Most of the people, maybe you, are still quite unfamiliar with the term “OSI layer”. Even though without you knowing it, you often use this object almost every day, you know. What do you think about OSI? Here’s the explanation.
What is the OSI Layer and How Does It Work?
OSI stands for “Open Systems Interconnection”, which in Indonesian means “Open Systems Interconnection”. The meaning itself has several, such as the following:
- OSI is a conceptual model created by the International Organization (ISO) to standardize various communication systems so that the communication process uses standard protocols.
- In a simpler sense, OSI provides standards for different computer systems to communicate with each other.
- There is also a definition of OSI as a conceptual framework used to describe the function of network systems.
- Other sources explain that OSI is the seven layers that computer systems use to communicate over the network.
OSI originated in the early 1980’s and was the first standard model for network communications, adopted by all major computer and telecommunications companies.
However, OSI was only officially introduced in 1983, and was adopted by ISO as an international standard in 1984.
The modern internet is not based on OSI, but on the simpler Transmission Control / Internet Protocol (TCP / IP) model.
However, the 7-layer OSI model is still widely used as it helps visualize and communicate how the network operates and helps isolate and troubleshoot network problems.
In other words, OSI helps provide a visual picture of what’s going on with a particular network system.
If you can understand the OSI model and its layers, you can also understand which protocols and devices can interoperate with each other as new technologies are developed and described.
The OSI layer is divided into two groups, namely the lower layer consisting of the first to the fourth layers, and the upper layer consisting of the fifth to seven layers.
The main function of the lower layers is to pay attention to the movement of data on the network.
Meanwhile, the top layer is responsible for distributing data more widely, even out of the network. Each description of each layer is as follows:
1. Physical Layer
The physical layer or also known as the physical layer is the first or lowest layer of the OSI.
This layer is concerned with the electric or optical transmission of unstructured raw data bits across the network from the physical layer of the sending device to the physical layer of the receiving device.
These transmissions can include specifications such as voltage, pin layout, wiring, and radio frequency.
At the physical layer, you can find physical resources such as network hubs, cables, repeaters, network adapters, or modems.
2. Data Link Layer
This layer has the following responsibilities:
- Transferring data frames without errors
- Fix errors that may occur on the physical layer
- Defines the data format on the network
- Provides reliable and efficient communication between two or more devices
- Identifies every device that is on the local network
The data link layer includes two sublayers, namely:
- The first layer is called the Logical Link Control Layer, which is responsible for transferring packets to the receiving network layer, identifying the network layer protocol address from the header, and providing flow control.
- The second layer is called the Media Access Control Layer, which is the connecting layer between the Logical Link Control layer and the Physical Layer of the network. This layer is used to transfer packets across the network.
3. Network Layer
The network layer is responsible for receiving frames from the data link layer, then sending them to their intended destination based on the addresses contained in the frame.
The network layer can find its destination by using logical addresses such as IP (Internet Protocol).
Because of this, the router is an essential component at this layer, which is useful for literally routing information where it needs to go and delivering the network to the destination node.
4. Transport layer
The transport layer is the fourth layer of the OSI, which ensures that messages are sent in the order they were sent and there is no duplication of data.
In other words, the main responsibility of the transport layer is to completely transfer data.
This layer receives data from the upper layer and converts it into smaller units known as segments.
This layer can be referred to as the end-to-end layer because it provides a point-to-point connection between source and destination to transmit data reliably. The two protocols used at this layer are the Transmission Control Protocol and the User Datagram Protocol.
5. The Session Layer
The session layer has two tasks. First, this layer acts as a dialog controller making the dialogue between two processes either half-duplex or full-duplex.
The second task is to add multiple checkpoints when sending data sequentially.
If an error occurs in the middle of sending data, the data package will be returned to the checkpoint and resend. This process is commonly known as synchronization and restoration.
6. Presentation Layers
The presentation layer is also known as the syntax layer because it deals with the syntax and semantics of the information exchanged between two systems.
This component is a part of the operating system that converts data from one presentation format to another. In short, this section acts as a data translator for the network.
But not only that, this layer can also handle encryption and compression. Encryption is needed to maintain privacy, by changing the information sent in other forms and sending the resulting message over the network.
While compression is the process of compressing data (reducing the number of bits to be sent). Data compression is very important in multimedia, such as text, audio and video.
7. Application Layer
This is the only OSI layer that interacts directly with user data. This layer provides a protocol that allows software to send and receive information as well as present meaningful data to the user.
Some examples of application layer protocols are Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS).
How the OSI Layer Works
The way OSI works is almost similar to sending a letter via the Post Office, as follows:
- First, you have to write a letter first
- Then put the letter in the envelope
- Next, you will need to write information about the sender and recipient on the envelope so that the letter can reach its destination
- Paste stamps
- Then go to the post office
In essence, the way OSI works has to go through a number of steps in a certain order like when you send a letter. This applies to two PCs in order to communicate with each other.
When a device wants to send information to another device, its data must move from the top layer to the bottom, and when the device receives information, it has to move from the bottom up to “decapsulate”.
So it can be concluded, the OSI layer is a protocol package implemented by computers to connect on the network.