A student is curious about how a Web site appears on his computer screen. On a piece of paper,
draw and explain the communication between a client and a server when the client requests a
Web page; use the OSI model as a reference. For example, what Application layer protocol is
required? How will the process differ if the student is sending or retrieving information to or from
a secure Web site? Explain to the student how each OSI model layer contributes to data arriving
in the correct place without errors.

When you go out to open a web page then you should know that It’s not the OSI model that comes into the picture, and in fact, it is just for study purposes, and it does not work in real network work, The exact one used is the TCP/IP model. However, the OSI model separates the concepts into various layers, and hence used for study purposes.

When you try to open a web address through a web browser, then the web browser uses the HTTP that is an Application layer protocol.

The web browser thus finds the IP address of the URL through the Domain Name System. And this is as well the Application layer protocol.

However, you will find that the actual process is even more complex.

The browser now forms an HTTP packet which mentions, “Hello I would like to get the web page from the server”. Now the browser sends the HTTP packet to the TCP, which stands for Transmission control protocol, and is a transport layer protocol.

Here the adjacent layer interaction works. However, that is on the same device, and currently, the packet is on your PC only. The ALI states that the higher layer asks the next lower layer protocol to get done the service, and the lower layer delivers the service to the higher layer just above it. And this interaction gets repeated until the data finds itself at the lowest layer.

The main job of the TCP is to create a pipe in between you and the server, such that the data can be transferred via the pipe. And for this the TCP on your PC talks to the TCP on the server.

Now the TCP puts up its details over the HTTP packet. And these are necessary for managing the pipe/session.

Now the packet is handed to the IP process or the internet protocol, which is an internet layer protocol. The main task performed by the IP is addressing and routing. It's like a postal service, that routes the letter via various postal offices to reach the correct one. IP now puts its info on top of the TCP packet. This info is required for routing on the internet.

The packet is now handed over to the network access or the network interface layer. And this defines the hardware and protocols that are required for delivering the data via the physical network. The majority of the times the physical network used is the Ethernet.

Your PC now binds the IP packet in between the Ethernet header and the Ethernet trailer, and thus forms an Ethernet frame. You should know that Ethernet has a MAC address that is being made use of for sending the frame within the LAN.  And now the PC transmits the Ethernet frame bits physically with the help of the electricity that flows through the Ethernet Cables.

The packet now reaches the server. The web server recreates the bits through the interpretation of the electrical signals. And the webserver now removes and discards the ethernet header and trailer from the ethernet frame, and de encapsulates it. And in the same manner, it reads through the TCP data, and finally transfers that to the HTTP process which can figure out the HTTP get request.

Now the webserver in s similar manner sends back the detail. And this process can be repeated any number of times.

Also, keep in mind that in case of secure website, there is one extra step, and that is the verification of the SSL certificate, at both the client and server end. Rest of the process is same.

Explanation:

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