OSI stands for Open Systems Interconnection model and consists of seven layers. It is perfect. It is necessary to consider what OSI layers are and how they work in practice.
The Principle Of The Network Model Device
The OSI network model has 7 layers arranged hierarchically from larger to smaller. The highest is the seventh, and the lowest is the first.
The sender device, the recipient device, and the data itself takes part in the process of data transmission. Information is presented as data at the seventh layer, in the form of bits at the first one. Information is presented in the form of protocol data blocks at every layer.
The First, Physical Layer (L1)
Let's look at everything in detail for beginners and we will start from the lower layer. The signal exchange between two or more devices occurs here. Hardware understands the image as a set of zeros and ones (bits).
Second, Channel (Data Link Layer, L2)
The second level of OSI solves the problem of addressing during transmitting information. The channel layer receives bits and turns them into frames. The main goal of the layer is to generate frames with the address of the sender and recipient, and then send them over the network.
The layer has two sublevels:
- MAC;
- LLC.
Switches transfer the generated frames from one device to another, while using physical MAC addresses. The channel layer uses the ARP protocol.
Third, Network Layer, L3
There is routing through routers at the third level of the OSI network model. They get the MAC-address of a device due to the contact with the previous layer.
Fourth, Transport Layer, L4
The layer is located between Host Layers and Media Layers in the OSI network model.Its duties include transporting packets. According to the practice, some packages can be lost during transportation. That is a normal process.
A segment is a part of a package. The lower level is datagram. Beginners rarely know something about it. A datagram is also part of a package. Datagrams have autonomy in the network model. Network engineers work with 1-4 levels.
Fifth, Session Layer, L5
The 5 level works with pure data and it is necessary for the session support. This level stands for:
- managing the interaction between applications;
- task synchronization feature;
- session termination;
- changing data.
Session-level services are used in apps that demand remote manipulation.
Sixth, Presentation layer, L6
It is responsible for protocol conversion and data coding. The 6 layer of the network models stands for the presentation of pictures, videos, and audio files. This is also a layer where data is encrypted when it needs to be protected.
Seventh, Application layer
The layer is for users. They engage with the network models. It serves as the visual representation of the entire model.
Criticism of the OSI model
The seven-level model was adopted as the ISO/IEC 7498 standard. It stands like the actual standard in spite of some disadvantages. They are the following:
- Late implementation. When OSI appeared, this model was perfectly released for research. The TCP/IP model became very popular by the time and investors didn’t want to spend money for the new project.
- Failed policy. There is no tie with UNIX and it was a real problem for many programmers.
- Using outdated technologies. Protocols are not as developed as those in TCP. . Additionally, the documentation is challenging to use. Moreover, errors manifest at every higher level.
- Does not reflect modern realities. There is a tendency to make everything easier. It’s impossible to simplify the system.
OSI couldn’t achieve wide popularity because it was designed as a closed model promoted by European telecommunications companies and the US government. But it is still in use and many networks are based on OSI structure.
Conclusion, The Role of The OSI Model in Building Networks
Every layer of the model stands for the task. In reality, the OSI architecture is more difficult than it is written here. There are other levels too. For instance, the eighth layer is a user. The OSI model serves as a tool for network diagnostics. If something is broken on the network, it is much easier to determine the level than to try to rebuild the network. That’s why the structure is used very often because it helps to reduce time to repair the network.
