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!
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