What is a computer network scientific articles. Shcherbakova S.M., Krupina T.A.

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Computer network is a collection of computers and various devices that provide information exchange between computers in a network without using any intermediate media.

The creation of computer networks is caused by the practical need of users of computers remote from each other for the same information.

Networks provide users with the opportunity not only to quickly exchange information, but also to collaborate on printers and other peripheral devices, and even to process documents at the same time.

All the variety of computer networks can be classified according to a group of features:

Territorial prevalence;
Departmental affiliation;
Information transfer rate;
The type of transmission medium.

In terms of territorial distribution, networks can be local, global, and regional.

By belonging, departmental and state networks are distinguished.

Departmental belong to one organization and are located on its territory.

By the speed of information transfer, computer networks are divided into low, medium and high speed.

By the type of transmission medium, they are divided into coaxial, twisted-pair, fiber-optic networks, with the transmission of information over radio channels, in the infrared range.

Local computer networks

The local network unites computers installed in one room (for example, a school computer class, consisting of 8-12 computers) or in one building (for example, in a school building several dozen computers installed in various subject rooms can be connected into a local network).

In small local networks, all computers are usually equal, that is, users independently decide which resources of their computer (disks, directories, files) to make public 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 be insufficiently productive.

To increase performance, as well as to ensure greater reliability when storing information on the network, some computers are specially allocated for storing files or application programs. These computers are called servers, and the LAN 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.

Network topology

The general scheme for connecting computers to local networks is called network topology... Network topologies can be different.

Ethernet networks can be in bus and star topologies. In the first case, all computers are connected to one common cable (bus), in the second, there is a special central device (hub), from which “rays” go to each computer, that is, each computer is connected to its own cable.

The bus structure is simpler and more economical because it does not require an additional device and uses less cable. But it is very sensitive to cabling faults. If the cable is damaged in even one place, then problems arise for the entire network. The fault location is difficult to locate.

Bus topology

Star topology

In this sense, the "star" is more stable. A damaged cable is a problem for one specific computer; it does not affect the operation of the network as a whole. No effort is required to isolate the fault.

Ring topology

In a network with a "ring" structure, it is transmitted between stations along a ring with a reception in each network controller. Reception is carried out through buffer drives, made on the basis of random access memory devices, therefore, if they fail, one network controller may disrupt the operation of the entire ring. The advantage of the ring structure is the ease of implementation of the devices, and the disadvantage is low reliability.

Regional computer networks

Local networks do not allow to provide shared access to information for users located, for example, in different parts of the city. Regional networks that unite computers within the same region (city, country, continent) come to the rescue.

Corporate computer networks

Many organizations interested in protecting information from unauthorized access (for example, military, banking, etc.) create their own, so-called corporate networks.

A corporate network can unite thousands and tens of thousands of computers located in different countries and cities (for example, the Microsoft Corporation network, MSN).

Global computer network Internet

At present, tens of millions of computers connected to the Internet store a huge amount of information (hundreds of millions of files, documents, and so on) and hundreds of millions of people use the information services of the global network.

The Internet 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 constant connection to the Internet using a high throughput (server).

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 Internet is based on more than one hundred million servers that are constantly connected to the network. Internet servers can be connected using local area networks or dial-up telephone lines hundreds of millions of web users.

Here is an example of one of the global center

Large Google Center for Internet Data Storage

Aygazieva Saltanat, Afanasyeva Svetlana, Kutepova Natalia

Group research topic

Computer networks

Problem question (research question)

What kind of networks are there?

Research hypothesis

Computer networks are: Local, Global, Regional

Research objectives

Study the structure of a computer network; Explore basic networking tools.

Research progress

What is a computer network? Network - a group of computers and / or other devices connected in any way to exchange information and share programs, data files and peripheral devices.

Server is a computer with a server operating system installed on it, which provides its software and hardware resources to network users.

A peer is an equal participant in the network that provides services to other participants in the peer-to-peer network and uses their services himself.

A backbone is a transmission channel between two points - nodes or switches.

The Internet is a collection of networks connected to each other by telecommunications infrastructure.

Domain is a group of computers under the same control and having a common segment in the Internet address. IP Address - 32-bit Internet Protocol address assigned to the host. An IP address contains two components: a node number and a network number. A modem is a device that converts digital signals into analog signals for transmission over a telephone line, and also converts incoming analog signals into digital signals for processing in a computer. Router (router) - network equipment operating at the network level and establishing communication between different networks. Network switch, switch, switch (jarg. From the English. Switch - switch) - a device designed to connect several nodes of a computer network within one or more network segments. A network hub or hub (jarg. From English. Hub - center of activity) is a network device designed to combine several Ethernet devices into a common network segment. Protocol is a standard that describes the rules for the interaction of functional blocks during data transmission. A packet is a formatted block of data transmitted over a network. What kind of networks are there? Classification of computer networks By territorial prevalence: PAN (Personal Area Network) - a personal network designed for the interaction of devices belonging to the same owner. LAN (Local Area Network) - local area networks with a closed infrastructure before reaching service providers. Access to local networks is allowed only to a limited number of users. CAN (Campus Area Network) is a campus network that connects local networks of closely located buildings. MAN (Metropolitan Area Network) - metropolitan area networks between institutions within one or more cities WAN (Wide Area Network) - a global network covering large geographic regions, including both local networks and other telecommunication networks and devices. By the type of functional interaction. Client-server is a computing or network architecture in which jobs or network load are distributed between service providers, called servers, and service customers, called clients. A mixed network is 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 according to the client-server scheme. A peer-to-peer network is an overlay computer network based on the equality of participants. In such a network there are no dedicated servers, and each node (peer) is both a client and a server. Multi-rank network - a network in which there is a master, or "master" - a controller that coordinates the work of "slave" controllers that actually control one or more access points. By type of network topology: Basic: A bus is a common cable (called a bus or backbone) to which all workstations are connected. There are terminators at the ends of the cable to prevent signal reflection. A ring is a topology in which each computer is connected by communication lines with only two others: from one it only receives information, and to the other it only transmits. Only one transmitter and one receiver operates on each link. A star is a computer network topology in which all computers on the network are connected to a central node (usually a switch), forming a physical network segment. Derivatives: A double ring is a topology built on two rings. The first ring is the main path for data transmission. The second is a backup path that duplicates the main one. Mesh is a basic fully meshed topology of a computer network, in which each workstation on a network is connected to several other workstations on the same network. A lattice is a topology in which the nodes form a regular multidimensional lattice. Moreover, each edge of the lattice is parallel to its axis and connects two adjacent nodes along this axis. The tree is a more developed configuration of the "bus" type. The connection of several simple buses to a common backbone bus occurs through active repeaters or passive multipliers. Fat Tree - computer network topology for supercomputers. In a thickened tree, connections between nodes become more bandwidth efficient with each level as they get closer to the root of the tree. By the type of transmission medium: Wired (telephone wire, coaxial cable, twisted pair, fiber-optic cable. Wireless (transmission of information over radio waves in a certain frequency range). By functional purpose: Storage networks - an architectural solution for connecting external storage devices, In the way that operating system recognized the connected resources as local. A server farm is an association of servers connected by a data network and working as a single unit. Process control networks are computerized systems capable of converting information, performing calculations, logical operations, using various types of computer networks and modern information technologies... SOHO networks & House network - a kind of local computer network, laid within one building or combining several nearby buildings. By transmission speed: low speed (up to 10 Mbps) medium speed (up to 100 Mbps) high speed (over 100 Mbps) By network OS: Based on Windows Based on UNIX Based on NetWare As required to maintain a constant connection: Packet network, for example Fidonet and UUCP Online network such as Internet and GSM How do computers on the network find each other? Each computer on a local network has its own unique address, just like a person has a mailing address. It is at these addresses that computers find each other on the network. There should not be two identical addresses on the same network. The address format is standard and defined by the IP protocol. The computer's IP address is recorded in 32 bits (4 octets). Each octet contains a decimal number from 0 to 255 (in binary, the entry represents a sequence of 0 and 1). The IP address is represented by four numbers, separated by a period. For example, a computer with an IP address of 192.168.3.24. The total number of IP addresses is 4.2 billion, all addresses are unique. An IP address can be assigned not only to a computer, but also to others network devicessuch as a print server or router. Therefore, all devices on the network are usually called nodes or hosts. One and the same physical device (computer or other) can have multiple IP addresses. For example, if a computer has multiple network adapters, then each adapter must have its own unique IP address. These computers are used to connect multiple local networks and are called routers. A large IP network is divided into several subnets, each of which has its own address. Subnets are separate, independently functioning parts of a network that have their own identifier. For the subnet address, in the IP address, space is allocated from the host address. The subnet mask is used to determine the network address and subnet. The subnet mask recording format is the same as the IP address format, with four fields separated by a period. Thus, paired with the IP address of the computers, the subnet mask must be specified.

conclusions

A computer network is a combination of several computers for the joint solution of information, computing, educational and other tasks.

All computer networks, without exception, have one purpose - to provide shared access to shared resources. Resources are of three types: hardware, software, information. According to the method of organization, networks are subdivided into real and artificial. By the speed of information transfer, computer networks are divided into low, medium and high speed. In terms of territorial distribution, networks can be local, global, regional and urban.

A local computer network is a collection of computers connected by communication lines that provide network users with the potential to share the resources of all computers. A local network is created for the rational use of computer equipment and the effective work of employees.

A wide area network (WAN or WAN - World Area NetWork) is a network that connects computers geographically remote at large distances from each other. It differs from a local network in more extended communications (satellite, cable, etc.). The global network connects local networks.

The Internet is a global computer network covering the entire world. The Internet is a constantly developing network, which still has everything ahead, let's hope that our country will not lag behind progress.

Articles on computer networks and modern telecommunication technologies present wireless computer networks, Internet communications, Web communications and IoT / WoT telecommunication technologies. Internet communications include: messaging systems; on-line video; VoIP. Messaging systems include off-line services: E-mail, SMS distribution and instant messaging services: IRC, chats, IM, PTT, and so on in on-line mode.

The most promising areas of Internet communications are Web communications in real time. Web communications include: p2p video chats on webRTC base; SIP softphones in the web interface based on WebRTC, SIPML5, webrtc2sip; file-sharing platform based on the WebRTC Data Channel API; video conferencing based on HTML5 and API WebRTC, etc. One of the modern solutions in the field of web communications are webRTC technologies, HTML5 with JavaScript and CSS3, the Node.JS framework, and the WebSocket protocol.

Browsers supporting WebRTC, WebSocket and SIPML5 is a single tool (interface) for all user devices (PCs, smartphones, iPads, IP phones, mobile phones etc.) that provide real-time Web communications.

"[Exam in Computer Science] [Ticket # 22]

Local and global computer networks. Addressing in networks.

A computer network is a collection of computers and various devices that provide information exchange between computers in a network without using any intermediate storage media.

The creation of computer networks is caused by the practical need of users of computers remote from each other for the same information. Networks provide users with the opportunity not only to quickly exchange information, but also to collaborate on printers and other peripheral devices, and even to process documents at the same time.

All the variety of computer networks can be classified according to a group of features:

Territorial prevalence;
Departmental affiliation;
Information transfer rate;
Type of transmission medium;

In terms of territorial distribution, networks can be local, global, and regional.

By belonging, departmental and state networks are distinguished. Departmental belong to one organization and are located on its territory.

By the speed of information transfer, computer networks are divided into low, medium and high speed.

By the type of transmission medium, they are divided into coaxial, twisted-pair, fiber-optic networks, with the transmission of information over radio channels, in the infrared range.

Local computer networks.

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

If more than ten computers are connected to the local network, then the peer-to-peer network may be insufficiently productive. To increase performance, as well as to ensure greater reliability when storing information on the network, some computers are specially allocated for storing files or application programs. These computers are called servers, and the LAN 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.

Network topology.

The general scheme for connecting computers in local networks is called network topology. Network topologies can be different.

Ethernet networks can be in bus and star topologies. In the first case, all computers are connected to one common cable (bus), in the second, there is a special central device (hub), from which "rays" go to each computer, i.e. each computer is connected to its own cable.

In a network with a "ring" structure, information is transmitted between stations along the ring with a relay in each network controller. Re-reception is carried out through buffer drives made on the basis of random access memory devices, therefore, if they fail, one network controller may disrupt the operation of the entire ring.
The advantage of the ring structure is the ease of implementation of the devices, and the disadvantage is low reliability.

Regional computer networks.

Corporate computer networks.

Many organizations interested in protecting information from unauthorized access (for example, military, banking, etc.) create their own, so-called corporate networks. A corporate network can unite thousands and tens of thousands of computers located in different countries and cities (for example, the Microsoft Corporation network, MSN).

Global computer network Internet.

In 1969, the ARPAnet computer network was created in the United States, uniting the computer centers of the Department of Defense and a number of academic organizations. This network was intended for a narrow purpose: mainly to learn how to keep in touch in the event of a nuclear attack and to help researchers share information. As this network grew, many other networks were created and developed. Even before the advent of the personal computer era, the creators of ARPAnet began developing the Internetting Project. The success of this project led to the following results. First, the largest in the United States was created internet network (with a lowercase letter i). Second, various options for the interaction of this network with a number of other US networks were tested. This created the preconditions for the successful integration of many networks into a single world network. This "network of networks" is now called the Internet everywhere (in Russian publications, the Russian-language spelling Internet is also widely used).

At present, 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 the information services of the global network.

The Internet is a global computer network that unites many local, regional and corporate networks and includes tens of millions of computers.

Every local or corporate network usually has at least one computer that has a persistent connection to the Internet using a high-bandwidth communication line (Internet server).

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 Internet is based on more than one hundred million servers that are constantly connected to the network.

Hundreds of millions of network users can connect to Internet servers using local area networks or dial-up telephone lines.

Internet addressing

In order to communicate with some computer on the Internet, you need to know its unique Internet address. There are two equivalent address formats that differ only in their form: IP address and DNS address.

IP address

An IP address is made up of four blocks of numbers, separated by periods. It may look like this:
84.42.63.1

Each block can contain a number from 0 to 255. Thanks to this organization, over four billion possible addresses can be obtained. But since some addresses are reserved for special purposes, and blocks are configured depending on the type of network, the actual number of possible addresses is slightly less. Nevertheless, it is more than enough for the future expansion of the Internet.

The concept of "host" is closely related to the concept of IP - addresses. A host is any device that uses the TCP / IP protocol to communicate with other equipment. It can be not only a computer, but also a router, hub, etc. All these devices connected to the network must have their own unique IP address.

DNS address

The IP address has a numeric form, as computers use it in their work. But it is very difficult to remember, so a domain name system was developed: DNS. The DNS address includes more user-friendly alphabetic abbreviations that are also separated by periods into separate information blocks (domains). For example:

If you enter a DNS address, it is first sent to a so-called name server, which translates it into a 32-bit machine readable IP address.

Domain names

A DNS address usually has three components (although there can be any number of them).

The domain name system has a hierarchical structure: top-level domains - second-level domains, and so on. Top-level domains are of two types: geographic (two-letter - each country has its own code) and administrative (three-letter).

Russia owns a geographic domain ru.

The Klyaks @ .net portal has registered the second level domain klyaksa in the administrative top-level domain net.

Computer names that are servers on the Internet include the fully qualified domain name and the actual computer name. So the full address of the Klyaks @ .net portal looks like www.site

gov - government agency or organization
mil - military institution
com - commercial organization
net - network organization
org - an organization that does not belong to one of the above

Among the frequently used domains - country identifiers, the following can be distinguished:

at - Austria
au from Australia
ca from Canada
ch - Switzerland
de - Germany
dk - Denmark
es from Spain
fi from Finland
fr - France
it from Italy
jp - Japan
nl - Netherlands
no - Norway
nz from New Zealand
ru - Russia
se from Sweden
uk - Ukraine
za from South Africa

Email address

Using an IP address or DNS address on the Internet, you can access any computer you need. If you want to send a message via e-mail, then specifying only these addresses will not be enough, since the message must get not only to the desired computer, but also to a specific user of the system.

A special protocol SMPT (Simple Mail Transport Protocol) is used to deliver and receive e-mail messages. The computer through which e-mail messages are transmitted to the Internet is called an SMPT server. Messages are delivered by e-mail to the computer specified in the address, which is responsible for further delivery. Therefore, data such as the username and the name of the corresponding SMPT server are separated by "@". This sign is called "at commercial" (in jargon - dog, dog). Thus, you are addressing your message to a specific user of a specific computer. For example:
[email protected]site Here ivanov is the user to whom the message is intended, and the site — SMPT — is the server on which his mailbox is located. IN mailbox the messages that arrived at a specific address are stored.

A URL (Uniform Resource Locator) is the address of some information on the Internet. It has the following format:
resource type: // node address / other information
The following types of resources are considered the most common:

Ftp: // ftp - server
gopher: // gopher menu
http: // WWW address
mailto: // email address
news: // UseNet newsgroup
telnet: // computer that can be logged in using telnet

The resource portion of a URL always ends with a colon and two or three forward slashes. What follows is the specific address of the site you want to visit. Behind it, as a limiter, there is a slash. In principle, this is quite enough. But if you want to view a specific document on a given site and know exactly its location, you can include its address in the URL. Below are some URLs and their meanings:

Http: //www..php main page of the information and educational portal Klyaks @ .net

ftp://ftp.microsoft.com/dirmap.txt file named dirmap.txt on ftp - server of Microsoft company

So, the following types of addresses are possible on the Internet.