How does the Internet work? How does he work?

How is the Internet arranged and working? Good question! Its growth is similar to an explosion, and .com sites are constantly mentioned on television, radio and in magazines. Since it has become a significant part of our life, it is necessary to understand it well in order to use this tool most effectively. This article explains the concepts and types of the Internet, its basic infrastructure and technologies that ensure its functioning.

Global network

The definition of the Internet is usually given as follows. This is a global network of computer resources connected by high-performance communication lines and a common address space. Therefore, each device connected to it must have a unique identifier. What is the IP address of the computer? IPv4 Internet addresses are written in the form nnn.nnn.nnn.nnn, where nnn is a number from 0 to 255. The abbreviation IP stands for Internet Protocol. This is one of the basic concepts of the Internet, but more on that later. For example, one computer has the identifier 1.2.3.4, and the other - 5.6.7.8.

If you connect to the Internet through your ISP, you will usually be assigned a temporary IP address for the duration of the remote access session. If the connection is made from a local area network (LAN), then the computer can have both a permanent identifier and a temporary one provided by the DHCP server (protocol for dynamic configuration of the host machine). In any case, if the PC is connected to the Internet, then it has a unique IP address.

Ping program

If you use the Microsoft Windows operating system or one of the varieties of Unix, there is a handy program that allows you to check your Internet connection. It is called ping, perhaps by the sound that old submarine sonars made. If you are using Windows, you must run a command prompt window. In the case of an operating system that is a variation of Unix, you should go to the command line. If you enter, for example, ping www.yahoo.com, the program will send an ICMP (Internet Control Message Protocol) echo request message to the specified computer. The interrogated machine will answer. The ping program counts the response time (if that happens). In addition, if you enter a domain name (for example, www.yahoo.com), the utility will display the IP address of the computer.

Protocol Packages

So, the computer is connected to the network and has a unique address. To make it clear for dummies how the Internet works, you need to understand how the PC “talks” to other machines. Suppose the IP address of the user's device is 1.2.3.4, and he wants to send the message “Hello, computer 5.6.7.8!” to the car with the address 5.6.7.8. Obviously, the message should be transmitted on any channel connecting the user's PC to the Internet. Suppose a message is sent over the phone. It is necessary to convert the text into electronic signals, transmit them, and then again present in the form of text. How is this achieved? Thanks to the use of the protocol package. It is necessary for every computer to communicate on a global network and is usually built into the operating system. The package is called TCP / IP because of the 2 main communication protocols used in it . The TCP / IP hierarchy is as follows:

• Application level. It uses protocols specific to WWW, email, FTP, etc.
• The level of the data transfer control protocol. TCP routes packets to specific programs using a port number.
• Internet Protocol Layer. IP routes packets to a specific computer using an IP address.
• Hardware level. Converts binary data to and from network signals (for example, an Ethernet network card, modem, etc.).

If you follow the path of the message “Hello, computer 5.6.7.8!” Sent from the user's PC to the machine with the IP address 5.6.7.8, then you can understand how the Internet works. The following will happen:

1. Message processing starts with the upper layer protocol and moves down.
2. If the sent message is long, each level through which it passes can break it down into smaller pieces of data. This is due to the fact that information sent over the Internet (and most computer networks) is presented in the form of controlled parts called packets.
3. Packets arrive for processing at the transport level. Each of them is assigned a port number. Many programs are capable of using the TCP / IP protocol suite and sending messages. You need to know which one on the destination computer should receive the message, because it will listen on a specific port.
4. Next, the packets go to the IP layer. Here, each of them receives the destination address (5.6.7.8).
5. Now that the message packets have a port number and IP address, they are ready to be sent over the Internet. The hardware level ensures that packets containing the message text are converted to electronic signals and transmitted over the communication line.
6. At the other end, the provider has a direct Internet connection. The router checks the destination address of each packet and determines where to send it. Often the next stop is another router.
7. In the end, packets reach the computer 5.6.7.8. Here, their processing begins with the protocols of the lower level and moves up.
8. As packets pass through higher TCP / IP layers, all routing data added by the sending computer (for example, IP address and port number) is deleted from them.
9. When a message reaches the top-level protocol, packets are collected in their original form.
   

Home Internet

So, all of the above explains how packets are moved from one computer to another through the global network. But what happens in between? How does the Internet really work?

Consider a physical connection through a telephone network to a communications service provider. This requires some explanation of how your ISP works. The service provider sets up a modem pool for customers. Usually it is connected to a dedicated computer that controls the direction of data flow from the modem to the Internet backbone or dedicated router. This setting can be called a port server, because it serves access to the network. It also collects information about the time of use, as well as the amount of data sent and received.

After the packets pass through the telephone network and the local equipment of the provider, they are sent to the provider's trunk or part of its capacity leased by it. From here, data usually passes through several routers and backbone networks, leased lines, etc., until they find their destination - a computer with the address 5.6.7.8. This is how the home Internet works. But would it be bad if the user knew the exact route of his packets on the global network? It is possible.

Traceroute program

When connecting to the Internet from a computer running Microsoft Windows or a variety of Unix, another convenient program is useful. It is called Traceroute and indicates the path that packets travel to reach a specific IP address. Like ping, it must be run from the command line. On Windows, use the tracert command www.yahoo.com, and on Unix use the traceroute www.yahoo.com. Like ping, the utility allows you to enter IP addresses instead of domain names. Traceroute prints a list of all routers, computers, and other Internet objects that packets must pass in order to reach their destination.

Infrastructure

How is the Internet backbone technically arranged? It consists of many large networks connected to each other. These large networks are known as network service providers or NSPs. Examples are UUNet, IBM, CerfNet, BBN Planet, PSINet, SprintNet, etc. These networks interact with each other to exchange traffic. Each NSP provider needs to connect to three network access points (NAPs). In them, packet traffic can go from one backbone network to another. NSPs also connect through the city's MAE routing stations. The latter perform the same role as NAP, but are privately owned. NAPs were used to connect to the global network initially. Both MAE and NAP are called Internet Exchange Points, or IX. Network providers also sell bandwidth to small networks such as ISPs.

The underlying NSP infrastructure itself is a complex scheme. Most network providers publish network infrastructure maps on their websites that are easy to find. It would be almost impossible to depict how the Internet is structured because of its size, complexity, and ever-changing structure.

Routing hierarchy

To understand how the Internet works, you need to deal with the question of how packets find the right path through the network. Does every PC connected to the network know where other computers are? Or are packages just “broadcast” to every machine on the Internet? The answer to both questions is no. No one knows where other computers are located, and packets are not sent to all machines at once. The information used to deliver data to its recipients is contained in tables stored on each router connected to the network — another concept of the Internet.

Routers are packet switches. Usually they connect between networks to redirect packets between them. Each router knows about its subnets and what addresses they use. The device, as a rule, does not know the IP addresses of the "upper" level. Large NSP trunks connect through NAPs. They serve several subnets, and they serve even more subnets. At the bottom are local networks with connected computers.

When a packet arrives at the router, the latter checks the IP address placed there by the IP protocol layer on the source machine. Then the routing table is checked . If a network containing an IP address is found, then the packet is sent there. Otherwise, it follows the default route, usually to the next router in the network hierarchy. With the hope that he will know where to send the packet. If this does not happen, the data will be sent higher until it reaches the NSP trunk. Top-level routers contain the largest routing tables, and here the packet will be sent to the correct trunk, where it will begin its journey “down”.

Domain Names and Address Definition

But what if the IP address of the computer to which you want to connect is not known? What if you need access to a web server called www.anothercomputer.com? How does the browser know where this computer is located? The answer to all these questions is the DNS Domain Name Service. This concept of the Internet refers to a distributed database that tracks computer names and their corresponding IP addresses.

Many machines are connected to a DNS database and software that allows access to it. These machines are known as DNS servers. They do not contain the entire database, but only a subset of it. If the DNS server does not have the domain name requested by another computer, then it redirects it to another server.

The domain name service is structured as a hierarchy similar to the IP routing hierarchy. The computer requesting name resolution will be redirected up the hierarchy until a DNS server is found that can resolve the domain name in the request.

When an Internet connection is configured (for example, over a local area network or over a telephone connection in Windows), the primary and one or more secondary DNS servers are usually specified during installation. Thus, any applications that require domain name resolution will be able to function normally. For example, when entering a domain name in a browser, the latter connects to the main DNS server. After receiving the IP address, the application will then connect to the target computer and request the desired web page.

Overview of Internet Protocols

As noted earlier in the section on TCP / IP, the global network uses many protocols. These include TCP, IP, routing, medium access control, application layer, etc. The following sections describe some of the most important and commonly used ones. This will allow you to better understand how the Internet works and how it works. Protocols are discussed in descending order of their level.

HTTP and World Wide Web

One of the most used services on the Internet is the World Wide Web (WWW). The application layer protocol that enables operation on the global network is the Hypertext Transfer Protocol, or HTTP. It should not be confused with the HTML hypertext markup language used to write web pages. HTTP is a protocol that browsers and servers use to communicate with each other. This is an application level protocol because it is used by some programs to communicate with each other. In this case, these are browsers and servers.

HTTP is a protocol that does not require a connection pre-installation. Clients (browsers) send requests to servers for web elements such as pages and images. After servicing, the connection is disconnected. For each request, you must establish a connection again.

Most protocols are connection oriented. This means that computers that communicate with each other communicate via the Internet. However, HTTP is not. Before a client can make an HTTP request, the server must establish a new connection.

To understand how the Internet works, you need to know what happens when you type the URL into a web browser:

1. If the URL contains the domain name, the browser first connects to the domain name server and obtains the corresponding IP address.
2. Then the browser connects to the server and sends an HTTP request for the desired page.
3. The server receives the request and checks the desired page. If it exists, then sends it. If the server cannot find the requested page, it sends an HTTP 404 error message (404 means "Page not found", as probably anyone who viewed the websites knows).
4. The browser receives the requested, and the connection closes.
5. The browser then analyzes the page and looks for other elements necessary to complete it. Usually these are images, applets, etc.
6. For each element, the browser makes additional connections and HTTP requests to the server.
7. When the download of all images, applets, etc. is completed, the page will be fully loaded in the browser window.
   

Using Telnet Client

Telnet is a remote terminal service used on the Internet. Its use has declined, but it is a useful tool for exploring the global network. In Windows, the program can be found in the system directory. After its launch, you need to open the “Terminal” menu and select Local Echo in the settings window. This means that you can see your HTTP request as you type it.

In the "Connection" menu, select "Remote System". Next, enter www.google.com for the host name and 80 for the port. By default, the web server listens for this particular port. By clicking Connect, you must enter GET / HTTP / 1.0 and press Enter twice.

This is a simple HTTP request to a web server to get its root page. The user should catch a glimpse of it, and then a dialog box will appear with a message about the loss of connection. If you want to save the extracted page, then enable logging. You can then view the web page and the HTML code that was used to create it.

Most Internet protocols that determine how the Internet works are described in documents known as Request For Comments or RFCs. They can be found on the Internet. For example, HTTP version 1.0 is described in RFC 1945.

Application Protocols: SMTP and Email

Another widely used internet service is email. It uses an application layer protocol called Simple Mail Transfer Protocol, or SMTP. This is also a text protocol, but unlike HTTP, SMTP is connection-oriented. In addition, it is also more complicated than HTTP. There are more commands and aspects to SMTP than to HTTP.

When you open an email client to read an email message, the following usually happens:

1. The mail client (Lotus Notes, Microsoft Outlook, etc.) opens a connection to the default mail server, the IP address or domain name of which is usually configured during installation.
2. The mail server always sends the first message to identify itself.
3. The client sends the SMTP HELO command, to which it receives a 250 OK response.
4. Depending on whether the client checks or sends mail, etc., the appropriate SMTP commands are sent to the server so that it can respond accordingly.

This request / response transaction will continue until the client sends a QUIT command. Then the server will say goodbye and the connection will be closed.

Transmission Control Protocol

TCP. , TCP. . . . , -. , . , TCP , .

-:

• FTP – 20/21.
• Telnet – 23.
• SMTP – 25.
• HTTP is 80.

Transport protocol

TCP works as follows:

• When the TCP layer receives application-level protocol data, it splits them into manageable “chunks,” and then adds a header with information about the port number to which data should be sent to each of them.
• When a TCP layer receives a packet from a lower IP layer, the header data from the packet is deleted. If necessary, they can be restored. Then the data is sent to the desired application based on the port number.

So messages, moving along the protocol stack, are sent to the correct address.

TCP is not a text protocol. It is a connection-oriented, reliable byte transfer service. Connection orientation means that two applications using TCP must establish a connection before exchanging data. The transport protocol is reliable, because for each packet received, a confirmation is sent to the sender to confirm delivery. The TCP header also includes a checksum to check for errors in the received data.

There is no space for an IP address in the transport protocol header. This is due to the fact that its task is to ensure reliable receipt of application-level data. The task of transferring data between computers is performed by IP.

Internet Protocol

Unlike TCP, IP is an unreliable, connectionless protocol. IP does not care if the packet reaches its destination or not. IP also does not know about connections and port numbers. The IP job is to forward data to other computers. Packages are independent entities and may arrive out of order or not achieve the goal at all. The task of TCP is to ensure that data is arriving and located correctly. The only thing that IP has in common with TCP is how it receives data and adds its own IP header information to TCP data.

Application-level data is segmented at the transport protocol level, and a TCP header is added to it. Next, the packet is formed at the IP level, an IP header is added to it, and then it is transmitted over the global network.

How the Internet works: books

Extensive literature is available for novice users on this topic. A series of "For Dummies" is popular with readers. How the Internet works, you can learn from the books "Internet" and "Users and the Internet." They will help you quickly select a provider, connect to the network, teach how to use a browser, etc. For beginners, books will become useful guides on the global network.

Conclusion

Now it should be clear how the Internet works. But how long will he stay that way? The previously used 4th version of IP, which allowed only 2 ³² addresses, was replaced by IPv6 with 2 ¹²⁸ theoretically possible addresses. The Internet has come a long way since its inception as a U.S. Department of Defense research project. No one knows what he will become. One thing is certain: the Internet unites the world like no other mechanism. The information age is in full swing, and witnessing this is a great pleasure.