Global Area Network (WAN or WAN - World Area NetWork) is a network that connects computers that are geographically located at great distances from each other. It differs from a local network in more extensive communications (satellite, cable, etc.). The global network connects local networks.

WAN (World Area Network) is a global network covering large geographic regions, including both local networks and other telecommunication 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.

Today, when the geographical boundaries of networks are expanding to connect users from different cities and states, LANs are turning into a global computer network [WAN], and the number of computers on the network can already vary from tens to several thousand.

Internet is a global computer network covering the whole world. Today the Internet has about 15 million subscribers in more than 150 countries. The network size increases monthly by 7-10%. The Internet forms a kind of core that connects various information networks belonging to various institutions around the world with one another.

If previously the network was used exclusively as a medium for transferring files and email messages, today more complex problems of distributed access to resources are being solved. About three years ago, shells were created that support network search functions and access to distributed information resources and electronic archives.

The Internet, which once served exclusively research and teaching groups whose interests extended to access to supercomputers, is becoming increasingly popular in the business world.

Companies are seduced by speed, cheap global communications, ease of collaboration, affordable programs, and a unique Internet database. They view the global network as a complement to their own local networks.

At a low cost of service (often just a flat monthly fee for the lines or telephone used), users can access commercial and non-commercial information services in the United States, Canada, Australia and many European countries. In the archives of free access to the Internet you can find information on almost all areas of human activity, from new scientific discoveries to weather forecasts for tomorrow.

In addition, the Internet provides unique opportunities for low-cost, reliable and confidential global communications around the world. This turns out to be very convenient for companies with branches around the world, transnational corporations and management structures. Typically, using the Internet infrastructure for international communications is much cheaper than direct computer communications via satellite or telephone.

E-mail is the most common Internet service. Currently, approximately 20 million people have an email address. Sending a letter by e-mail is much cheaper than sending a regular letter. In addition, a message sent by e-mail will reach the recipient in a few hours, while a regular letter may take several days, or even weeks, to reach the recipient.

Currently, the Internet uses almost all known communication lines from low-speed telephone lines to high-speed digital satellite channels.

In fact, the Internet consists of many local and global networks belonging to various companies and enterprises, interconnected by various communication lines. The Internet can be imagined as a mosaic made up of small networks of different sizes that actively interact with one another, sending files, messages, etc.

Like any other network on the Internet, there are 7 levels of interaction between computers: physical, logical, network, transport, session level, presentation and application level. Accordingly, each level of interaction corresponds to a set of protocols (i.e. rules of interaction).

Physical layer protocols determine the type and characteristics of communication lines between computers. The Internet uses almost all currently known communication methods, from a simple wire (twisted pair) to fiber-optic communication lines (FOCL).

For each type of communication line, a corresponding logical level protocol has been developed to control the transmission of information over the channel. Logical layer protocols for telephone lines include SLIP (Serial Line Interface Protocol) and PPP (Point to Point Protocol).

For communication via LAN cable, these are package drivers for LAN cards.

Network layer protocols are responsible for transmitting data between devices on different networks, that is, they are responsible for routing packets in the network. Network layer protocols include IP (Internet Protocol) and ARP (Address Resolution Protocol).

Transport layer protocols control the transfer of data from one program to another. Transport layer protocols include TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

Session layer protocols are responsible for establishing, maintaining, and destroying appropriate channels. On the Internet, this is done by the already mentioned TCP and UDP protocols, as well as the UUCP (Unix to Unix Copy Protocol).

Representative layer protocols serve application programs. Representative-level programs include programs that run, for example, on a Unix server to provide various services to subscribers. These programs include: telnet server, FTP server, Gopher server, NFS server, NNTP (Net News Transfer Protocol), SMTP (Simple Mail Transfer Protocol), POP2 and POP3 (Post Office Protocol), etc.

Application layer protocols include network services and programs for providing them.

Global network - These are associations of computers located at a remote distance for the common use of the world's information resources. Today there are more than 200 of them in the world. Of these, the most famous and most popular is the Internet.

Unlike local networks, global networks do not have any single control center. The network is based on tens and hundreds of thousands of computers connected by one or another communication channels. Each computer has a unique identifier, which allows you to “plot a route to it” for the delivery of information. Typically, a global network unites computers that operate according to different rules (having different architectures, system software, etc.). Therefore, gateways are used to transfer information from one type of network to another.

Gateways are devices (computers) used to connect networks with completely different exchange protocols.

Exchange protocol is a set of rules (agreement, standard) that defines the principles of data exchange between different computers on the network.

Protocols are conventionally divided into basic (lower level) responsible for transmitting information of any type, and applied (higher level) responsible for the functioning of specialized services.

The host computer of a network that provides access to a common database, enables sharing of input/output devices and user interaction is called server.

A network computer that only uses network resources, but does not give its resources to the network itself is called client(often also called workstation).

To work on the global network, the user must have the appropriate hardware and software.

Software can be divided into two classes:

server programs that are located on the network node serving the user’s computer;

client programs located on the user's computer and using the services of the server.

Global networks provide users with a variety of services: e-mail, remote access to any computer on the network, search for data and programs, etc.

Hardware implementation of LAN

In the simplest case, network cards and a cable are enough to operate the network. If you need to create a fairly complex network, you will need special network equipment.

Computers within a local network are connected using cables that transmit signals. A cable connecting two network components (for example, two computers) is called a segment. Cables are classified depending on the possible values ​​of information transfer speed and the frequency of failures and errors. There are three main categories of cables most commonly used:

unshielded twisted pair . The maximum distance at which computers connected by this cable can be located reaches 90 m. Information transfer speed is from 10 to 155 Mbit/s; shielded twisted pair. Information transfer speed is 16 Mbit/s over a distance of up to 300 m.

To oaxial cable . It is characterized by higher mechanical strength, noise immunity and allows you to transmit information over a distance of up to 2000 m at a speed of 2-44 Mbit/s;

fiber optic cable . An ideal transmission medium, it is not affected by electromagnetic fields, allows you to transmit information over a distance of up to 10,000 m at a speed of up to 10 Gbit/s.

Twisted pair cables are now most widely used to build local networks. Inside, such a cable consists of two or four pairs of copper wire twisted together. Twisted pair also has its own varieties: UTP (Unshielded Twisted Pair) and STP (Shielded Twisted Pair). These types of cable are capable of transmitting signals over a distance of about 100 m. As a rule, UTP is used in local networks. STP has a braided copper filament jacket, which has a higher level of protection and quality than the jacket of a UTP cable. In an STP cable, each pair of wires is additionally shielded (it is wrapped in a layer of foil), which protects the data that is transmitted from external interference. This solution allows you to maintain high transmission speeds over longer distances than when using UTP cable. The twisted pair cable is connected to the computer using an RJ-45 (Registered Jack 45) connector, which is very similar to an RJ-11 (Registered Jack 11) telephone connector.

Twisted pair cable is capable of providing network operation at speeds of 10, 100 and 1000 Mbit/s.

Coaxial cable consists of a copper wire covered with insulation, a metal braided shield, and an outer sheath. The central wire of the cable transmits signals into which the data has previously been converted. Such a wire can be either solid or multi-core. To organize a local network, two types of coaxial cable are used: ThinNet. (thin, 10Base2) and ThickNet (thick, 10Base5). At the moment, local networks based on coaxial cable are practically not found. The information transmission speed in such a network does not exceed 10 Mbit/s. Both types of cable, ThinNet and ThickNet, connect to a BNC connector, and terminators must be installed at both ends of the cable.

At the heart of a fiber optic cable are optical fibers (light guides), through which data is transmitted in the form of pulses of light. No electrical signals are transmitted through a fiber optic cable, so the signal cannot be intercepted, which virtually eliminates unauthorized access to data. Fiber optic cable is used to transport large amounts of information at the highest available speeds. The main disadvantage of such a cable is its fragility: it is easy to damage, and can only be mounted and connected using special equipment,

2. Network cards

Network cards make it possible to connect a computer and a network cable. The network card converts the information that is intended to be sent into special packets. A packet is a logical collection of data that includes a header with address information and information itself. The header contains address fields, which contain information about the origin and destination of the data. The network card analyzes the destination address of the received packet and determines whether the packet was actually destined for that computer. If the output is positive, the board will transmit the packet to the operating system. Otherwise, the package will not be processed. Special software allows you to process all packets that pass within the network. This opportunity is used by system administrators when analyzing the operation of the network, and by attackers to steal data passing through it. Any network card has an individual address built into its chips. This address is called a physical or MAC address (Media Access Control). The order of actions performed by the network card is as follows. Receiving information from the operating system and converting it into electrical signals for further sending over the cable. Receiving electrical signals over a cable and converting them back into data that the operating system can work with. Determining whether the received data packet is intended specifically for this computer. Controlling the flow of information that passes between a computer and a network.

Increasingly, network cards are integrated into the motherboard and connected to the south bridge. The processor communicates with the south bridge, and all equipment that is connected to it, through the north bridge.

In addition, the operating system of each computer connected to the network must have network support tools: special system and user programs, as well as a set of specific rules governing the forms and procedures for exchanging information over the network between two or more devices (or processes), which are called network protocols

3. Repeaters

The local network can be expanded through the use of a special device called a “repeater” (Repeater). Its main function is to, having received data on one of the ports, redirect it to the remaining ports. These ports can be of any type: RJ-45 or Fiber-Optic. Combinations also do not play a role, which allows you to combine network elements that are built on the basis of different types of cable. Information during transmission to other ports is restored to eliminate deviations that may appear during the movement of the signal from the source.

Repeaters can perform a separation function. If the repeater determines that there are too many collisions on one of the ports, it concludes that there is a problem on that segment and isolates it. This feature prevents failures in one segment from spreading to the entire network.

The repeater allows you to:

§ connect two network segments with the same or different types of cable;

§ regenerate the signal to increase the maximum transmission distance;

§ transmit data flow in both directions.

4. Hubs

A hub is a device that can connect computers into a physical star topology. The hub has several ports that allow you to connect network components. A hub with only two ports is called a bridge. A bridge is required to connect two network elements.

The network together with the hub constitutes a “common bus”. Data packets when transmitted through the hub will be delivered to all computers connected to the local network.

There are two types of hubs:

§ Passive concentrators. Such devices send the received signal without preprocessing it.

§ Active hubs (multiport repeaters). They receive incoming signals, process them and transmit them to connected computers.

5. Switches

Switches are needed to organize a closer network connection between the sending computer and the destination computer. During data transfer through the switch, information about the MAC addresses of computers is recorded in its memory. Using this information, the switch compiles a routing table, in which for each computer it is indicated that it belongs to a specific network segment.

When a switch receives data packets, it creates a special internal connection (segment) between its two ports using a routing table. It then sends a data packet to the appropriate port on the destination computer, based on the information described in the packet header.

Thus, this connection is isolated from other ports, which allows computers to exchange information at the maximum speed that is available for this network. If a switch has only two ports, it is called a bridge.

The switch provides the following features:

§ send a packet with data from one computer to the destination computer;

§ increase data transfer speed.

6. Routers

A router is similar in principle to a switch, but has a greater range of functionality. It studies not only the MAC, but also the IP addresses of both computers involved in the data transfer. When transporting information between different network segments, routers analyze the packet header and try to calculate the optimal path for the packet to travel. The router is able to determine the path to an arbitrary network segment using information from the route table, which allows you to create a shared connection to the Internet or WAN.

Routers allow packets to be delivered in the fastest way, which increases the throughput of large networks. If some segment of the network is overloaded, the data flow will take a different path.

An ordinary computer can be used as a simple router.

Global computer network Internet

Composition of the Internet

The Internet is a network of networks. Local networks They usually combine several dozen computers located in one building, but they do not allow shared access to information among users located, for example, in different parts of the city. In this case, remote access to information is provided by regional networks, connecting computers within one region (city, country, continent).

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 connect thousands and tens of thousands of computers located in different countries and cities.

The needs of creating a single world information space have led to the unification of local, regional and corporate networks into the global computer network Internet. As a result, more than three hundred million servers currently form the backbone of the Internet (as of January 2005).

The reliability of the global network is ensured by a large number of high-bandwidth information transmission channels between local, regional and corporate networks. For example, the Russian regional computer network Runet (RU) is connected by numerous information transmission channels to the North American (US), European (EU) and Japanese (JP) regional networks (Fig. 6.5).

Internet is a global computer network in which local, regional and corporate networks are interconnected by numerous high-bandwidth information transmission channels.

Internet connection. Every local, regional or corporate network has at least one computer (Internet server) that has a permanent connection to the Internet.

To connect local networks they are most often used fiber optic lines communications. However, in cases of connecting inconveniently located or remote computer networks, when laying cables is difficult or impossible, wireless communication lines are used. If the transmitting and receiving antennas are within line of sight, then use radio channels, otherwise information is exchanged via satellite channel using special antennas (Fig. 6.6).

Hundreds of millions of user computers may periodically connect to the Internet via dial-up telephone lines by using Internet providers. Internet providers have high-speed connections from their servers to the Internet and therefore can provide Internet access via telephone channels to hundreds or thousands of users simultaneously.

To connect the user's computer via a telephone channel to the Internet provider's server, modems must be connected to both computers. Modems provide transmission of digital computer data over analog telephone channels at speeds of up to 56 Kbps.

Modern ADSL- technologies allow you to use regular telephone channels for high-speed (1 Mbit/s and higher) Internet connections. It is important that the phone number remains free.

Regular and ADSL modems are connected to the USB port of the computer and to the telephone jack (Fig. 6.7).

Rice. 6.7. Regular and ADSL modems

Laptop computer users can connect to the Internet using Wi-Fi wireless technology. Wireless access points connected to the Internet are installed at train stations, airports and other public places. Within a radius of 100 m, a laptop equipped with a wireless connection automatically receives Internet access at speeds of up to 11 Mbps.

Control questions

1. What types of computer networks make up the Internet?

2. What methods of connecting to the Internet are there and what are their advantages and disadvantages?

Internet addressing

Internet address. In order for computers to find each other during the exchange of information, there is a unified addressing system on the Internet based on the use of Internet addresses.

Every computer connected to the Internet has its own unique 32-bit binary Internet address.

There is a formula that relates the number of possible information messages N and the amount of information I carried by the received message:

An Internet address carries an amount of information I = 32 bits, then the total number N of different Internet addresses is equal to:

N = 2 I = 2 32 = 4 294 967 296

A 32-bit Internet address allows more than 4 billion computers to connect to the Internet.

Using the new Smart Home technology, not only computers will be able to be connected to the Internet, but also household appliances (refrigerators, washing machines, etc.) and audio and video equipment, which can be controlled remotely. In this case, four billion Internet addresses may not be enough and you will have to switch to a longer Internet address.

For ease of perception, a binary 32-bit Internet address can be divided into four parts of 8 bits and each part represented in decimal form. A decimal Internet address consists of four numbers ranging from 0 to 255, separated by periods (for example, 213.171.37.202) (Table 6.1).

All Internet servers have permanent Internet addresses. However, Internet providers often provide Internet access to users with a temporary Internet address rather than a permanent one. The Internet address may change each time you connect to the Internet, but remains unchanged during the session and can be determined by the user.

Domain name system. It is not easy for a person to remember a numeric address, therefore, for the convenience of Internet users, a domain name system was introduced, which matches the numeric Internet address of a computer with a unique domain name.

The domain name system has a hierarchical structure: top-level domains - second-level domains - third-level domains.

There are two types of top-level domains: geographic and administrative. Each country in the world is assigned its own geographic domain, designated by a two-letter code. For example, Russia owns the geographical domain ru, in which Russian organizations and citizens have the right to register a second-level domain.

Administrative domains are designated by three or more letters and are intended for registration of second-level domains by organizations of various types (Table 6.2).

Thus, Microsoft has registered a second-level domain Microsoft in the administrative top-level domain com, and the Moscow Institute of Open Education is a second-level domain methodist in a geographic top-level domain ru(Fig. 6.8).

Rice. 6.8. Domain name system

An Internet server domain name consists of a sequence (from right to left) of the top-level domain name, the second-level domain name, and the computer name itself. Thus, the main Microsoft server is named www.microsoft.com, and the institute’s server is named iit.metodist.ru.

Every computer connected to the Internet has an Internet address, but it may not have a domain name. Internet servers have domain names, but computers that connect to the Internet over telephone lines usually do not have a domain name.

Control questions

1. Does every computer connected to the Internet have an Internet address? Domain name?

2. How is the domain name system built?

Tasks for independent completion

6.3 Short answer task. The binary 32-bit Internet address of the computer is represented in decimal form.

6.4 Short answer task. Write down the domain name of a computer registered in the first-level domain ru, the second-level domain schools and having its own name www.

Routing and transporting data over computer networks

The Internet, which is a network of networks and unites a huge number of different local, regional and corporate networks, operates and develops through the use of a single principle of routing and data transportation.

Data routing. Data routing ensures the transfer of information between network computers. Let's consider the principle of data routing by analogy with the transfer of information using regular mail. In order for the letter to reach its intended destination, the address of the recipient (who the letter is to) and the address of the sender (from whom the letter is from) are indicated on the envelope.

Similarly, information transmitted over the network is “packed in an envelope” on which the Internet addresses of the recipient’s and sender’s computers are “written”, for example: “To: 198.78.213.185”, “From: 193.124.5.33”. The contents of the envelope in computer language are called Internet package and is a set of bytes.

In the process of forwarding regular letters, they are first delivered to the post office closest to the sender, and then transferred along the chain of post offices to the post office closest to the recipient. At intermediate post offices, letters are sorted, i.e., it is determined to which next post office a particular letter should be sent.

On the way to the recipient computer, Internet packets also pass through numerous intermediate Internet servers where the routing operation is performed. As a result of routing, Internet packets are directed from one Internet server to another, gradually approaching the recipient computer.

Routing Internet packets ensure the delivery of information from the sending computer to the receiving computer.

The delivery routes of Internet packets can be completely different, and therefore the first Internet packets may be the last to reach the recipient computer. For example, in the process of transferring a file from a From server to a To server, the route of the first Internet packet may be From-1-2-To, the second - From-To and the third - From-3-4-5-To (Fig. 6.9).

Rice. 6.9. Routing and data transport

The “geography” of the Internet differs significantly from the geography we are accustomed to. The speed of obtaining information does not depend on the distance of the Internet server, but on the route of information, i.e. the number of intermediate servers and the quality of communication lines (their capacity) through which information is transmitted from server to server.

You can get acquainted with the route of information on the Internet using special programs that allow you to track through which servers and with what delay information is transmitted from the selected Internet server to your computer.

Data transportation. Now let’s imagine that we need to send a multi-page manuscript by mail, but the post office does not accept parcels or parcels. The idea is simple: if the manuscript does not fit into a regular postal envelope, it must be disassembled into sheets and sent in several envelopes. In this case, the sheets of the manuscript must be numbered so that the recipient knows in what order to collect these sheets later.

A similar situation often occurs on the Internet when computers exchange large files. If you send such a file as a whole, it can “clog” the communication channel for a long time, making it inaccessible for sending other messages.

To prevent this from happening, it is necessary to split a large file into small parts on the sending computer, number them and transport them in the form of separate Internet packets to the receiving computer.

On the recipient computer, it is necessary to assemble the source file from individual parts in the correct sequence, so the file cannot be assembled until all Internet packets have arrived.

Data transport is done by splitting files into Internet packets on the sending computer, individually routing each packet, and assembling the files from the packets in the original order on the receiving computer.

The transport time of individual Internet packets between the local computer and the Internet server can be determined using special programs.

Routing and transport of data on the Internet is based on the TCP/IP protocol, which is the basic “law” of the Internet. The term "TCP/IP" includes the name of two data transfer protocols:
- TCP (Transmission Control Protocol - transport protocol);
- IP (Internet Protocol - routing protocol).

Control questions

1. How is data delivered to the specified Internet address?

2. For what purposes, when transferring files over computer networks, are they divided into Internet packets?

Global networks Wide re Networks WN, which are also called territorial computer networks, serve to provide their services to a large number of end subscribers scattered over a large territory within the region of a country on a continent or the entire globe. Typical subscribers of a global computer network are local networks of enterprises located in different cities and countries that need to exchange data with each other.

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Lecture No. 27

Topic: Global networks

1. CONCEPT OF GLOBAL NETWORK.

Global networks (Wide Area Networks - WAN), also calledterritorial computer networks, serve to provide their services to a large number of end subscribers scattered over a large area - within a region, region, country, continent or the entire globe.

Typical subscribers global computer network arelocal enterprise networkslocated in different cities and countries that need to exchange data with each other. Individual computers also use the services of global networks. Large mainframe computers typically provide access to corporate data, while personal computers are used to access corporate data and public Internet data.

WANs are usually created by large telecommunications companies to provide paid services to subscribers. Such networks are called public or public . There are also concepts such as network operator and network service provider.

Network operator is the company that maintains the normal operation of the network.

Service provider (provider ) is a company that provides paid services to network subscribers. The owner, operator, and service provider may be one company, or they may represent different companies.

Types of territorial networkstransmission of information:

• Telephone;
• Telegraph;
• Telex.

In global networks, the following are used to transmit information:types of switching:

• circuit switching(used when transmitting audio information over regular telephone lines);
• message switching(mainly used for transmitting email, teleconferences, electronic news);
• packet switching(for data transmission, recently also used for transmitting audio and video information).

Global Area Networks- These are computer networks that unite local networks and individual computers remote from each other over long distances. The most famous and popular global network is Internet , worldwide non-profit network FidoNet, CREN, EARNet, EUNet, corporate, etc.

WAN subscribers can be LANs of enterprises, geographically distant from each other, that need to exchange information with each other, and individual computers can use WAN services to access both corporate data and public Internet data.

All Internet services are built on the client-server principle. All information on the Internet is stored on servers. Information exchange between network servers is carried out viahigh-speed communication channels or highways.

These highways include:

• dedicated telephone analog and digital lines,
• optical channels communications and radio channels,
• satellite links communications.

Servers connected by high-speed highways make up the basic part of the Internet.

Individual users connect to the network through PCs of local Internet service providers (ISPs) that have a permanent connection to the Internet. A regional provider connects to a larger national provider that has nodes in various cities of the country.
Networks of national providers are combined into networks of transnational providers or first-tier providers. United networks of first-tier providers make up the global Internet network

2. TYPES OF GLOBAL NETWORKS

Depending on the components, corporate networks built using:

• dedicated channels;
• circuit switching;
• packet switching

2.1. Dedicated channels

Leased channels can be obtained from telecommunications companies that own long-distance channels or from telephone companies that typically lease channels within a city or region.

You can use leased lines in two ways.

1. With their help, building a territorial network of a certain technology, in which leased leased lines serve to connect intermediate, geographically distributed packet switches.

Connection by dedicated lines only of local networks being connected or end subscribers of another type without installing transit packet switches operating using global network technology.

2.2. Circuit-switched wide area networks

The advantage of circuit-switched networks is their prevalence, which is typical especially for analog telephone networks.

The disadvantage of analog telephone networks is the low quality of the composite channel, which is explained by the use of telephone switches of outdated models operating on the principle of frequency division multiplexing (FDM technology). Such switches are strongly affected by external interference, which is difficult to distinguish from the useful signal. In analogue telephone networks, digital PBXs are increasingly being used, which transmit voice between each other in digital form. In such networks, only the subscriber end remains analog. The more digital telephone exchanges there are in the telephone network, the higher the quality of the channel.

Telephone networks built entirely on digital switches and ISDN networks provide users with high-quality communication lines, and the connection setup time in ISDN networks is significantly reduced.

When connecting mass subscribers to a corporate network, for example, enterprise employees working from home, the telephone network turns out to be the only suitable type of global service for reasons of availability and cost (with a short connection time between a remote employee and the corporate network).

2.3. WAN packet switching networks

To reliably connect local networks and large PCs into a corporate network, packet-switched wide area network technology was used. Also, TCP/IP territorial networks were used to connect local networks.

SMDS (Switched Multi-megabit Data Service) technology was developed to connect local networks across a metropolitan area, as well as provide high-speed access to global networks.

This table shows the characteristics of the main types of networks.

Network type	Access speed	Traffic	Note
X.25	1.2-64 Kbps	Terminal	High protocol redundancy, works well on low quality channels
FRAME RELAY	From 64 Kbps Up to 2 Mbit/s	Computer	They transmit traffic pulsations well and support permanent virtual circuits.
SMDS	1,544 45 Mbit/s
	1.544 -155 Mbit/s		Used to transmit computer traffic
TCP/IT	1.2 2.045 Kbps	Terminal, computer	Distributed on the Internet Internet

2.4. Backbone and access networks

• backbone networks;
• access networks.

Backbone territorial networksare used to form peer-to-peer connections between large local networks belonging to large departments of the enterprise. Backbone territorial networks must provide high throughput, since the backbone combines the flows of a large number of subnets. In addition, they must be constantly available, i.e. provide a very high availability factor, since they carry the traffic of many applications critical for the successful operation of the enterprise.

Used as backbone networksdigital dedicated channelswith speeds from 2 - 622 Mbit/s, which transport IP, IPX or IBM SNA architecture protocols, packet switching networks frame relay, ATM, X.25 or TCP/IP.

In the presence of dedicated channels, a mixed redundant topology of connections is used to ensure high availability of the backbone.

Under access networks refers to territorial networks necessary for connecting small local networks and individual remote computers with the central local network of an enterprise. For many types of enterprise activities, quick access to corporate information from any geographical location determines the quality of decision-making by its employees.

ATMs or cash registers that require access to a central database to obtain information about legal bank clients, whose plastic cards must be authorized on site, can also act as separate remote nodes. ATMs or cash registers are usually designed to communicate with a central computer over a network X.25 , which was developed as a network for remote access of non-intelligent terminal equipment to a central computer.

As access networks usually usedanalogue telephone networks, ISDN networks and, less commonly, frame relay networks.

Software and hardware that provide connection of computers or local networks of remote users to the corporate network are calledremote access means. On the client side, these tools are represented by a modem and related software.

The organization of mass remote access from the central local network is ensured byremote access server.

Remote access serveris a software and hardware complex that combines the functions of a router, bridge and gateway. The server performs one or another function depending on the type of protocol used by the remote user or the remote network. Remote access servers typically have quite a few low-speed ports to connect users via analogue telephone networks or ISDN.

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	This diploma project solved the problem of building a multi-service broadband data transmission network to provide Triple Play services based on FTTB technology. An analysis of the initial data was carried out. A justification for the selected technology and network topology has been proposed, equipment has been calculated, as well as its configuration has been selected, the load on the network has been calculated, technical and economic indicators have been given, and life safety measures have been developed.
13425.		FDDI networks	2.53 MB
	FDDI (Fiber Distributed Data Interface) is a set of network standards focused on data transmission via fiber optic lines at a speed of 100 Mbit/s. The main part of the FDDI standard specifications was developed by the HZT9.5 problem group (ANSI - American Nation Standards Institute)
15250.		Water supply networks	256.94 KB
	Modern water supply and sewerage systems are complex engineering structures and devices that provide water supply to consumers, as well as drainage and wastewater treatment. The correct solution of engineering problems in water supply and sanitation largely determines the high level of improvement of settlements, residential, public and industrial buildings, as well as the rational use and reproduction of natural resources and environmental protection from pollution.
3391.		Local networks	259.41 KB
	Local networks are characterized by a short distance (usually within hundreds of meters), a small number of nodes (within several dozen) and, therefore, a simple topology of connections. Thanks to these features, the tasks of organizing interaction are significantly simplified and in some cases
9080.		Telecommunications and Networks	165.29 KB
	Computer networks When working on a PC in offline mode, users can exchange information only by copying it to various external media. Networks provide users with the opportunity not only to quickly exchange information, but also to share printers and other peripheral devices and even work with documents simultaneously. Each network participant enjoys the benefits of independence on the one hand and access to shared resources on the other.

Lecture 15. Global computer network Internet

Lecture 15. Global computer network Internet

The need for information exchange and modern technological advances have made global computer networks an integral part of the implementation of cooperation programs between countries. Many computer networks have been created for scientific and educational purposes, for business, financial and economic activities, the implementation of joint scientific and technical projects and many other applications.

A network that can unite many networks and allow one to join the global community is the Internet. The Internet is a worldwide computer network that unites individual local, regional and global computer networks into a single information space. The word “Internet” is a tracing of the English name of this network – “Internet”, which is translated as “between networks” (“internetworking”). The Internet provides the user with virtually unlimited information resources. To access these resources, you must use the appropriate application software. The user-friendly graphical interface of this software has made Internet services accessible to everyone. Many of these programs run in the user's familiar Windows environment. Programs with a graphical interface have an important feature: they hide the entire system architecture from the user and allow you to work in the same way with information stored on computers of any platform.

A global computer network unites computers that are distant from each other over a long distance and which can be located in different cities, states and continents. The exchange of information between computers in such a network can be carried out using telephone lines, dedicated communication channels, including fiber optics, radio communication systems and satellite communications.

Global network structure

In general, a wide area network includes a communications subnetwork to which computers and terminals are connected (data input and display only). The global network may include local and regional networks as components (Fig. 15.1). The combination of global, regional and local computer networks makes it possible to create multi-network hierarchies. They provide powerful, cost-effective means of processing huge amounts of information and access to unlimited information resources. This is precisely the structure adopted in the most famous and popular now worldwide super-global information network, the Internet 1. The communication subnetwork consists of data transmission channels and communication nodes.

Rice. 15.1. Global network structure

Computers (usually personal) used by client users are called workstations. Computers that are sources of network resources provided to users are called servers. User workstations are connected to global networks most often through network access service providers - providers.

Communication nodes of the communication subnet are designed for fast transmission of information over the network, for choosing the optimal route for transmitting information and for switching packets of transmitted information. A communication node is either a hardware device or a computer that performs specified functions using appropriate software. These nodes ensure the efficient functioning of the communication network as a whole. The considered network structure is called a node structure and is used primarily in global networks.

Global Internet

About 20 years ago, the US Department of Defense created a network that was the progenitor of the Internet, it was called ARPAnet. ARPAnet was an experimental network; it was created to support scientific research in the military-industrial sphere, in particular, to study methods for constructing networks that are resistant to partial damage received, for example, during aircraft bombing and are capable of continuing normal functioning under such conditions. This requirement provides the key to understanding the principles of construction and structure of the Internet. In the model ARPAnet there was always a connection between the source computer and the destination computer (destination station). It was assumed that any part of the network could disappear at any moment.

Administrative device Internet

The Internet is an all-volunteer organization. It is governed by something like a council of elders, but the Internet does not have a president. The highest authority, wherever the Internet is, remains with ISOC (Internet Society). ISOC is a voluntary membership society. Its goal is to facilitate the global exchange of information via the Internet. It appoints a council of elders that is responsible for technical policy, support and management of the Internet.

The Council of Elders is a group of invited volunteers called IAB (Internet Architecture Council). The IAB meets regularly to approve standards and allocate resources, such as addresses.

It should be noted that there is no such organization that collects fees from all Internet networks or users. Instead, everyone pays their share. N.S.F. pays for maintenance NSFNET. NASA pays for the Scientific Network NASA (NASA Science Internet). Representatives of the networks get together and decide how to connect to each other and contain these relationships. A university or corporation pays for its connection to some regional network, which, in turn, pays a national network owner for its access.

Internet structure

The Internet is a collection of interconnected communication centers to which regional network service providers are connected and through which

their interaction takes place, i.e. The Internet has a structure typical of global networks (Fig. 15.1).

Until 1995, the Internet was controlled by the National Science Foundation (NSF), which created three powerful communications centers: in New York, Chicago and San Francisco. Centers were then established on the East and West Coasts and many other federal and commercial communications centers. Contractual relations are established between these centers on the transfer of information and maintenance of high-speed communications. The collection of communication centers forms a communications subnetwork supported by a number of powerful companies.

From the user's point of view, the service providers on the Internet are: providers(from English provider– “supplier”), maintaining information on servers and specializing in providing Internet access services, and consumers of these services – clients. The interaction of suppliers with consumers is carried out through a communication system with many nodes (Fig. 15.2).

Fig. 15.2. Logical diagram of the global Internet network

Principles of operation of the global network

The Internet is possible because standard methods of communication between computers and application programs have been developed. This allows computers of different types to communicate with each other without any problems. IAB responsible for standards; he decides when a standard is needed and what it should be. When a standard is required, the council considers the problem, adopts the standard, and broadcasts it to the world over the network. IAB also keeps track of various numbers (and other things) that must remain unique. For example, every computer on the Internet has its own unique 32-bit binary address. How is this address assigned? IAB cares about these kinds of problems. He does not assign addresses personally, but develops rules, rules for how to assign these addresses. The address is assigned by the specific provider that connects the computer to the network.

Let us consider in very general terms the principles of operation of a global packet-switching network using the TCP/IP protocol. This protocol underlies both the Internet and many others. Knowledge of the basics of network construction allows you to understand the meaning of many of the actions that the user will have to perform to gain access to numerous and varied network resources.

Network architecture

The network architecture is based on the multi-level principle of message transmission. At the lowest level, a message is a sequence of bits, accompanied by the address of the recipient and the sender. The message is divided into packets by network equipment and transmitted over communication channels. Added to this layer is a base software layer that controls the data communications hardware. The following levels of software are aimed at expanding the functionality of the network and creating a friendly, convenient and simple environment that provides user access to network resources and presentation of messages in a form familiar to the user.

The message is generated by the user at the highest level of the system. It sequentially passes through all levels of the system to the lowest, where it is transmitted via a communication channel to the recipient. As the message passes through each level of the system, it is provided with an additional header, which provides information to a similar level at the recipient node. At the recipient node, the message travels from the lower layer to the upper layer, stripping itself of headers. As a result, the recipient receives the message in its original form.

The standards provide for a seven-level network architecture model: Basic Reference Model for Open Systems Interconnection ( OSI). However, in practice, particularly on the Internet, the number of these levels is smaller.

Packet switching

A message (including a file) is transmitted over the network packages, which have a fixed length. The message is broken down into packets by the network adapter. Most adapters use packets between 500 and 4000 bytes in length. A data packet, similar to an envelope with a letter, has the address of the computer to which it is sent and the address of the computer that is sending the message. Obviously, the address of a computer on the network must be unique. On the receiving computer, the packets are compiled into a message.

When considering the operation of a network, natural associations arise with telephone communications. However, this is actually a misconception. Unlike the telephone network, it does not use circuit switching, in which some part of the network is allocated and blocked for direct communication between the transmitting and receiving nodes. The Internet is a packet-switched network and can be compared to the organization of regular mail. In postal services, all correspondence, regardless of where it is addressed, arrives at the post office. There it is sorted and further forwarded to various post offices with which there is communication, and which are not necessarily the final destinations, but bring the correspondence closer to its destination. The procedure is repeated at these post offices. The mail delivery service allows you to very accurately represent the procedure for transmitting packets over the network.

Routing

Delivery of packets in the network is carried out using communication nodes, which can be implemented in hardware or are programs on computers. These nodes connect individual computers and networks of different organizations and form a communications subnet. The main function of communication nodes is to select the optimal route delivery of the package to the recipient - routing. Each communication node does not have connections with all other communication nodes, and its function, like the function of the post office, is to determine the next node on the route that will best bring the package closer to its destination.

TCP/IP networks use 32-bit IP addresses to identify networks and computers. When written, these addresses are divided into 4 parts. Each 8-bit part can have a value from 0 to 255. The parts are separated from each other by dots. For example, 234.049.123.255.

An IP address includes the network number and the number of the computer on it. The addresses of each network are issued by the Internet Information Center ( NIC). A business must register with the NIC to obtain such an address before using the Internet. Even if you are not yet connected to the Internet, but are just about to connect, it is advisable to use IP addressing on your local network. The goal is to prepare the necessary address system.

As with postal mail, every packet sent over the network must have a recipient address and a sender address. At the communication node, the address of the packet recipient is checked and, based on it, the optimal path for sending the packet to its destination is determined. In each communication node, internal tables are built in which locations and all possible routes to all registered networks are recorded. The route includes all communication nodes on the way to the destination. Using these tables, the router calculates the shortest path to the destination, and if there is a failure in the route, it looks for another path.

The package and the addresses indicated on it must be issued according to certain rules. These rules are called protocol. The IP (Internet Protocol) protocol, responsible for addressing, ensures that the communication node determines the best route for delivering the packet.

Internet addressing

When exchanging data on a network, it is necessary that each computer has its own unique address. On a local network, computer addresses are most often determined by the addresses of the network cards inserted into the computers. Network cards (Ethernet) have unique addresses that are set during their manufacture. In addition, it is possible to enter addresses that are more convenient for a given organization when configuring the board. The host address is a 12-digit hexadecimal number. Each LAN segment also has a network address. This addressing is used on a NetWare network.

IP addresses are used when sending and receiving messages over the TCP/IP protocol. However, it is inconvenient for the user to use such addresses when organizing communication with another computer on the network to receive some service. Therefore, the Domain Name System (DNS) was introduced into the Internet. In this system, computers on the network are given user-friendly names, behind which the corresponding addresses are hidden.

Domain name system

Networks and computers connected to the Internet have unique symbolic identifiers called domain names. These unique names, as well as network addresses, are registered with the NIC and stored in the Internet database.

A domain name consists of two parts: a business identifier and a domain identifier (top-level domain), separated by a dot. For example, com– domain identifier, which is a standard for identifying commercial organizations. Domain ID edu is standard for educational organizations. There are six standard domain identifiers registered with the NIC - two named ( com And edu), and gov(government organizations), mil (military organizations), org(non-profit organizations), net(network organizations). These domain identifiers are mainly used by US organizations.

In other countries, the two-letter country in which the organization is located is used as domain identifiers. There are identifiers for all countries of the world. Identifiers are valid for our country ru And su.

Network names below the root domain ( com, edu, su etc.) are enterprise identifiers and must be registered in the NIC network information center to ensure their uniqueness. An enterprise that has a primary domain is responsible for administering its address space and determines the names located to the left of the organization's name in the domain name.

Network domain addresses contain a sequence of names separated by dots. Moreover, the clarification of which computer the address belongs to is made from right to left. For example, nvp.finec.ru means that the computer is located in Russia (ru), at the University of Economics and Finance (finec), and in the university network it has the name nvp.

On the Internet, the Domain Name System (DNS) handles the translation of names into addresses. Essentially, it is a database that records the correspondence between domain names and IP addresses. This system allows you to use domain names instead of IP addresses. The TCP/IP protocol works with IP addresses and cannot (by itself) use domain addresses. The communications node (gateway) must know the addresses of several DNS servers in order to resolve user-entered names into equivalent IP addresses. If the DNS name server does not have name information, it returns the IP address of another (capable of answering the query) DNS name server.

IP addresses are assigned to a computer from a set of IP addresses reserved for the organization. In this case, the IP address of the gateway to which the message must be sent that does not have a destination address is also indicated. Registration of a domain name, assignment of an IP address, and provision of access to network services may be the responsibility of the provider.

Internet transmission control

Transmission control is implemented by the TCP (Transmission Control Protocol), which breaks the transmitted message into packets and assembles the received message from the packets. The TCP protocol monitors the integrity of the transmitted packet and controls the delivery of all message packets. Thus, on the Internet at the internetwork level, the IP protocol provides non-guaranteed data delivery between any two network points, and the TCP transmission control protocol, being a superstructure over the IP protocol, ensures guaranteed data delivery.

These protocols, by defining the formats of data packets transmitted over the network, allow programs running on different hardware and software platforms to exchange information.

TCP/IP protocol is not limited to the lower-level protocols IP and TCP included in it. Being a family of protocols (more than a dozen) used in both global and local networks, TCP/IP defines the rules for the operation of other network layers.

FTP-protocol, part of the TCP/IP protocol family, is a user-level protocol that allows file transfer from one computer to another. This protocol allows you to send files in various formats, most often text or binary, without loading the remote computer's CPU, since it does not involve running sessions on the remote computer.

Telnet protocol belongs to the same group of protocols as FTP, but is a remote terminal access protocol that allows one computer to connect to another and work on it, as if working directly on a computer. Thus, Telnet allows you to connect to a host computer, log on to it, and run programs on it.

SMTP protocol(Simple Mail Transfer Protocol) enables the transfer of email between computers.

SNMP protocol(Simple Network Management Protocol) transmits information about the state of the network and devices connected to it.

The TCP/IP protocol has well-defined specifications and is supported by many manufacturers of both hardware and software, ensuring compatibility, and is the most popular protocol in the world.

Internet connection methods

Connecting an individual computer

To connect an individual computer to the Internet, it is enough to have a modem, a telephone line and an organization that has a gateway to the Internet. Numerous providers offer dial-up ( dial-up) access of an individual computer with a modem via telephone lines. In this case, it is possible to use the supplier’s computer directly connected to the Internet to gain access to Internet resources. Such a computer is called host (leading computer, or host machine). On the host, the user runs client programs available from the supplier and available to him, which allow him to gain access to the desired server and its information.

Modem is a device that is simultaneously connected to a computer and a telephone line. It receives digital information from a computer and turns it into an analog signal suitable for transmission over a telephone line ( modulation). In addition, it is capable of receiving a modulated signal from another modem, converting it into digital form and transmitting it to its computer ( demodulation).

Hence the name MODEM - MOdulator-DEMOdulator.

In addition, the modem can interact with the switched telephone network - dial a number and recognize free and busy signals. Modems perform a number of other functions, the most important of which are error correction and information compression.

Direct connection to the Internet of the organization's local network

Direct ( on- line) connection to the Internet of the organization's local network is carried out via dedicated leased communication lines using additional software. Typically used by organizations that connect a large number of computers connected to a local network. To access Web servers and other Internet resources, each user must have an IP address.

The NetWare LAN connects to the Internet through a gateway. The gateway provides access to the Internet for every network user. The user can run all programs receiving Internet services from the standard NetWare client environment. Moreover, most of the work can be performed in the Windows environment (Fig. 15.3).

Rice. 15.3. Direct connection to the Internet local network

organizations

Internet services

The Internet service is built on the client-server model. A server is a program that supports a specific network service. Users of other Internet nodes have access to this service through a client program. Most client programs provide the user with a graphical interface that makes access to the service simple and convenient. The service server allows you to organize information in a standard form, as well as receive client requests, process them and send a response to the client.

Let's look at the most well-known services provided by servers on the global Internet.

Email

One of the means of interaction between users in networks is electronic mail (e-mail). The creation of the Internet began with e-mail and it remains the most popular type of activity on it.

In general, email is a broad term used to describe the process of transmitting messages between computers. There are emails used in local and global networks. Next we will talk about global email systems.

The advantages of e-mail include: speed and reliability of correspondence delivery; relatively low cost of services; the ability to quickly familiarize a wide range of correspondents with the message; sending not only text messages, but also programs, graphic images, audio files; saving paper, etc.

General principles of operation of e-mail systems

Let's look at the basic diagram underlying the operation of various email systems.

To send an email message using your computer, you call your email program, specify the recipient of the message, create the message itself, and instruct the program to send it. A signal to transmit a message establishes a connection between your computer and an email host computer directly connected to one or another global network. The message, reaching the sender's host computer, is then transmitted via communication channels to the recipient's machine and there it is placed in a disk memory area owned by the recipient and called a mailbox. The recipient user takes incoming mail from the mailbox to his computer and processes it.

Any email system consists of two main subsystems:

1) client software with which the user directly interacts;

2) server software that controls the reception of a message from the sending user, the transmission of the message, the sending of the message to the recipient's mailbox and its storage in this mailbox until the recipient user takes it from there.

Different email programs can be classified according to different criteria. For example, what operating system they can run on. Nowadays, the most widespread products are those running on the Windows OS. Mail processing programs included in the Microsoft Internet Explorer and Netscape Navigator browsers are widely used. A browser (from the English browser) is a program that searches the Internet. (For more information about browsers, see below in “World Wide Web WWW”). There are programs for users of UNIX and OS/2 systems.

Special programs are required for email to work. There are two main e-mail standards:

SMTP (Simple Mail Transfer Protocol);

SMTP standard It is attractive due to its simplicity, low cost, and many service functions and, as a result, has become widespread, in particular, on the Internet. There is also the POP-3 standard, which differs from SMTP mainly in that in this standard the client works with a program installed on the provider's computer, and not on his own computer.

X.400 standard It is distinguished by rigor, strict standardization, the presence of commercial operators with a guaranteed level of service, and support for a large number of national codes. Due to these features, this standard is very popular among government organizations around the world when working, in particular, on government telecommunication lines.

Among the many e-mail programs running under Windows in the SMTP standard, we can name, for example:

Outlook Express, used in the MS Internet Explorer browser;

Netscape Mail, part of the Netscape Navigator browser;

Mail, HotMail, Hotbox and other free programs on the Internet;

MSMail, part of the Outlook office application;

Qualcomm's Eudora Pro and many others.

Despite the variety of client programs for various email systems, they all have common functions:

notification of the arrival of new mail;

reading incoming mail;

creating outgoing mail;

message addressing;

using an address book containing a list of subscribers to whom mail is often sent;

sending messages;

message processing and storage. Message processing includes functions such as printing, deleting, forwarding messages, sorting, archiving messages, and storing related messages. Particular attention should be paid to programs that allow you to work with folders and create your own folders for storing messages on various topics. This is very convenient and helps you process mail faster and more efficiently.

Working with attached files. Using the file attachment capabilities of email messages, you can send any binary file via email.

Mail message structure

Any message consists of a header and the message body itself (Fig. 15.4).

Rice. 15.4. Mail message structure

Heading includes: email recipient address (field That); your return address (field From); email subject (field Subject; it should be short and informative); date and time of sending the letter (field Date); recipients who will receive a copy of the letter (fields Ss And Vss, the differences between these fields are that the recipients listed in the field Vss, will not appear in the email header in the recipients field, this field is called the blind carbon copy field); a list of files sent along with the letter.

The email address generally looks like this:

[email protected]

The address consists of two parts: the username and the address of the mail host computer on which the user is registered. The two parts of the address are separated by the @ sign.

The specific address of the subscriber may look, for example, like this: [email protected]. The part of the address to the right of the @ sign means: ru – Russia, uef – St. Petersburg University of Economics and Finance, main is the name of the host computer on which the user lina is registered (or a mailbox with that name is installed).

The header is separated from the message text by a blank line. At the end of the text there may be signature– electronic signature, but this is not required.

After reading the mail, you can: reply to the letter, redirect (the recipient will receive it on behalf of the original sender) or forward it to another recipient with your comments, print, save and, finally, delete.

Mail on the user's computer is stored in folders. Folders are divided into those built into the package and those created by the user. Built-in folders include incoming mail folders ( In), outgoing mail ( Out) and garbage ( Trash). A folder is accessed by clicking on its name in the menu Mailbox. You can open several folders at the same time. The window of any folder contains the following information about the messages included in it: status/priority, sender/recipient, date, size, subject. You can create your own folders to complement the built-in ones. The user himself determines which folders are convenient for him to have.

Transferring files

If you find the information you need online, it's often best to work with a copy of it on your computer. To receive a copy of a file, the FTP program is used, which gets its name from the corresponding protocol – File Transfer Protocol.

The FTP program is part of the standard set of application level programs of the TCP/IP protocol family and is designed for transferring files between computers. It allows you to access FTP servers connected to the Internet and containing files that can be retrieved by any user.

Working with the FTP program is simple. By running the program on your computer, you can give the command OPEN - open the server. Next, you can view the contents of the directories and use the GET command to get the file to your computer. HELP will help you learn about the purpose of other commands. Work with FTP servers can take place in real time. It is possible to receive files from FTP servers and via Internet e-mail. Anonymous access to numerous open databases, implemented by a special FTP service program, is widespread. Due to this, you can receive files without presenting your name and password. To receive a file in the FTP system, indicate: the exact name of the node, the name of the directory, subdirectory, file name.

Receiving network services through a remote computer

Telnet, a protocol for remote terminal access to the network, allows you to receive Internet services using the resources of a remote computer. Telnet connects your computer to a remote computer connected to the Internet, and you can work on your computer as if you were sitting at a terminal on the remote system. All commands entered on your computer are executed by the remote computer system.

Working on a remote computer using Telnet, you can run any client programs available on it that will allow you to receive the desired service. Telnet can also transfer files, but FTP is more efficient and uses less CPU. The Telnet program has many versions.

Teleconferences

Systems that allow you to read and send messages to open information groups, called electronic bulletin boards or newsgroups, are very popular on the Internet. These systems are designed to facilitate discussions and exchange of news. The largest teleconferencing system in the world is USENET NEWS. It has groups - teleconferences on a wide variety of topics. A user can subscribe to any of these topics to take part in a discussion on the topic of that conference or view the news.

If you have direct access to the Internet, work in the teleconferencing system begins by entering the program name news at the command line. Through the displayed menus, you can get a list of groups available to you on the specified news server, select the desired group and simply click subscribe to it. Having opened the group, you can view the news, take part in the discussion by sending your message to the group.

To make it easier for the user to navigate a huge number of groups, the group names use abbreviations accepted by the system. Groups can be selected using a set of keywords you specify. Access to teleconferences can be made not only in on-line mode. Teleconferences can also be accessed via email. Of course, you will receive news only after some time.

The procedure for filling out conferences is provided by the participants themselves. Therefore, there are rules of conduct that may vary from conference to conference, for example:

news.answers- rules of world conferences, in English

relcom.answers- teleconference rules in Russian

USENET NEWS can be accessed in a variety of ways. The most convenient and correct way is to use special reading programs, for example, nn or tin. This method is usually used by users of Unix systems. These programs have a fairly long history, have advanced capabilities, and are preferred by experienced users. However, for beginners, we can recommend the tin program, if it is available and configured.

Mobile communications and Internet

The development trend of modern communication technologies eloquently suggests that in the next few years a new section will appear in the communication services market - mobile Internet or Internet using mobile communications.

Now in St. Petersburg the standard is used WAP(Wireless Application Protocol), which today is the basis for data transmission through cellular operators. In addition, the standard is checked in test mode GPRS(General Packet Radio Service). The difference between these protocols is that the first uses a dedicated channel to transmit information, while the latter uses packets when transmitting data that can be transmitted without using a dedicated channel, which significantly increases the throughput of the transmitting equipment.

In order to provide Internet information to mobile phone users, it must be created using the language WML(Wireless Markup Language). In this case, we are not talking about using a mobile phone as a switching device, in other words, a modem, but about using it as a means of viewing information.

There are now a sufficient number of resources that can be used in this area. For example , http://www.nevru.com/wap/index.shtml. Information provided for mobile phones can also be viewed using standard browsers. To do this, you need to enter, for example, http://wapsilon.com/ in the address bar - a special server for viewing WAP resources, and then in the window that opens, enter the desired resource in the input line, for example, wap. rosweb. ru. In addition, mobile phones allow you to transmit information using short SMS text messages. The limitation for SMS messages is their size - 160 characters in one message; moreover, if the message is written in Russian, the message is reduced to 80 characters.

Interactive communication between users in natural language

Interactive communication between users in natural language or teleconferences in real time is implemented by the IRC (Internet Relay Chat) system. This system is designed for live conversations and exists thanks to the high speed of information transfer on the Internet.

A group of users can communicate in real time at once. IRC servers provide support for communication on a variety of topics. Typically, each group united by a topic communicates almost continuously (in the sense that the response delay time is extremely short). Some people stop communicating, new ones come and get involved in the conversation. When working with this program, the user on one part of the screen sees constantly incoming information on the selected topic, and on the other part he can place his messages in the same group, which are immediately sent to the displays of all other participants in this group.

To connect to IRC, you must have the appropriate client program and type its name on the command line to start it. The program will automatically connect you to one of the IRC servers. Since all IRC servers are connected into a single world space, contacting one of them puts you in that space.

World Wide Web WWW

WWW 1 (World Wide Web) is an attempt to combine the capabilities of all these means in one information tool, and even add to them the transmission (in addition to texts and programs) of graphic images, sounds, and videos. All these information objects are connected by the hypertext structure.

Hypertext is a system of documents with cross-references, i.e. pointers from one document to another. Since the WWW system allows these documents to include not only texts, but also graphics, sound and video, a hypertext document has become a hypermedia document. Documents contain links to other documents that are related in meaning, for example, that deepen the understanding of a given text. Pictures, sound clips, and video clips can be associated with links. Pictures or parts of them may also include links to text, new pictures or sound. Documents referenced may be located on remote computers. Using links you can move significantly away from the original source of information, but you can easily return to it. Thus, when reading an article about an art gallery, you can immediately view its paintings, and when studying musical instruments, you can hear their sound.

Hypermedia documents are stored on WWW servers on the Internet. To work with hypermedia documents, many different client programs have been developed, called WWW viewers, or browsers 2 . Viewing programs allow you to call up the documents you need at a known exact address, accumulate them, sort them, combine them, edit them, and print them.

The most popular browsing programs are Microsoft Internet Explorer and Netscape Navigator. These browsers have a lot in common. Therefore, having mastered one of them, it is easy to switch to working with another. If you do not know the exact address of the document you are interested in, you need to contact search servers.

Search servers can be classified according to the principle of information presentation:

search engines,

yellow Pages,

When using WWW technology, resource developers can set keywords in the service information section. For example, for the website of a university of economics and finance, the keywords could be: education, training, university, etc.

Search engines read these keywords and write them to their database. When searching for the required keyword, the searched information is compared with the database and with information on the Internet, after which the user is provided with a list of search results. The list is created based on the principle of the most suitable answer to the query.

To search for information on the WWW, there are international search engines (search programs) AltaVista, Lycos, Yahoo, etc. For Russian-language searches, domestic search engines Rambler, Yandex and Aport are more convenient. When working with search engines, the user sets search image- keywords of the topic of interest, and the system provides lists and addresses of those documents in which these words appear. Note that although there are many good search programs available, it is best to have an exact address. The method for specifying the address is determined by the system of unified URLs(URL = Uniform Resource Locator - unified resource locator).

The search program accesses search servers accessible via the Web interface to select the desired addresses. The main function of these servers is to process information from documents on various servers (Web, FTP, Usenet, etc.), enter it into a database and provide addresses of this information at the request of search program users.

To search servers “ yellow Pages” refer to servers that not only search for information of interest, but also store in their databases the phone, fax, regular and email addresses of the organization.

An example would be:

www. yellow. com

An example would be:

www. rmp. ru