Have you ever thought about what happens behind the scenes when your colleague sends you a document over a local network? How does a funny picture that you sent to your friend get to their computer? What processes occur on the network that allow us to exchange information with other computers on the web? In this topic, you will find answers to all these questions because we are going to talk about the OSI model - a reference model of application interaction over the network.
What is the OSI model?
OSI stands for Open Systems Interconnection. The OSI model provides a visual representation of how each communication layer is built on top of another: starting with physical cables and ending with applications on the devices. The goals of the OSI reference model are to explain the structure and functions of a network system and to instruct developers so that digital communications products and software programs they develop can interact.
Open System Interconnection Model was introduced in 1983 and was adopted as an international standard in 1984. All major computer and telecommunications firms embraced it as the first industry standard for network communications in the early 1980s.
The OSI layers
The OSI model consists of 7 layers that follow each other and represent the path from physical cables and computers to applications that the user interacts with:
Physical Layer — The lowest level. It is responsible for the exchange of physical signals between physical devices using cables.
Data Link Layer — The second level solves the problem of addressing when transmitting the information. The data link layer establishes a connection between two physical devices in the network.
Network Layer — The network layer provides package routing by discovering the best path across the network.
Transport Layer — This layer is responsible for data transport over the network built by the router on the previous layer.
Session Layer — The session layer manages the interaction between applications and opens up the possibility of task synchronization, session termination, and information exchange.
Presentation Layer — The name of the layer speaks for itself again. The presentation layer defines how data will be represented in the application. At this level, processes such as encoding, encryption, and decryption occur, according to the system requirements.
Application Layer — The final level where interactions with the end user occur through applications. At this layer, the transmitted data is presented, and user input and output take place.
Of course, the description of the model given in this topic is slightly simplified. But it is the reference and describes the basic concepts. In more specific cases, the OSI model may contain more levels. For example, some sources talk about the 8th level, which is the user himself.
As you can see, the OSI model is quite abstract and it is used more as an academic concept. In actual conditions, a more simplified TCP/IP model is used. The Internet, which you now use to read this article, works based on the TCP/IP model.
Unlike OSI, the TCP/IP model has only 4 layers: Link Layer, Network Layer, Transport Layer, and Application Layer. The purpose of each of them coincides with the corresponding levels in OSI.
But this doesn't mean that OSI is an outdated model. Despite its age, it is still used in many companies as a standard for building networks.
Conclusion
This was a short topic about an important technology. In this topic, you have looked at the Open System Interconnection Model which is the standard for all other models and is used everywhere. Knowing the architecture of the network, it is much easier to build, diagnose and troubleshoot the network itself.