7 layers of the OSI model
Introduction
As a regular user of the Internet, I’m sure you have come across the term ‘HTTP.’ You may even have typed it yourself as you searched for information on the Internet. What you may have not realized, however, is that you were actually typing a particular layer of the OSI model. But, just what is OSI model, and what are the different layers of OSI model?
What is OSI Model?
OSI Model is an acronym for the Open Systems Interconnection model. It can simply be defined as computer networking‘s unique way of thinking.
Computers usually think in layers. Each layer generates functions, which is in turn received and processed by the layer above it. This process happens from the most beneath layer to the top-most layer.
OSI Model with Layers (end to end layers in OSI model)
The standard OSI model consists of 7 different layers, these 7 layers are also known as end to end layers in OSI model.
Each of these 7 OSI model layers is dependent on the layer beneath it, for it to function.
The following is a diagram to illustrate the 7 end to end layers in OSI Model.
Now let’s look into the 7 different end to end layer in OSI model and their respective functions;
1. Layer 7 Application Layer in OSI model
In order to understand the OSI Model, think of it as a burger with 7 layers. The top-most layer of the burger represents layer 7 of the OSI model.
This top-most layer of a burger is the one closest to the mouth; it is what a person will bite first. In a similar way, layer 7 of the OSI Model is the one closest to the user, as is demonstrated in the diagram above.
Therefore, Layer 7 (application layer) of the OSI model is basically what a user operating a device sees, for instance, when the user loads a browser or an application like the e-mail.
The data that the user will see upon opening this application or browser is what constitutes the application layer.
Examples of Layer 7 of the OSI Model include; the Internet Browser (such as Google Chrome, Firefox, etc), Microsoft word and applications, such as Skype and Office.
2. Layer 6 Presentation Layer in OSI model
Layer 6 of the OSI Model is the operating system of a network. Examples of these operating systems are Windows and OS X. The main function of this layer is to properly translate and/or interpret data.
In other words, Layer 6 functions to present data for the application later (layer 7). For instance, layer 6 is where data is usually encrypted and decrypted so as to ensure its safe transmission.
3. Layer 5 Session Layer in OSI model
In order for two computers/devices to communicate, a session has to be created. Layer 5 of the OSI Model is what creates and maintains these sessions. The sessions are usually created between the operating system in Layer 6, and the third-party devices.
For instance, as you browse the Internet, you are at the time interacting with layer 7 of the OSI Model. At the same time, Layer 7 (web server) will be interacting with Layer 6 (operating system). Layer 5 (session Layer) allows layer 6 to interact with layer 7.
In other words, there would be no communication between the web server and the operating system, if layer 6 did not come to play.
4. Layer 4 Transport Layer in OSI model
Layer 4 of the OSI model can be described as the quality control layer. It ensures the quality of the system, as well as its reliability. It does so by checking for errors in the system and also managing traffic flow in the network.
The transport layer also resends data in cases where the available data has been corrupted.
The most common examples of layer 4 are TCP and UDP.
5 Layer 3 Network Layer in OSI model
Layer 3 is where all the routers in a network operate. Its main function is to ensure that the transferring process of all the large files is always a success.
This layer ensures this by coordinating all the related sectors of a data conversation, such that all the files are completely transferred. The IP addresses of devices and computers come from this layer.
6. Layer 2 Data Link Layer in OSI model
Layer 2 is where all the routers in a network operate. It oversees the movement of data, both in and out of the physical layer of a network. It also detects and corrects errors, as well as engages in some addressing, making it possible for devices to differentiate each other in the larger networks.
The Data link layer consists of two sub-layers; Media Access Control (MAC) layer and the Logical Link Control (LLC) layer.
7. Layer 1 Physical Layer in OSI model
The physical layer is the physical hardware making up a computer network. It monitors the sending and receiving of information by a device. This information is usually transported using different interfaces, mainly electrical and mechanical interfaces.
Examples of Layer 1 are Ethernet cables and Bluetooth.
Conclusion
Having learned about the OSI model, you realize that it is the main protocol used in all Internet operations today.
TCP/IP is also a layered protocol but does not use all of the layers.
This gives the OSI model an added advantage over all other protocols.
So, the next time you browse the Internet and see the term ‘HTTP,’ don’t just see a complicated computer term; see a specific layer of the OSI Model.
See also: Why We Need Protocols for Communication?
Let us know what you think about 7 end to end layers in OSI model and its tutorial in the comment section below.
Also, put your views on the Application layer and Physical layer in OSI model.
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References
1.) Li, Yadong, et al. “Research based on OSI model.” 2011 IEEE 3rd International Conference on Communication Software and Networks. IEEE, 2011.
2.) Bora, Gaurav, et al. “OSI reference model: An overview.” International Journal of Computer Trends and Technology (IJCTT) 7.4 (2014): 214-218.
3.) Briscoe, Neil. “Understanding the OSI 7-layer model.” PC Network Advisor 120.2 (2000).
