In a narrow sense, a network refers to a data communication network for information exchange and information processing between computers. In a broad sense, it refers to the combination of communication devices and devices and transmission lines that enable information to be exchanged between devices that are separated by geographical distances. One of the reasons for this is that the OSI model has evolved so rapidly as today.

OSI( Open Systems Interconnection ) model is a standard for the connection between open systems established by the ISO( International Organization for Standardization ) and is an opportunity for active networks today. The OSI model consists of seven layers, and each layer corresponds to the TCP/IP model for the Internet.

The structure of the OSI 7Layer model and its role in each layer are as shown in the figure above. The communication function is divided into 7 vertical layers, and each layer is configured to support its own independent functions regardless of other layers. It is designed to be independent of the other layers in order to minimize the impact of changes to one module on the entire module. In other words, if you have some module changes, you have more flexibility to change only those modules that have changed, rather than the entire module.

The above image shows the correspondence relationship between the OSI model and TCP / IP model. The protocol used differs for each layer. For the user, the network service is used by various protocols of the application layer.

For reference, a protocol such as TCP / IP refers to the rules and promise of communication methods to facilitate communication between transmitting and receiving. Typically there are TCP / IP protocols for Internet and various other protocols exist.

In the following post, we will discuss IP address and subnetting, which are 3-tier addresses, in order to communicate with each other.

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