When talking about OSI, or Open System Interconnection Model, most people find themselves a little bit confused. If you try to search more about it on the web, you will find a lot of different opinions and later on, you won’t learn anything. That is exactly why we wanted to teach you what you need to know about OSI in Network Fundamentals Certification Course! So, let’s see!
OSI was released in 1984, containing seven layers and two of the running processes. What would that mean? The best way to understanding it is to definitely remember two facts:
-the data is moving from the layer number seven to the layer number one=the process that happens is Encapsulation;
-the data is moving in the opposite way, from layer number one to layer number seven=the process that happens is Decapsulation.
We will now go through all of the layers, and we have already mentioned that there are seven of them.
The first layer is a Physical Layer. Here, the data is traveling in the bit form (0 and 1). What happens in the layer one is actual data transmission. For example, Repeaters, or Wires devices work on the layer one.
The second one was named Data Link Layer. The data is converted into frames and Source MAC. The destination of the MAC header is removed or added. This layer allows the user to switch work and to get all the details by broadcasting the ARP.
Layer number three is a Network Layer, a ”place” where data gets converted (into Sources and Packets). Here, the destination header can be added or removed.
Layer four is known as a Transport Layer and it adds the header to data which are converted into TCP or UDP and segments. When talking about these two protocols, it is important to remember that UDP Protocol is actually very unreliable and also connectionless (mostly used in live scenarios), while TCP Protocol is strongly reliable because it has a ‘three-way handshake’ and also a flow control.
Session Layer is the name of the layer number five. What Session Layer does is that it manages and establishes, but also terminates the sessions that are happening peer to peer. Besides all those important functions, the layer five also keeps some different kinds of the applications and its data separated from other unimportant apps.
Layer number six is known as a Presentation Layer. The most important thing this layer does is definitely ensuring that all the data which are transferred from the app’s layer from one system can actually be read by some other app’s layer on the system.
The Application Layer is the last layer, number seven. The Application Layer can be best described as the User Interface. The layer number seven is always concerned with user’s interaction, network, and computer. The App’s Layer is actually acting as an interface between the real app’s program. It contains many utilities and protocols too, like HTTP, SMTP, and FTP.
Hope that you got an idea how OSI model looks like! There is much more for you learn from us, so stay informed and keep learning!