Application Layer in OSI Model | Top 12 Application layer Protocols

Do you know about the application layer in OSI model? What is the function of this application layer in our computer network? If you are looking for all these things then you have come to the right website. Here you will get complete information about Application Layer. No need to go to another website for this. So without delay, let’s know what is the application layer.

What is the Application layer in OSI model?

The application layer is the 7th layer of the OSI model. The biggest importance of this layer is that it interacts with the user and exchanges information. The application layer is the topmost layer of the OSI model. This layer is responsible for the user interface and application services. The application layer acts as a window for users to access data and applications over a network. It also provides end-to-end communication and supports file transfer, email, and other network services.

This application layer communicates information between the presentation layer and the user. The application layer uses many protocols to communicate well with the user. A user may or may not interact with the applications directly. Application layers are where the actual communication is initiated and reflected. Because this layer is on top of the layers it does not serve any other layers. Application layers take the help of the transport and all the layers below it so that their data can be delivered to the remote host.

Functions of Application layer

There are so many functions of application layer, some of them are given below.

Network Virtual Terminal

In this functions of application layer, one user can access another user’s computer remotely. In this, a user is able to access that computer by giving the address of the remote software installed on his computer to the user of the other end. Due to this, a user is able to communicate with another user through remote software in the application layer.

Mail service

With the help of Simple Mail Transfer Protocol, the application layer is able to transfer emails from one system to another. Apart from this, it is also used to store email.

File transfer, access, and management

This application helps in transferring files from one device to another. It also helps in accessing and managing files. All this work can be done with the help of a remote computer.

Directory Services

This application can access and show all kinds of information happening in the world.

Application layer Protocols

There are many protocols used in the application layer. But it is not necessary to know all the protocols from the point of view of examination. So, all the protocols asked in the exam are explained in detail below. TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) is used for transportation in the protocols of the application layer in OSI model.


In this echo protocol, the user sends a request to the server. After that request reaches the server, the server sends a response to the user in return for that request. The time is taken from sending the user request till the response reaches the server is called round trip time. This shows whether that computer is connected to the server or not.

All of you must have seen occasionally that network operators ping an IP by going to the command prompt of the computer. This ping command shows that the computer is not connected to the server.

The port number of the echo protocol is 7. This echo protocol uses both TCP and UDP for transmission.

FTP (File Transfer Protocol)

FTP stands for File Transfer Protocol. With the help of this protocol, files can be sent from one system to another. FTP protocol uses two port numbers which are 20 and 21. You must have a doubt that why does it use 2 port numbers.

There are generally two types of protocols. Inline Protocol and Out Off Line Protocol. Out-of-line protocol means that in this data transfer is done from a different port number and control is in a different port number. Similarly, FTP also uses port 20 to transfer data, and port 21 is used for controlling.

Examples of controlling commands are: Start, Quit, Stack, etc.

The FTP protocol generally uses TCP for transmission. Because its transmission requires reliability. so that the data can reach the receiver securely.

SSH (Secure Shell Protocol)

SSH stands for Secure Shell Protocol. This protocol is generally used for security purposes. For example, if a client is connected with the server, then they are connected through the secure key. Due to this a private connection is made between them and the connection remains secure.

This SSH protocol uses the number 22 port. This protocol uses TCP for transmission.


This protocol is used for remote login. This means that you can use someone else’s system by taking it in the remote. This protocol uses the 23-number port and also uses TCP.

SMTP (Simple Mail Transfer Protocol)

Mail is sent through this protocol. Whatever email you send from your mail to someone else’s mail, it is done with the help of protocol. This protocol uses port number 25 for mail transfer. Uses TCP for transmission.

DNS (Domain Name System)

DNS stands for Domain Name System. The only purpose of using DNS is that we have the domain name, but by accessing it, the IP is with the server. Therefore, it is used to establish a connection with the server. this protocol used 53 port numbers and use UDP (user datagram protocol) for transmission.

A question must have come to your mind that why UDP is used in DNS. Because we need the IP of the domain as soon as possible. Therefore, the UDP protocol is used for speed transmission.

DHCP (Dynamic Host Control Protocol)

The full form of DHCP is Dynamic Host Control Protocol. Generally, the computer in which we run the Internet in the office, school, or college has a static IP address. If a separate IP address is required, then we have to send the request to the network administrator. After that dynamic IP address is provided to that system.

This protocol also uses 2 number of ports. Like 67 and 68. It uses 67 port for data transmission and 68 to control that transmission. Also, it is used UDP for transmission. Because this work requires speed.

TFTP (Trivial File Transfer Protocol)

The full form of TFTP protocol is Trivial File Transfer Protocol. It transfers speed files as compared to FTP. In this, the client transfers files directly to the server without making any connections. This protocol is a fast process because it uses the UDP protocol for transmission. Its port number is 69.

HTTP (Hypertext Transfer Protocol)

Whenever you send a request to the server from any browser or from any application, this request always goes to the server through the HTTP protocol. Without the HTTP protocol, you cannot access anything on the Internet. Its port number is 80. To secure its transmission, the TCP protocol is used.

POP (Post Office Protocol)

The full form of POP is Post Office Protocol. Usually, it is used to fetch mail in your system. The SMTP protocol is used to send mail, but the POP protocol is used to retrieve the mail and bring it into the system.

There are different versions of the POP protocol. In version 2 it used port number 109. But the latest version 3 uses port number 110. The POP protocol uses the TCP protocol for transmission.


This protocol is the secure version of the HTTP protocol. Nowadays this protocol will be found on all the sites. For this, SSL (Secure Sockets Layer) certification has to be installed on the website. If the website has an SSL certificate installed, then HTTPS takes automatic but if an SSL certificate is not installed, then Not Secure is written before the URL of the website. It uses 443 port numbers. It uses the TCP protocol for transmission.

RIP (Routing Information Protocol)

The RIP protocol is used to measure the distance factor. In this, information is sent to the Neighbour Node. This protocol uses the 520-port number and uses the UDP protocol for transmission.


The application layer is the first layer of the OSI model and presents information directly to the user. In addition, they provide the necessary protocols for sharing email, files, and other information across networks. Using which information can be shared across networks in a secure and confidential manner. Whether someone uses his computer to open a website or he sends an email, the protocols used for these are managed by the application layer itself.

Complete information about the application layer has been given in this article Application Layer in OSI model. I hope you all have understood this. If anyone has any doubt then you can tell us in the comment box. We will do our best to solve your doubts. If you liked this article, then share it with your friends on social media.

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