7 OSI Layer: The Building Blocks of Networking
7 OSI Layer (Open System Interconnection) is a standard developed by the International Organization for Standardization (ISO) to provide a structured and logical framework for how data is communicated over a network. This model is very dominant and has become the main reference in data communication literature, especially before 1990. The implementation of data communication in the 7 OSI Layer Model allows for more efficient communication methods between devices, such as in PC to PC communication. Each layer in the 7 OSI Layer Model has a specific function that is supported by the layer below it, thus forming a complex but orderly communication process.
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In general, the role and description of each of the 7 OSI layers can be described as follows:
- Physical Layer
The physical layer in the 7 OSI layers is the foundation of all network communications. As the lowest layer in the OSI model, this layer is responsible for converting digital data in the form of a string of bits into physical signals that can be transmitted through transmission media such as copper cables, fiber optics, or radio waves. Hardware that operates on this physical layer includes various components, ranging from network cards (NICs) installed in computers to network devices such as hubs and repeaters. The NIC functions as a bridge between the computer device and the transmission media, while hubs and repeaters are used to amplify signals and distribute them to various devices in the network. In addition, the physical layer also defines the physical characteristics of the transmission media, such as the type of cable used, data transmission speed, and signal encoding method. In other words, the physical layer is the layer that directly interacts with the physical world and provides the basis for the layers above it to carry out data communication.
- Data Link Layer
- Network Layer
The network layer in the 7 OSI layers is responsible for determining the best path (routing) to transmit data from source to destination across various networks. IP (Internet Protocol) is the most commonly used protocol in this layer. In addition, this layer also handles logical addressing through IP addresses.
- Transport Layer
The transport layer of the 7 OSI layers is responsible for ensuring that data is delivered reliably and in order to its destination. Protocols that work at this layer include TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). TCP provides reliable data delivery, while UDP allows for faster but unsecured data delivery.
- Session Layer
The session layer in the 7 OSI layers manages communication between devices, including opening, maintaining, and terminating communication sessions. It also manages the ongoing exchange of data between two devices. Examples of the use of the session layer include video conferencing and remote desktop applications.
- Presentation Layer
The presentation layer of the 7 OSI layers is responsible for converting data into a format that can be understood by the application layer above. This involves encryption, decryption, compression, and data formats such as ASCII, JPEG, or MP3. This layer ensures that the data being transmitted can be interpreted correctly on both sides of the communication.
- Application Layer
The application layer in the 7 OSI layers is the highest layer in the OSI model, which provides a direct interface for users to interact with the network. Applications such as web browsers, email, and FTP (File Transfer Protocol) work at this layer. This layer also interacts with application software to send data to the layers below.
How OSI 7 layers work
How the 7 OSI layers work is that information is first processed in the Application layer. Then, the information passes through the Presentation and Session layers without changing form. At this stage, the information is still called PDU (Protocol Data Unit) or just data. When it reaches the Transport layer, the data begins to be converted into segments. These segments are then sent to the Network layer and converted into packets. These packets continue to the Data Link layer and are converted into frames. Finally, the frames enter the Physical layer and are broken down into bits. In this layer, the bits are converted into physical forms such as electric current or electromagnetic waves.
References Ramadhani SI, Humainah RF, Nugroho A, Ariwibowo D. 2024. Implementation of Data Communication on OSI Layer PC to PC Using Cisco Packet Trace. Journal of Engineering Science Cluster Research (JUPRIT). 3(2): 66-77.