Hardware and software components of networks. Basic software and hardware components of the network Basic software and hardware components of the network

Purpose and brief description of the main components of computer networks.

Computer network called a set of interconnected and distributed computers over a certain territory.

computer network– a computing complex that includes a geographically distributed system of computers and their terminals combined into a single system.

According to the degree of geographical distribution, computer networks are divided into local, city, corporate, global, etc.

The computer network consists of three components:

Data transmission networks, including data transmission channels and switching facilities;

Computers connected by a data network;

Network software.

computer network- this is a complex complex interconnected software and hardware components:

computers(host computers, network computers, workstations, servers) located in network nodes;

network operating system and application software, managing computers;

communication equipment– equipment and data transmission channels with accompanying peripheral devices; interface cards and devices (network cards, modems); routers and switching devices.

Software and hardware components of a computer network

Computer network- a spatially distributed system of software and hardware components connected by computer communication lines.

Among the hardware Computers and communications equipment can be distinguished. Software components consist of operating systems and network applications.

Currently, computers of various types and classes with different characteristics. This is the basis of any computer network. Computers and their characteristics determine the capabilities of a computer network. But recently, communication equipment (cable systems, repeaters, bridges, routers, etc.) has begun to play an equally important role. Some of these devices, given their complexity, cost and other characteristics, can be called computers that solve very specific tasks to ensure the operability of networks.

For efficient operation of networks, we use special network OS(network OS), which, unlike personal operating systems, are designed to solve special problems of managing the operation of a network of computers. Network operating systems are installed on specially dedicated computers.

Network Applications- These are application software systems that expand the capabilities of network operating systems. Among them we can highlight mailers, group work systems, network databases, etc.

As network operating systems develop, some functions of network applications become normal functions OS.

All devices connected to the network can be divided into three functional groups:

1) workstations;

2) network servers;

3) communication nodes.

1) Workstation A workstation is a personal computer connected to a network on which a network user performs his or her work. Each workstation processes its own local files and uses its own operating system. But at the same time, network resources are available to the user.

There are three types of workstations:

Workstation with local disk,

Diskless workstation,

Remote workstation.

On a workstation with a disk (hard or floppy), the operating system boots from that local disk. For a diskless station, the operating system is loaded from the file server disk. This possibility is provided by a special microcircuit installed on network adapter diskless station.

A remote workstation is a station that connects to a local network via telecommunications channels (for example, using a telephone network).

2) Network server, a network server is a computer connected to a network and providing certain services to network users, such as storing public data, printing jobs, processing a request to a DBMS, remote processing of jobs, etc.

Based on the functions they perform, the following groups of servers can be distinguished.

File server, file server - a computer that stores data of network users and provides user access to this data. Typically, this computer has a large amount of disk space. The file server allows users to access shared data simultaneously.

The file server performs the following functions:

Data storage;

Data archiving;

Data transfer.

Database server - a computer that performs the functions of storing, processing and managing database files (DB).

The database server performs the following functions:

Storing databases, maintaining their integrity, completeness, and relevance;

Receiving and processing requests to databases, as well as sending processing results to the workstation;

Coordination of data changes made by different users;

Support for distributed databases, interaction with other database servers located in another location.

Application server, application server - a computer that is used to run user applications.

A communications server is a device or computer that provides LAN users with transparent access to its serial I/O ports.

Using a communications server, you can create a shared modem by connecting it to one of the server's ports. The user, having connected to the communication server, can work with such a modem in the same way as if the modem was connected directly to the workstation.

An access server is a dedicated computer that allows remote processing of tasks. Programs initiated from a remote workstation are executed on this server.

Commands entered by the user from the keyboard are received from the remote workstation, and the results of the task are returned.

Fax server, fax server - a device or computer that sends and receives fax messages to local network users.

Server Reserve copy data, backup server - a device or computer that solves the problem of creating, storing and restoring copies of data located on file servers and workstations. One of the network file servers can be used as such a server.

It should be noted that all of the listed types of servers can operate on one computer dedicated for these purposes.

3) The communication nodes of the network include the following devices:

Repeaters;

Switches (bridges);

Routers;

The length of the network and the distance between stations are primarily determined by the physical characteristics of the transmission medium (coaxial cable, twisted pair, etc.). When transmitting data in any environment, signal attenuation occurs, which leads to distance limitations. To overcome this limitation and expand the network, special devices are installed - repeaters, bridges and switches. The part of the network that does not include the expansion device is usually called a network segment.

Repeater, repeater - a device that amplifies or regenerates a signal received by it. The repeater, having received a packet from one segment, transmits it to all others. In this case, the repeater does not decouple the segments attached to it. At any given time, in all segments connected by the repeater, data exchange is supported only between two stations.

Switch, switch, bridge, bridge is a device that, like a repeater, allows you to combine several segments. Unlike a repeater, a bridge decouples the segments connected to it, that is, it simultaneously supports several data exchange processes for each pair of stations of different segments.

Router- a device that connects networks of the same or different types using the same data exchange protocol. The router analyzes the destination address and routes the data along the optimal route.

Gateway is a device that allows you to organize data exchange between different network objects using different data exchange protocols.

The main hardware components of the network are the following:

1. Subscriber systems: computers (workstations or clients and servers); printers; scanners, etc.

2. Network hardware: network adapters; concentrators (hubs); bridges; routers, etc.

3. Communication channels: cables; connectors; devices for transmitting and receiving data in wireless technologies.

The main software components of the network are the following:

1. Network operating systems, where the most famous of them are: MS Windows; LANtastic; NetWare; Unix; Linux, etc.

2. Network software(Network Services): network client; LAN card; protocol; remote access service.

LAN (Local Area Network) is a collection of computers, communication channels, network adapters running a network operating system and network software.

In a LAN, each PC is called a workstation, with the exception of one or more computers that are designed to serve as servers. Each workstation and server have network cards (adapters) that are connected to each other through physical channels. In addition to the local operating system, each workstation runs network software that allows the station to communicate with the file server.

Computers included in the client LAN – server architecture, are divided into two types: workstations, or clients, intended for users, and servers, which, as a rule, are inaccessible to ordinary users and are designed to manage network resources.

Workstations

A workstation is a subscriber system specialized for solving certain tasks and using network resources. The workstation network software includes the following services:

Client for networks;

File and Printer Access Service;

Network protocols for this type of network;

Network card;

Remote access controller.

A workstation differs from a conventional stand-alone personal computer in the following ways:

Availability of a network card (network adapter) and a communication channel;

Additional messages appear on the screen while the OS is loading, informing you that the network operating system is loading;

Before you begin, you must provide your network software with a username and password. This is called the network logon procedure;

After connecting to the LAN, additional network disk drives appear;

it becomes possible to use network equipment that may be located far from the workplace.

Network adapters

To connect a PC to a network, you need an interface device called a network adapter, interface, module, or card. It is inserted into the motherboard socket. Network adapter cards are installed on each workstation and on the file server. The workstation sends a request through the network adapter to the file server and receives a response through the network adapter when the file server is ready.

Network adapters, together with network software, are able to recognize and handle errors that may occur due to electrical interference, collisions, or poor hardware performance.

Various types network adapters differ not only in their methods of accessing the communication channel and protocols, but also in the following parameters:

Transmission speed;

Packet buffer size;

Tire type;

Bus performance;

Compatible with various microprocessors;

Using direct memory access (DMA);

Addressing I/O ports and interrupt requests;

connector design.

Basic Concepts

Computer network (computer network, data network)- communication system of computers or computer equipment (servers, routers and other equipment). Various physical phenomena can be used to transmit information, usually - different kinds electrical signals, light signals or electromagnetic radiation.
Data transfer(data exchange, digital transmission, digital communication) - physical transfer of data (digital bit stream) in the form of signals from point to point or from point to several points by means of telecommunications over a communication channel, as a rule, for subsequent processing by computer technology. Examples of such channels include copper wires, optical fiber, wireless communication channels or storage device.
Data transfer may be analog or digital (that is, a stream of binary signals), and can be modulated either through analog modulation or through digital encoding.
Server called a computer separated from a group personal computers(or workstations) to perform any service task without direct human intervention. The server and workstation may have the same hardware configuration, since they differ only in the participation of the person at the console in their work.
Some service tasks can be performed on the workstation in parallel with the user's work. Such a workstation is conventionally called a non-dedicated server.
Console(usually a monitor/keyboard/mouse) and human participation are required by servers only at the stage initial setup, during hardware maintenance and management in emergency situations (normally, most servers are managed remotely). For emergency situations, servers are usually provided with one console kit per group of servers (with or without a switch, such as a KVM switch).
Router- specialized network computer, which has at least two network interfaces and forwards data packets between different network segments, making forwarding decisions based on information about the network topology and certain rules set by the administrator.
Electromagnetic radiation e (electromagnetic waves) - a disturbance (change in state) of the electromagnetic field propagating in space (that is, electric and magnetic fields interacting with each other).
Signal(in information and communication theory) - a material carrier of information used to transmit messages in a communication system. A signal can be generated, but its reception is not required, unlike a message, which must be accepted by the receiving party, otherwise it is not a message. A signal can be any physical process whose parameters change in accordance with the transmitted message.

Principles of formation and types of networks

A computer connected to a network is called workstation(Workstation); the computer that provides FAILED resources is a server; a computer that has access to shared resources is a client.
Several computers located in the same room or functionally performing the same type of work (accounting or planning accounting, registration of incoming products, etc.) are connected to each other and combined into working group so that they can share various resources: programs, documents, printers, fax, etc.
A workgroup is organized so that the computers included in it contain all the resources necessary for normal operation. As a rule, a workgroup that includes more than 10-15 computers includes a dedicated server - enough powerful computer, which houses all shared directories and special software for controlling access to all or part of the network.
There are two types of computer networks – peer-to-peer and server-based networks.
A peer-to-peer network is more suitable for those people who do not have the opportunity to organize a large network, but want to check how it works and what benefits it brings. As for the server-based network, it is usually used to control all workstations.
In fact, these two types of computer networks practically do not differ in the basics of operation, and this makes it possible to transition from a peer-to-peer network to a server-based network quite easily and quickly.
Peer-to-peer network
A peer-to-peer network is actually several computers that are connected to each other through one of the common types of communication. It is precisely because of the lack of a server in this type network, it is considered simpler and more accessible. But it should also be noted that in a peer-to-peer network, computers must be as powerful as possible, since they will have to independently cope not only with the main work, but also with various problems.
In such a network there is no computer that plays the role of a server, and therefore any of the working computers can be one. It is usually monitored by the user himself, and this is the main disadvantage of a peer-to-peer network: the user must not only work on the computer, but also perform administrator functions. He should also be responsible for troubleshooting computer problems and ensuring maximum computer protection from virus attacks.
A peer-to-peer network supports any operating system, so it could be Windows 95, for example.
Typically, a peer-to-peer network is built to connect a small number of computers (up to 10) via cable and in cases where there is no need for strict data protection. And yet, one incompetent network user can jeopardize not only its functionality, but also its existence!
Server based network
A server-based network is the most common type of network.
It may use one or more servers that control workstations. The server is distinguished by power and speed, it processes user requests very quickly and its work is usually monitored by one person, called a system administrator. The system administrator monitors the updating of anti-virus databases, troubleshoots network problems, and also processes shared resources.
As for the number of jobs in such a network, it is unlimited. Only to maintain normal network operation, additional servers are installed if necessary.
Servers differ depending on the type of work they perform.
File – server is used to store various information in files and folders. Such a server is controlled by any OS such as Windows NT 4.0.
The print server is in charge of maintenance network printers and provides access to them.
The database server provides maximum speed searching and recording the necessary data into the database.
The application server runs requests that require high performance.
There are also other servers: mail, communication, etc.
A server-based network provides many more features and services than a peer-to-peer network, and is characterized by high performance and reliability.

Purpose of computer networks

All computer networks, without exception, have one purpose - to provide shared access to common resources.
The word resource is very convenient. Depending on the purpose of the network, one or another meaning can be attached to it. There are three types of resources: hardware, software and information. For example, a printing device (printer) is a hardware resource. Capacities hard drives- also a hardware resource. When all members of a small computer network use one common printer, this means that they share a common hardware resource. The same can be said about a network that has one computer with increased hard capacity disk (file server) on which all network participants store their archives and work results.
In addition to hardware resources, computer networks allow the sharing of software resources. So, for example, to perform very complex and time-consuming calculations, you can connect to a remote mainframe computer and send a computational task to it, and after completing the calculations, receive the result back in the same way. .
Data stored on remote computers forms an information resource. The role of this resource today is most clearly visible in the example of the Internet, which is perceived, first of all, as a giant information and reference system.
Examples of dividing resources into hardware, software and information are quite conventional. In fact, when working on a computer network of any type, sharing all types of resources. So, for example, when turning to the Internet for information about the content of an evening television program, we are certainly using someone else's hardware, which runs someone else's programs that provide the data we require.

Basic software and hardware components of the network

Computer network- a complex complex of interconnected and coordinated functioning software and hardware components.
Studying the network as a whole presupposes knowledge of the operating principles of its individual elements:
– computers;
– communication equipment;
– operating systems;
– network applications.
The entire network hardware and software complex can be described by a multilayer model:
1. At the heart of any network is hardware layer of standardized computer platforms, i.e., the system of the end user of the network, which can be a computer or a terminal device (any input/output or information display device). Computers on network nodes are sometimes called host machines, or simply hosts.
Currently, computers of various classes are widely and successfully used in networks - from personal computers to mainframes and supercomputers. The set of computers on the network must correspond to the variety of tasks solved by the network.
2. Second layer - communication equipment. Although computers are central to data processing in networks, communications devices have recently begun to play an equally important role.
Cabling systems, repeaters, bridges, switches, routers and modular hubs have gone from being ancillary network components to being core components, along with computers and system software. Today, a communications device may be a complex, specialized multiprocessor that must be configured, optimized, and managed.
3. The third layer that forms the network software platform is OS(OS). The efficiency of the entire network depends on which concepts for managing local and distributed resources form the basis of the network OS.
When designing a network, it is important to consider how easily a given OS can interact with other operating systems on the network, how much it ensures safety and security of data, to what extent it allows you to increase the number of users, whether it can be transferred to a different type of computer, and much more.
4. The topmost layer network tools are different network applications, such as network databases, mail systems, data archiving tools, teamwork automation systems, etc.
It is important to understand the range of capabilities that applications provide for different applications and how compatible they are with other network applications and operating systems.

Classification of computer networks

By territorial distribution

PAN (Personal Area Network)- a personal network designed for interaction various devices belonging to the same owner.
LAN (Local Area Network)- local networks that have a closed infrastructure before reaching service providers. The term “LAN” can describe both a small office network and a network at the level of a large factory covering several hundred hectares. Foreign sources even give a close estimate of about six miles (10 km) in radius. Local networks are closed networks; access to them is permitted only to a limited number of users for whom work in such a network is directly related to their professional activities.
CAN (Campus Area Network)- campus network - unites local networks of nearby buildings.
MAN (Metropolitan Area Network)- urban networks between institutions within one or several cities, connecting many local computer networks.
WAN (Wide Area Network)- covering large geographic regions, including both local networks and other telecommunications networks and devices. An example of a WAN is a packet-switching network (Frame relay), through which various computer networks can “talk” to each other. Global networks are open and focused on serving any users.
Term "corporate network" also used in the literature to refer to the combination of several networks, each of which can be built on different technical, software and information principles.

By type of functional interaction

Point-to-point network - simplest form computer network, in which two computers are connected directly to each other through communications equipment. The advantage of this type of connection is its simplicity and low cost, the disadvantage is that only 2 computers can be connected in this way and no more.

Client-server- a computing or network architecture in which tasks or network load are distributed between service providers, called servers, and service customers, called clients. Often, clients and servers interact through a computer network and can be either different physical devices or software.

Fig. 1 - Client-server network architecture diagram

Peer-to-peer network (decentralized, peer-to-peer, P2P) is an overlay computer network based on equal rights of participants. Often in such a network there are no dedicated servers, and each node (peer) is both a client and performs server functions. Unlike the client-server architecture, this organization allows the network to remain operational with any number and any combination of available nodes. Participants in the network are called peers.

Fig. 2 - Peer-to-peer network diagram

Multi-Peer Network is a network that includes one or more dedicated servers. The remaining computers of such a network (workstations) act as clients.

Mixed network- a network architecture in which there are a number of servers that form a peer-to-peer network among themselves. End users each connect to their own server using a client-server scheme. Searching for information is possible online, both on your own server and (through it) on other servers on the network. The advantage of mixed networks is their ability to perform simultaneous searches on a large number of computers. The main disadvantage is the reduced reliability of the network.

By type of network topology

Tire- The physical transmission medium consists of a single cable, called a common bus, to which all computers on the network are connected in parallel. The disadvantages are the connection of a small number of workstations (no more than 20) and the complete interruption of network operation if the common cable is damaged. Failures of individual computers do not affect the operation of the network. To prevent signal distortion, it is necessary to install terminators at the ends of the cable.

Fig.3 - Bus topology

Ring- this is a topology in which each computer is connected by communication lines to only two others: from one it only receives information, and to the other it only transmits. On each communication line, as in the case of a star, there is only one transmitter and one receiver. This allows you to avoid using external terminators. Computers in a ring are not completely equal (unlike, for example, a bus topology). Some of them necessarily receive information from the computer that is transmitting at this moment earlier, while others - later. Each computer relays (restores) the signal coming to it, that is, it acts as a repeater, so the attenuation of the signal throughout the ring does not matter, only the attenuation between neighboring computers of the ring is important.

Fig.4 - Ring topology

Double ring- topology built on two rings. The first ring is the main path for data transfer. The second is a backup path that duplicates the main one. During normal operation of the first ring, data is transmitted only through it. When it fails, it merges with the second one and the network continues to function. In this case, data is transmitted through the first ring in one direction, and through the second in the opposite direction. An example is the FDDI network.

Star- all computers are connected to a central node. All information exchange takes place exclusively through the central computer, which is subject to a very large load in this way, so it cannot do anything else except the network. As a rule, it is the central computer that is the most powerful, and it is on it that all functions for managing the exchange are assigned. In principle, no conflicts are possible in a network with a star topology, because management is completely centralized.

Fig.5 - Star topology

Cellular- Each workstation on the network connects to several other workstations on the same network. It is characterized by high fault tolerance, complexity of configuration and excessive cable consumption, allows the connection of a large number of computers and is typical, as a rule, for large networks. Each computer has many possible ways connections with other computers. A cable break will not result in loss of connection between two computers.

Lattice is a topology in which the nodes form a regular multidimensional lattice. In this case, each lattice edge is parallel to its axis and connects two adjacent nodes along this axis. By connecting both external nodes of a one-dimensional lattice, a “ring” topology is obtained. Two- and three-dimensional lattices are used in supercomputer architecture. Characterized by high reliability and complexity of implementation.

Fig.6 - Lattice topology

Tree- characterized by the fact that between any pair of network nodes with such a topology there is only one path. The number of communication channels in an n-node tree network is minimal and equal to (n - 1). The reliability of the network is low, since the failure of even one of the links can lead to the network being split into two isolated subnetworks.

Fig.7 - Tree topology

Fat Tree- Unlike the classic tree topology, in which all connections between nodes are the same, connections in a Fat Tree become wider (thicker, more bandwidth-efficient) with each level as you approach the root of the tree. Doubling the bandwidth at each level is often used.

Fig.8 - "Fat tree" topology

By type of transmission medium

Wired ( telephone wire, coaxial cable, twisted pair, fiber optic cable)
Wireless (transmitting information via radio waves in a certain frequency range, WI-FI)

The main types of transmission media used in computer networks are:
– public analogue telephone channels;
– digital channels;
– narrowband and broadband cable channels;
– radio channels and satellite channels communications;
– fiber optic communication channels.

By functional purpose

Storage Area Networks
Server farms
Process Control Networks
SOHO networks, home networks

By transmission speed

low-speed (up to 10 Mbit/s),
medium-speed (up to 100 Mbit/s),
high-speed (over 100 Mbit/s);

By network operating systems

Windows based
UNIX based
NetWare based
Based on Cisco

If necessary to maintain a constant connection

Packet network, such as Fidonet and UUCP
Online network such as Internet and GSM

Local computer networks

A local network unites computers installed in one room (for example, a school computer lab consisting of 8-12 computers) or in one building (for example, in a school building several dozen computers installed in different subject rooms can be combined into a local network).

Fig.9 - Local network (LAN) diagram

In small local networks, all computers usually have equal rights, i.e., users independently decide which resources of their computer (disks, directories, files) to make publicly available over the network. Such networks are called peer-to-peer.
If more than ten computers are connected to the local network, then the peer-to-peer network may not be efficient enough. To increase productivity, as well as to ensure greater reliability when storing information on the network, some computers are specifically dedicated to storing files or application programs. Such computers are called servers, and a local area network is called a server-based network.
Each computer connected to the local network must have a special card (network adapter). Computers (network adapters) are connected to each other using cables.

Global computer network Internet.

Currently, tens of millions of computers connected to the Internet store a huge amount of information (hundreds of millions of files, documents, etc.) and hundreds of millions of people use information services global network.
is a global computer network that unites many local, regional and corporate networks and includes tens of millions of computers.
Each local or corporate network usually has at least one computer that has a permanent connection to the Internet using a high-bandwidth link (Internet server).

Fig. 10 - Global network - Internet
The reliability of the global network is ensured by the redundancy of communication lines: as a rule, servers have more than two communication lines connecting them to the Internet.
The basis, the “framework” of the Internet consists of more than one hundred million servers constantly connected to the network.
Internet servers can be connected using local networks or dial-up telephone lines for hundreds of millions of network users.

Basic network protocols

Simply connecting one computer to another is a necessary step to create a network, but not sufficient. To start transmitting information, you need to make sure that computers “understand” each other. How do computers “communicate” over a network? To provide this capability, we have developed special means, called "protocols". A protocol is a set of rules according to which information is transmitted through a network. The concept of a protocol is not only applicable to the computer industry. Even those who have never dealt with the Internet have most likely worked in Everyday life with any devices whose operation is based on the use of protocols. Yes, normal telephone network public devices also have their own protocol, which allows devices, for example, to determine whether the handset has been picked up at the other end of the line or to recognize the disconnection signal and even the caller’s number.

Based on this natural need, the world of computers needed a single language (that is, a protocol) that would be understandable to each of them.

Network protocol is a set of rules and standards by which data exchange occurs on a computer network.

The most common classification system for network protocols is the so-called OSI model, according to which protocols are divided into 7 levels according to their purpose - from physical (generation and recognition of electrical or other signals) to application (application programming interface for transmitting information by applications).
Network protocols prescribe rules for the operation of computers that are connected to the network. They are built on a multi-level principle. A protocol at some level defines one of technical rules communications. Currently, network protocols use the OSI model ( Open System Interconnection - interaction of open systems, OSI).
The OSI model is a 7-layer logical model of network operation. The OSI model is implemented by a group of protocols and communication rules organized into several layers:
There are 7 levels of interaction between computers in a computer network:
1) physical;
2) logical (or channel);
3) network;
4) transport;
5) level of communication sessions;
6) representative;
7) application level.
1. Physical Layer defines the electrical, mechanical, procedural, and functional specifications and provides for the link layer to establish, maintain, and terminate a physical connection between two computer systems directly coupled through a transmission medium, such as an analog telephone circuit, a radio circuit, or a fiber optic circuit.
2. Data Link Layer controls data transfer over a communication channel. The main functions of this layer are to split the transmitted data into pieces called frames, extract data from the stream of bits transmitted at the physical layer for processing at the network layer, detect transmission errors and recover incorrectly transmitted data.
3. Network Layer provides communication between two computer systems on a network that exchange information with each other. Another function of the network layer is to route data (called packets at this layer) within and between networks (internet protocol).
4. Transport Layer ensures reliable transfer (transportation) of data between computer systems of the network for higher levels. For this purpose, mechanisms are used to establish, maintain and terminate virtual channels (analogous to dedicated telephone channels), detect and correct transmission errors, and control the data flow (in order to prevent overflow or data loss).
5. Session Layer provides establishment, maintenance and termination of a communication session for the presentation layer, as well as resuming an abnormally interrupted session.
6. Presentation Layer provides transformation of data from a representation used in an application program on one computer system to a representation used in another computer system. The functions of the presentation layer also include conversion of data codes, their encryption/decryption, as well as compression of transmitted data.
7. Application Level differs from other layers of the model in that it provides services for application tasks. This layer determines the availability of application tasks and communication resources, synchronizes interacting application tasks, and establishes agreements on error recovery procedures and data integrity management. Important functions of the application layer are network management, as well as performing the most common system application tasks: Email, file sharing and others.
Since each layer of the ISO/OSI model has its own characteristics, the implementation of all these features is impossible within a single protocol.

The main protocols used in the Internet:

IMAP4
Gorpher

Brief description of protocols

The most common transport layer protocol in both local and global networks, developed by the US Department of Defense more than 20 years ago.
is not one protocol, but a whole set of protocols working together. It consists of two levels. The upper-level protocol, TCP, is responsible for the correct conversion of messages into information packets, from which the original message is assembled at the receiving side. The lower layer protocol, IP, is responsible for ensuring that messages are correctly delivered to the specified address. Sometimes packets of the same message can be delivered via different paths.
The standards are open and continuously improved.

Fig. 11 - Operating principle of the TCP/IP protocol

POP (Post Office Protocol)

Standard mail connection protocol. POP servers process incoming mail, and the POP protocol is designed to handle mail requests from client mail programs.

SMTP (Simple Mail Transfer Protocol)

A protocol that specifies a set of rules for transmitting mail. The SMTP server returns either an acknowledgment or an error message, or requests additional information.

The HTTP protocol (Hypertext Transfer Protocol) is a higher-level protocol than the TCP/IP protocol, an application-level protocol. HTTP was designed to transport Web pages efficiently over the Internet. It is thanks to HTTP that we have the opportunity to contemplate the pages of the Web in all their splendor. The HTTP protocol is the basis of the World Wide Web.

You issue HTTP commands using the browser interface, which is an HTTP client. When you click on a link, the browser requests the Web server for data from the resource to which the link points - for example, the next Web page.

In order for the text that makes up the content of Web pages to be displayed on them in a certain way - in accordance with the intent of the page creator - it is marked up using special text marks - HyperText Markup Language (HTML) tags.

The addresses of Internet resources that you access via the HTTP protocol look something like this: http://www.tut.by

Using this protocol, you can connect to a remote computer as a user (if you have the appropriate rights, that is, you know the username and password) and perform actions on its files and applications in the same way as if you were working on your own computer.

Telnet is a terminal emulation protocol. Work with him is carried out from command line. If you need to use the services of this protocol, you should not scour the wilds of the Internet in search of a suitable program. A Telnet client is supplied, for example, with Windows 98.

To command the Telnet client to connect to a remote computer, connect to the Internet, select Run from the Start menu and type in the input line, for example, the following: telnet lib.ru

(Instead of lib.ru, you can, of course, enter another address.) After this, it will start Telnet program, and the communication session will begin.

WAIS stands for Wide-Area Information Servers. This protocol was developed for searching information in databases. The WAIS information system is a distributed database system where individual databases are stored on different servers. Information about their content and location is stored in a special database - the server directory. View information resources carried out using the WAIS client program.

The search for information is carried out using keywords, which are specified by the user. These words are entered for a specific database, and the system finds all the corresponding fragments of text on all servers where the data in this database is located. The result is presented as a list of links to documents indicating how often the searched word and all searched words in the aggregate appear in this document.

Even today, when the WAIS system may be considered obsolete, experts in many fields, when conducting scientific research, nevertheless turn to it in search of specific information that they cannot find through traditional means.

The WAIS resource address on the Internet looks something like this: wais://site.edu

The Gopher protocol is an application layer protocol developed in 1991. Before the widespread adoption of the World Wide Web hypertext system, Gopher was used to extract information (mostly textual) from a hierarchical file structure. Gopher was the forerunner of the WWW, allowing you to navigate from one page to another using a menu, gradually narrowing the range of information displayed. Gopher client programs had a text interface. However, Gopher menu items could point not only to text files, but also, for example, to telnet connections or WAIS databases.

Gopher translates as “gopher”, which reflects the glorious university background of the developers of this system. The student sports teams at the University of Minnesota were called the Golden Gophers.

Gopher resources can now be viewed using a regular Web browser, as modern browsers support this protocol.

Gopher information resource addresses look something like this: gopher://gopher.tc.umn.edu

WAP (Wireless Application Protocol) was developed in 1997 by a group of companies Ericsson, Motorola, Nokia and Phone.com (formerly Unwired Planet) in order to provide access to Internet services to users wireless devices- such as mobile phones, pagers, electronic organizers, etc., using various communication standards.

For example, if your mobile phone supports the WAP protocol, then by typing the address of the desired Web page on its keyboard, you can see it (in a simplified form) directly on the phone’s display. Currently, the vast majority of device manufacturers have already switched to producing models with WAP support, which also continues to improve.

Network devices and equipment

Technical means of communication include cables (shielded and unshielded twisted pair, coaxial, fiber optic), connectors and terminators, network adapters, repeaters, splitters, bridges, routers, gateways, as well as modems that allow the use of various protocols and topologies in a single heterogeneous system.
Network card (adapter)- a device for connecting a computer to a network cable.
The physical media for information exchange are typically thick coaxial cable, thin coaxial cable, fiber optic cable, and Unshielded Twisted-Pair (UTP).
To solve the problem of internetworking, equipment manufacturers offer various interface devices - repeaters, bridges, routers, bridges/routers and gateways.
The main difference between these devices is that repeaters operate at layer 1 (physical), bridges operate at layer 2, routers are devices that operate at layer 3 (networking), and gateways operate at layer 4. –7 levels.
Routers- devices for connecting network segments, operating at the network level and using network level routing information. Routers exchange information with each other about the properties, state of the network, the health of links and the availability of nodes in order to select the optimal path for transmitting a packet. This process of selecting a route based on the address of the subscriber system that receives the packet is called routing.
Distinguish single-protocol And multi-protocol routers that can simultaneously support several protocols, such as IPX/SPX, TCP/IP and others. Since there are protocols that do not contain network layer information, routers also have to perform bridge functions. That's why modern multiprotocol routers are called "bridge routers." Among the advantages of routers, it is worth noting the ability to select a route, breaking long messages into several short ones and using alternative paths for their transmission, leading to the alignment of traffic along parallel paths, thereby allowing the connection of networks with packets of different lengths and facilitating the interconnection of networks.
Bridges- devices for connecting network segments, operating at the Media Access Control sublayer of the OSI/ISO model link layer. Bridges have the property of transparency for protocols of higher levels, that is, they transmit a frame from one segment to another at the physical address of the recipient station, which is extracted from the link-level header, analyze the integrity of frames and filter out damaged ones. These devices can have the property of self-learning, that is, as frames pass through the bridge, it fills two tables with the addresses of stations sending messages, physically placing them on opposite sides of the bridge and recording them in different tables.
Network segments that are connected by a bridge can use either the same or different channel protocols. In the latter case, the bridge translates a frame of one format into a frame of another format.
Bridges automatically adapt to changing network configurations and can connect networks with different network layer protocols. Unfortunately, these devices cannot distribute the load using alternative paths in the network, which sometimes leads to traffic congestion (the flow of information exchange on the communication line).
Repeater- a device operating at the physical level, designed to compensate for attenuation in the data transmission medium by amplifying signals in order to increase their propagation distance. One of the types of repeaters are media converters. They allow signals to be converted, for example, when connecting coaxial and fiber optic cables, when moving from one transmission medium to another.
Splitter- passive device for connecting more than two cable segments.
Gateways- devices operating at the upper layers of the OSI model (session, presentation and application). They represent a method of connecting network segments and computer networks to central computers. The need to use gateways arises when two systems with completely different architectures are combined to translate the flow of data passing between these systems.
Modems are used to connect to other communication lines. The most widely used modems are those aimed at connecting to a dial-up network. telephone line.
Modem- a device designed to exchange information between remote computers via communication channels. A modem for connecting to a dial-up telephone line converts computer data into an analog audio signal for transmission over the telephone line (modulation), as well as the reverse conversion (demodulation).
Modems can be internal or external. Internal modems are inserted inside system unit computer. External modems are presented as a separate device that is connected by a cable to a computer's serial port, the same one to which a mouse is often connected. Internal modems contain a built-in serial port and are powered by the computer; external modems have a separate power supply. Internal modems are cheaper than external modems, all other characteristics being equal, the main one being speed.
Fax modem- a device that provides electronic transmission of plain text, drawings, photographs, diagrams, documents, conversion of information into a form suitable for transmission via an existing communication channel, and the formation of a duplicate on paper on the receiving side - facsimile - original document. Generally speaking, any telefax includes a scanner for reading a document, a modem that transmits and receives information over a telephone line, and a printer that prints the received message on thermal or plain paper. Of course, fax modem boards do not contain components such as a scanner and printer. The information is presented only in “electronic” form.

FAQ

What is an IP address (IP address)?

Each computer on the network has its own unique address(number) - the so-called IP address - it is a number of the form aaa.bbb.ccc.ddd, (for example 10.240.51.23), where the first and second digits (10.240.) are the same for all DOM networks, the third digit indicates for the network segment to which the computer is connected, the fourth digit is the computer number itself.
Each computer has two IP addresses: internal (local) and external (when connected to the Internet).

How to find out the IP address?
What is a gateway (server)?

This is a computer on our network through which you access the Internet. A request from your computer is transmitted through the network to the server, it checks your data (IP address, MAC address, login and password) and after that you gain access to the Internet.

What is a DNS server?

DNS server(pronounced "de-en-es") is a special server that contains information about IP addresses. The Domain Name System (DNS), which is used on the Internet, maps host and domain names on one side to IP addresses on the other. DNS uses a hierarchical database of names distributed across multiple computers.

What is traffic?

Traffic is the amount of information coming to your computer from the network and sent from it to the network. Every time you browse the Internet, a certain amount of information, measured in bytes, is sent to your computer.
The fact is that any Internet resource, be it www pages, music videos, www chats, IRC, news servers, etc. is traffic. You are viewing a www page, which means that some information has arrived on your computer from the network; you are listening to music from the Internet, which means that information is being transferred to your computer from the network.
What is "incoming" and "outgoing" traffic?
Incoming traffic is the volume of information coming to your computer from the network, and outgoing traffic, accordingly, is the volume leaving your computer on the network.

How to connect two computers to a network (network bridge)?

Answer: One of the computers connects to the Internet, the second computer connects to the first. The main disadvantage in this case is that in order for the second computer to connect to the network, the first computer must also be on the network. And also, if your connection to the Internet is via a network card, then you need an additional network card to connect the second computer to the first, because the built-in network card is already occupied (it receives the Internet).

Please help me choose the most appropriate network topology.

Answer: First of all, decide on the type of carrier. The fact is that the use of coaxial cable or twisted pair implies fundamentally different local network architectures. In the first case, the network will be built on the principle of a “common bus” - all computers included in it are sequentially connected to each other in a chain using cable segments, forming a single backbone. This is quite convenient if all users of your network live on the same landing or in apartments located one below the other. However, if computers are scattered throughout the entrance (or house), the coaxial cable will loop, which is inconvenient even at the stage of initial network installation. If you need to connect several more new users to it, the problems will increase exponentially. In addition, the “common bus” is dangerous: if a section of the network between two computers is damaged, the entire network is disconnected. Twisted pair allows you to create a completely different network architecture. A twisted pair cable is similar to a regular telephone cable, but instead of 2 (or 4) wires, it uses 8 wires divided into 4 pairs. Twisted pair cable is a more flexible and practical cable, easy to install and well protected from external influences. However, the main advantage of this option is different: a local network of the “star” or “tree” type is based on twisted pair cables - in the center of it there is a communication device (in the simplest case, a hub) with several ports, to each of which the end computer is connected via a cable. When using such an architecture, the failure of one or more sections of the network will not lead to its stop, and other users will be able to continue working. The only danger lies in the failure of communication equipment.

We have installed a network cable between houses and are afraid that the network will fail during a thunderstorm. How to deal with thunderstorms?

Answer: Thunderstorms are generally the scourge of networks. In a large network, not a single thunderstorm passes without losses. There are many devices to protect network equipment from this scourge. Basically these are adapters between devices and network cable. The adapter is grounded, and when lightning strikes the cable, only the adapter burns out. According to advertising, the effectiveness of their work reaches 90%. Which device to choose is up to you. A more reliable remedy during a thunderstorm is the use of fiber-optic network technology, at least in open sections of the network.

Even as a result of a fairly superficial examination of networking, it becomes clear that a computer network is a complex set of interconnected and coordinated software and hardware components. Studying the network as a whole presupposes knowledge of the operating principles of its individual elements:

computers;

communication equipment;

operating systems;

network applications.

The entire network hardware and software complex can be described by a multilayer model. At the heart of any network is a hardware layer of standardized computer platforms. Currently, computers of various classes are widely and successfully used in networks - from personal computers to mainframes and supercomputers. The set of computers on the network must correspond to the variety of tasks solved by the network.

The second layer is communications equipment. Although computers are central to data processing in networks, communications devices have recently begun to play an equally important role. Cabling systems, repeaters, bridges, switches, routers, and modular hubs have gone from being ancillary network components to becoming essential components, along with computers and system software, in both their impact on network performance and cost. Today, a communications device may be a complex, specialized multiprocessor that must be configured, optimized, and managed. Learning how communications equipment works requires familiarity with big amount protocols used in both local and global networks.

The third layer that forms the network software platform is operating systems (OS). The efficiency of the entire network depends on which concepts for managing local and distributed resources form the basis of the network OS. When designing a network, it is important to consider how easily a given operating system can interact with other operating systems on the network, how secure and secure it is for data, the extent to which it can increase the number of users, whether it can be transferred to a different type of computer, and many other considerations.

The topmost layer of networking tools are various network applications, such as network databases, mail systems, data archiving tools, collaboration automation systems, etc. It is very important to understand the range of capabilities provided by applications for different application areas, as well as to know how compatible they are with other network applications and operating systems.

The simplest case of interaction between two computers

In the simplest case, the interaction of computers can be realized using the same means that are used to interact a computer with peripherals, for example, through the RS-232C serial interface. Unlike the interaction of a computer with peripheral device, when a program works, as a rule, only on one side - on the computer side, in this case there is an interaction between two programs running on each computer.

A program running on one computer cannot gain direct access to the resources of another computer - its disks, files, printer. She can only “ask” the program running on the computer to which these resources belong. These "requests" are expressed as messages transmitted over communication channels between computers. Messages can contain not only commands to perform certain actions, but also actual information data (for example, the contents of a file).

Consider the case when a user working with text editor on personal computer A, you need to read part of a file located on the disk of personal computer B (Fig. 4). Let's assume that we connected these computers via a communication cable through COM ports, which, as is known, implement the RS-232C interface (such a connection is often called a null modem). To be sure, let the computers run MS-DOS, although this is not of fundamental importance in this case.

Rice. 4. Interaction between two computers

The COM port driver together with the COM port controller work in approximately the same way as in the case of interaction between the control unit and the computer described above. However, in this case, the role of the PU control device is performed by the controller and driver of the COM port of another computer. Together they ensure the transfer of one byte of information over a cable between computers. (In “real” local networks, similar functions of transferring data to the communication line are performed by network adapters and their drivers.)

The driver of computer B periodically polls the reception completion sign, set by the controller when the data is transferred correctly, and when it appears, reads the received byte from the controller buffer into RAM, thereby making it available to programs on computer B. In some cases, the driver is called asynchronously, by interrupts from the controller.

Thus, the programs of computers A and B have the means to transmit one byte of information. But the task considered in our example is much more complicated, since it is necessary to transfer not one byte, but a certain part of a given file. All related to this additional problems must be solved by higher-level programs than COM port drivers. For definiteness, we will call such programs of computers A and B application A and application B, respectively. So, application A must generate a request message for application B. The request must specify the file name, the type of operation (in this case, reading), the offset and the size of the file area containing the required data.

To transmit this message to computer B, application A contacts the COM port driver, telling it the address in RAM, where the driver finds the message and then transmits it byte by byte to application B. Application B, having received the request, executes it, that is, reads it the required area of the file from the disk using local OS tools to the buffer area of its random access memory, and then, using the COM port driver, transmits the read data via a communication channel to computer A, where it reaches application A.

The described functions of application A could be performed by the text editor program itself, but it is not very rational to include these functions in every application - text editors, graphic editors, database management systems and other applications that need access to files. It is much more profitable to create a special software module that will perform the functions of generating request messages and receiving results for all computer applications. As mentioned earlier, such a service module is called a client. On the side of computer B, another module must operate - a server, constantly waiting for requests for remote access to files located on the disk of this computer. The server, having received a request from the network, accesses the local file and performs specified actions with it, possibly with the participation of the local OS.

The software client and server perform system functions for servicing requests from applications on computer A for remote access to files on computer B. In order for applications on computer B to be able to use files on computer A, the described scheme must be symmetrically supplemented with a client for computer B and a server for computer A.

The interaction diagram of the client and server with applications and the operating system is shown in Fig. 5. Despite the fact that we have considered a very simple hardware communication scheme for computers, the functions of programs that provide access to remote files are very similar to the functions of modules of a network operating system operating on a network with more complex hardware connections of computers.

Rice. 5. Interaction of software components when connecting two computers

A very convenient and useful feature of the client program is the ability to distinguish a request to remote file from a request to a local file. If the client program can do this, then applications do not have to care about which file they are working with (local or remote), client program recognizes and redirects request to a remote machine. Hence the name often used for the client part of a network OS - redirector. Sometimes recognition functions are separated into a separate software module; in this case, not the entire client part is called a redirector, but only this module.

A computer network is a complex set of interconnected and coordinated software and hardware components. Studying a network requires knowledge of the operating principles of its individual elements:

computers;

communication equipment;

operating systems;

network applications.

The entire network hardware and software complex can be described by a multilayer model. At the heart of any network is the hardware layer. Currently, computers of various classes are widely and successfully used in networks - from personal computers to mainframes and supercomputers.

The third layer is operating systems (OS). The operating efficiency of the entire network depends on the operating system. When designing a network, it is important to consider how easily this OS can interact with other operating systems on the network, how much it ensures safety and security of data, to what extent it allows you to increase the number of users, and whether it can be transferred to a different type of computer. Network adapter driver - special. support program interaction OS with new devices.

The topmost layer of network tools are various network applications, such as network databases, mail systems, data archiving tools, teamwork automation systems, etc.

5 Ethernet .Network technology - This is an agreed set of standard protocols and software and hardware that implement them, sufficient to build a computer network.

Sometimes network technologies are called basic technologies, on their basis the basis of any network is built. Examples of basic network technologies include Ethernet, Token Ring and FDDI, X.25 and frame relay. The Ethernet standard was adopted in 1980. The number of networks is 5 million, and the number of computers is 50 million. The basic principle underlying Ethernet is random access method to a shared data transmission medium. Such a medium can be thick or thin coaxial cable, twisted cable, optical fiber or radio waves. The Ethernet standard strictly defines the topology of electrical connections. Computers are connected to a shared medium in accordance with the typical “common bus” structure. Data transfer occurs at a speed of 10 Mbit/s (this value is the throughput of the Ethernet network). The essence of the random access method is as follows. A computer on an Ethernet network can transmit data over the network only if the network is free. Therefore, an important part of Ethernet technology is the procedure for determining the availability of the medium. After the computer is convinced that the network is free, it begins transmission, while “capturing” the medium. The time of exclusive use of the shared medium by one node is limited by the time of transmission of one frame. Frame - it is a unit of data exchanged between computers on an Ethernet network. Ethernet network is designed in such a way that when a frame enters a shared data transmission medium, all network adapters simultaneously begin to receive this frame. They all analyze the destination address located in one of the initial fields of the frame, and if this address matches their own address, the frame is placed in the internal buffer of the network adapter. Thus, the destination computer receives the data intended for it. Sometimes a situation may arise when two or more computers simultaneously decide that the network is free and begin transmitting information. This situation is called collision. The Ethernet standard provides an algorithm for detecting and correctly processing collisions. Once a collision is detected, the network adapters that were attempting to transmit their frames stop transmitting and, after a pause, attempt to access the medium again and transmit the frame that caused the collision. Advantages 1) cost-effectiveness and simplicity (cable, adapter); 2) the use of bus topology leads to a simplification of the network adapter; 3) network adapters are simple; 4) easy network expandability

6 OSI model

In the early 1980s, a number of international standards organizations developed a model that played a significant role in the development of networks. This model is called open systems interaction model or OSI model. The OSI model defines different levels of interaction between systems, gives them standard names and specifies what functions each level should perform. There are seven layers in the OSI model: Application Representative Sessions Transport Network Channel Physical. The OSI model distinguishes between two main types of protocols. The protocols with connection establishment and protocols without first establishing a connection. Such protocols are also called datagram protocols.

Physical layer deals with the transmission of bits over physical communication channels. The characteristics of physical media (data transmission, bandwidth, noise immunity, characteristic impedance) relate to this level. Physical layer functions are implemented in all devices connected to the network. On the computer side, the physical layer functions are performed by the network adapter or serial port.

Data link level.One One of the tasks of the link layer is to check the availability of the transmission medium. Another task of the link layer is to implement error detection and correction mechanisms. To do this, the link layer groups bits into sets called personnel. The link layer ensures that each frame is transmitted correctly by placing a special sequence of bits at the beginning and end of each frame to distinguish it, and also calculates a checksum. When a frame arrives over the network, the receiver calculates a checksum of the received data and compares the result with the checksum from the frame. If they match, the frame is considered correct and accepted. If the checksums do not match, an error is recorded. The link layer can not only detect errors, but also correct them by retransmitting damaged frames. The data link layer is a very powerful and complete set of functions for sending messages between network nodes.

Network layer serves to form a unified transport system , connecting several networks. Local network link layer protocols ensure data delivery between any nodes only in a network with the appropriate standard topology. A composite network is formed. The networks are connected to each other by special means. devices called routers (this is a device that collects information about the topology of internetwork connections and, based on it, forwards network layer packets to the destination network). Transport layer ensures data transmission with the required degree of reliability. In the OSI model, there are 5 classes of transport service (0-4). Each class corresponds. parameters that determine urgency, the possibility of restoring interrupted communication, the presence of multiplexing media, the ability to detect and restore errors. All parameters are defined. transmission reliability.

Session layer provides dialogue management: records which party is currently active, provides synchronization tools.

Representative level provides information presentation over the network without changing its content. Encryption or decryption.

Application layer this is a set of various protocols with the help of which network users gain access to shared resources, such as files, printers or hypertext Web pages, and organize their joint work .

The OSI model, although very important, is only one of many communication models. These models and their associated protocol stacks may differ in the number of layers, their functions, message formats, services supported at the upper layers, and other parameters.

OSI protocol stack

The OSI protocol stack fully complies with the OSI model. The protocols of the OSI stack are ambiguous, because The stack was developed when many protocol stacks already existed. On the other hand, the OSI stack is supported by the most popular protocols.

Stack levels

Network level: It includes rare protocols (connection ONP, CLNP). The names indicate that the first is connection-oriented, the second is not. There are other protocols of this level that are very popular

Transport level: in accordance with the functions of the OSI model, the user specifies the required services

Application level: provides file transfer, mail, directory service. The most popular protocols are the X.500 standard - directory service, X-400 e-mail, VTP - remote terminal standard, FTAM - file management access transfer protocol, JTM - forwarding protocol

8 IPX/SPX stack

This stack is the original Novell protocol stack, developed for the NetWare network operating system back in the early 80s. The network and session layer protocols Internetwork Packet Exchange (IPX) and Sequenced Packet Exchange (SPX), which give the stack its name, are a direct adaptation of the Xerox XNS protocols, which are much less widespread than the IPX/SPX stack. The popularity of the IPX/SPX stack is directly related to the Novell NetWare operating system, which still retains world leadership in the number of installed systems, although recently its popularity has decreased somewhat and its growth rate lags behind Microsoft Windows NT.Many features of the IPX/SPX stack are due to the orientation of early versions of the NetWare OS (up to version 4.0) for working in small local networks consisting of personal computers with modest resources. It is clear that for such computers, Novell needed protocols that would require a minimum amount of RAM (limited in IBM-compatible computers running MS-DOS with a capacity of 640 KB) and that would run quickly on processors of low processing power. As a result, the IPX/SPX stack protocols until recently worked well in local networks and not so well in large corporate networks, since they overloaded slow global links with broadcast packets that are intensively used by several protocols in this stack (for example, to establish communication between clients and servers). This circumstance, as well as the fact that the IPX/SPX stack is proprietary to Novell and requires a license to implement it (that is, open specifications were not supported), for a long time limited its distribution only to NetWare networks. However, since the release of NetWare 4.0, Novell has made and continues to make major changes to its protocols aimed at adapting them to work in corporate networks. Now the IPX/SPX stack is implemented not only in NetWare, but also in several other popular network operating systems, for example SCO UNIX, Sun Solaris, Microsoft Windows NT.

9 NetBIOS/SMB stack

This stack is widely used in products from IBM and Microsoft. All the most common protocols Ethernet, Token Ring, FDDI and others are used at the physical and data link layers of this stack. The NetBEUI and SMB protocols operate at the upper levels.

The NetBIOS (Network Basic Input/Output System) protocol appeared in 1984 as a network extension standard features IBM PC basic input/output system (BIOS) for the IBM PC Network program. This protocol was later replaced by the so-called NetBEUI - NetBIOS Extended User Interface protocol. To ensure application compatibility, the NetBIOS interface was retained as an interface to the NetBEUI protocol. The NetBEUI protocol was designed to be an efficient, low-resource protocol for networks of no more than 200 workstations. This protocol contains many useful network functions, which can be attributed to the network, transport and session layers of the OSI model, but it cannot be used to route packets. This limits the use of the NetBEUI protocol to local networks that are not divided into subnets, and makes it impossible to use it in composite networks. Some of the limitations of NetBEUI are addressed by the NBF (NetBEUI Frame) implementation of this protocol, which is included in the Microsoft Windows NT operating system.

The SMB (Server Message Block) protocol performs the functions of the session, representative and application layers. SMB is used to implement file services, as well as printing and messaging services between applications.

The SNA protocol stacks from IBM, DECnet from Digital Equipment Corporation, and AppleTalk/AFP from Apple are used primarily in the operating systems and network equipment of these companies.

The correspondence of some of the most popular protocols to the layers of the OSI model is shown. Often this correspondence is very conditional, since the OSI model is only a guide to action, and quite general, and specific protocols were developed to solve specific problems, and many of them appeared before the development of the OSI model. In most cases, stack developers have prioritized networking speed over modularity—no stack other than the OSI stack is split into seven layers. Most often, 3-4 levels are clearly distinguished in the stack: the level of network adapters, in which the protocols of the physical and data link layers are implemented, network layer, transport layer and service layer, which includes the functions of the session, presentation and application layers.

10 Currently, the TCP/IP stack is the most popular means of organizing composite networks. There are 4 levels defined in the TCP/IP stack (application, main, internetworking, network interfaces). Each of these levels bears some load on solving the main task - organizing reliable and productive operation of a composite network, parts of which are built on the basis of different network technologies.

Interconnection LayerRod The entire architecture is the internetworking layer, which implements the concept of packet transmission in connectionless mode. This layer provides the ability to move packets across the network using the route that is in this moment is the most rational. The main network layer protocol in the stack is the Internet Protocol (IP). This protocol was originally designed as a protocol for transmitting packets in composite networks. The IP protocol works well in networks with complex topologies. The internetworking layer also includes all protocols related to the compilation and modification of routing tables.

Main level Because connections are not established at the network layer, there is no guarantee that all packets will arrive at their destination intact or arrive in the same order in which they were sent. This problem is solved main level TCP/IP stack, also called transport. The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) operate at this layer. The TCP protocol provides reliable transmission of messages between remote application processes through the formation of logical connections. The UDP protocol provides the transmission of application packets in a datagram manner and serves only as a bridge between the network protocol and numerous application-level services or user processes.

The application layer integrates all the services provided by the system to user applications. It is implemented by software systems based on lower-level protocols. This level is constantly expanding by joining the old ones

Network Interfaces Layer Protocols at this level must ensure integration of other networks into the composite network: the TCP/IP network must have the means to include any other network. This level cannot be determined once and for all. For each technology included in the composite subnetwork, its own interface facilities must be developed. The network interface layer in the TCP/IP protocols supports all popular standards of the physical and data link layers: for local networks these are Ethernet, Token Ring, FDDI, Fast Ethernet, Gigabit Ethernet, for global networks - point-to-point connection protocols SLIP and PPP, territorial network protocols with X.25 packet switching, frame relay.

Correspondence of TCP/IP stack levels to the seven-layer ISO/OSI model)

Considering the multi-layer TCP/IP architecture, we can distinguish in it, like the OSI architecture, layers whose functions depend on the specific technical implementation of the network, and levels whose functions are focused on working with applications

11 In accordance with IEEE 802 standards, the data link layer in local networks consists of two sublayers - LLC and MAC.

LLC - logical channel control level

The LLC protocol provides local network technologies with the required quality of transport services by transmitting its frames. It occupies a layer between network protocols and MAC layer protocols. The LLC protocol is based on the HDLC protocol, which is an ISO standard.

Three types of LLC level procedures: connectionless and acknowledgmentless procedure;

procedure with connection establishment and confirmation; procedure without establishing a connection, but with confirmation.

The LLC protocol provides local network technologies with the required quality of transport service by transmitting its frames either in a datagram manner or using connection establishment and frame recovery procedures. The logical channel of the LLC2 protocol is full-duplex, so that data can be transferred in both directions.

The MAC sublayer performs the following functions:

Supports services for the LLC sublayer; Forms a frame of a certain format; Manages the token transfer procedure; Addresses stations on the network; Copies frames intended for a given station; Generates a frame check sequence and checks it for all frames circulating around the ring; Removes from the ring all frames generated by this station; Manages timers; maintains a number of event counters, which helps to detect and localize faults, etc.;

In each MAC block, two processes operate in parallel: the process of transmitting symbols and the process of receiving symbols. Due to this, the MAC can simultaneously transmit symbols of one frame and receive symbols of another frame.

MAC layer operations. Using MAC layer operations, stations access the ring and transmit their data frames. The cycle of frame transmission from one station to another consists of several stages: capture of a token by the station to which it is necessary to transmit the frame, transmission of one or more data frames, release of the token by the transmitting station, retransmission of the frame by intermediate stations, recognition and copying of the frame by the receiving station and removal of the frame from network by the sending station.

12 Classic Ethernet suited most users for about 15 years. However, in the early 90s, its insufficient capacity began to be felt. Many Ethernet segments became overloaded, and the frequency of collisions increased.

There is an urgent need to develop a “new” Ethernet, that is, a technology that would be effective in terms of price/quality ratio with a performance of 100 Mbit/s. In 1992, a group of network equipment manufacturers formed the non-profit association Fast Ethernet Alliance to develop a standard new technology, which was supposed to preserve the features of Ethernet technology to the maximum extent possible. Especially when you consider the high cost of troubleshooting a large coaxial cable system. All the differences between Fast Ethernet technology and Ethernet are concentrated on the physical layer. More complex structure physical layer of Fast Ethernet technology is due to the fact that it uses three types of cabling systems: fiber-optic multimode cable;

Coaxial cable is not included in the list of permitted data transmission media of the new Fast Ethernet technology. Because over short distances, twisted pair allows data to be transferred at the same speed as coaxial cable, but the network is cheaper and more convenient to use. The abandonment of coaxial cable has led to the fact that Fast Ethernet networks always have a hierarchical tree structure built on hubs.

The official 802.3 standard established three different specifications for the Fast Ethernet physical layer and gave them the following names:

100Base-TX ;100Base-T4 ;100Base-FX

Rules for constructing Fast Ethernet segments when using repeaters

Fast technology Ethernet, like all non-coaxial variants of Ethernet, is designed to use repeater hubs to form connections in the network. Rules for correctly constructing Fast Ethernet network segments include:

restrictions on maximum segment lengths;

restrictions on the maximum network diameter;

restrictions on the maximum number of repeaters and the maximum length of the segment connecting the repeaters.

13 1OOVG-AnyLAN technology differs from classic Ethernet to a much greater extent than Fast Ethernet. Differences

1 A different access method is being used. Additionally, this method supports priority access for synchronous applications.

2 Frames are not transmitted to all network stations, but only to the destination station.

3 The network has a dedicated access arbiter - a concentrator.

4 Frames of two technologies are supported - Ethernet and Token Ring (it is this circumstance that gives the addition AnyLAN in the name of the technology).

5 Data is transmitted simultaneously over 4 pairs of Category 3 UTP cable. For each pair, data is transmitted at a speed of 25 Mbit/s, which gives a total of 100 Mbit/s. Unlike Fast Ethernet, there are no collisions in 100VG-AnyLAN networks, so it was possible to use all four pairs of a standard category 3 cable for transmission. A 5V/6V code is used for data encoding.

The network consists of a central hub, also called the root, and end nodes and other hubs connected to it. Each lOOVG-AnyLAN hub and network adapter must be configured to handle either Ethernet frames or Token Ring frames, and both types of frames are not allowed to circulate simultaneously. The hub polls the ports cyclically. A station wanting to transmit a packet sends a special low-frequency signal to the hub. The lOOVG-AnyLAN network uses two priority levels - low and high. A low priority level corresponds to normal data (file service, print service, etc.), and a high priority level corresponds to time-sensitive data (such as multimedia). If the network is free, then the hub allows the packet to be transmitted. If the network is busy, the hub puts the received request into a queue, which is processed in accordance with the order in which requests were received and taking into account priorities. If another hub is connected to the port, polling is suspended until the downstream hub completes polling.

An important feature of lOOVG-AnyLAN technology is the preservation of Ethernet and Token Ring frame formats. To support very demanding applications, Gigabit Ethernet technology is available, which, while maintaining continuity with Ethernet and Fast Ethernet, provides data transfer rates of 1000 Mbit/s.

The main idea of the developers of the Gigabit Ethernet Standard was to preserve as much as possible the ideas of classical Ethernet technology while achieving a bit speed of 1000 Mbit/s.

The Gigabit Ethernet standard does not support at the protocol level:

Quality of service;

Redundant connections;

Testing the performance of components and equipment.

Switches have all these features in local networks today. Therefore, the technology developers decided that the basic protocol should simply transfer data quickly, and the more complex ones should be transferred to the upper-layer protocols that run in the switches.

14Token Ring technology (802.5)

The divided medium consists of cable sections to which all stations are connected into a ring. Difference from Ethernet: the separation of the medium occurs in the definition. ok. Special data is transmitted over the network. electrical signal(frame). Token Ring technology was developed by IBM in 1984. IBM uses Token Ring technology as its main network technology to build local networks based on computers of various classes - mainframes, minicomputers and personal computers. Mixing of stations operating on various speeds, in one ring is not allowed. In T.R. technology the sent frame is returned to the sender => there is a chance to check the quality of the transmission. The token transfer process has begun. with incl. one car, called an active monitor. If there are several machines in the network, then the active monitor is the station with the maximum MAC-@. Active monitor every 3 seconds. generates a special frame. destination. If a frame is not generated for more than 7 seconds, then the active monitor is re-selected on the network. Having received the marker, the station analyzes it and ensures its progress to the next station. A station that has data to transmit, upon receiving the token, removes it from the ring, which gives it the right to access the physical medium and transmit its data. The transmitted data always passes along the ring in one direction from one station to another. Frame equipped

@destination and @source. If the frame passes through the destination station, then, having recognized its address, this station copies the frame to its internal buffer and inserts an acknowledgment sign into the frame. The station that issued the data frame to the ring, upon receiving it back with confirmation of receipt, removes this frame from the ring and transmits a new token to the network. This access algorithm is used in Token Ring networks with an operating speed of 4 Mbit/s. The ownership time of the shared medium in the Token Ring network is limited marker retention time, Typically the default token hold time is 10ms. For 4 Mbit/s networks, the frame size is usually 4 KB, and for 16 Mbit/s networks - 16 KB. T.R. 16 Mbit/s networks use the algorithm early release of the marker. In accordance with it, a station transmits an access token to the next station immediately after the end of transmission of the last bit of the frame, without waiting for the return of this frame along the ring with an acknowledgment bit. In this case, the ring capacity is used more efficiently, since frames from several stations move along the ring simultaneously.

Physical layer of Token Ring technology

IBM built T.R. networks. based on MAU or MSAU hubs. The T.R hub can be active (has self-powered power) or passive (it simply connects the ports with internal connections so that the stations form a ring). Main difference the concentrator is that the concentrator type MSAU provides. bypassing those ports to the connections. inactive computers Because an active hub restores the signal. In the case of a passive hub, the role of an amplifier is played by the network adapter until the signal has reached. With a large number of transmitting stations, a resynchronization function is present. T.R. is based on the star-ring topology, i.e. connection nodes to the hub with a star, and the hub itself. others to others via special ports. The purpose of the ports is the formation of a backbone physical. rings. All stations in the ring must operate at the same speed - either 4 Mbit/s or 16 Mbit/s. The maximum length of a Token Ring is 4000 m. There is a large number of hardware for Token Ring networks that improves some of the standard characteristics of these networks: maximum network length, distance between hubs, reliability (by using double rings). IBM recently introduced a new variant of Token Ring technology called High-Speed Token Ring, HSTR. This technology supports bit rates of 100 and 155 Mbps, while maintaining the core features of 16 Mbps Token Ring technology.

15 TechnologyFDDI - This is the first lock technology. networks in which the data transmission medium is fiber-optic cable. Work began in the 80s Main characteristics of the technology

FD0DI technology is largely based on TokenRing technology, developing and improving its basic ideas.

FDDI Objectives: 1 increase data transfer speed up to 100 Mbit/s; 2 increase the fault tolerance of the network through standard procedures for restoring it after various types of failures - cable damage, incorrect operation node, hub, high level of interference on the line, etc.; 3 make the most of potential network bandwidth for both asynchronous and synchronous (latency-sensitive) traffic.

The FDDI network is built on the basis of two fiber optic rings that form basic And spare data transmission paths between network nodes. Having two rings is the primary way to increase fault tolerance in an FDDI network, and nodes that want to take advantage of this increased reliability potential must be connected to both rings. In normal network operation mode, data passes through all nodes and all cable sections of the primary ring only; this mode is called the “end-to-end” or “transit” mode. The secondary ring is not used in this mode.

In the event of some type of failure where part of the primary ring cannot transmit data, the primary ring is combined with the secondary ring, again forming a single ring. This mode of network operation is called "folding" or "folding" the rings. To simplify this procedure, data is always transmitted on the primary ring in one direction, and on the secondary ring in the opposite direction. Therefore, when a common ring of two rings is formed, the transmitters of the stations remain connected to the receivers of neighboring stations, which allows information to be correctly transmitted and received by neighboring stations. Resiliency of FDDI technology

To ensure fault tolerance, the FDDI standard provides for the creation of two fiber optic rings - primary and secondary, and two types of connecting stations to the network. Simultaneous connection to the primary and secondary rings is called double connection. Connecting only to the primary ring is called a single connection. The FDDI standard provides for the presence of end nodes in the network - stations, as well as hubs. For stations and hubs, any type of connection to the network is acceptable - both single and double. Typically, hubs have a double connection, and stations have a single connection. In the event of a single cable break between dual-connected devices, the FDDI network will be able to continue normal work due to automatic reconfiguration of internal frame transmission paths between hub ports. A double cable break will result in the formation of two isolated FDDI networks. If the cable to a single-connection station breaks, it becomes cut off from the network, but the ring continues to operate. The physical layer is divided into two sublayers: media-independent and media-dependent

16In TCP/IP stack Three types of addresses are used: local (hardware), IP addresses and symbolic domain names.

In TCP/IP terminology, under local address refers to the type of address that is used by the underlying technology to deliver data within a subnet. Different network technologies and different protocol stacks are allowed in different subnets. Technologies (Ethernet, FDDI, T.R.) identification. interfaces via MAC address. In other technologies used. St. node addressing schemes. Complexity arises when networks of different technologies are combined. Such @ becomes component components, respectively. Technologies. A computer on a local network can have several local addresses even with one network adapter. Some network devices do not have local addresses. For example, such devices include global router ports designed for point-to-point connections.

IP addresses represent the main type of addresses on the basis of which the network layer transmits packets between networks. These addresses consist of 4 bytes 109.26.17.100. The IP address is assigned by the administrator. An IP address consists of two parts: the network number and the host number. The network number can be chosen arbitrarily by the administrator, or assigned on the recommendation of a special Internet division. The host number in the IP protocol is assigned independently of the local address of the host. An IP address does not characterize a single computer or router, but a single network connection.

Symbolic domain names. Symbolic names in IP networks are called domain names and are built on a hierarchical basis. The components of a full symbolic name in IP networks are separated by a dot and listed in the following order: first the simple name of the end node, then the name of a group of nodes, then the name of a larger group, and so on until the name of the highest level domain RU - Russia. An example of a domain name is the name base2.sales.zil.ru. There is no algorithmic correspondence between the domain name and the host's IP address, so it is necessary to use some additional tables or services so that the network host is uniquely identified by both the domain name and the IP address. TCP/IP networks use a special distributed DNS service that establishes this mapping based on lookup tables. Therefore, domain names are also called DNS names.

IP addresses.

FORMAT.

An IP address is 4 bytes long and is usually written as four numbers representing the value of each byte in decimal form and separated by dots, for example 128.10.2.30 is the traditional decimal form of representing an address. An address consists of two logical parts - the network number and the node number online. Which part of the address refers to the network number and which part refers to the node number is determined by the values of the first bits of the address. The values of these bits are also indications of which class refers to one or another IP address.

IP Address Classes

If the address starts with 0, then the network is classified as class A and the network number occupies one byte, the remaining 3 bytes are interpreted as the node number in the network. Class A networks have numbers ranging from 1 to 126. (Number 0 is not used, and number 127 is reserved for special purposes, as discussed below.) Class A networks are few, but the number of nodes in them can reach 2 24. - If the first two bits of the address are 10, then the network belongs to class B. In class B networks, 16 bits, that is, 2 bytes, are allocated for the network number and for the node number. Thus, a class B network is a medium-sized network with a maximum number of nodes 2 16. - If the address begins with the sequence 110, then it is a network class C. In this case, 24 bits are allocated for the network number, and 8 bits for the node number. Networks of this class are the most common; the number of nodes in them is limited to 2 8 .

If the address begins with the sequence 1110, then it is an address class D denotes a special, group address - multicast.

If the address begins with the sequence 11110, then this means that this address belongs to class E.

Special IP addresses

The Internet Protocol has several conventions for interpreting IP addresses differently. If the entire IP address consists of only binary zeros, then it represents the address of the node that generated the packet; this mode is used only in some ICMP messages. If the network number field contains only zeros, then by default it is assumed that the destination node belongs to the same network as the node that sent the packet. If all binary digits of an IP address are 1, then a packet with that destination address must be broadcast to all hosts on the same network as the source of the packet. If the destination node number field contains only ones, then a packet with such an address is sent to all network nodes with a given network number. - The IP address has a special meaning, the first octet of which is 127. It is used for testing programs and interaction of processes within one machine.--Group addresses.

Using masks in IP addressing

The traditional scheme of dividing an IP address into a network number and a host number is based on the concept of a class, which is determined by the values of the first few bits of the address. It is precisely because the first byte of the address 185.23.44.206 falls in the range 128-191 that we can say that this address belongs to class B, which means that the network number is the first two bytes, supplemented by two zero bytes - 185.23.0.0, and the number node - 0.0.44.206. Mask - this is the number that is used in conjunction with the IP address; The binary mask entry contains ones in those bits that should be interpreted as a network number in the IP address. Since the network number is an integral part of the address, the ones in the mask must also represent a continuous sequence. For standard network classes, masks have the following values: class A - (255.0.0.0); class B- (255.255.0.0); class C- (255.255.255.0).

Related information.

The combination of the components discussed above into a network can be done in various ways and means. Based on the composition of their components, methods of their connection, scope of use and other characteristics, networks can be divided into classes in such a way that the belonging of the described network to a particular class can sufficiently fully characterize the properties and quality parameters of the network.

However, this kind of classification of networks is rather arbitrary. The most widespread today is the division of computer networks based on territorial location. Based on this feature, networks are divided into three main classes: ·

LAN - local area networks; ·
MAN - Metropolitan Area Networks. ·
WAN - global networks (Wide Area Networks);

A local area network (LAN) is a communications system that supports one or more high-speed transmission channels within a building or some other limited area digital information, provided to connected devices for short-term exclusive use. The areas covered by the drug may vary significantly.
The length of communication lines for some networks can be no more than 1000 m, while other networks are able to serve an entire city. The serviced areas can be factories, ships, airplanes, as well as institutions, universities, and colleges. As a rule, coaxial cables are used as a transmission medium, although networks on twisted pair and optical fiber are becoming increasingly widespread, and recently the technology of wireless local networks has also been rapidly developing, which uses one of three types of radiation: broadband radio signals, low-power radiation ultrahigh frequencies (microwave radiation) and infrared rays.
The short distances between network nodes, the transmission medium used and the associated low probability of errors in the transmitted data make it possible to maintain high exchange rates - from 1 Mbit/s to 100 Mbit/s (at present there are already industrial designs of LANs with speeds of about 1 Gbit /With).

City networks, as a rule, cover a group of buildings and are implemented on fiber optic or broadband cables. According to their characteristics, they are intermediate between local and global networks. Recently, in connection with the laying of high-speed and reliable fiber optic cables in urban and intercity areas, and new promising network protocols, for example, ATM (Asynchronous Transfer Mode), which in the future can be used both in local and global networks.

Global networks, unlike local ones, as a rule, cover much larger territories and even most regions of the globe (an example is the Internet). Currently, analogue or digital wire channels, as well as satellite communication channels (usually for communication between continents), are used as transmission media in global networks. Limitations on transmission speed (up to 28.8 Kbps on analog channels and up to 64 Kbps on user sections digital channels) and the relatively low reliability of analog channels, requiring the use of error detection and correction tools at the lower levels of protocols, significantly reduce the speed of data exchange in global networks compared to local ones.
There are other classification features of computer networks. For example:

According to the scope of operation, networks can be divided into banking networks, networks of scientific institutions, university networks;

Based on the form of operation, commercial networks and free networks, corporate and public networks can be distinguished;

Based on the nature of the implemented functions, networks are divided into computational ones, designed to solve control problems based on computational processing of initial information; informational, intended to obtain reference data at the request of users; mixed, in which computational and information functions;

According to the control method, computer networks are divided into networks with decentralized, centralized and mixed control. In the first case, each computer included in the network includes a complete set software to coordinate ongoing network operations. Networks of this type are complex and quite expensive, since the operating systems of individual computers are developed with a focus on collective access to the common memory field of the network. In mixed networks, under centralized control, tasks that have the highest priority and, as a rule, are associated with processing large volumes of information, are solved;

According to software compatibility, networks can be homogeneous or homogeneous (consisting of software-compatible computers) and heterogeneous or heterogeneous (if the computers included in the network are software incompatible).