How does the Internet work? How does he work?

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How does the Internet work? How does he work?
How does the Internet work? How does he work?
Anonim

How does the Internet work? Good question! Its growth has been exploding, and.com sites are constantly featured on TV, radio, and magazines. Since it has become a significant part of our lives, 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 the technologies that make it possible.

Global Network

The Internet is usually defined as follows. It 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. How is a computer's IP address arranged? IPv4 Internet addresses are written in the form nnn.nnn.nnn.nnn, where nnn is a number between 0 and 255. The abbreviation IP stands for Internetworking Protocol. This is one of the basic concepts of the Internet, but more on that later. For example, one computer hasthe id is 1.2.3.4 and the other is 5.6.7.8.

If you connect to the Internet through an ISP, the user is usually 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 either a permanent ID or a temporary ID provided by a DHCP (Dynamic Host Configuration Protocol) server. In any case, if the PC is connected to the Internet, then it has a unique IP address.

Ping program

If you are using the Microsoft Windows operating system or one of the flavors of Unix, there is a handy program that allows you to check your Internet connection. It's called ping, probably after the sound the old submarine sonars made. If you are using Windows, you must launch a command prompt window. In the case of an operating system that is a variety of Unix, then you should go to the command line. If you type, for example, ping www.yahoo.com, the program will send an ICMP (Internet Control Message Protocol) echo request message to the specified computer. The polled machine will answer. The ping program counts the time it takes to return a response (if it does). Also, if you enter a domain name (for example, www.yahoo.com), the utility will display the computer's IP address.

Internet Development
Internet Development

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 a PC"talks" to other machines. Suppose the user's device IP address is 1.2.3.4 and he wishes to send a message "Hi, computer 5.6.7.8!" to the machine with the address 5.6.7.8. Obviously, the message must be transmitted over any channel connecting the user's PC to the Internet. Let's say a message is sent by phone. It is necessary to convert the text into electronic signals, transmit them, and then re-present them as text. How is this achieved? Through the use of a protocol package. It is necessary for every computer to communicate on the 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 layer. It uses protocols specific to WWW, email, FTP, etc.
  • Transmission control protocol layer. TCP directs packets to specific programs using a port number.
  • Internet protocol layer. IP directs packets to a specific computer using an IP address.
  • Hardware level. Converts binary data to network signals and vice versa (for example, Ethernet network card, modem, etc.).

If you follow the path of the "Hi, computer 5.6.7.8!" Something like this will happen:

  1. Message processing starts from the top layer protocol and works its way down.
  2. If the message being sent is long, each level through which itpasses, can break it into smaller pieces of data. This is because information sent over the Internet (and most computer networks) is in manageable pieces called packets.
  3. Packets are sent to the transport layer for processing. Each one is assigned a port number. Many programs are capable of using the TCP/IP protocol package and sending messages. You need to know which one on the destination computer should receive the message because it will be listening on a specific port.
  4. Further, the packets go to the IP level. Here each of them receives a destination address (5.6.7.8).
  5. Now that the message packets have a port number and an IP address, they are ready to be sent over the Internet. The hardware level takes care that the packets containing the text of the message are converted into electronic signals and transmitted over the communication line.
  6. At the other end, the ISP has a direct connection to the Internet. The router checks the destination address of each packet and determines where to send it. Often the next stop is another router.
  7. Eventually, the packets reach computer 5.6.7.8. Here, their processing starts from the lower layer protocols and works their way up.
  8. As packets traverse higher levels of TCP/IP, they remove any routing information added by the sending computer (such as IP address and port number).
  9. When a message reaches the upper layer protocol, the packets are reassembled in their original form.
  10. Hierarchyrouting
    Hierarchyrouting

Home Internet

So all of the above explains how packets move from one computer to another across the WAN. But what happens in between? How does the Internet really work?

Consider a physical connection through the telephone network to a telecom service provider. This requires some explanation of how an ISP works. The service provider sets up a pool of modems for its clients. It is usually connected to a dedicated computer that controls the direction of data flow from the modem to the Internet backbone or a dedicated router. This setup can be called a port server because it handles network access. 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 backbone of the provider or the part of its bandwidth leased by him. From here, data usually passes through several routers and backbone networks, leased lines, etc., until it finds its destination - a computer with the address 5.6.7.8. This is how home Internet works. But would it be bad if the user knew the exact route of his packets through the global network? It is possible.

Traceroute

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

How Traceroute works
How Traceroute works

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 communicate with each other to exchange traffic. Each NSP requires a connection to three Network Access Points (NAPs). In them, packet traffic can move from one backbone network to another. NSPs are also connected through the city's MAE routing stations. The latter fulfill the same role as NAP, but are privately owned. NAPs were originally used to connect to the global network. Both MAE and NAP are referred to as Internet Exchange Points, or IX. Network providers also sell bandwidth to smaller networks such as ISPs.

The underlying infrastructure of NSP itself is a complex scheme. Most network providers publish network infrastructure maps on their websites which can be easily found. Realistically portray howthe Internet is set up, it would be almost impossible due to its size, complexity and ever-changing structure.

Routing hierarchy

To understand how the Internet works, you need to understand how packets find the right path through the network. Does every PC connected to the network know where other PCs are located? Or are the packets just "translated" to every machine on the internet? The answer to both questions is negative. Nobody knows where other computers are, and packets are not sent to all machines at the same time. The information used to deliver data to its destinations is contained in tables stored on each router connected to the network - another concept of the Internet.

Routers are packet switches. They usually connect between networks to forward 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 are connected through NAPs. They serve several subnets, and those serve even more subnets. At the bottom are local networks with connected computers.

When a packet arrives at a router, the router checks the IP address placed there by the IP protocol layer on the source machine. Then the routing table is checked. If the network containing the 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 package. If this does not happen, then the data will go up until it reaches the NSP backbone. Upstream routers contain the largest routing tables and this is where the packet will be sent to the correct backbone where it will begin its "downward" journey.

Internet connection
Internet connection

Domain names and address resolution

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

Many machines are connected to the DNS database and software that allows you to access 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 that of IP routing. The computer requesting name resolution will be redirected "up" in 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 through a dial-up connection on Windows), the primary and one or more secondary DNS servers are usually specified during installation. Thus,any applications that need domain name resolution will be able to function normally. For example, when you enter a domain name in a browser, the latter connects to the primary DNS server. After obtaining 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, there are many protocols used in the WAN. These include TCP, IP, routing, media access control, application layer, and so on. The following sections describe some of the more important and commonly used protocols. This will allow you to better understand how the Internet is organized and how it works. Protocols are discussed in descending order of their level.

Internet protocol layers
Internet protocol layers

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 the WAN 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 the protocol that browsers and servers use to communicate with each other. It is an application layer protocol because it is used by some programs to communicate with each other. In this case, these are browsers and servers.

HTTP is a connectionless protocol. Clients (browsers) send requests to servers for web elements such as pages and images. After their service, the connectionturns off. For each request, the connection must be established again.

Most protocols are connection oriented. This means that computers that communicate with each other communicate over 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 a URL into a web browser:

  1. If the URL contains a domain name, the browser first connects to the domain name server and obtains the corresponding IP address.
  2. The browser then connects to the server and sends an HTTP request for the desired page.
  3. The server receives the request and checks the correct page. If it exists, send it. If the server cannot find the requested page, it sends an HTTP 404 error message. (404 stands for Page Not Found, as anyone who has browsed websites probably knows).
  4. The browser receives what is requested and the connection is closed.
  5. The browser then parses the page and looks for other elements needed 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 all images, applets, etc. have finished loading, the page will be fully loaded in the browser window.
  8. What is behind an IP address?
    What is behind an IP address?

Using the 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. On Windows, the program can be found in the system directory. After launching it, you need to open the "Terminal" menu and select Local Echo in the settings window. This means you can see your HTTP request as you enter it.

In the "Connection" menu, select the "Remote system" item. Next, enter www.google.com for the hostname and 80 for the port. By default, the web server listens on this port. After 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 get a glimpse of it, and then a dialog box will appear stating that the connection has been lost. If you want to save the retrieved page, you must enable logging. You can then view the web page and the HTML that was used to create it.

Most of the Internet protocols that define 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 the 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 complex than HTTP. There are more commands and aspects in SMTP than in

When opening the mail client for readinge-mail messages usually goes like this:

  1. The mail client (Lotus Notes, Microsoft Outlook, etc.) opens a connection to the default mail server, whose IP address or domain name is usually configured during installation.
  2. The mail server always sends the first message to identify itself.
  3. Client sends an SMTP HELO command, to which it receives a 250 OK response.
  4. Depending on whether the client is checking or sending mail, etc., 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. The server will then say goodbye and the connection will be closed.

backbone router
backbone router

Transmission Control Protocol

Below the application layer in the protocol stack is the TCP layer. When programs open a connection to another computer, the messages they send are passed up the stack to the TCP layer. The latter is responsible for routing application protocols to the appropriate software on the destination computer. For this, port numbers are used. Ports can be thought of as separate channels on each computer. For example, while reading email, you can browse the web at the same time. This is because the browser and mail client use different port numbers. When a packet arrives at a computer and makes its way up the protocol stack, the TCP layer determines which program receives the packet onport number.

The port numbers for some of the most commonly used Internet services are listed below:

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

Transport Protocol

TCP works like this:

  • When the TCP layer receives application layer protocol data, it divides it into manageable "chunks" and then adds a header to each of them with information about the port number to which the data should be sent.
  • When the TCP layer receives a packet from a lower IP layer, the header data is removed from the packet. If necessary, they can be restored. The data is then sent to the required application based on the port number.

This is how messages move through the protocol stack to the correct address.

TCP is not a text based protocol. It is a connection-oriented, reliable byte transfer service. Connection-oriented means that two applications using TCP must establish a connection before exchanging data. The transport protocol is reliable because for each packet received, an acknowledgment 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 provide reliable receipt of application layer data. The task of transferring data between computers is performed by IP.

Internet Protocol

BUnlike TCP, IP is an unreliable, connectionless protocol. IP doesn't care if the packet gets to its destination or not. IP is also unaware of connections and port numbers. The IP job is to send data to other computers. Packets are independent entities and may arrive out of order or may not reach their destination at all. The task of TCP is to make sure that the data is received and located correctly. The only thing IP has in common with TCP is how it receives data and adds its own IP header information to TCP data.

Application layer data is segmented at the transport protocol layer and appended with a TCP header. 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

For novice users, extensive literature is available on this topic. The series "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 you how to use a browser, etc. For beginners, books will be useful guides to the global network.

Conclusion

Now it should be clear how the Internet works. But how long will it stay that way? The previously used version 4 of IP, which allowed only 232 addresses, has been replaced by IPv6 with 2128 addresses theoretically possible. The Internet has come a long way since its inception as a US Department of Defense research project. Nobody knows what he will become. One thing is certain: the Internet connects the world like no other mechanism. The Information Age is in full swing, and it is a great pleasure to witness it.

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