OSI Model - Application Layer (Layer 7)

OSI Model – Application Layer (Layer 7)

When a Data is transferred by a User from one host to a different host, the first layer who provides the service is the Application layer.

Application Layer provides the application service to the user to communicate. These services may be like a web browser application, or an email application, or a messenger application, etc. So, the applications which are meant for communication and data transfer purpose, provides service here.

 This layer will actually work and provide service if you have a valid internet connection. Now what does that mean, right?? Well, application such as a Web browser can be used to open up any HTML that is saved on a host computer, but can you communicate with any other host, if you don’t have an internet connection or if you are not in any kind of network?? No. So, in order to communicate one has to be in a network, so that the application layer can provide the service.

So to keep it simple, Application Layer provides service to a User to communicate, with application software like Email Client, Web Browser, FTP, etc.

When a User inputs some kind of data in the Application layer, it will pass the data streams to the next layer which is the Presentation Layer.

For example:

A User on Host A is sending an Email to a different host.

So, the User will open up any application software through which he can send email, here let us suppose Microsoft Office Outlook.

Where he types in his email and provides the destination host email address, and clicks on send.

This layer will check if there is any valid internet connection, if yes, it will start sending the mail, so its job of providing the interface to the User for typing in the mail and checking for a valid connection is done. Now it will pass the Data (Mail) to the next layer which is the Presentation Layer.

User
Application Layer	Web Browser, Email Clients

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