OSI BEST METHOD TO UNDERSTAND

Layering

Okay, so here we go: layers. Why this division?

Stages of communication occur in layers. The division - standardization - was made thinking about it, mainly to facilitate the developments. A person can develop technologies to any layer, without having to worry about the others. Interesting, no?

To begin to familiarize ourselves with them, following its listing: Physical (1), Link (2), Network (3), Transportation (4), Session (5), Presentation (6) and Application (7).

But to explain further, it is easier to first make an analogy.

Imagine the following situation, where William, NY - United States sends a letter to Manuel, in Lisbon, Portugal's capital.

Let's start from the transmitter point: William. The first thing that William needs to do is write the letter, along with the Manuel address [7-Application].

William is with his injured hand, and can not write. Then he dictates the contents of the letter to his wife Rose, who writes a letter to Manuel [6-Presentation].

William's wife then put the letter in an envelope, goes to the post, put the letter [Session 5].

Then the postal worker in the United States decides to outsource the service. He asks a third party logistics - Fedex - to carry the envelope, which in turn puts everything in an secure envelope of his Company. [4-Transportation]

The dispatch of the envelope is now on the Logistics company, who decides that the quickest route is to Lisbon Airport - using air. So put the letter in another envelope with your address information, and they take the airline. [3-Network]

Officials of the airline put the envelope in it's company's box on the plane, adding a label with the destination address. [2-Link]

The box with the envelope follows our trip on the plane to Portugal [1-Physics].

Arriving in Portugal, we start the reverse process, ie the reception.

The box is then unloaded from the plane, the envelope is removed from within the same and delivered to an officer who is in charge of directing the envelope to its destination, which is the company Fedex in Lisbon [2-Link].

The delivery of the envelope as we know is with the company Fedex, which verifies that the same should follow for the post office in Lisbon. [3-Network]

An official of the Post Office in Portugal receives the company's FedEx envelope, the envelope of removing it, then deliver to the address of Manuel in Lisbon [4-Transportation].

Mary, the wife of Manuel checks the local post office, and receives the original envelope with the letter. [5-Session].

She then read the contents to him [6-Presentation].

Finally, Manuel learns the news of Willian [7-Application].

This was a very simplified example. We do not talk for example of the routers that may occur, eg if you plane scales, being necessary to add and remove new mailing labels. However, I believe it has served to demonstrate the idea.

Also, remember that all analogy is not always perfect, but helps us understand the idea.

Now that we have done our analogy, we will bring the side a bit more technical, and talk a little about each layer.

We will not follow the entire process - starting from seventh to first, and then the other way. Let's talk at once, taking the road of first layer to last - the seventh.

Note: This description is a long subject, as the description of devices, protocols and aplicatiovs used. Anyway, let's try to keep a simplified line to describe the layers.