The OSI network model (Open systems interconnection basic reference model) is the ideal model for open systems interoperability. She found implementation in different protocols. Using this model, different devices that work on the network interact with each other. Through the use of this model, the levels of interaction of the system are distributed from the lower to the upper. The lower level is physical equipment that interacts with binary signals and transfers to a higher level. The highest level is the level of applications that interact with different protocols, such as HTTP or WebSocket. In fact, the OSI model is a visual representation of the interaction of network equipment and other components that allow the end user to access the Internet.
OSI Model Levels
According to the existing model, OSI consists of seven levels:
- Physical.
- Channel.
- Network level.
- Transport.
- Session.
- Level of submission.
- OSI model application layer.
It is worth considering each of them in more detail.
Physical part of the system
This structure is a type of switching equipment, which includes various hubs, network adapters. This level processes incoming bits and transfers to higher levels. In fact, using the means of the physical class, it is possible to process only bits that are voltage in a certain range. Thus, the transmission of a positive or negative signal is realized. Further data processing is performed by the higher levels.
Channel
A characteristic feature of this part of the model is the appearance of addressing. Moreover, the transmitted bits are sent taking into account the existing physical level of the computer. This system in the OSI network model is required to send and receive destination frames and ensure integrity during transmission over physical means. A characteristic feature for conventional networks is the work on the protocol for determining the address, that is, the protocol for determining the final recipient. There is also second-level addressing, which works for devices limited to one segment. In addition, this type of addressing cannot be routed.
Network
The unit that this level of the system operates with is a PDU packet. This device most often uses the IP protocol. Address search and packet delivery are carried out by address, with each IP address including three bytes. A feature of this protocol is the ability to find a route through almost any number of routers, without which access to the network is impossible. At this level, the activity of routing devices is carried out.
Transport
This level works with segments of the protocol unit (Protocol Data Unit). Also, on the transport segment of the OSI model, the analysis of datagrams is carried out, which are a block of information transmitted through the Network without establishing additional connections and creating a channel.
At the current level, there are protocols that interact with applications and ensure the reliability and security of data delivery over the Network. The most common protocol is TCP, which may request a re-sending of information with a partial or incorrect data reception procedure. In addition, a protocol of this level can lead to a decrease or increase in the speed of receiving and sending information, depending on the receiving capabilities of the receiving side.
Host levels
The transport layer and higher are related to the host level, while the first three belong to the media level. Normal implementation is done exclusively through the RFC (comment request document). Almost all protocols operate at several levels simultaneously. based on which are closely related. That is why the most commonly used protocol stack is TCP / IP (network and transport layers).
Session
At this level, packet data is managed. Session layer structures manage the current switching session with the ability to exchange information. In multi-peer networks, it is through this protocol that the users are divided into different levels.
Executive
The level structures correspond to the work on deciphering the received data so that the application level can reproduce the received information on the screen. In this way, ASCII text format, JPEG images and MPEG multimedia files are decrypted.
Application level
The highest in rank and diverse level. It is his structures that manage various high-ranking protocols: SMTP, HTTP, and others. Due to the interaction with the underlying structures, certain actions are implemented and the information received is displayed on the screen.
The application level is closest to the user and interacts directly with him.