7 Layers of OSI Model

In this article, we are going to discuss 7 layers of OSI (Open System Interconnection). We will discuss how the 7 layers work, what are the functions and many more.

Working of 7 layers

Application layer: It is the seventh layer of the OSI (open system interconnection) model. It supports the end-user process. The Application Layer contains a range of protocols that are typically required by users. One commonly used application protocol is the HTTP (Hypertext Transfer Protocol), which is the basis for the World Wide Web.

The application layer includes different functions. Let’s see the use of application layer:

· It helps the user to view, download, and manage data on a remote computer.

· The application layer provides the basis for email forwarding and storage facilities.

· Also, some of other functions like directory services, remote job entry, graphics, information communication, and so on are included in this layer.

Applications:

DNS (Domain Name System): DNS is a hierarchical unified naming system for machines, services, or other resources connected to the Internet or a private network. This incorporates precise information with the domain names assigned to each of the concerned organizations.

HTTP (Hypertext Transfer Protocol): HTTP is shared and hypermedia information systems. HTTP is the basis for data exchange on the World Wide Web. HTTP is a request and response (TCP) client and server-side interface. The client is the end-user, the server is the database. The client initiates an HTTP request to the designated port on the server using a web browser, web crawler, or other devices.

FTP: FTP (File Transfer Protocol) usually runs on ports 20 and 21. Port 20 is used to transfer data flow between the client and the server, while port 21 is used to transfer control flow and is the import command to the FTP server. The control flow remains idle, while the data is transmitted. If the control flow is idle for a long time, the client’s firewall, the session will be set to overtime, and when a large volume of data is passed through the firewall, there will arise some issues. At this stage, while the file can be successfully transmitted, it can be broken by a firewall due to a control session; the transfer can result in some errors.

Attributes of the application layer protocol:

· Define the mechanism for coordination between the two parties.

· Define the form of a message.

· Define the message syntax.

· Description of the definition of any area of knowledge.

· Define the method of sending the message and the expected response.

· Define the next step of interaction.

Presentation layer: It is the sixth layer of OSI (open system interconnection). It is used for data representation. Sometimes, it is also called a syntax layer. It also encrypts the login information of your account before transmission. The display layer on your financial institution’s Internet server has decrypted your account login information, making it accessible for processing. It ensures that the data is transmitted in such a way that the data receiver recognizes the information (data) and can use the data.

Presentation contains several functions. Let’s discuss one by one:

• Translation: Processes or programs operating in two machines normally share information in the form of numbers, strings, and so on, before they are transmitted. It is responsible for the reliability of such encoding methods.
• Encryption: The program must be able to protect the privacy of the message or information because it also carries confidential information. It means that the sender needs to convert the original information or message to another type, that is encrypting the data, known as Ciphertext, and that ciphertext sends the resulting message over the network. Decryption involves the transfer of the message back to its original form. The decrypted data is known as plain text.
• Comparison: It means that the number of bits to be transmitted reduces the bandwidth of the data. It is especially important in the transmission of multimedia such as audio, video, text, etc.

Certain protocols often considered at this stage (though not strictly in line with the OSI model) include:

• The Apple File Protocol (AFP), more correctly referred to as the AppleTalk Filing Protocol, is for Apple systems, NFS is for Linux / UNIX systems, and SMB or IFCS is for Windows systems.
• The next protocol is ICA (Independent Device Architecture) is a proprietary protocol for the Citrix Systems application server system.
• The next one is LPP (lightweight presentation protocol) is used between the Location Server and the target device to obtain location-related measurements or location estimates or to transfer assistance data.
• Network Control Protocol (NCP) was an early protocol introduced by ARPANET, the world’s first working packet-switching network that eventually developed into what became the Internet.

Ref: https://www.linkedin.com/pulse/7-layers-osi-model-mahesh-sharma/