OSI-licious


We send e-mails each day, surf the web, send files from one computer to another. It all became very simple these days to stay connected.
There are, however, a lot of people who don’t exactly know how the data they send, is going from one place to another.

I figured it would be nice (I just keep on dreaming, don’t I) that I explain a few things. Well at least the things I know myself about networking.

For starters, it is important to know that there is a way to describe the flow of data over a network. This system is called the OSI model. Open Systems Interconnect.
This is the standard model which makes sure there is compatibility between different network components (switch, router, ethernet cable, …).

The OSI model describes 7 layers, each network component can be placed in one of these layers.
Generally the model is represented starting by layer 7.
Here are the 7 layers of the OSI model and a short description.

  • Layer 7 – Application: This is a great start, because it’s quite confusing to begin with. It’s called the application layer, but it only communicates with applications. So it communicates with e-mail, browser, FTP, that sort of things. But we’re not talking about applications itself here.
    Once again, this layer communicates with applications and gives commands to the presentation layer (the 6th layer of the model).
    Some typical layer 7 protocols are POP3, IMAP, FTP, HTTP, …
  • Layer 6 – Presentation: This layer will encrypt data so it can be send over the network. It receives information from applications, translates this information into “network language” and by doing this it resolves incompatibility issues.
  • Layer 5 – Session: This layer creates, manages and ends connections between different applications. (that wasn’t too hard now, was it)
  • Layer 4 – Transport: As the name implies it takes data transfer to it’s account. It will make sure the data transfer done is complete. Protocols used on this layer are typically TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).
  • Layer 3 – Network: This layer should seem somewhat familiar to you since we already discussed this for a bit. This layer is responsible for routing and forwarding of data.
  • Layer 2 – Data Link: At this layer the data packages which are sent are translated to bits. The actual sending of the data from a computer’s network card and the router/swich/whatever is managed here.
  • Layer 1 – Fysical Layer: the lowest layer. Here data and commands are defined as electrical impulses.

It may all seem a bit conceptual at this point in time. But you’ll soon enough get the hang of it.
Take for example a router, this is a layer 3 device, while a switch or a hub is layer 2.

Let me know if you have questions

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2 thoughts on “OSI-licious

  1. Pingback: The Networkcable: your best friend « Tech-o-rama

  2. Pingback: The Wall of Fire « Tech-o-rama

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