Network management methods. Classifications of computer networks Data transmission media, their characteristics

A computer network is a complex system through which data is transferred and exchanged according to a certain principle between several objects. Using the network has a number of advantages, mainly due to almost unlimited possibilities due to access to additional resources. The organization of a computer network allows you to install powerful units to run software that is too heavy for a weak computer. Users also get […]

Allows you to install powerful units to run software that is too heavy for a weak computer. Users also have the opportunity to exchange information with other participants in the process, and they can save on installing additional peripheral devices, for example, by connecting several computers to one printer or scanner.

Computer networks are classified according to a number of criteria, such as:

length of lines;
topology (construction method);
control method.

To better understand the different management methods that networks differ in, it is necessary to become familiar with their varieties according to the scale and specifics of their functioning.

PAN is a personal network that ensures the interaction of several devices within one project.

LAN is a local network with a closed infrastructure, regardless of scale. Access to local networks is available to a limited number of users defined by the administrator.

CAN is an association of several local networks of nearby objects.

MAN – computer networks between institutions within the same locality, connecting many local networks.

WAN is an open global network serving large-scale geographic regions, which includes both local networks and other telecommunications nodes.

There are several scenarios for constructing a computer network, providing for the order of location of individual workstations and the method of connecting them by communication highways.

This area determines the type of equipment used, cable, management methods, etc. Three network configurations are most widespread:

tire;
ring;
star.

The bus implies equal rights for all subscribers connected one by one via a single communication line. The peculiarity of this topology is the absence of a central subscriber, and the connection of new participants in the process is carried out in the simplest way; moreover, the least amount of low-current cable is used here.

The ring topology is characterized by the simplicity of the device, where each individual computer is connected by a cable line to two others. There is also no clearly defined center here, and each computer has equal rights.

The star provides for the presence of a central computer, which bears the main burden of managing the exchange. In this case, it is the main computer that has the greatest power, and there are no conflicts between individual subscribers in the network itself. Depending on the control method, each of the topologies has distinctive characteristics, and below we will tell you what control methods the networks differ in.

Classification of computer networks by management method

Considering that a complex system requires constant monitoring and correct interaction of all nodes, it is constantly under control. Based on the management method, networks are divided into:

centralized, where the main management functions are performed by the server, providing users with access to available resources. If a server (or several servers at the same time) is a powerful computer that bears the main load, then the remaining machines are workstations;
decentralized, or as they are also called, peer-to-peer (peer-to-peer). In this case, there are no local network management tools such as servers, and all computers have equal rights, and control can be carried out from any of the machines;
mixed, in which the most complex and priority tasks are solved through centralized control.

Since networks come in different types according to the way they are managed, there are certain standards for this process.

Network management system standards are a complex, protocol-based discipline that regulate the way in which host and managed entities interact.

Considering the fact that the design and installation of local networks is a responsible and difficult process, its implementation can only be carried out by experienced professionals.

Involving competent designers and installers in setting up a computer network guarantees a high level of work and also ensures the reliable functioning of each element that is part of it.

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 in the section 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 are required to create a network and what exist types of networks.

Computer network is a collection 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 the ability to connect to a network (for example, a network card, which is found 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 accessing Internet service providers. The term “local area network” can describe both a small office network and a 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 closed networks; access to them is allowed only to a limited number of users (for example, company employees). Global networks are focused on serving any users.

Global network(Wide Area Network - WAN) covers large geographic regions and consists of many local 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 regular user computer connected to a local network is called workstation . A computer that makes its resources available for shared use by other computers on the network is called server ; and the computer accessing shared resources on the server is client .

There are various types of servers: file servers (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 a 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 speed in modern local networks can be 100Mbit/s or 1Gbit/s

Currently, in the world there is a huge amount of all kinds of network and computer equipment that allows you to organize a wide variety of computer networks. The entire 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 – formed by combining local networks in separate territories;
global (Internet).

According to the method of computer connection:

wired (computers are connected via cable);
wireless (computers exchange information via radio waves, for example, using WI-FI or Bluetooth technology).

By control method:

with centralized control - one or more machines (servers) are allocated to manage the data exchange process on 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 tools:

homogeneous – combine homogeneous computing means (computers);
heterogeneous - combines various computing tools (for example: PCs, trading terminals, web cameras and network data storage).

By type of transmission medium networks are divided into fiber optics, 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, a system administrator has to deal with local wired networks with centralized or decentralized control.

Communication network– a system of nodes and connections between them. The nodes carry out the functions of creating, transforming, storing and consuming a communication product. Connections (transmission channels, communication lines) serve to transfer the product between nodes. Depending on the type of product, material, energy, and information networks are distinguished. Examples of physical networks: road and railway communications; water and gas supply.

Information network– a communication network in which the product of communication is information. Examples: telephone networks, television, radio broadcasting.

Computing, or computer network– an information network whose nodes are computers and other computing equipment. In addition to specialized networking hardware, networking software is also required. Thanks to the interaction of computers on a network, a number of new possibilities become available.

The first is the sharing of hardware and software resources. Thus, with shared access to an expensive peripheral device (printer, plotter, scanner, fax, etc.), the costs for each individual user are reduced. Network versions of application software are used in the same way.

The second is shared access to data resources. With centralized storage of information, the processes of ensuring its integrity, as well as backup, are greatly simplified, which ensures high reliability. Having alternate copies on two machines at the same time allows you to continue working if one of them is unavailable.

Third, accelerating data transfer and providing new forms of interaction between users in one team when working on a common project.

Fourth, the use of common means of communication between various application systems (communication services, data transmission, video, speech, etc.).

One of the important classification features of networks is their size. The size of the network influences the choice of equipment used and transmission technologies used.

Local area network(LAN, or LAN - Local Area Network) unites nearby computers within a limited area, room, building. Distinctive features of the LAN are minimal latency and low error rates. LANs can be elements of larger-scale formations: a campus or corporate network (CAN - Campus Area Network), uniting local networks of nearby buildings; municipal network, or city-scale network (MAN - Metropolitan Area Network); regional, or wide-scale network (WAN - Wide Area Network), covering a large area; wide area network(WAN, or GAN - Global Area Network), which has the size of a country and a continent.

Based on the management method, networks are divided into peer-to-peer and with dedicated server(centralized control). In peer-to-peer networks, all nodes have equal rights - each node can act as both a client and a server. Under client refers to a hardware and software object that requests some services. And under server– a combination of hardware and software that provides these services. A computer connected to a local network, depending on the tasks solved on it, is called a workstation or server.

Peer-to-peer LANs are quite easy to maintain, but cannot provide adequate information protection if the network size is large. The costs of organizing peer-to-peer computer networks are relatively small. However, as the number of workstations increases, the efficiency of network use decreases sharply. Therefore, peer-to-peer LANs are used only for small workgroups - no more than 20 computers.

A dedicated server implements network management (administration) functions in accordance with specified policies - sets of rules for dividing and limiting the rights of network participants. LANs with a dedicated server have good data security features and are capable of supporting thousands of users, but require constant qualified maintenance by a system administrator.

Depending on the data transmission technology used, there are different broadcast networks and networks with transmission from node to node. Broadcast transmission is used mainly in small networks, and in large networks it is used for transmission from node to node.

In broadcast networks, all network nodes share a single communication channel. Messages sent by one computer, called packets, are received by all other machines. Each packet contains the address of the message recipient. If the packet is addressed to another computer, it is ignored. Thus, after verifying the address, the recipient processes only those packets that are intended for it.

Networks with transmission from node to node consist of pairwise connected machines. In such a network, to get to its destination, a packet passes through a number of intermediate machines. However, there are often alternative paths from the source to the recipient.

The method of connecting computers together in a network is called topology. There are three most common topologies used in LANs. These are the so-called tire, ring And star-shaped structures.

In the case of a bus (linear) structure, all computers are connected in a chain using one common coaxial cable. If at least one of the sections of the network with a bus structure is damaged, the entire network as a whole becomes inoperable. The fact is that then there is a break in the only physical channel necessary for the movement of the signal.

The ring structure is used mainly in Token Ring networks and differs from the bus structure in that all computers are connected in pairs to each other, forming a closed loop. Also, if one of the network segments malfunctions, the entire network goes down.

In a star network, the central node to which all others connect is hub(Hub – “hub”). Its main function is to ensure communication between computers on the network. This structure is preferable because if one of the workstations or the cable connecting it to the hub fails, all the others remain operational.

When building networks, cellular ( fully connected) a topology in which each node is connected to all other individual links. The costs of creating redundant channels are offset by high reliability - there are almost always several paths for signals to pass from sender to recipient, so if some channels are disconnected, signals can be transmitted through others.

The following are distinguished: switching methods data in information networks: circuit switching, packet switching And message switching.

When switching circuits, the entire connection path is first established - from the sender to the recipient. This path consists of several sections connected by switches and/or multiplexers. All data is transmitted along the established route. Once the transfer is complete, the connection is terminated. An example is a telephone conversation: the channel is busy throughout the conversation, even if the subscribers are silent. The transmission speed over such a channel is limited to the area with the lowest bandwidth.

With the second method, messages are divided into packets of a fixed length, which can be delivered across the network via independent routes, ensuring uniform network load. In this case, packets of different messages can be transmitted over one channel. As an example, let's give an analogy: during rush hour, a group of students gets from the hostel to the university using different transport, each in their own way.

Message switching is similar to packet switching, but at a higher level (message switching nodes can be connected by either a circuit-switched network or a packet-switched network). The main difference is that the size of the data block is determined not by technological limitations, but by the content of the information in the message. This could be a text document, email, file. Example - a group of tourists follows a route, and at each point the composition of the group is checked. This scheme is used to transmit messages that do not require an immediate response, such as email messages.

15.3 OSI/ISO network model

The functioning of network equipment is impossible without interconnected standards. Harmonization of standards is achieved both through consistent technical solutions and through grouping of standards. Each specific network has its own basic set of protocols - the “language” of data transmission. Protocol– formalized rules for the interaction of several computers, which can be described as a set of procedures that determine the sequence and format of messages exchanged between network components located at the same level, but in different nodes.

The International Organization for Standardization (ISO) has proposed model computer network architecture OSI(Open System Interconnection - connection of open networks). This model, which most users try to adhere to, divides communication functions on the network into seven levels. Data exchange occurs by moving it on the sender's computer from the upper level to the lower one, then transporting it over the communication channel and converting it back on the recipient's computer from the lower level to the upper one.

The highest level is application layer(Application Layer) is the interface between application programs and processes of the OSI model.

The Presentation Layer defines the format for data exchange and serves for encryption, compression and code conversion of data.

The Session Layer performs the functions of coordinating communications between workstations. The layer provides the creation of a communication session, control of the transmission and reception of message packets, and termination of the session.

The Transport Layer divides or assembles messages into packets when more than one packet is in the process of transmission or reception, as well as controls the order in which message components pass through. In addition, at this level, through gateways, the network layers of various incompatible networks are negotiated. Guarantees delivery of packets without errors, in the same sequence, without losses and duplication with confirmation of receipt.

The Network Layer provides the translation of logical address names into physical ones. Based on specific network conditions and the priority of the service, routing is carried out, that is, the choice of transmission route for a data packet in the network, and control of the data flow in the network (data buffering, error control when establishing a connection).

The Data Link layer defines the rules for using the physical layer by network nodes. This layer is divided into two sublayers: Media Access Control, associated with network access and management, and Logical Link Control, associated with the transmission and reception of user messages. It is at the Data Link level that data transmission is ensured in frames, which are blocks of data containing additional control information. Error correction is performed automatically by resending the frame. In addition, at this level the correct sequence of transmitted and received frames is ensured.

Lowest – physical layer(Physical Layer) defines the physical, mechanical and electrical characteristics of communication lines. This layer converts data coming from the data link layer into signals that are then transmitted over communication lines. In local networks, this conversion is carried out using network adapters; in global networks, modems are used for this purpose.

Each level actually interacts only with neighboring levels (upper and lower), and virtually only with a similar level at the end of the line. Real interaction is the direct transfer of information in which the data remains unchanged. Virtual interaction is indirect interaction and data transfer, and the data can be modified during the transfer process.

Physical connection really takes place only at the lowest level. Horizontal connections between all other levels are virtual; in reality they are carried out by transferring and converting information first downwards, sequentially to the lowest level, where the real transfer occurs, and then at the other end - reverse transmission upwards sequentially to the appropriate level.

LAN classification

Local networks can be classified according to:

management level;
purpose;
homogeneity;
administrative relations between computers;
topology;
architecture.

According to the level of management, the following are distinguished: LAN :

Workgroup LANs, which consist of several PCs running the same operating system. In such a LAN, as a rule, there are several dedicated servers: a file server, a print server;
LAN of structural units (departments). These LANs contain several dozen PCs and servers such as: file server, print server, database server;
LAN of enterprises (firms). These LANs can contain over 100 computers and servers such as: file server, print server, database server, mail server and other servers.

Based on their purpose, networks are divided into :

computer networks, intended for calculation work;
information and computer networks, which are intended both for conducting settlement work and for providing information resources;
information and advisory, which, based on data processing, produce information to support decision-making;
information and control networks, which are designed to control objects based on information processing.

The types of computers used can be distinguished:

homogeneous networks that contain the same type of computers and system software;
heterogeneous networks that contain different types of computers and system software.

According to the administrative relationships between computers, we can distinguish:

LAN with centralized control (with dedicated servers);
LANs without centralized control (decentralized) or peer-to-peer (single-level) networks.

In local networks with centralized management, the server ensures interactions between workstations, performs the functions of storing public data, organizes access to this data and transmits the data to the client. The client processes the received data and provides the processing results to the user. It should be noted that data processing can also be carried out on the server.

Local networks with centralized control, in which the server is intended only for storing and issuing information to clients upon requests, are called networks with a dedicated file server. Systems in which the server, in addition to storing information, also processes information are called “client-server” systems.

It should be noted that in server local networks, only server resources are directly available to the client. But workstations that are part of a centrally managed LAN can simultaneously organize a peer-to-peer local network with all its capabilities among themselves.

The software that controls the operation of a centrally managed LAN consists of two parts:

network operating system installed on the server;
software on a workstation, which is a set of programs running under the operating system that is installed on the workstation. At the same time, different operating systems can be installed on different workstations on the same network.

In large hierarchical local networks, UNIX and LINUX are used as network operating systems, which are more reliable. For medium-sized local networks, the most popular network OS is Windows 2008 Server.

Depending on how the server is used in hierarchical networks, the following types of servers are distinguished:

File server. In this case, the server contains shared files and/or shared programs.
Database server. The server hosts a network database.
Print server. A fairly powerful printer is connected to the computer, on which information can be printed from several workstations at once.
Mail server. The server stores information sent and received both over a local network.

Advantages:

higher data processing speed;
has a reliable system for protecting information and ensuring secrecy;
easier to manage compared to peer-to-peer networks.

Flaws:

the network is more expensive due to a dedicated server;
less flexible compared to a peer-to-peer network.

All computers on the local network are connected by communication lines. The geometric location of communication lines relative to network nodes and the physical connection of nodes to the network is called physical topology. Depending on the topology, networks are distinguished: bus, ring, star, hierarchical and arbitrary structures.

There are physical and logical topologies. Logical and physical network topologies are independent of each other. Physical topology is the geometry of the network, and logical topology determines the directions of data flows between network nodes and methods of data transmission.

All existing configurations can be divided into two main classes: broadcast and serial.

In the case of a broadcast LAN configuration, signals transmitted by one device connecting to the physical medium are perceived by all others. In a broadcast LAN, only one station can operate at any time. All workstations can communicate directly with any workstation on the network.

To build a broadcast configuration, it is necessary to use relatively powerful receivers and transmitters. Consequently, there is a need to limit the length of cable segments and the number of connections. If limits are exceeded, an analog amplifier or digital repeater is used. In addition, the means of connection to the physical medium are selected such that they do not cause significant signal attenuation.

The main types of broadcast topologies "bus", "tree" and "star" are shown in the diagrams (Figure 3).

Figure 3 - Types of broadcast topologies:

a) “tire”; b) “tree”; c) "star"

In the case of a sequential LAN configuration, each device connecting to the physical medium transmits information to only one device. At the same time, the requirements for transmitters and receivers are reduced, since all stations actively participate in the transmission.

The main types of sequential topologies: “ring”, “chain”, “snowflake” and “mesh” are shown in the diagram (Figure 4).

Figure 4 - Types of sequential topologies “ring”, “chain”, “snowflake” and “mesh”

Consider the following physical topologies:

physical “bus” (bus);
physical “star” (star);
physical “ring” (ring);

Bus topology

easy to connect a new PC;
there is the possibility of centralized management;
The network is resistant to failures of individual PCs and to interruptions in the connection of individual PCs.

Disadvantages of topology networks " star »:

hub failure affects the operation of the entire network;
high cable consumption;

Ring topology

In a network with a ring topology, all nodes are connected by communication channels into a continuous ring (not necessarily a circle) through which data is transmitted. The output of one PC is connected to the input of another PC. Having started the movement from one point, the data ultimately ends up at its beginning. Data in a ring always moves in the same direction.

The receiving workstation recognizes and receives only the message addressed to it. A network with a physical ring topology uses token access, which grants a station the right to use the ring in a specific order. The logical topology of this network is a logical ring.

This network is very easy to create and configure. The main disadvantage of ring topology networks is that damage to the communication line in one place or PC failure leads to the inoperability of the entire network.

As a rule, in its pure form the topology " ring"is not used due to its unreliability, so in practice various modifications of the ring topology are used.

In general, the IT infrastructure of various enterprises can be distinguished by:

scale;
composition of components;
equipment level, etc.

Based on this, certain types of IT infrastructures can be presented in the form of basic configurations, which are shown in Figures 5, 6 and 7.

Figure 5 - Small local network.

Small local network. Typically consists of 1-3 servers, network switches, 5-30 workstations.

Figure 6 - Local network and telephone network with MiniPBX.

Local network and telephone network with MiniPBX. Includes all the components of a “small local network” with the addition of an internal MiniPBX for switching phones within the office

Figure 7 - Local network and digital telephone network at several sites.

Local network and digital telephone network at several sites, united into a virtual private network. The organization's local network is used for IP telephony. It is possible to combine digital telephone networks of organizational units via the Internet using virtual private networks.

The level of training of specialists servicing the IT infrastructure of enterprises must be very high, requiring responsibility for work on which the functioning and security of corporate computer networks will depend.