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Author Topic: How does the web work?  (Read 6678 times)

Offline dentstudent

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How does the web work?
« on: 18/07/2007 08:43:58 »
I realised yesterday that i use the web a little bit (!) but I have no idea how it actually works. How does a search engine like Google work? Where does it store the information? How does it access it? When I post a blog, how does it become placed on the web so quickly?

I'm sure a lot of this stuff is obvious, but, apparently, not to me!


 

Offline kdlynn

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« Reply #1 on: 18/07/2007 08:54:31 »
easy... it's magic! lol
 

Offline dentstudent

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« Reply #2 on: 18/07/2007 09:03:42 »
I knew it was something like that! I bet there are some little men in there too, eh?
 

Offline kdlynn

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« Reply #3 on: 18/07/2007 09:50:07 »
yes, they're very small. smaller than the people that live in the radio an tv
 

paul.fr

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« Reply #4 on: 18/07/2007 10:02:08 »
Very simply put, The Web is known as a client-server system. Your computer is the client; the remote computers that store electronic files are the servers. Here's how it works:

Let's say you want to visit the Naked Scientist website. First you enter the address or URL of the website in your web browser then your browser requests the web page from the web server that hosts the Naked Scientist site. The server sends the data over the Internet to your computer. Your web browser interprets the data, displaying it on your computer screen.

Then you need to go in to Hyperlinks, Hypertext and HTML and other languages...if only i had the time for that.

 

Offline DoctorBeaver

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« Reply #5 on: 18/07/2007 12:24:24 »
*nudges Paul* ahem - you omitted DNS
 

Offline Soul Surfer

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« Reply #6 on: 18/07/2007 12:26:28 »
The route lies in a lot of work done on computer connection called open systems interconnect  OSI  quite some years ago now.  It defines a miltilayered structure from the physical interconnection right up to the encoding and degoding of high level information.  In the early days of computing when you connected something to it you had to specify before you started to both pieces exactly how they would operate together.  If you got one detail wrong they wouldn't work.  OSI allows systems to "negotiate" through each of the different levels to find an optimum communication process and speed.  That still doesnt stop things going wrong but it's a lot easier than it used to be!
« Last Edit: 18/07/2007 13:58:24 by Soul Surfer »
 

Offline dentstudent

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« Reply #7 on: 18/07/2007 13:10:44 »
The route lies in a lot of work done on computer connection called open systems interconnect  OSI  quite some years ago now.  It defines a miltilatered structure from the physical interconnection right up to the encoding and degoding of high level information.  In the early days of computing when you connected something to it you had to specify before you started to both pieces exactly how they would operate together.  If you got one detail wrong they wouldn't work.  OSI allows systems to "negotiate" through each of the different levels to find an optimum communication process and speed.  That still doesnt stop things going wrong but it's a lot easier than it used to be!
 

Offline Soul Surfer

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« Reply #8 on: 18/07/2007 13:56:38 »
LOL ;D
 

another_someone

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« Reply #9 on: 18/07/2007 15:12:04 »
The route lies in a lot of work done on computer connection called open systems interconnect  OSI  quite some years ago now.  It defines a miltilayered structure from the physical interconnection right up to the encoding and degoding of high level information.  In the early days of computing when you connected something to it you had to specify before you started to both pieces exactly how they would operate together.  If you got one detail wrong they wouldn't work.  OSI allows systems to "negotiate" through each of the different levels to find an optimum communication process and speed.  That still doesnt stop things going wrong but it's a lot easier than it used to be!

Except ofcourse that most of the real network protocols (such as TCP/IP) don't strictly conform toe the OSI 7 layer model (although that does not mean that the model still does not have its value as a reference point, but not as a reality).
 

another_someone

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« Reply #10 on: 18/07/2007 15:51:33 »
The web, as Paul mentioned, is a collection of servers that deliver content to your PC that your PC can display, and that maybe you might be able to interact with in some way.

There are three separate phases to this.

1)locating the correct server.
2)Delivering the content.
3)Displaying the content.

The various machines on the internet talk to each other in a language known as TCP/IP (Transmission Control Protocol/Internet Protocol).

Every machine on the Internet is given a unique number, known as an IP address, and this is like a telephone number for voice telephones.  Like telephone numbers, a given machine can be located by first using the first digits of the IP address as an area code, and then finding the actual machine within the local area by using the remainder of the IP address.

The first problem you have is that most users use URL's to find a machine rather than an IP address.  A URL is a more user friendly address (e.g. if is much easier to remember www.nakedscientist.com than it is to remember 80.244.178.132, which is the IP address of the naked scientist also if the Naked Scientist were to move to a different server, its IP address would probably change, but URL will remain the same but if you want to type in 80.244.178.132 where you would otherwise type www.nakenscientist.com, it would still work).  So we have the DNS (that Eth mentioned above this is the Domain Name Server) that is like a telephone directory, in that you can use it to look up the URL of a site, and it will tell you what the current IP address for that site is.  Because you cannot ask where the DNS is, your computer has to have ways of finding out the address of the DNS first, and it usually does this when it first connects to your local ISP, and your ISP will tell your computer where it can find the closest DNS.

Now that you have found the right server to deliver your content, the rest of the URL is used to determine which piece of content is desired (e.g. http://www.thenakedscientists.com/forum/index.php?refreshtime=&starttime=43200&action=recenttopics&sort=board will say that it is to use the HTTP protocol (which simply means it is delivering an unencrypted web page although the http protocol can be used for other things as well, but the assumption is otherwise), and the rest of the URL will say it wants the web page for the recently updates topics, giving details such as what is meant by recent, and what order to deliver the content is to be sorted by).

The content itself is delivered in a language known as HTML, which tells your computer what is to be displayed on the screen, and how it is to be arranged on the screen.  Embedded within this content are 'links', which are displayed as a description on the screen, but behind that hold a URL, so when you click on the link, the whole process of interpreting the URL and retrieving the new content starts all over again.
 

Offline dentstudent

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« Reply #11 on: 18/07/2007 15:59:16 »
Thanks George (and others, or course!) - but I think I'm going to have to read it at least twice more to fully understand!
 

Offline DoctorBeaver

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« Reply #12 on: 18/07/2007 19:25:56 »
Then there's XHTML, DHTML, CSS, XML, Java, Ajax, SSIs, static IPs, Variable IPs, blah blah blah  [xx(]
 

Offline engrByDayPianstByNight

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« Reply #13 on: 18/07/2007 19:43:04 »
Google's search engine is different from earlier generations of search engines such as AltaVista. Google's smartness lies in its use of the idea of discrete Markov chains that leads a user who searches for, say, a particular keyword, to the websites (hits) where most other users have visited in the past. In a sense, the more a website is visited by users, the more popular it becomes, and the more ahead it is displayed in the search result list. This is also very intuitive if you think about it, from the user's standpoint.
 

Offline DoctorBeaver

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« Reply #14 on: 18/07/2007 20:23:32 »
Google's search engine is different from earlier generations of search engines such as AltaVista. Google's smartness lies in its use of the idea of discrete Markov chains that leads a user who searches for, say, a particular keyword, to the websites (hits) where most other users have visited in the past. In a sense, the more a website is visited by users, the more popular it becomes, and the more ahead it is displayed in the search result list. This is also very intuitive if you think about it, from the user's standpoint.

Google's latest ranking formula doesn't even consider the number of visitors. The most important criterion is the number of backlinks; and if those backlinks are from high-ranked sites then they are worth more.

The density and position of keywords also make a big difference to the ranking, as does an XML sitemap. (The sitemap itself doesn't score but it tells the Googlebots which pages to look at)
« Last Edit: 18/07/2007 20:25:49 by DoctorBeaver »
 

another_someone

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« Reply #15 on: 19/07/2007 22:02:26 »
Then there's XHTML, DHTML, CSS, XML, Java, Ajax, SSIs, static IPs, Variable IPs, blah blah blah  [xx(]

Nor did I get into the intricacies of sub-nets, gateways, static routing, source routing, NATing, Apache configuration files, ICMP, SSL, Certificate Authorities (CA), MAC addresses, PPP, CHAP, SMTP, POP3,IMAP, W3C, or SOAP, XRPC, or endless other things.

I was not asked to boil an alphabet soup.
 

Offline DoctorBeaver

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« Reply #16 on: 19/07/2007 22:36:03 »
Then there's XHTML, DHTML, CSS, XML, Java, Ajax, SSIs, static IPs, Variable IPs, blah blah blah  [xx(]

Nor did I get into the intricacies of sub-nets, gateways, static routing, source routing, NATing, Apache configuration files, ICMP, SSL, Certificate Authorities (CA), MAC addresses, PPP, CHAP, SMTP, POP3,IMAP, W3C, or SOAP, XRPC, or endless other things.

I was not asked to boil an alphabet soup.

 :D
 

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Offline ukmicky

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« Reply #17 on: 19/07/2007 22:47:00 »
Shrunk
The spider makes an intricately designed web of silk which it then coats with blobs of sticky stuff for it unsuspecting prey to stick to. when an insect flies in to the web or when a child drops an ant into it the wiggling of the insect causes  vibrations which the spider then feels through its legs. THAT WAS EASY.:)
 

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Offline DoctorBeaver

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« Reply #18 on: 19/07/2007 23:13:02 »
Shrunk
the spider then feels through its legs. )

A contortionist spider!  :D
 

Offline engrByDayPianstByNight

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« Reply #19 on: 20/07/2007 04:34:00 »
One way of looking at the World Wide Web, in a somewhat outdated fashion, is to think of it like the postal service. Suppose Alice wants to send a letter from Shanghai to Bob in Los Angeles, she drops it off in the nearest mailbox to her home. The letter is collected by the mailman, who sends it to the local post office. From there the letter could go to a regional distribution center, where it gets sorted according to the destination address on the envelope, and has some mail carrier carry it to the regional distribution center in San Francisco. The distribution center then sends it to the local post office in Los Angeles, where the mailman delivers it to Bob's home address.

The Internet works in much the same way as mail delivery. The user specifies the IP address of the recipient of some data (i.e., the address on the envelope), and the various components of the Internet (mostly routers and hubs which act like the local post office and distribution center) do the work to make sure that your data gets delivered to the correct recipient.

That's about the gist of it. I should point out though that this post-office analogy is appropriate probably for the Internet of the late 1990s. Since then, there have been great advances made in make the Internet more ubiquitous and accessible by anyone (AAA: Anyone, Anytime, Anywhere), and some more paradigms have since been developed (e.g., Mobile Internet).
 

lyner

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« Reply #20 on: 22/07/2007 17:32:10 »
No one seems to have brought out the importance of 'packets' in such  network systems. The data passing from computer to computer is broken down into long or short burst or 'packets', each of which carries information about its sender and its destination. Along the way, it comes to lots of possible branches on its route and, at each branch, a relatively dumb piece of equipment sends the packet the right way.
The clever thing about the internet is that a packet can eventually  find its way from A to B  even if parts of the network are not functioning - each packet of a message could go  via a different route yet the final message would be reconstructed to its original form.
One of the original reasons for such a system was the possibility of nuclear war knocking l out all the main comms routes. The internet could, in principle,  still function with most of its bits missing - a sort of biological , co operative system, almost.
And, of course, the World Wide Web is only one of many systems which all use the same  internet hardware for transferring data.
 

Offline engrByDayPianstByNight

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« Reply #21 on: 23/07/2007 04:18:59 »
Along the way, it comes to lots of possible branches on its route and, at each branch, a relatively dumb piece of equipment sends the packet the right way.
The clever thing about the internet is that a packet can eventually  find its way from A to B  even if parts of the network are not functioning - each packet of a message could go  via a different route yet the final message would be reconstructed to its original form.
One of the original reasons for such a system was the possibility of nuclear war knocking l out all the main comms routes. The internet could, in principle,  still function with most of its bits missing - a sort of biological , co operative system, almost.

While sophiecentaur is essentially correct in pointing out the significance and the nature of packets and the Internet, I'm not too sure about the the following two claims though:

1)The claim that "a packet can eventually find its way from A to B even if parts of the network are not functioning" is true if there is some kind of end-to-end Quality-of-Service support (e.g., ATM). Much of today's Internet traffic is still serviced on a best-effort basis, meaning that the network does its best to deliver the data packets, but does not guarantee their eventual arrival at Point B (the destination) or the correctness of the re-constructed. Some packets can well be lost in the Internet for a variety of reasons.

    2)The packet-switching nature of the Internet indeed allows data packets to take alternative routes in the event of some path failure/breakdown. But this has more to do with concerns such as traffic throughput, end-to-end delay, etc., than the threat of a nuclear war. Maybe it's a silver lining, but I'm not sure it can be claimed as one of the original reasons of this approach.
 

another_someone

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« Reply #22 on: 23/07/2007 05:57:04 »
1)The claim that "a packet can eventually find its way from A to B even if parts of the network are not functioning" is true if there is some kind of end-to-end Quality-of-Service support (e.g., ATM). Much of today's Internet traffic is still serviced on a best-effort basis, meaning that the network does its best to deliver the data packets, but does not guarantee their eventual arrival at Point B (the destination) or the correctness of the re-constructed. Some packets can well be lost in the Internet for a variety of reasons.

ATM has QoS, but even with that, there is not as far as I am aware any guarantee of delivery.  Nor does Ethernet, which is still a key component of the Internet at the end points, even if not the WAN (although some broadband too is PPPoE rather than PPPoA).

On the other hand, it is the layers above that which may or may not guarantee delivery.  UDP and ICMP give no guarantee of delivery, but TCP does (but then TCP is not packet oriented but stream oriented - in fact, you cannot talk about restructuring anything at packet level, since a packet is an atomic unit that cannot be split - it either exists or does not - it is only the stream or multi-packet message that can be reconstructed).

    2)The packet-switching nature of the Internet indeed allows data packets to take alternative routes in the event of some path failure/breakdown. But this has more to do with concerns such as traffic throughput, end-to-end delay, etc., than the threat of a nuclear war. Maybe it's a silver lining, but I'm not sure it can be claimed as one of the original reasons of this approach.

The distributed nature of the Internet also creates its own vulnerabilities to malicious redirection of traffic (i.e. if you create a DoS to the legitimate path, and then present your malicious server as an alternative to the legitimate path, then you can potentially hijack parts of the network).
« Last Edit: 23/07/2007 06:04:24 by another_someone »
 

lyner

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« Reply #23 on: 23/07/2007 14:14:32 »
Am I wrong about the early history of the internet, then? I thought that the inter-university connection of computers was the original (engineers') idea, along with the military interest.
Is that just an urban myth?
 

another_someone

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« Reply #24 on: 23/07/2007 14:20:45 »
Am I wrong about the early history of the internet, then? I thought that the inter-university connection of computers was the original (engineers') idea, along with the military interest.
Is that just an urban myth?

As far as I know, the forerunner of the Internet is usually regarded as the ARPAnet, which was military funded, but was not specifically for a military agenda (i.e. it was blue skies research, rather than a specific project with clear military objectives).
 

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