this name is best reserved for the network layer. .So channeled. layer provides the network layer with a channel for reliable transmission of packets. The functions of the physical and link layers in local networks are performed by network cards. The first modems performed only the functions of the physical layer. Modern modems, implementing data transfer protocols with error correction, began to perform the functions of the link layer.

1 - physical. Defines electrical, mechanical, functional, and procedural parameters for physical communication in systems. The layer interfaces with the data transmission medium and provides the link layer with a virtual channel to transfer bits.

The individual layers of the base model run downward from the data source (from layer 7 to layer 1) and upward from the data sink (from 1 to 7). The user data is transmitted in chunks-frames to the lower layer, along with a header specific to each layer, until the last layer is reached. On the receiving side, the incoming data is parsed and passed on to the higher layer until it is transferred to the user application layer. Different networks may not have separate layers.

The functions performed by each layer must be implemented either in hardware or in software. The functions of the physical layer are always implemented by hardware (adapters, data transfer multiplexers, network cards, etc.), and the functions of other levels, as a rule, are implemented by software modules (drivers).

2.2.Computer network protocols.

Protocol- a set of rules that determines the interaction of two levels of the same name of the open systems interaction model in various subscriber computers. Functions of protocols of various levels are implemented in drivers for various computer networks.

Modern networks are built on a multi-level principle. To organize communication 2 | | computers, you must first determine the set of rules for their interaction, determine the language of their communication, i.e. determine what the signals they send mean, and so on. These rules and definitions are called protocols.

A protocol can also be viewed as a set of definitions (agreements, rules) that govern the format and procedures for exchanging information between two or more independent devices or processes. Those. a description of how programs, computers, or other devices should act when they interact with each other.

Protocol definitions range from the order in which bits travel on a wire to the format of an email message. Standard protocols allow computers to communicate with each other various manufacturers. The interacting computers may use completely different software, ; but must respect the accepted convention on how to send and receive received data.

For networks to work, it is necessary to stock up on many different protocols: for example, managing physical communication, establishing communication over a network, accessing various resources, and so on. A layered structure is used to simplify this vast array of protocols and relationships. It also makes it possible to compose network systems from products - software modules - released by different manufacturers.

The set of protocols that work simultaneously and together on a water network is called a protocol stack.

The Internet is based on the TCP/IP (Transfer Communication Protocol/Internet Protocol) protocol stack. Its peculiarity lies in the delivery of information from one computer to another by any means, if both computers are in the IP space. Belonging to this space is determined by the presence of an IP address for each of these computers.

2.3. Network management

Let's take a closer look at LAN management. According to the control method, local area networks can be organized as peer-to-peer or dual-rank.

AT peer-to-peer The LAN does not have a single control center for the interaction of computers included in the network and there is no single device for storing data. Network operating system distributed across all computers and all network devices (disks, printers) are available to the user. The advantage of peer-to-peer networks is their low cost, but in such networks it is difficult to ensure the protection of information, it is difficult to manage the entire network and update software.

AT two-rank The network has a dedicated computer - a server that performs the functions of storing data intended for sharing and managing the interaction of computers and other devices that are part of the network.

Work station is a personal computer from which the user gets access to network resources. On it, he does his work, processes his files and uses his operating system (for example, Windows 2000, Windows XP). Additionally, the workstation contains a network interface card (network adapter) and is physically connected to the file server.

Server is a computer on the network that provides users with its resources. It coordinates the work of all workstations and regulates the distribution of network resources and the flow of data in the network. To manage the computer network, the server uses a special (network) operating system. The server is the core of the LAN. This is usually a more powerful computer running a network operating system. It is he who indicates who can use the printer first, which file can be opened by which user, etc. The server hosts a shared database.

The server can be specialized and non-specialized. The dedicated server is only used to manage the network, while the non-dedicated server manages the network and at the same time works as a normal workstation. In general, there are the following types of servers:

a file server is a repository of files, access to which is predetermined;

application server - performs processing of user requests, involving various software packages for this (for example, a DBMS);

print server;

mail server;

Internet server.

The server in the LAN, just like the workstations, contains a network adapter card, through which it connects to the workstations.

2.DATA TRANSFER

Various types of communication channels are used to send messages in computer networks. A LAN uses twisted-pair, coaxial, and fiber optic cables as the transmission medium.

Separate remote LAN equipment (computers, peripheral equipment, other networks) can be connected via modems and communication lines (telephone, radio, satellite).

The LAN server and workstations can be connected based on three types of topology: bus, star, or ring.

Topology LAN is a geometric scheme for connecting network nodes. Detailed description topologies used for LANs and their features can be found in the textbook “Local Area Networks. Working with databases for collective use ”, as well as in the literature. The choice of one or another topology is determined by the scope and size of a particular LAN, the location of its nodes. Network topology is associated with access methods to network nodes and the choice of network equipment.

Many systems have been developed for the LAN, including hardware and communication protocol. These systems are supported by appropriate networking software. The network access system (hardware and protocol) provides the electronic backbone for data transmission, and the network operating system manages the entire system's resources and data processing.

2.1 Classical topologies

Topology is an average geometric diagram of the connection of network nodes. Under the structure of a computer network, we mean a display, a description of the links between its elements.

Common bus

Channel users can be ringed by a single channel or by independent channels. The first case is like a general bus. The difference is that the transmitted data must be removed from the ring. The most popular use is token ring technology. Requires channel access control. In the second case, the cable system is more expensive, the data is transmitted, with retransmission, but the stations can exchange data relatively independently of each other. Having two paths for data transmission is of great importance, which improves the performance and reliability of the network. It is most often used for large distances between nodes, when dedicated channels are used to connect them.

Star

It is at the same time an element of a hierarchical structure. Differs in rather high cost of cable system. Especially if the nodes are at large distances. Allows you to concentrate in one place all the problems of data transmission, addressing. It is the basis for building structured cable systems, broadcast radio networks, radio cells.