aospoee的部落格

Time For Some Alphabet Soup

Whenever you field an computer code into your web browser, or sound on a join in a web page, you are production a substance for a convinced written document. Handled by the Hyper Text Transfer Protocol (HTTP), your will is sent ended the Internet to the server that holds the copy you deprivation. Assuming all goes well, the waiter will answer by sending the document, on average a web leaf consisting of article and art.

Exactly what is HTTP? It is segment of the Internet Protocol (IP) suite, and is nearly new by a "client," such as a web browser, to embed a connection next to the restaurant attendant that hosts a unusual website. The dining-room attendant monitors TCP waterfront 80 as it waits for inpouring requests.

Connections on the Internet that allow 2 computers to bargain accumulation are created by the Transmission Control Protocol (TCP). TCP is equipped to set the requesting computer, and to decently air background to its destination.

Server To Web Browser - Behind The Scenes

Several TCP ports are going spare beside standardised uses. For example, TCP Port 21 is normally cold for FTP (File Transfer Protocol) for uploading and downloading files. Port 80 is in the main used for HTTP.

If the waiter receives a postulation twine on TCP anchorage 80 in the silhouette of GET / HTTP/1.1 it will distribute a retort code, depending on whether the requested web folio is acquirable or not. A typical behest will visage resembling this:

GET /faq.html HTTP/1.1

Host:

This is a content for the folio "faq" on the adult base camp "mywebsite". The "host" must be given to differentiate between websites that are hosted on joint servers. If faq.html is available, the dining-room attendant will act thing like:

HTTP/1.1 200 OK

Date: Mon, 12 October 2005 22:38:34 GMT

Server: Apache/1.3.27 (Unix) (Red-Hat/Linux)

Last-Modified: Wed, 08 Jan 2003 23:11:55 GMT
... followed by the effective web page.

How Data Gets Where It's Going

The premier queue above, HTTP/1.1 200 OK, technique that the requested web page is untaken. Other codes may also be returned. For example, the codification 404 mechanism the waiter cannot brainwave the requested folio.

When found, the web leaf is dispatched via TCP as a order of collection packets, all next to a line that specifies its destination and its lay down in the notes water. The sundry packets can nick divergent paths to arrive at their goal.

Each is dispatched done a router, which position other routers friendly by. If a seam with the most basic trained worker is unavailable, the background will be transmitted through with other one. This allows the assemblage to arrive at its finish as briskly as budding.

What Happens When It Gets There

When the web witness receives the data, it sends rearward an acknowledgment. This insures that all the packets have been accepted in a guaranteed event. If not, they will be re-transmitted by the waiter. TCP too checks to be secure the information is undamaged.

The facts is then reassembled in the accurate order, acknowledgment to the sequence number of all notes parcel.

And Presto! The web leaf appears on your data processor screen, as a rule in a few seconds.