We almost done covering all the aspects of our TCP/IP Networking Model. Which means we have discussed how computers process electrical or Optical signals to send communication data across the cable at the Physical Layer. We also covered how individual computers can address each other and send each other data using Ethernet at Data Link Layer. We talked about how in the Network Layer, Computers and Routers communicate between different Networks using IP. Also in our previous lessons we have discussed how TCP Segment, and Three-Way Handshake in Transportation Layer ensure the data received and sent by the proper applications. So now in this article we will talk about Application Layer that how the real applications send and receive data using this layer. We’ll also see next that how all the layers of TCP/IP Networking Model work together to establish data communication.
The Application Layer
As we have learned that similar with any other Layers, TCP segments also have a generic Data section to them. So the Payload Section in TCP segment is actually the entire contents that whatever data applications want to send to each other. Here the data could be content of web pages if a web browser connected to web server. It could be the content video streaming. The data could also be the content of a document that word processor is sending to a printer, and so on.
There are lots of [numerous, diverse] protocols reside in Application layer. As at the Data Link Layer the most common protocol is the Ethernet. IP is the protocol for Network Layer. Also TCP, and UDP protocols cover the most of the use cases at the Transport Layer. But at the application Layer there are just so many protocols is in use that it is quite impossible to cover them in this article. Because Application Layer Protocols have been standardized across ‘application types.’ For example: a web browser and web server communicates each other using individual protocol. There are lots of web browsers, such as: Chrome, Firefox, Opera, etc they all need to speak through that protocol. Also there are lots of servers. The most commons are: Microsoft IIS, Apache, and nginx. They also need to use the same protocol to communicate with browsers. This way we can communicate to any server doesn’t matter what browser we’re using.
For web traffic the Application Layer protocol is HTTP. So all of the different web browsers and web servers have to communicate using the same HTTP protocol specifications in order to ensure interoperability. This same is true for more other classes of application. There might have lots of choices for FTP client, but they all need to speak the FTP protocol in the same way.
Next we will see how all layers of TCP/IP Networking Model work together to establish data communication.