Application Layer of the Internet

Today we will be talking about the application layer. Below are a few of the services provided by the Application layer.

• The application layer provides services for an application program to ensure that effective with communication another application program on a network is possible

• The application layer is a component within an application that controls the communication method to other devices

• It’s an abstraction layer service that masks the rest of the application from the transmission process.

• The application layer relies on all the layers below it to complete its process. At this stage, the data, or the application, is presented in a visual form the user can understand.

A few protocols used in the Application layer

TELNET

Telnet stands for the TELecomunications NETwork. It helps in terminal emulation. It allows Telnet client to access the resources of the Telnet server. It is used for managing the files on the internet

FTP

FTP stands for file transfer protocol. It is the protocol that actually lets us transfer files. It can facilitate this between any two machines using it. But FTP is not just a protocol but it is also a program. FTP promotes sharing of files via remote computers with reliable and efficient data transfer

DHCP

It stands for Domain Name Service. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address

DNS

It stands for Domain Name Service. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address

HTTP

HTTP means HyperText Transfer Protocol. HTTP is the underlying protocol used by the World Wide Web and this protocol defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands.

What Happens when you type a URL into the Web Browser?

When you type a URL into a web browser, this is what happens:

1. If the URL contains a domain name, the browser first connects to a domain name server and retrieves the corresponding IP address for the web server.
2. The web browser connects to the web server and sends an HTTP request (via the protocol stack) for the desired web page.
3. The web server receives the request and checks for the desired page. If the page exists, the web server sends it. If the server cannot find the requested page, it will send an HTTP 404 error message. (404 means ‘Page Not Found’ as anyone who has surfed the web probably knows.)
4. The web browser receives the page back and the connection is closed.
5. The browser then parses through the page and looks for other page elements it needs to complete the web page. These usually include images, applets, etc.
6. For each element needed, the browser makes additional connections and HTTP requests to the server for each element.
7. When the browser has finished loading all images, applets, etc. the page will be completely loaded in the browser window.

References

https://www.informit.com/articles/article.aspx?p=169578

http://www.theshulers.com/whitepapers/internet_whitepaper/index.html