Open System Interconnection (OSI) describes the functions of the networking system. Within the communication system, the interoperability is maintained by the seven OSI model layers. However, the main purpose of the OSI layer model was to define a clear standard for network communication and interoperability. Hence, this will make communication among the vendors much better. 

A Detailed Explained of OSI Model:

So, let’s take a closer look at what are the 7 different layers of the OSI model and what are their purpose.

  • Physical

This is the first layer in the OSI network model. It deals with the communication of data by physical transmission in the form of electromagnetic, optic, or electrical signals. Hence, the transmission takes place between infrastructures and networking devices. 

This layer takes help in communicating raw data over some physical medium. However, the part of communications that falls under this OSI network model layer are:- 

  1. Physical, mechanical, and electrical networking devices which require signal frequency, voltages, cables, etc.
  2. Topologies like Mesh, Ring, Star, and Bus.
  3. Ethernet, Wi-Fi, and other common protocols.
  4. Hubs, repeaters and other intermediate devices.
  5. Full Duplex, Half Duplex, Simplex, and other communication modes. 

  • Data Link

This is the second layer of the OSI layer model. This layer deals with the connection between physically connected devices. Hence, the devices like switches help the transmission of data between nodes within a network. However, the raw data from the physical layer are synchronized and packaged into data frames. So, this helps to send information between the correct nodes. This layer has two sublayers:-

  1. MAC or Media Access Control– This layer manages the transmission of data among the nodes of the network. Moreover, the MAC layer deserves an acknowledgment of its sequential transmission of raw data.    
  2. LLC or Logic Link Control is another sublayer. This deals with error control and slow control of the data. Additionally, It helps to ensure an accurate and error-free data transfer among the nodes of the network. 

  • Network

This is the third layer of the OSI reference model. It is responsible for data transmission between networks. Also, this layer uses the physical path for the better transmission of the data depending on the different factors. So, these factors are- the priority of service, congestion of data packets, traffic control, best available path, and network characteristics. Logical addressing is used in this layer to distinguish the destination from its source. 

Some other functions of this layer include error handling, congestion control, fragmentation, and encapsulation. When the data is sent, it is divided into several packets. In the same way, to form the information, the incoming data is reassembled. 3-layer switches, bridge routers, and protocols like Internet Protocol version 6 (IPv6) and Internet Protocol version 4 (IPv4) are the hardware that are used for this layer. 

  • Transport

This is the fourth layer of the OSI layer model. It ensures that the data packets are delivered successfully and without any error. The features of this layer are congestion control, flow control, and error control. All these features help in keeping track of the data, scan for any duplication and error. Also, it helps in delivering the information again if it gets failed while the delivery process. 

The function of service-point addressing helps to make sure that the sending of the packet is done for a particular process. Moreover, the reassembly and packet segmentation feature ensure that the data is sent to the correct location. This process is done after the data has been divided and numbered sequentially. At the location, the receiving sequence will help to check the data from any error.

  • Session

This is the fifth layer of the OSI network model. The coordination of communication is done in this layer by managing sessions between servers. Moreover, the exchange between any two entities within a network is managed by this layer. HTTPS is a common example of the session layer. However, the users on the internet are allowed to browse and visit a website for a particular period of time. 

The function of this layer includes authorization, authentication, re-establishing session activities, opening and closing of the communication. This is done among some specific servers and apps. Additionally, it can synchronize and identify half-duplex, and full-duplex operations in data streams. 

The common protocols of this layer are the Session Description Protocol (SDP), Session  Control Protocol (SCP), Point-to-Point Tunneling Protocol (PPTP), and Remote Procedure Call Protocol (RPC). 

  • Presentation

It helps in converting the formats of the data between the networks and the applications. Moreover, this is the sixth layer of the OSI model layers. In addition, the encryption, decryption, data compression, character code translation, and data conversion are also the responsibilities of this layer. 

This is also known as the syntax layer. Moreover, it helps in mapping the syntax and the semantics of the data. This makes the data consumable to each individual network entity. The data is encrypted and formatted from the encryption-based communication app when the data is about to be transferred. After it is sent, at the end of the receiving side, the decryption of the data is done into the information it was originally intended for.  

The serialization of the complex information is done into a transportable format in this layer. After that, the data is reassembled and deserialized. Thereafter, in the destination, the data is transformed in the form of information it was intended for. 

  • Application

This is the seventh and final layer of the OSI model layers. However, the application layer deals with application-level networking processes. In addition, this layer involves in the directory, file transfer, network data sharing, and email services. This provides support to the end-users. Additionally, to facilitate networking requests, this layer identifies the networking entities. Other than requests from the end-users, it also facilitates application-specific networking, synchronizes communication, and determines resource availability. 

Thus, the common protocols of the application layer are Domain Name System (DNS), Simple Mail Transfer Protocol (SMTP), and File Transfer Protocol (FTP).    

Hopefully, you have well understood the OSI model layers. However, If you want to get a good knowledge of the concepts of the computer networking system, then understanding the OSI model is very important. The above OSI model layers explanation will give you the main idea behind this OSI model.