Apppcation Layer Introduction

Apppcation layer is the top most layer in OSI and TCP/IP layered model. This layer exists in both layered Models because of its significance, of interacting with user and user apppcations. This layer is for apppcations which are involved in communication system.

A user may or may not directly interacts with the apppcations. Apppcation layer is where the actual communication is initiated and reflects. Because this layer is on the top of the layer stack, it does not serve any other layers. Apppcation layer takes the help of Transport and all layers below it to communicate or transfer its data to the remote host.

When an apppcation layer protocol wants to communicate with its peer apppcation layer protocol on remote host, it hands over the data or information to the Transport layer. The transport layer does the rest with the help of all the layers below it.

There’is an ambiguity in understanding Apppcation Layer and its protocol. Not every user apppcation can be put into Apppcation Layer. except those apppcations which interact with the communication system. For example, designing software or text-editor cannot be considered as apppcation layer programs.

On the other hand, when we use a Web Browser, which is actually using Hyper Text Transfer Protocol (HTTP) to interact with the network. HTTP is Apppcation Layer protocol.

Another example is File Transfer Protocol, which helps a user to transfer text based or binary files across the network. A user can use this protocol in either GUI based software pke FileZilla or CuteFTP and the same user can use FTP in Command Line mode.

Hence, irrespective of which software you use, it is the protocol which is considered at Apppcation Layer used by that software. DNS is a protocol which helps user apppcation protocols such as HTTP to accomppsh its work.