HTTP(2), Apr/11/2023

This time we are gonna talk about the Web and HTTP.

Review:

• Web page consists of objects
• Object can be HTML, JPEG image, Java applet, audio file...
• Web page consists of base HTML-file which includes severall referenced objects
• Each object is addressable by a URL
• ex) www.someschool.edu(host name)/someDept/pic.gif(path name)

HTTP: Hypertext transfer protocol

• Web's application layer protocol
• Client/Sever model
  • Client: browser that requests, recieves, (using HTTP protocol) and displays Web objects
  • Server: Web server sends (using HTTP protocol) objects in response to requests.

With TCP:

• Client initiates TCP connection to server, port 80
• Server accepts TCP connection from client
• HTTP messages(application-layer protocol message) exchanged between browser(HTTP cient) and Web server(HTTP server)
• TCP connection closed

At this point, we. should know that HTTP is "stateless"

Server maintains no information about past client requests.

 

In contrast, protocols that maintain "state" are complex!

•  Past history(state) must be maintained
• If server/client crashes, their views of "state" may be inconsistent, must be reconciled.

 

Here is the picture to explain about the TCP3-way handshake to open a connection

 

And this is the picture describing how TCP close a connection

Next time, we are gonna talk about the HTTP connections!