DCN - Application Layer Introduction

The application layer is the highest layer in the OSI and TCP / IP layer model. This layer is found in both models in layers due to its importance, for interacting with the user and user applications. This layer is intended for applications participating in the communication system.

The user may or may not interact directly with the applications. The application layer is where real communication begins and is reflected. Because this layer is at the top of the layer stack, it does not serve any other layer. The application layer takes Transport instructions and all the layers below to connect your data or transfer it to the remote host.

When the application layer protocol wants to communicate with its peer application layer protocol on a remote host, it delivers data or information to the transport layer. The transport layer does the rest with all the layers beneath it.

There is ambiguity in understanding the application layer and its protocol. Not all user apps can be placed in the application layer. Except for those applications that interact with the communication system. For example, program design or text editor cannot be considered application layer programs.

On the other hand, when we use a web browser, we actually use Hypertext Transfer Protocol (HTTP) to interact with the network. HTTP is the application layer protocol.

Another example is File Transfer Protocol, which helps the user to transfer text or binary files over the network. User can use this protocol in graphical user interface-based programs like FileZilla or CuteFTP and the same user can use FTP in command line mode.

Therefore, no matter which program you use, it is the protocol that is considered in the application layer used by this program. DNS is a protocol that helps a user’s application protocols, such as HTTP, to function.


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