Application Protocols (FTP, HTTP, SMTP, SSH)

Introduction. Hypertext Transfer Protocol (HTTPFile Transfer Protocol (FTPSimple Mail Transfer Protocol (SMTPSecure Shell (SSHConclusion. List of References.

In addition, this layer is also the top layer of the TCP/IP model too. Just all three upper layers of the OSI model are compressed into a single application layer of the TCP IP model. The application layer contains many protocols that are most commonly required by users. One widely used application protocol is HTTP (Hypertext Transfer Protocol), which is the backbone of the web. Also, there are some other widely used Application protocols like File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), Secure Shell (SSH), etc. We are going to discuss several of these Application layer protocols in this work.

When we browse the web we always use the communication protocol called HTTP – Hypertext Transfer Protocol. Essentially, when we browse through the internet, our browser makes an HTTP request to a server. Then that server responds using a source (e.g. image, video, or webpage HTML) that your browser shows you. This is a model based on HTTP messages. Every HTTP interaction has a request and a response. It is important to know that HTTP is a stateless protocol because each request is executed separately, without knowing about the requests that were executed before, this means that as soon as the operation is completed, the connection between the browser and the server will also be lost. The HTTP protocol is based on the exchange of requests/responses between the client and the server. A web browser can be a client, and an application on a computer that has a website can be a server.

GET – is one of the most widely used methods. When used, the specified resource is downloaded to the client.

HEAD – this request performs almost the same operation as a GET request but without the response body. This is useful for retrieving metadata.

POST – sends data from an HTML form to the specified resource.

CONNECT – this method is typically used to create a tunneled connection through which an encrypted SSL traffic can be transmitted.

OPTIONS – returns a list of methods supported by the server. It can be used to check server functionality.

TRACE – sends back the received request. In this way, the client can see the proxies through which the request travels.

PATCH – the method which is used to adapt changes to resources.

POST, PUT, DELETE considered as unsafe methods. They can be used to send user data and make certain changes to the web server. Therefore, it is recommended that when creating web pages, such methods are displayed not as links, but with the help of buttons, so that the user understands the possible consequences.