Seven Layers of ISO/OSI
Suat Seçgin · 2023
In the days when communication systems were first established, one channel was allocated between users, to be unique to them. In this system, called circuit switching, once the circuit was installed, even if the users did not use this circuit, it could not be put into the service of another user. This led to inefficient use of communication channels. With the beginning of the use of packet switching systems, a transmission medium (channel) has become available to more than one user at the same time. The phases in which a packet switched system will pass the data from the application layer to the physical layer (electrical signals) have been defined by ISO (International Organization for Standardization) with the OSI (The Open System Interconnection) 7-layer model. With this model, it is explained how peer systems will communicate mutually at each layer. All packet-based communication systems work according to this model.