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Web Server overview |
The Internet is one giant distributed network allowing users (servers and surfers) to exchange information. This exchange follows a well-defined sequence of events you need to understand a few basic concepts to make your life easier.
Transaction
In any data exchange, there are only two participants one that makes a request for data and the other that servers the requested data. I use participants in the general sense they can be humans, computers, rooters, integrated circuits.
Addresses
Participants have one thing in common they are uniquely identifiable. In other words, they each have a unique address.
Information exchange
These unique addresses make a transaction between two participants possible. For example, take two people one living in the USA and the other in the UK. The UK person requires some information from the USA person.
He writes a letter detailing the information required and includes his address for a reply. The letter is sent to the USA address and may take a path via plane, sea, road, ferry or a combination of these paths. The journey is un-important so long as the letter reaches its destination.
On receiving this letter, our recipient reads it and writes a reply containing the information requested. He also includes his address for reference. The letter is addressed to the UK person and posted.
Internet information exchange
The Internet works on the same principal with only minor differences. Participants are computers connected via modems to the Internet. Each computer has a unique address. Data is packaged with both sender and destination addresses this bundle is sent via a modem to the Internet where routers deliver it to the destination address.
Address Numbers (IP Address)
Computers, modems and rooters work with binary numbers. Addresses consist of 32 bits with each bit having a value of 0 or 1. A typical address would look like 00100110000100010000001110000000 hard for the human to read so you will see it represented in this format 1234.1234.1234.1234 not a great improvement.
To the rescue names like this www.fred.com what a relief something humans can understand.
You will have noticed I slipped in the word domain the WWW part is an extension and not part of the domain name (address). The domain is fred.com more of this later.
World Wide Problem
Service providers are allocated a range of IP address within their domain. They are free to assign these (fixed or dynamic address) as they please. When you connect to your ISP they will assign a unique address to you.
When you disconnect this unique address may be assigned to another user (dynamic address). This maximizes the number of users a provider can support . It is not a major problem until you come to run your own web server which requires a fixed IP address.
Every name (like www.fred.com) needs to be mapped to a binary address allowing data to be routed through the Internet. There are millions and millions of names on the Internet that need matching to a binary address. The vast numbers involved make it impossible to store these in one place in addition, if a central repository failed the World Wide Web would come to a grinding halt.
Data is continually changing new name-address pairs added daily, your ISP most likely changes your IP address every time you connect yet another change. Enough of this rambling I hope the above has given you some idea of the problems magnitude. To the rescue DNS.
DNS
Domain Name Service, it is the largest dynamic database in the world updated and accessed more than any other. It is the backbone of the Internet and comprises of active and redundant name servers distributed worldwide. The point of all this you will need an entry in one of these DN (Domain Name) servers to make your home web server work.
Putting it all together
The following diagram shows you the main components of the Internet well one user accessing your home server.
Don’t worry about the details all you need to understand, behind the seens is numerous transactions take place to establish connections and data transfers. To give you a feel for this process I have provided some of the main interactions.
Before making any data transfers, both parties connect to the Internet super highway via their ISP's (ISP1 and ISP2). The following events take place.
Home Web Server (PC)
- Dial ISP1 using the ISP dialler software [6] to make a connection.
- ISP1 sets up the connection and allocates an IP address and returns it back to the dialler.
- Dialler saves this IP address for later use.
- The DNS up dater [5] sends this IP address to the dynamic name server [8]
where your new IP address is assigned to your domain name (domain names do not change).
Your home server is on-line waiting for someone to access it.
Home Web Browser (PC)
- Dial ISP2 using the ISP dialler [6] to make a connection.
- ISP2 setups the connection and allocates an IP address and returns it back to the dialler.
- Dialler saves this IP address for later use.
- User starts a browser such as IE, Firefox or Opera.
This user is now ready to surf the Internet.
Browser access
Lets assume the home web server's domain name is fred.com. Further lets assume the user has never accessed the home server before. The reason for this assumption no data will have been cashed (cashing is a method to speed up page accesses).
- Our surfer types fred.com into the browser address window and presses enter.
- Browsers checks to see if requested page has been cashed. Not cashed
- Browser checks local DNS to resolve name no address found.
- Browser sends a request to the ISP's DN server to resolve the name. Not stored here.
- ISP's DN server sends a request to a Root Server (These only contain TLD server addresses)
- The Root server knows a TLD that can handle the request and passes it on.
- The TLD cannot resolve the name but knows of a server that does and passes the request to the Dynamic server
- DynDns is hosting your domain name (remember it contains a new IP address) it retrieves the binary address and returns it to the ISP's DN server.
- The ISP's DN server has resolved the name (OK it called on a number of other servers) and returns it to the browser.
- The browser takes the returned address adds it to a server router request. (remember routers only understand number).
- The browser send this to the ISP where the routers send the page request to the home web server.
- The home server looks at the page request. No page found so extracts an index.html page.
- Sends this page along with the return address to ISP1 routers.
- The routers deliver the page to ISP2 routers these in turn deliver it to the surfer's browser.
Summary
This overview has shown how the Internet operates. The principals are easy to understand what makes it look over complex is DNS.
Where to next
No need to get bogged down in technical stuff, just install and enjoy Single Page Guide .
| | Ric |
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