In this blog post, we will learn about the importance of the OSI 7-layer model, which is the foundation and core structure of network communication, and the principles of interaction between each layer.
A protocol is an internationally standardized agreement for accurately and reliably transmitting information from a sender to a receiver in a communication situation. In order for these protocols to be applied in actual communication situations, a standardized logical structure is necessary, and the most representative example of this is the OSI 7-layer model, which divides communication functions into seven stages. In this model, the information that the sender wants to send goes through the process from stage 7 to stage 1 of transmission and is delivered to the recipient through the process from stage 1 to stage 7 of reception.
The OSI 7-layer model plays an important role in systematically managing complex communication processes and helping various network devices and software to be compatible with each other. The main purpose of this model is to divide the communication process into multiple layers and assign specific roles to each layer to ensure smooth communication between different systems. This allows network designers and developers to easily diagnose and resolve problems that occur at each layer. This layered approach reduces network complexity and makes communication system development and maintenance more efficient.
Levels 1 through 5 of this model have in common that information is handled from a software perspective, and these are referred to as the upper layers. The top layer, layer 7, is called the application layer, which is where the sender or software accesses the network. For example, when a sender accesses a website and logs in, this corresponds to this layer. At this layer, application programs such as web browsers and email clients that users access are mainly involved, and these programs mediate the interaction between users and the network. The sixth layer, the presentation layer, converts the information to be sent into a standard computer format, such as strings and numbers, so that it can be compatible with other computers. It also compresses the information during transmission and decompresses it during reception. For example, when sending graphic or video files, compression is used to reduce the file size, and decompression is required on the receiving end to restore the original data. This process enables efficient use of network bandwidth and reduces data transmission time. The fifth layer, the session layer, adds checkpoints to the information to be sent and provides a reference point for retransmission in case of errors. This layer also establishes, maintains, and terminates the communication connection between the sender and the receiver, which is essential for ensuring reliable data transmission between the two systems.
In contrast, layers 4 to 1 are called lower layers, which have the common feature of functioning physically to enable information to be transmitted. Among these, the transmission layer, which is layer 4, divides information into units called “frames” and enters the Internet address of the recipient in each frame to ensure that the information is transmitted correctly. At this stage, data flow control and error control are performed, which play an important role in improving network stability. In addition, the network layer, which is the third layer, sets the optimal route for transmitting the information to be sent to the recipient in the fastest and safest way. At this stage, network devices such as routers determine the route of data packets and deliver the information to its destination through packet switching. Once the route is set, the second layer, the data link layer, converts the information converted into frames into bits represented by binary 0s and 1s that can be physically transmitted and sends them to the physical layer. The data link layer applies error detection and correction mechanisms to minimize damage that may occur during data transmission and ensure reliability. Finally, the physical layer checks the mechanical conditions, such as the type of cable and electrical signals, for sending information, and if there are no abnormalities, it sends the information through the cable. In the physical layer, data is actually transmitted through transmission media, which include electrical signals, optical signals, and radio frequencies.
In the process of transmitting and receiving such information, except for the physical layer connected by cables, the n layers of transmission and reception are not directly connected. However, in order to accurately convey information, the n layers of transmission and reception must interact functionally based on the protocols of the corresponding layers, so the protocols of each layer of transmission must be added to the information and sent. The protocols added at each layer are interpreted by the corresponding layer at the receiver, immediately deleted, and only the information to be received remains at the seventh layer of the receiver. This method is essential for maintaining the integrity and reliability of information in network communications, enabling smooth communication between the sender and receiver.
The OSI 7-layer model can be used in various network environments, and the same principles can be applied to small-scale internal networks as well as large networks such as the Internet. It is an important tool for network design and implementation, and is an essential model for network engineers and IT professionals to understand systems and solve problems.
