Structure of the Internet

Really, all we use the Internet, for many of us it(he) already became a part of a life, whether and many know, how it(he) is arranged? Considering(examining) such global question into three parts: 1) a computer of the user plus its(his) modem, 2) the provider, 3) set of servers all over the world - with all connections and network devices which form the Worldnet the Internet. To begin, certainly, costs(stands) all over again. That is, from itself. Therefore as in the majority you also are the end user, sitting at home behind the computer, listening "singing" of the modem during installation of communication(connection). You also are last (among millions) a point of the Internet. " " Points are not present the first. Why Ц about it(this) the separate story. Hence, we begin with you, as from the extremest. Here the scheme(plan), to which I shall refer further (1 Ц a computer of the user with the modem, 2 Ц modems of the provider, 3 Ц a router, 4 Ц a local network of a server of the provider, 5 Ц a server of the provider, 1a Ц a local network of users, 6 Ц the concentrator for an exchange of the traffic between a local network and the provider).

What in general occurs(happens) after you or on work (if at you communication(connection) with the provider not through a local network) press houses the button " To establish(install) communication(connection) "? After a set of number, your modem [1] will incorporate with провайдерским [2]. Since this moment it is better to tell, how it occurs(happens), looking " from that end " - with провайдерского. To a router [3] the modem pool [2] is picked up (a set of a quantity of modems), the router adjusts(sets up) them on an autorespond. After receipt of a call and successful passage handshaking (i.e. adjustments(options) of both modems when they "agree" about speed and the report of an exchange), both of the modem, together with a line between them, start to represent already simply transport for communication(connection) a router <-> your computer. Everything, since this moment it is already possible to not recollect modems. Communication(connection) is established(installed).

Now the router should agree with your operational system (it(he) in fact yet does not know what at you costs(stands)) about authorization of your connection. For this purpose there are some special reports. Windows uses report CHAP. After the router will make it, it(he) sends a package with your name and the password on авторизующий a server [5]. As soon as authorization will pass(take place) successfully (if is not present Ц connection is closed from the provider), the router should agree with your computer about the report by means of which your system will communicate with the Internet in the further. Particularly for OS Windows this report refers to PPP (point-to-point protocol) is it is possible to see in adjustments(options). After reception of the positive answer from a server the router still should appoint(nominate) to you the next IP-address from among free at present, but only from the certain range appointed(nominated) to your provider. Each computer should have the address in a network that the network knew where it(her) to send the information intended for this computer. For example, 16 telephone lines are connected to a router. Inside of a router the range of addresses among which it(he) and can choose registers. For example: with on - just 16 addresses. Here in this rank to you the address also will be appointed(nominated).

With corporate networks [1a] business(affairs) are a little bit easier - they simply directly (or through the concentrator [6]) are included in a router, and the address of their network is already in advance registered. An abrupt piece - this router. Takes, as you can see, on itself enough most part of work together with that is engaged also actually, routing. As a matter of fact, it is a separate computer. It(he) even has a IP-address. On it(him) it is possible to come, as on a server, to program it(him) as it is necessary, etc. in general, without it(him) - anywhere. Well and, by itself, the provider has a server [5] which comprises base of users, is engaged in processing of mail, ftp, http, etc. Basically the provider for granting is simple services on connection in the Internet is capable to manage only one computer which will be engaged in authorization (here and 386-th will go). The rest will do(make) a router. So, communication(connection) is established(installed), the browser is started and expects input of the network address. In a browser you type(collect), for example, in line URL (notice, here - without the additive http: // - it(she) will be added by a browser). The full name ( leaves in a package of inquiry on DNS (Domain Name Service), which should return the normal IP-address to a browser to work further. That it was more clear, I shall distract on terms DNS and "IP-address". The matter is that the habitual names designating the Internet addresses, actually are intended only for the person - that it was more convenient to remember names. The computer operates with digital addresses in the form of four groups of the numbers divided(undressed) by points. For example, is one of representations of the IP-address. Basically, the name of a resource in a line of a browser can be typed(collected) and thus, but it is inconvenient. Hence, there should be a system which will compare habitual to us with names to numerical representation.

In it(this) just service DNS (domain name service) also is engaged. Transformations of type> Refer to as direct transformation. And> refers to as return transformation. That is, there are two types of service of transformation. Each provider should have the DNS which transforms your inquiries that you did not climb far behind simple and often used names and that others DNS could ask it(him) about its(his) own domains. But on the Internet it(he), certainly, cannot know all names. Actually, DNS is the distributed(allocated) database. At "ignorance" of any DNS address the provider starts to request it(him) in parts of other DNS-servers. Begins with the main thing (or root, root) a DNS-server, more truly, from the several main things Ц a root-server not one. The address is not those, what we have got used to see it(him). For example, looks(appears) actually as - with a point in the end. The point also specifies "root", i.e. "main thing" DNS ask: - and who there at us is responsible for a zone "ru"? To It(Him) answer: such and such DNS, and it(he) already now at these(it) DNS asks: - and who is responsible for a zone irk? - " such that "... And so on, yet will not receive necessary IP. That is, if somewhere not on a server requested first time the name - that the server of that provider has received final decoding just from a DNS-server with the domain Now there is clear an inscription during work of browser Looking up host... is it(he) waits, while DNS will find the necessary IP-address.

After that the browser receives a package with the present(true) (digital) IP-address, and now it(he) will request a resource to already real IP-address. Also will substitute port 80 to the inquiries. Why to substitute port, and 80? It is done(made) to differentiate types of resources. In fact the FTP-server can be on the same IP-address, as WWW. To the report http there corresponds(meets) under the standard port 80 and the browser by default works with www, i.e. with 80 port, in fact having written, for example,, I get on WWW, instead of on FTP. Besides the browser tries to define(determine) port by the first word in URL. If it is written, means it is necessary to substitute 80 port, and if, 21 - port for work with FTP. You this port do not write, it(he) is substituted by the automatic device, as well as many other things. Certainly, it is possible to write in line URL instead of - is there will be the same. So, your browser has received the IP-address of that resource which you want. What should make a browser? It(he) should something request of that server. The package with inquiry of a resource about the removed server (the IP-address now is known) is sent. But here the interesting moment. There is such thing, as alias - a virtual host. IP-addresses at different hosts can be identical. For example, IP-addresses and is the same, and typing(collecting) in line URL the "pure(clean)" IP-address, you will get only on any one. The virtual host is done(made) that you had not to remember the long name of a directory where the file necessary to you could lay, for example -, etc. simply system administrator so has registered adjustments(options), that the directory on a server where is siberia, now like as is a separate server But, nevertheless, physically it(he) is on the core - Though, certainly, on the Internet all is very virtual, and the server can be on any other server.

Now there is a question: how the server distinguishes, what exactly you want - or when you fairly write the normal address in line URL? In fact the IP-address at them the same (when DNS will return it(him) after comparison). And so, after reception of the real IP-address, a browser sends a server a package containing inquiry about a resource from IP address (which browser has already received) and in it(him) (in a package) the usual name will be obligatory to be present a line, that is. Actually, the address of a virtual host contains in inquiry GET under the HTTP-report, but I describe the general(common) case. Most popular of programs of www-servers is program Apache, (there is also a same project for the Russian version which works under operational system UNIX. The program not named an American Indian tribe, and on an abbreviation " A PAtCHy sErver is named "i.e." The server collected from patch-files " (from modules). Apache is engaged directly in that answers your inquiries and on demand carries out scripts (script) CGI, gives files, pictures and a html-code of the document. Apache is HTTPd - hypertext transfer protocol daemon, i.e. on русски Ц a www-server. And so, this HTTP-demon, perceiving the IP-address with a normal name of a resource, looks at itself in configuration files (слэнговое "configs" - they in advance have been adjusted(have been set up) by the system administrator), which resource to give the user - with or, in fact a name it(he) has received together with the IP-address, preliminary having noticed there the address of the server. And here if the server will be not it(him) it(he) such package and will not receive at all as the router will send it(him) further.

So, Apache starts to give out a resource from a directory containing files on port 80. What should it(he) give out? In fact you obviously did not specify, what exactly you want, and it have simply written the name of a site (the truth also have obviously or implicitly specified the report of top level on which will communicate Ц HTTP). In Apache it is registered, that by default for 80 ports from such directory the file index.html always stands out. It can Sometimes be default.html or still something. For each type of files there is a heading which is sent your browser before посылкой the file (using report HTTP). It is done(made) that the browser understood, what exactly it is necessary to do(make) with this file - to show it(him) in a window or to offer record on a disk (for example, - it is not necessary to show in a window, and it is necessary to keep - whence the browser should learn(find out) it?) . There are also other instructions(indications) from a server to a browser, that to it(him) to do(make) with the files which are being on a server. For example, when still the type of files .mp3 was not known enough, heading on it(him), naturally, nobody registered (it is done(made) separately in configurations of a server), therefore you could notice, that sticking on the reference(link) specifying a file with expansion mp3, a browser it(him) honesty loaded to you in a window, as a file html. It was necessary to bypass it, clamping Shift at click by a mousy. It, by the way, standard reception of the instruction(indication) to a browser to write down the specified resource on the disk irrespective of heading. Basically, on the description of work of the Internet from the user it is possible to stop and pass to following item(point) Ц work of systems of the provider Е Though, all is so coordinated, that at the description of one always it is necessary to mention(touch) all parts of huge and complex(difficult) system - the Internet.

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