Describe what happens at each specific layer in the TCP/IP protocol after you click on a link to a Web site.

Question

What will be an ideal response?

Answer 1

First, the operating system and browser software (operating at layer 7, the Application layer) recognize the mouse click, determine where on the Web page it was clicked, see that a link has been selected, extract the link from the Web page, and build an HTTP GET request containing the URL of the link that was clicked. The GET request is sent down to layer 6.

At layer 6, the Presentation layer, the GET request may need to be formatted for proper transmission before sending it on to layer 5.

At layer 5, the Session layer, the use of HTTP requires that a TCP session be setup between the user's computer and the Web server pointed to by the URL. This involves performing a DNS lookup of the URL to get the IP address of the Web server. Then the Session layer uses a three-way handshake to establish a TCP session with the Web server. After all this, the GET request is sent on to layer 4.
At layer 4, the Transport layer, the HTTP GET request is encapsulated inside TCP, and all TCP header fields are adjusted, such as the port numbers used, and sent to layer 3.

At layer 3, the TCP datagram is encapsulated inside IP, and all IP fields are filled in, including the IP addresses of the source (the user's computer) and the destination (the Web server). The IP datagram is sent to layer 2.

At layer 2, the Data Link layer, the source MAC address (the user's computer) and the destination MAC address (the router on the user's network) are inserted into an Ethernet frame along with the IP datagram and some other fields. The frame is sent down to layer 1.

At layer 1, each bit in the Ethernet frame is converted into its electronic representation on the network media and transmitted out of the computer.