7 OSI Model Layers Explained with Functions and Architecture

What is the OSI model? What are the OSI layers and their functions?

These are the common questions about OSI model architecture.

What is OSI Model?

The International Standards Organisation (ISO) has proposed a reference model that covers all the aspects of network communication across all types of computer systems. This model is called the Open System Interconnect (OSI) model.

What are the different layers in OSI model?

The OSI Model is a layered architecture consisting of seven layers. In this article, I will explain 7 layers of the OSI model in networking with layered architecture.

The standard model is necessary to ensure that worldwide data communication systems are developed in a way that they are compatible with each other.

Beginners, here is a trick for you to remember all 7 layers of the OSI model in networking. You can memorize it in the right order using the mnemonic:

Please Do Not Throw Sausage Pizza Away

It’s easy!

7 OSI Layers and Their Functions in Networking

The functionalities of these layers are as follows:

1. Physical Layer

It maintains the physical connection and defines the voltages and data rates. Everything related to signals is handled here including transmission of digital bits as electronic signals. It decides if the transmission mode will be simplex, half-duplex or full-duplex. It defines the topology configuration, synchronization, and various such issues.

2. Data Link Layer

The data here is in the form of frames. It performs synchronization, error detection, and correction, and assembling messages into frames. Here is also the responsibility of receiving acknowledgments for messages and taking further steps accordingly. Hence it ensures reliable transmission of each message.

3. Network Layer

The data here is in the form of packets. It manages the routing of data. This layer takes decisions for routing and acts as a network controller. It divides the outgoing messages into packets and assembles the incoming packets into messages.

Internet Protocol is also equipped with a Network layer. There are two IP address versions as IPv4 and IPv6. Do read the difference between IPv4 and IPv6 IP address to know in particular.

4. Transport Layer

It decides if the transmission is to take place in parallel or a single path. It takes care of multiplexing and guarantees transmission of data from one end to the other.

Tansport layer also breaks the data into smaller groups hence performing splitting and segmentation.

TCP and UDP are the two most useful protocol that works on the transport layer.

Application Oriented OSI Model Layers:

Following are the application-oriented OSI model layers. It deals with actual application data and its related activities such as encoding-decoding, data representation, session management. Let’s dig into it.

5. Session Layer

It manages and synchronizes conversations between two different applications by establishing a session and ending a session. It includes logging in and out of the users with user authentication details and auditing for the purpose of billing as well.

6. Presentation Layer

This, as the name suggests, works on how the data is presented to the users. It ensures that the receiver system can read the data sent by the sender. This is done by translation of the file format into a universal code or into the code apt for the receiver machine.

7. Application Layer

This is the top-most layer in 7 layers of the OSI model in networking. It directly interacts with the user. The login and password check takes place here. Re-transmission of files due to any errors, manipulation of information, etc. takes place here. It deals with user interface design.

Finally…

I have touched different OSI layers and their functions.

Further reading: This OSI model layered architecture has its own pros and cons. To understand it, read 12 Advantages and Disadvantages of OSI model Layered Architecture.

Hope this is helpful to get a clear understanding of OSI layers and their functions. You can use the comment section if you come across any doubt while understanding these 7 layers of the OSI model in networking.